tor-browser

cord_test.cc (112732B)

---

// Copyright 2020 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "absl/strings/cord.h"

#include <algorithm>
#include <array>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <iterator>
#include <limits>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>

#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/internal/endian.h"
#include "absl/base/macros.h"
#include "absl/base/no_destructor.h"
#include "absl/base/options.h"
#include "absl/container/fixed_array.h"
#include "absl/functional/function_ref.h"
#include "absl/hash/hash.h"
#include "absl/hash/hash_testing.h"
#include "absl/log/check.h"
#include "absl/log/log.h"
#include "absl/random/random.h"
#include "absl/strings/cord_buffer.h"
#include "absl/strings/cord_test_helpers.h"
#include "absl/strings/cordz_test_helpers.h"
#include "absl/strings/internal/cord_internal.h"
#include "absl/strings/internal/cord_rep_crc.h"
#include "absl/strings/internal/cord_rep_flat.h"
#include "absl/strings/internal/cordz_statistics.h"
#include "absl/strings/internal/cordz_update_tracker.h"
#include "absl/strings/internal/string_constant.h"
#include "absl/strings/match.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"
#include "absl/strings/string_view.h"
#include "absl/types/compare.h"
#include "absl/types/optional.h"

// convenience local constants
static constexpr auto FLAT = absl::cord_internal::FLAT;
static constexpr auto MAX_FLAT_TAG = absl::cord_internal::MAX_FLAT_TAG;

typedef std::mt19937_64 RandomEngine;

using absl::cord_internal::CordRep;
using absl::cord_internal::CordRepBtree;
using absl::cord_internal::CordRepConcat;
using absl::cord_internal::CordRepCrc;
using absl::cord_internal::CordRepExternal;
using absl::cord_internal::CordRepFlat;
using absl::cord_internal::CordRepSubstring;
using absl::cord_internal::CordzUpdateTracker;
using absl::cord_internal::kFlatOverhead;
using absl::cord_internal::kMaxFlatLength;
using ::testing::ElementsAre;
using ::testing::Le;

static std::string RandomLowercaseString(RandomEngine* rng);
static std::string RandomLowercaseString(RandomEngine* rng, size_t length);

static int GetUniformRandomUpTo(RandomEngine* rng, int upper_bound) {
 if (upper_bound > 0) {
   std::uniform_int_distribution<int> uniform(0, upper_bound - 1);
   return uniform(*rng);
 } else {
   return 0;
 }
}

static size_t GetUniformRandomUpTo(RandomEngine* rng, size_t upper_bound) {
 if (upper_bound > 0) {
   std::uniform_int_distribution<size_t> uniform(0, upper_bound - 1);
   return uniform(*rng);
 } else {
   return 0;
 }
}

static int32_t GenerateSkewedRandom(RandomEngine* rng, int max_log) {
 const uint32_t base = (*rng)() % (max_log + 1);
 const uint32_t mask = ((base < 32) ? (1u << base) : 0u) - 1u;
 return (*rng)() & mask;
}

static std::string RandomLowercaseString(RandomEngine* rng) {
 int length;
 std::bernoulli_distribution one_in_1k(0.001);
 std::bernoulli_distribution one_in_10k(0.0001);
 // With low probability, make a large fragment
 if (one_in_10k(*rng)) {
   length = GetUniformRandomUpTo(rng, 1048576);
 } else if (one_in_1k(*rng)) {
   length = GetUniformRandomUpTo(rng, 10000);
 } else {
   length = GenerateSkewedRandom(rng, 10);
 }
 return RandomLowercaseString(rng, length);
}

static std::string RandomLowercaseString(RandomEngine* rng, size_t length) {
 std::string result(length, '\0');
 std::uniform_int_distribution<int> chars('a', 'z');
 std::generate(result.begin(), result.end(),
               [&]() { return static_cast<char>(chars(*rng)); });
 return result;
}

static void DoNothing(absl::string_view /* data */, void* /* arg */) {}

static void DeleteExternalString(absl::string_view data, void* arg) {
 std::string* s = reinterpret_cast<std::string*>(arg);
 EXPECT_EQ(data, *s);
 delete s;
}

// Add "s" to *dst via `MakeCordFromExternal`
static void AddExternalMemory(absl::string_view s, absl::Cord* dst) {
 std::string* str = new std::string(s.data(), s.size());
 dst->Append(absl::MakeCordFromExternal(*str, [str](absl::string_view data) {
   DeleteExternalString(data, str);
 }));
}

static void DumpGrowth() {
 absl::Cord str;
 for (int i = 0; i < 1000; i++) {
   char c = 'a' + i % 26;
   str.Append(absl::string_view(&c, 1));
 }
}

// Make a Cord with some number of fragments.  Return the size (in bytes)
// of the smallest fragment.
static size_t AppendWithFragments(const std::string& s, RandomEngine* rng,
                                 absl::Cord* cord) {
 size_t j = 0;
 const size_t max_size = s.size() / 5;  // Make approx. 10 fragments
 size_t min_size = max_size;            // size of smallest fragment
 while (j < s.size()) {
   size_t N = 1 + GetUniformRandomUpTo(rng, max_size);
   if (N > (s.size() - j)) {
     N = s.size() - j;
   }
   if (N < min_size) {
     min_size = N;
   }

   std::bernoulli_distribution coin_flip(0.5);
   if (coin_flip(*rng)) {
     // Grow by adding an external-memory.
     AddExternalMemory(absl::string_view(s.data() + j, N), cord);
   } else {
     cord->Append(absl::string_view(s.data() + j, N));
   }
   j += N;
 }
 return min_size;
}

// Add an external memory that contains the specified std::string to cord
static void AddNewStringBlock(const std::string& str, absl::Cord* dst) {
 char* data = new char[str.size()];
 memcpy(data, str.data(), str.size());
 dst->Append(absl::MakeCordFromExternal(
     absl::string_view(data, str.size()),
     [](absl::string_view s) { delete[] s.data(); }));
}

// Make a Cord out of many different types of nodes.
static absl::Cord MakeComposite() {
 absl::Cord cord;
 cord.Append("the");
 AddExternalMemory(" quick brown", &cord);
 AddExternalMemory(" fox jumped", &cord);

 absl::Cord full(" over");
 AddExternalMemory(" the lazy", &full);
 AddNewStringBlock(" dog slept the whole day away", &full);
 absl::Cord substring = full.Subcord(0, 18);

 // Make substring long enough to defeat the copying fast path in Append.
 substring.Append(std::string(1000, '.'));
 cord.Append(substring);
 cord = cord.Subcord(0, cord.size() - 998);  // Remove most of extra junk

 return cord;
}

namespace absl {
ABSL_NAMESPACE_BEGIN

class CordTestPeer {
public:
 static void ForEachChunk(
     const Cord& c, absl::FunctionRef<void(absl::string_view)> callback) {
   c.ForEachChunk(callback);
 }

 static bool IsTree(const Cord& c) { return c.contents_.is_tree(); }
 static CordRep* Tree(const Cord& c) { return c.contents_.tree(); }

 static cord_internal::CordzInfo* GetCordzInfo(const Cord& c) {
   return c.contents_.cordz_info();
 }

 static Cord MakeSubstring(Cord src, size_t offset, size_t length) {
   CHECK(src.contents_.is_tree()) << "Can not be inlined";
   CHECK(!src.ExpectedChecksum().has_value()) << "Can not be hardened";
   Cord cord;
   auto* tree = cord_internal::SkipCrcNode(src.contents_.tree());
   auto* rep = CordRepSubstring::Create(CordRep::Ref(tree), offset, length);
   cord.contents_.EmplaceTree(rep, CordzUpdateTracker::kSubCord);
   return cord;
 }
};

ABSL_NAMESPACE_END
}  // namespace absl



// The CordTest fixture runs all tests with and without expected CRCs being set
// on the subject Cords.
class CordTest : public testing::TestWithParam<bool /*useCrc*/> {
public:
 // Returns true if test is running with Crc enabled.
 bool UseCrc() const { return GetParam(); }
 void MaybeHarden(absl::Cord& c) {
   if (UseCrc()) {
     c.SetExpectedChecksum(1);
   }
 }
 absl::Cord MaybeHardened(absl::Cord c) {
   MaybeHarden(c);
   return c;
 }

 // Returns human readable string representation of the test parameter.
 static std::string ToString(testing::TestParamInfo<bool> useCrc) {
   if (useCrc.param) {
     return "BtreeHardened";
   } else {
     return "Btree";
   }
 }
};

INSTANTIATE_TEST_SUITE_P(WithParam, CordTest, testing::Bool(),
                        CordTest::ToString);

TEST(CordRepFlat, AllFlatCapacities) {
 // Explicitly and redundantly assert built-in min/max limits
 static_assert(absl::cord_internal::kFlatOverhead < 32, "");
 static_assert(absl::cord_internal::kMinFlatSize == 32, "");
 static_assert(absl::cord_internal::kMaxLargeFlatSize == 256 << 10, "");
 EXPECT_EQ(absl::cord_internal::TagToAllocatedSize(FLAT), 32);
 EXPECT_EQ(absl::cord_internal::TagToAllocatedSize(MAX_FLAT_TAG), 256 << 10);

 // Verify all tags to map perfectly back and forth, and
 // that sizes are monotonically increasing.
 size_t last_size = 0;
 for (int tag = FLAT; tag <= MAX_FLAT_TAG; ++tag) {
   size_t size = absl::cord_internal::TagToAllocatedSize(tag);
   ASSERT_GT(size, last_size);
   ASSERT_EQ(absl::cord_internal::TagToAllocatedSize(tag), size);
   last_size = size;
 }

 // All flat size from 32 - 512 are 8 byte granularity
 for (size_t size = 32; size <= 512; size += 8) {
   ASSERT_EQ(absl::cord_internal::RoundUpForTag(size), size);
   uint8_t tag = absl::cord_internal::AllocatedSizeToTag(size);
   ASSERT_EQ(absl::cord_internal::TagToAllocatedSize(tag), size);
 }

 // All flat sizes from 512 - 8192 are 64 byte granularity
 for (size_t size = 512; size <= 8192; size += 64) {
   ASSERT_EQ(absl::cord_internal::RoundUpForTag(size), size);
   uint8_t tag = absl::cord_internal::AllocatedSizeToTag(size);
   ASSERT_EQ(absl::cord_internal::TagToAllocatedSize(tag), size);
 }

 // All flat sizes from 8KB to 256KB are 4KB granularity
 for (size_t size = 8192; size <= 256 * 1024; size += 4 * 1024) {
   ASSERT_EQ(absl::cord_internal::RoundUpForTag(size), size);
   uint8_t tag = absl::cord_internal::AllocatedSizeToTag(size);
   ASSERT_EQ(absl::cord_internal::TagToAllocatedSize(tag), size);
 }
}

TEST(CordRepFlat, MaxFlatSize) {
 CordRepFlat* flat = CordRepFlat::New(kMaxFlatLength);
 EXPECT_EQ(flat->Capacity(), kMaxFlatLength);
 CordRep::Unref(flat);

 flat = CordRepFlat::New(kMaxFlatLength * 4);
 EXPECT_EQ(flat->Capacity(), kMaxFlatLength);
 CordRep::Unref(flat);
}

TEST(CordRepFlat, MaxLargeFlatSize) {
 const size_t size = 256 * 1024 - kFlatOverhead;
 CordRepFlat* flat = CordRepFlat::New(CordRepFlat::Large(), size);
 EXPECT_GE(flat->Capacity(), size);
 CordRep::Unref(flat);
}

TEST(CordRepFlat, AllFlatSizes) {
 const size_t kMaxSize = 256 * 1024;
 for (size_t size = 32; size <= kMaxSize; size *=2) {
   const size_t length = size - kFlatOverhead - 1;
   CordRepFlat* flat = CordRepFlat::New(CordRepFlat::Large(), length);
   EXPECT_GE(flat->Capacity(), length);
   memset(flat->Data(), 0xCD, flat->Capacity());
   CordRep::Unref(flat);
 }
}

TEST_P(CordTest, AllFlatSizes) {
 using absl::strings_internal::CordTestAccess;

 for (size_t s = 0; s < CordTestAccess::MaxFlatLength(); s++) {
   // Make a string of length s.
   std::string src;
   while (src.size() < s) {
     src.push_back('a' + (src.size() % 26));
   }

   absl::Cord dst(src);
   MaybeHarden(dst);
   EXPECT_EQ(std::string(dst), src) << s;
 }
}

// We create a Cord at least 128GB in size using the fact that Cords can
// internally reference-count; thus the Cord is enormous without actually
// consuming very much memory.
TEST_P(CordTest, GigabyteCordFromExternal) {
 const size_t one_gig = 1024U * 1024U * 1024U;
 size_t max_size = 2 * one_gig;
 if (sizeof(max_size) > 4) max_size = 128 * one_gig;

 size_t length = 128 * 1024;
 char* data = new char[length];
 absl::Cord from = absl::MakeCordFromExternal(
     absl::string_view(data, length),
     [](absl::string_view sv) { delete[] sv.data(); });

 // This loop may seem odd due to its combination of exponential doubling of
 // size and incremental size increases.  We do it incrementally to be sure the
 // Cord will need rebalancing and will exercise code that, in the past, has
 // caused crashes in production.  We grow exponentially so that the code will
 // execute in a reasonable amount of time.
 absl::Cord c;
 c.Append(from);
 while (c.size() < max_size) {
   c.Append(c);
   c.Append(from);
   c.Append(from);
   c.Append(from);
   c.Append(from);
   MaybeHarden(c);
 }

 for (int i = 0; i < 1024; ++i) {
   c.Append(from);
 }
 LOG(INFO) << "Made a Cord with " << c.size() << " bytes!";
 // Note: on a 32-bit build, this comes out to   2,818,048,000 bytes.
 // Note: on a 64-bit build, this comes out to 171,932,385,280 bytes.
}

static absl::Cord MakeExternalCord(int size) {
 char* buffer = new char[size];
 memset(buffer, 'x', size);
 absl::Cord cord;
 cord.Append(absl::MakeCordFromExternal(
     absl::string_view(buffer, size),
     [](absl::string_view s) { delete[] s.data(); }));
 return cord;
}

// Extern to fool clang that this is not constant. Needed to suppress
// a warning of unsafe code we want to test.
extern bool my_unique_true_boolean;
bool my_unique_true_boolean = true;

TEST_P(CordTest, Assignment) {
 absl::Cord x(absl::string_view("hi there"));
 absl::Cord y(x);
 MaybeHarden(y);
 ASSERT_EQ(x.ExpectedChecksum(), absl::nullopt);
 ASSERT_EQ(std::string(x), "hi there");
 ASSERT_EQ(std::string(y), "hi there");
 ASSERT_TRUE(x == y);
 ASSERT_TRUE(x <= y);
 ASSERT_TRUE(y <= x);

 x = absl::string_view("foo");
 ASSERT_EQ(std::string(x), "foo");
 ASSERT_EQ(std::string(y), "hi there");
 ASSERT_TRUE(x < y);
 ASSERT_TRUE(y > x);
 ASSERT_TRUE(x != y);
 ASSERT_TRUE(x <= y);
 ASSERT_TRUE(y >= x);

 x = "foo";
 ASSERT_EQ(x, "foo");

 // Test that going from inline rep to tree we don't leak memory.
 std::vector<std::pair<absl::string_view, absl::string_view>>
     test_string_pairs = {{"hi there", "foo"},
                          {"loooooong coooooord", "short cord"},
                          {"short cord", "loooooong coooooord"},
                          {"loooooong coooooord1", "loooooong coooooord2"}};
 for (std::pair<absl::string_view, absl::string_view> test_strings :
      test_string_pairs) {
   absl::Cord tmp(test_strings.first);
   absl::Cord z(std::move(tmp));
   ASSERT_EQ(std::string(z), test_strings.first);
   tmp = test_strings.second;
   z = std::move(tmp);
   ASSERT_EQ(std::string(z), test_strings.second);
 }
 {
   // Test that self-move assignment doesn't crash/leak.
   // Do not write such code!
   absl::Cord my_small_cord("foo");
   absl::Cord my_big_cord("loooooong coooooord");
   // Bypass clang's warning on self move-assignment.
   absl::Cord* my_small_alias =
       my_unique_true_boolean ? &my_small_cord : &my_big_cord;
   absl::Cord* my_big_alias =
       !my_unique_true_boolean ? &my_small_cord : &my_big_cord;

   *my_small_alias = std::move(my_small_cord);
   *my_big_alias = std::move(my_big_cord);
   // my_small_cord and my_big_cord are in an unspecified but valid
   // state, and will be correctly destroyed here.
 }
}

TEST_P(CordTest, StartsEndsWith) {
 absl::Cord x(absl::string_view("abcde"));
 MaybeHarden(x);
 absl::Cord empty("");

 ASSERT_TRUE(x.StartsWith(absl::Cord("abcde")));
 ASSERT_TRUE(x.StartsWith(absl::Cord("abc")));
 ASSERT_TRUE(x.StartsWith(absl::Cord("")));
 ASSERT_TRUE(empty.StartsWith(absl::Cord("")));
 ASSERT_TRUE(x.EndsWith(absl::Cord("abcde")));
 ASSERT_TRUE(x.EndsWith(absl::Cord("cde")));
 ASSERT_TRUE(x.EndsWith(absl::Cord("")));
 ASSERT_TRUE(empty.EndsWith(absl::Cord("")));

 ASSERT_TRUE(!x.StartsWith(absl::Cord("xyz")));
 ASSERT_TRUE(!empty.StartsWith(absl::Cord("xyz")));
 ASSERT_TRUE(!x.EndsWith(absl::Cord("xyz")));
 ASSERT_TRUE(!empty.EndsWith(absl::Cord("xyz")));

 ASSERT_TRUE(x.StartsWith("abcde"));
 ASSERT_TRUE(x.StartsWith("abc"));
 ASSERT_TRUE(x.StartsWith(""));
 ASSERT_TRUE(empty.StartsWith(""));
 ASSERT_TRUE(x.EndsWith("abcde"));
 ASSERT_TRUE(x.EndsWith("cde"));
 ASSERT_TRUE(x.EndsWith(""));
 ASSERT_TRUE(empty.EndsWith(""));

 ASSERT_TRUE(!x.StartsWith("xyz"));
 ASSERT_TRUE(!empty.StartsWith("xyz"));
 ASSERT_TRUE(!x.EndsWith("xyz"));
 ASSERT_TRUE(!empty.EndsWith("xyz"));
}

TEST_P(CordTest, Contains) {
 auto flat_haystack = absl::Cord("this is a flat cord");
 auto fragmented_haystack = absl::MakeFragmentedCord(
     {"this", " ", "is", " ", "a", " ", "fragmented", " ", "cord"});

 EXPECT_TRUE(flat_haystack.Contains(""));
 EXPECT_TRUE(fragmented_haystack.Contains(""));
 EXPECT_TRUE(flat_haystack.Contains(absl::Cord("")));
 EXPECT_TRUE(fragmented_haystack.Contains(absl::Cord("")));
 EXPECT_TRUE(absl::Cord("").Contains(""));
 EXPECT_TRUE(absl::Cord("").Contains(absl::Cord("")));
 EXPECT_FALSE(absl::Cord("").Contains(flat_haystack));
 EXPECT_FALSE(absl::Cord("").Contains(fragmented_haystack));

 EXPECT_FALSE(flat_haystack.Contains("z"));
 EXPECT_FALSE(fragmented_haystack.Contains("z"));
 EXPECT_FALSE(flat_haystack.Contains(absl::Cord("z")));
 EXPECT_FALSE(fragmented_haystack.Contains(absl::Cord("z")));

 EXPECT_FALSE(flat_haystack.Contains("is an"));
 EXPECT_FALSE(fragmented_haystack.Contains("is an"));
 EXPECT_FALSE(flat_haystack.Contains(absl::Cord("is an")));
 EXPECT_FALSE(fragmented_haystack.Contains(absl::Cord("is an")));
 EXPECT_FALSE(
     flat_haystack.Contains(absl::MakeFragmentedCord({"is", " ", "an"})));
 EXPECT_FALSE(fragmented_haystack.Contains(
     absl::MakeFragmentedCord({"is", " ", "an"})));

 EXPECT_TRUE(flat_haystack.Contains("is a"));
 EXPECT_TRUE(fragmented_haystack.Contains("is a"));
 EXPECT_TRUE(flat_haystack.Contains(absl::Cord("is a")));
 EXPECT_TRUE(fragmented_haystack.Contains(absl::Cord("is a")));
 EXPECT_TRUE(
     flat_haystack.Contains(absl::MakeFragmentedCord({"is", " ", "a"})));
 EXPECT_TRUE(
     fragmented_haystack.Contains(absl::MakeFragmentedCord({"is", " ", "a"})));
}

TEST_P(CordTest, Find) {
 auto flat_haystack = absl::Cord("this is a flat cord");
 auto fragmented_haystack = absl::MakeFragmentedCord(
     {"this", " ", "is", " ", "a", " ", "fragmented", " ", "cord"});
 auto empty_haystack = absl::Cord("");

 EXPECT_EQ(flat_haystack.Find(""), flat_haystack.char_begin());
 EXPECT_EQ(fragmented_haystack.Find(""), fragmented_haystack.char_begin());
 EXPECT_EQ(flat_haystack.Find(absl::Cord("")), flat_haystack.char_begin());
 EXPECT_EQ(fragmented_haystack.Find(absl::Cord("")),
           fragmented_haystack.char_begin());
 EXPECT_EQ(empty_haystack.Find(""), empty_haystack.char_begin());
 EXPECT_EQ(empty_haystack.Find(absl::Cord("")), empty_haystack.char_begin());
 EXPECT_EQ(empty_haystack.Find(flat_haystack), empty_haystack.char_end());
 EXPECT_EQ(empty_haystack.Find(fragmented_haystack),
           empty_haystack.char_end());

 EXPECT_EQ(flat_haystack.Find("z"), flat_haystack.char_end());
 EXPECT_EQ(fragmented_haystack.Find("z"), fragmented_haystack.char_end());
 EXPECT_EQ(flat_haystack.Find(absl::Cord("z")), flat_haystack.char_end());
 EXPECT_EQ(fragmented_haystack.Find(absl::Cord("z")),
           fragmented_haystack.char_end());

 EXPECT_EQ(flat_haystack.Find("is an"), flat_haystack.char_end());
 EXPECT_EQ(fragmented_haystack.Find("is an"), fragmented_haystack.char_end());
 EXPECT_EQ(flat_haystack.Find(absl::Cord("is an")), flat_haystack.char_end());
 EXPECT_EQ(fragmented_haystack.Find(absl::Cord("is an")),
           fragmented_haystack.char_end());
 EXPECT_EQ(flat_haystack.Find(absl::MakeFragmentedCord({"is", " ", "an"})),
           flat_haystack.char_end());
 EXPECT_EQ(
     fragmented_haystack.Find(absl::MakeFragmentedCord({"is", " ", "an"})),
     fragmented_haystack.char_end());

 EXPECT_EQ(flat_haystack.Find("is a"),
           std::next(flat_haystack.char_begin(), 5));
 EXPECT_EQ(fragmented_haystack.Find("is a"),
           std::next(fragmented_haystack.char_begin(), 5));
 EXPECT_EQ(flat_haystack.Find(absl::Cord("is a")),
           std::next(flat_haystack.char_begin(), 5));
 EXPECT_EQ(fragmented_haystack.Find(absl::Cord("is a")),
           std::next(fragmented_haystack.char_begin(), 5));
 EXPECT_EQ(flat_haystack.Find(absl::MakeFragmentedCord({"is", " ", "a"})),
           std::next(flat_haystack.char_begin(), 5));
 EXPECT_EQ(
     fragmented_haystack.Find(absl::MakeFragmentedCord({"is", " ", "a"})),
     std::next(fragmented_haystack.char_begin(), 5));
}

TEST_P(CordTest, Subcord) {
 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 const std::string s = RandomLowercaseString(&rng, 1024);

 absl::Cord a;
 AppendWithFragments(s, &rng, &a);
 MaybeHarden(a);
 ASSERT_EQ(s, std::string(a));

 // Check subcords of a, from a variety of interesting points.
 std::set<size_t> positions;
 for (int i = 0; i <= 32; ++i) {
   positions.insert(i);
   positions.insert(i * 32 - 1);
   positions.insert(i * 32);
   positions.insert(i * 32 + 1);
   positions.insert(a.size() - i);
 }
 positions.insert(237);
 positions.insert(732);
 for (size_t pos : positions) {
   if (pos > a.size()) continue;
   for (size_t end_pos : positions) {
     if (end_pos < pos || end_pos > a.size()) continue;
     absl::Cord sa = a.Subcord(pos, end_pos - pos);
     ASSERT_EQ(absl::string_view(s).substr(pos, end_pos - pos),
               std::string(sa))
         << a;
     if (pos != 0 || end_pos != a.size()) {
       ASSERT_EQ(sa.ExpectedChecksum(), absl::nullopt);
     }
   }
 }

 // Do the same thing for an inline cord.
 const std::string sh = "short";
 absl::Cord c(sh);
 for (size_t pos = 0; pos <= sh.size(); ++pos) {
   for (size_t n = 0; n <= sh.size() - pos; ++n) {
     absl::Cord sc = c.Subcord(pos, n);
     ASSERT_EQ(sh.substr(pos, n), std::string(sc)) << c;
   }
 }

 // Check subcords of subcords.
 absl::Cord sa = a.Subcord(0, a.size());
 std::string ss = s.substr(0, s.size());
 while (sa.size() > 1) {
   sa = sa.Subcord(1, sa.size() - 2);
   ss = ss.substr(1, ss.size() - 2);
   ASSERT_EQ(ss, std::string(sa)) << a;
   if (HasFailure()) break;  // halt cascade
 }

 // It is OK to ask for too much.
 sa = a.Subcord(0, a.size() + 1);
 EXPECT_EQ(s, std::string(sa));

 // It is OK to ask for something beyond the end.
 sa = a.Subcord(a.size() + 1, 0);
 EXPECT_TRUE(sa.empty());
 sa = a.Subcord(a.size() + 1, 1);
 EXPECT_TRUE(sa.empty());
}

TEST_P(CordTest, Swap) {
 absl::string_view a("Dexter");
 absl::string_view b("Mandark");
 absl::Cord x(a);
 absl::Cord y(b);
 MaybeHarden(x);
 swap(x, y);
 if (UseCrc()) {
   ASSERT_EQ(x.ExpectedChecksum(), absl::nullopt);
   ASSERT_EQ(y.ExpectedChecksum(), 1);
 }
 ASSERT_EQ(x, absl::Cord(b));
 ASSERT_EQ(y, absl::Cord(a));
 x.swap(y);
 if (UseCrc()) {
   ASSERT_EQ(x.ExpectedChecksum(), 1);
   ASSERT_EQ(y.ExpectedChecksum(), absl::nullopt);
 }
 ASSERT_EQ(x, absl::Cord(a));
 ASSERT_EQ(y, absl::Cord(b));
}

static void VerifyCopyToString(const absl::Cord& cord) {
 std::string initially_empty;
 absl::CopyCordToString(cord, &initially_empty);
 EXPECT_EQ(initially_empty, cord);

 constexpr size_t kInitialLength = 1024;
 std::string has_initial_contents(kInitialLength, 'x');
 const char* address_before_copy = has_initial_contents.data();
 absl::CopyCordToString(cord, &has_initial_contents);
 EXPECT_EQ(has_initial_contents, cord);

 if (cord.size() <= kInitialLength) {
   EXPECT_EQ(has_initial_contents.data(), address_before_copy)
       << "CopyCordToString allocated new string storage; "
          "has_initial_contents = \""
       << has_initial_contents << "\"";
 }
}

TEST_P(CordTest, CopyToString) {
 VerifyCopyToString(absl::Cord());  // empty cords cannot carry CRCs
 VerifyCopyToString(MaybeHardened(absl::Cord("small cord")));
 VerifyCopyToString(MaybeHardened(
     absl::MakeFragmentedCord({"fragmented ", "cord ", "to ", "test ",
                               "copying ", "to ", "a ", "string."})));
}

static void VerifyAppendCordToString(const absl::Cord& cord) {
 std::string initially_empty;
 absl::AppendCordToString(cord, &initially_empty);
 EXPECT_EQ(initially_empty, cord);

 const absl::string_view kInitialContents = "initial contents.";
 std::string expected_after_append =
     absl::StrCat(kInitialContents, std::string(cord));

 std::string no_reserve(kInitialContents);
 absl::AppendCordToString(cord, &no_reserve);
 EXPECT_EQ(no_reserve, expected_after_append);

 std::string has_reserved_capacity(kInitialContents);
 has_reserved_capacity.reserve(has_reserved_capacity.size() + cord.size());
 const char* address_before_copy = has_reserved_capacity.data();
 absl::AppendCordToString(cord, &has_reserved_capacity);
 EXPECT_EQ(has_reserved_capacity, expected_after_append);
 EXPECT_EQ(has_reserved_capacity.data(), address_before_copy)
     << "AppendCordToString allocated new string storage; "
        "has_reserved_capacity = \""
     << has_reserved_capacity << "\"";
}

TEST_P(CordTest, AppendToString) {
 VerifyAppendCordToString(absl::Cord());  // empty cords cannot carry CRCs
 VerifyAppendCordToString(MaybeHardened(absl::Cord("small cord")));
 VerifyAppendCordToString(MaybeHardened(
     absl::MakeFragmentedCord({"fragmented ", "cord ", "to ", "test ",
                               "appending ", "to ", "a ", "string."})));
}

TEST_P(CordTest, AppendEmptyBuffer) {
 absl::Cord cord;
 cord.Append(absl::CordBuffer());
 cord.Append(absl::CordBuffer::CreateWithDefaultLimit(2000));
}

TEST_P(CordTest, AppendEmptyBufferToFlat) {
 absl::Cord cord(std::string(2000, 'x'));
 cord.Append(absl::CordBuffer());
 cord.Append(absl::CordBuffer::CreateWithDefaultLimit(2000));
}

TEST_P(CordTest, AppendEmptyBufferToTree) {
 absl::Cord cord(std::string(2000, 'x'));
 cord.Append(std::string(2000, 'y'));
 cord.Append(absl::CordBuffer());
 cord.Append(absl::CordBuffer::CreateWithDefaultLimit(2000));
}

TEST_P(CordTest, AppendSmallBuffer) {
 absl::Cord cord;
 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(3);
 ASSERT_THAT(buffer.capacity(), Le(15));
 memcpy(buffer.data(), "Abc", 3);
 buffer.SetLength(3);
 cord.Append(std::move(buffer));
 EXPECT_EQ(buffer.length(), 0);    // NOLINT
 EXPECT_GT(buffer.capacity(), 0);  // NOLINT

 buffer = absl::CordBuffer::CreateWithDefaultLimit(3);
 memcpy(buffer.data(), "defgh", 5);
 buffer.SetLength(5);
 cord.Append(std::move(buffer));
 EXPECT_EQ(buffer.length(), 0);    // NOLINT
 EXPECT_GT(buffer.capacity(), 0);  // NOLINT

 EXPECT_THAT(cord.Chunks(), ElementsAre("Abcdefgh"));
}

TEST_P(CordTest, AppendAndPrependBufferArePrecise) {
 // Create a cord large enough to force 40KB flats.
 std::string test_data(absl::cord_internal::kMaxFlatLength * 10, 'x');
 absl::Cord cord1(test_data);
 absl::Cord cord2(test_data);
 const size_t size1 = cord1.EstimatedMemoryUsage();
 const size_t size2 = cord2.EstimatedMemoryUsage();

 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(3);
 memcpy(buffer.data(), "Abc", 3);
 buffer.SetLength(3);
 cord1.Append(std::move(buffer));

 buffer = absl::CordBuffer::CreateWithDefaultLimit(3);
 memcpy(buffer.data(), "Abc", 3);
 buffer.SetLength(3);
 cord2.Prepend(std::move(buffer));

#ifndef NDEBUG
 // Allow 32 bytes new CordRepFlat, and 128 bytes for 'glue nodes'
 constexpr size_t kMaxDelta = 128 + 32;
#else
 // Allow 256 bytes extra for 'allocation debug overhead'
 constexpr size_t kMaxDelta = 128 + 32 + 256;
#endif

 EXPECT_LE(cord1.EstimatedMemoryUsage() - size1, kMaxDelta);
 EXPECT_LE(cord2.EstimatedMemoryUsage() - size2, kMaxDelta);

 EXPECT_EQ(cord1, absl::StrCat(test_data, "Abc"));
 EXPECT_EQ(cord2, absl::StrCat("Abc", test_data));
}

TEST_P(CordTest, PrependSmallBuffer) {
 absl::Cord cord;
 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(3);
 ASSERT_THAT(buffer.capacity(), Le(15));
 memcpy(buffer.data(), "Abc", 3);
 buffer.SetLength(3);
 cord.Prepend(std::move(buffer));
 EXPECT_EQ(buffer.length(), 0);    // NOLINT
 EXPECT_GT(buffer.capacity(), 0);  // NOLINT

 buffer = absl::CordBuffer::CreateWithDefaultLimit(3);
 memcpy(buffer.data(), "defgh", 5);
 buffer.SetLength(5);
 cord.Prepend(std::move(buffer));
 EXPECT_EQ(buffer.length(), 0);    // NOLINT
 EXPECT_GT(buffer.capacity(), 0);  // NOLINT

 EXPECT_THAT(cord.Chunks(), ElementsAre("defghAbc"));
}

TEST_P(CordTest, AppendLargeBuffer) {
 absl::Cord cord;

 std::string s1(700, '1');
 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(s1.size());
 memcpy(buffer.data(), s1.data(), s1.size());
 buffer.SetLength(s1.size());
 cord.Append(std::move(buffer));
 EXPECT_EQ(buffer.length(), 0);    // NOLINT
 EXPECT_GT(buffer.capacity(), 0);  // NOLINT

 std::string s2(1000, '2');
 buffer = absl::CordBuffer::CreateWithDefaultLimit(s2.size());
 memcpy(buffer.data(), s2.data(), s2.size());
 buffer.SetLength(s2.size());
 cord.Append(std::move(buffer));
 EXPECT_EQ(buffer.length(), 0);    // NOLINT
 EXPECT_GT(buffer.capacity(), 0);  // NOLINT

 EXPECT_THAT(cord.Chunks(), ElementsAre(s1, s2));
}

TEST_P(CordTest, PrependLargeBuffer) {
 absl::Cord cord;

 std::string s1(700, '1');
 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(s1.size());
 memcpy(buffer.data(), s1.data(), s1.size());
 buffer.SetLength(s1.size());
 cord.Prepend(std::move(buffer));
 EXPECT_EQ(buffer.length(), 0);    // NOLINT
 EXPECT_GT(buffer.capacity(), 0);  // NOLINT

 std::string s2(1000, '2');
 buffer = absl::CordBuffer::CreateWithDefaultLimit(s2.size());
 memcpy(buffer.data(), s2.data(), s2.size());
 buffer.SetLength(s2.size());
 cord.Prepend(std::move(buffer));
 EXPECT_EQ(buffer.length(), 0);    // NOLINT
 EXPECT_GT(buffer.capacity(), 0);  // NOLINT

 EXPECT_THAT(cord.Chunks(), ElementsAre(s2, s1));
}

class CordAppendBufferTest : public testing::TestWithParam<bool> {
public:
 size_t is_default() const { return GetParam(); }

 // Returns human readable string representation of the test parameter.
 static std::string ToString(testing::TestParamInfo<bool> param) {
   return param.param ? "DefaultLimit" : "CustomLimit";
 }

 size_t limit() const {
   return is_default() ? absl::CordBuffer::kDefaultLimit
                       : absl::CordBuffer::kCustomLimit;
 }

 size_t maximum_payload() const {
   return is_default() ? absl::CordBuffer::MaximumPayload()
                       : absl::CordBuffer::MaximumPayload(limit());
 }

 absl::CordBuffer GetAppendBuffer(absl::Cord& cord, size_t capacity,
                                  size_t min_capacity = 16) {
   return is_default()
              ? cord.GetAppendBuffer(capacity, min_capacity)
              : cord.GetCustomAppendBuffer(limit(), capacity, min_capacity);
 }
};

INSTANTIATE_TEST_SUITE_P(WithParam, CordAppendBufferTest, testing::Bool(),
                        CordAppendBufferTest::ToString);

TEST_P(CordAppendBufferTest, GetAppendBufferOnEmptyCord) {
 absl::Cord cord;
 absl::CordBuffer buffer = GetAppendBuffer(cord, 1000);
 EXPECT_GE(buffer.capacity(), 1000);
 EXPECT_EQ(buffer.length(), 0);
}

TEST_P(CordAppendBufferTest, GetAppendBufferOnInlinedCord) {
 static constexpr int kInlinedSize = sizeof(absl::CordBuffer) - 1;
 for (int size : {6, kInlinedSize - 3, kInlinedSize - 2, 1000}) {
   absl::Cord cord("Abc");
   absl::CordBuffer buffer = GetAppendBuffer(cord, size, 1);
   EXPECT_GE(buffer.capacity(), 3 + size);
   EXPECT_EQ(buffer.length(), 3);
   EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc");
   EXPECT_TRUE(cord.empty());
 }
}

TEST_P(CordAppendBufferTest, GetAppendBufferOnInlinedCordCapacityCloseToMax) {
 // Cover the use case where we have a non empty inlined cord with some size
 // 'n', and ask for something like 'uint64_max - k', assuming internal logic
 // could overflow on 'uint64_max - k + size', and return a valid, but
 // inefficiently smaller buffer if it would provide is the max allowed size.
 for (size_t dist_from_max = 0; dist_from_max <= 4; ++dist_from_max) {
   absl::Cord cord("Abc");
   size_t size = std::numeric_limits<size_t>::max() - dist_from_max;
   absl::CordBuffer buffer = GetAppendBuffer(cord, size, 1);
   EXPECT_GE(buffer.capacity(), maximum_payload());
   EXPECT_EQ(buffer.length(), 3);
   EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc");
   EXPECT_TRUE(cord.empty());
 }
}

TEST_P(CordAppendBufferTest, GetAppendBufferOnFlat) {
 // Create a cord with a single flat and extra capacity
 absl::Cord cord;
 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
 const size_t expected_capacity = buffer.capacity();
 buffer.SetLength(3);
 memcpy(buffer.data(), "Abc", 3);
 cord.Append(std::move(buffer));

 buffer = GetAppendBuffer(cord, 6);
 EXPECT_EQ(buffer.capacity(), expected_capacity);
 EXPECT_EQ(buffer.length(), 3);
 EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc");
 EXPECT_TRUE(cord.empty());
}

TEST_P(CordAppendBufferTest, GetAppendBufferOnFlatWithoutMinCapacity) {
 // Create a cord with a single flat and extra capacity
 absl::Cord cord;
 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
 buffer.SetLength(30);
 memset(buffer.data(), 'x', 30);
 cord.Append(std::move(buffer));

 buffer = GetAppendBuffer(cord, 1000, 900);
 EXPECT_GE(buffer.capacity(), 1000);
 EXPECT_EQ(buffer.length(), 0);
 EXPECT_EQ(cord, std::string(30, 'x'));
}

TEST_P(CordAppendBufferTest, GetAppendBufferOnTree) {
 RandomEngine rng;
 for (int num_flats : {2, 3, 100}) {
   // Create a cord with `num_flats` flats and extra capacity
   absl::Cord cord;
   std::string prefix;
   std::string last;
   for (int i = 0; i < num_flats - 1; ++i) {
     prefix += last;
     last = RandomLowercaseString(&rng, 10);
     absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
     buffer.SetLength(10);
     memcpy(buffer.data(), last.data(), 10);
     cord.Append(std::move(buffer));
   }
   absl::CordBuffer buffer = GetAppendBuffer(cord, 6);
   EXPECT_GE(buffer.capacity(), 500);
   EXPECT_EQ(buffer.length(), 10);
   EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), last);
   EXPECT_EQ(cord, prefix);
 }
}

TEST_P(CordAppendBufferTest, GetAppendBufferOnTreeWithoutMinCapacity) {
 absl::Cord cord;
 for (int i = 0; i < 2; ++i) {
   absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
   buffer.SetLength(3);
   memcpy(buffer.data(), i ? "def" : "Abc", 3);
   cord.Append(std::move(buffer));
 }
 absl::CordBuffer buffer = GetAppendBuffer(cord, 1000, 900);
 EXPECT_GE(buffer.capacity(), 1000);
 EXPECT_EQ(buffer.length(), 0);
 EXPECT_EQ(cord, "Abcdef");
}

TEST_P(CordAppendBufferTest, GetAppendBufferOnSubstring) {
 // Create a large cord with a single flat and some extra capacity
 absl::Cord cord;
 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
 buffer.SetLength(450);
 memset(buffer.data(), 'x', 450);
 cord.Append(std::move(buffer));
 cord.RemovePrefix(1);

 // Deny on substring
 buffer = GetAppendBuffer(cord, 6);
 EXPECT_EQ(buffer.length(), 0);
 EXPECT_EQ(cord, std::string(449, 'x'));
}

TEST_P(CordAppendBufferTest, GetAppendBufferOnSharedCord) {
 // Create a shared cord with a single flat and extra capacity
 absl::Cord cord;
 absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
 buffer.SetLength(3);
 memcpy(buffer.data(), "Abc", 3);
 cord.Append(std::move(buffer));
 absl::Cord shared_cord = cord;

 // Deny on flat
 buffer = GetAppendBuffer(cord, 6);
 EXPECT_EQ(buffer.length(), 0);
 EXPECT_EQ(cord, "Abc");

 buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
 buffer.SetLength(3);
 memcpy(buffer.data(), "def", 3);
 cord.Append(std::move(buffer));
 shared_cord = cord;

 // Deny on tree
 buffer = GetAppendBuffer(cord, 6);
 EXPECT_EQ(buffer.length(), 0);
 EXPECT_EQ(cord, "Abcdef");
}

TEST_P(CordTest, TryFlatEmpty) {
 absl::Cord c;
 EXPECT_EQ(c.TryFlat(), "");
}

TEST_P(CordTest, TryFlatFlat) {
 absl::Cord c("hello");
 MaybeHarden(c);
 EXPECT_EQ(c.TryFlat(), "hello");
}

TEST_P(CordTest, TryFlatSubstrInlined) {
 absl::Cord c("hello");
 c.RemovePrefix(1);
 MaybeHarden(c);
 EXPECT_EQ(c.TryFlat(), "ello");
}

TEST_P(CordTest, TryFlatSubstrFlat) {
 absl::Cord c("longer than 15 bytes");
 absl::Cord sub = absl::CordTestPeer::MakeSubstring(c, 1, c.size() - 1);
 MaybeHarden(sub);
 EXPECT_EQ(sub.TryFlat(), "onger than 15 bytes");
}

TEST_P(CordTest, TryFlatConcat) {
 absl::Cord c = absl::MakeFragmentedCord({"hel", "lo"});
 MaybeHarden(c);
 EXPECT_EQ(c.TryFlat(), absl::nullopt);
}

TEST_P(CordTest, TryFlatExternal) {
 absl::Cord c = absl::MakeCordFromExternal("hell", [](absl::string_view) {});
 MaybeHarden(c);
 EXPECT_EQ(c.TryFlat(), "hell");
}

TEST_P(CordTest, TryFlatSubstrExternal) {
 absl::Cord c = absl::MakeCordFromExternal("hell", [](absl::string_view) {});
 absl::Cord sub = absl::CordTestPeer::MakeSubstring(c, 1, c.size() - 1);
 MaybeHarden(sub);
 EXPECT_EQ(sub.TryFlat(), "ell");
}

TEST_P(CordTest, TryFlatCommonlyAssumedInvariants) {
 // The behavior tested below is not part of the API contract of Cord, but it's
 // something we intend to be true in our current implementation.  This test
 // exists to detect and prevent accidental breakage of the implementation.
 absl::string_view fragments[] = {"A fragmented test",
                                  " cord",
                                  " to test subcords",
                                  " of ",
                                  "a",
                                  " cord for",
                                  " each chunk "
                                  "returned by the ",
                                  "iterator"};
 absl::Cord c = absl::MakeFragmentedCord(fragments);
 MaybeHarden(c);
 int fragment = 0;
 int offset = 0;
 absl::Cord::CharIterator itc = c.char_begin();
 for (absl::string_view sv : c.Chunks()) {
   absl::string_view expected = fragments[fragment];
   absl::Cord subcord1 = c.Subcord(offset, sv.length());
   absl::Cord subcord2 = absl::Cord::AdvanceAndRead(&itc, sv.size());
   EXPECT_EQ(subcord1.TryFlat(), expected);
   EXPECT_EQ(subcord2.TryFlat(), expected);
   ++fragment;
   offset += sv.length();
 }
}

static bool IsFlat(const absl::Cord& c) {
 return c.chunk_begin() == c.chunk_end() || ++c.chunk_begin() == c.chunk_end();
}

static void VerifyFlatten(absl::Cord c) {
 std::string old_contents(c);
 absl::string_view old_flat;
 bool already_flat_and_non_empty = IsFlat(c) && !c.empty();
 if (already_flat_and_non_empty) {
   old_flat = *c.chunk_begin();
 }
 absl::string_view new_flat = c.Flatten();

 // Verify that the contents of the flattened Cord are correct.
 EXPECT_EQ(new_flat, old_contents);
 EXPECT_EQ(std::string(c), old_contents);

 // If the Cord contained data and was already flat, verify that the data
 // wasn't copied.
 if (already_flat_and_non_empty) {
   EXPECT_EQ(old_flat.data(), new_flat.data())
       << "Allocated new memory even though the Cord was already flat.";
 }

 // Verify that the flattened Cord is in fact flat.
 EXPECT_TRUE(IsFlat(c));
}

TEST_P(CordTest, Flatten) {
 VerifyFlatten(absl::Cord());
 VerifyFlatten(MaybeHardened(absl::Cord("small cord")));
 VerifyFlatten(
     MaybeHardened(absl::Cord("larger than small buffer optimization")));
 VerifyFlatten(MaybeHardened(
     absl::MakeFragmentedCord({"small ", "fragmented ", "cord"})));

 // Test with a cord that is longer than the largest flat buffer
 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 VerifyFlatten(MaybeHardened(absl::Cord(RandomLowercaseString(&rng, 8192))));
}

// Test data
namespace {
class TestData {
private:
 std::vector<std::string> data_;

 // Return a std::string of the specified length.
 static std::string MakeString(int length) {
   std::string result;
   char buf[30];
   snprintf(buf, sizeof(buf), "(%d)", length);
   while (result.size() < length) {
     result += buf;
   }
   result.resize(length);
   return result;
 }

public:
 TestData() {
   // short strings increasing in length by one
   for (int i = 0; i < 30; i++) {
     data_.push_back(MakeString(i));
   }

   // strings around half kMaxFlatLength
   static const int kMaxFlatLength = 4096 - 9;
   static const int kHalf = kMaxFlatLength / 2;

   for (int i = -10; i <= +10; i++) {
     data_.push_back(MakeString(kHalf + i));
   }

   for (int i = -10; i <= +10; i++) {
     data_.push_back(MakeString(kMaxFlatLength + i));
   }
 }

 size_t size() const { return data_.size(); }
 const std::string& data(size_t i) const { return data_[i]; }
};
}  // namespace

TEST_P(CordTest, MultipleLengths) {
 TestData d;
 for (size_t i = 0; i < d.size(); i++) {
   std::string a = d.data(i);

   {  // Construct from Cord
     absl::Cord tmp(a);
     absl::Cord x(tmp);
     MaybeHarden(x);
     EXPECT_EQ(a, std::string(x)) << "'" << a << "'";
   }

   {  // Construct from absl::string_view
     absl::Cord x(a);
     MaybeHarden(x);
     EXPECT_EQ(a, std::string(x)) << "'" << a << "'";
   }

   {  // Append cord to self
     absl::Cord self(a);
     MaybeHarden(self);
     self.Append(self);
     EXPECT_EQ(a + a, std::string(self)) << "'" << a << "' + '" << a << "'";
   }

   {  // Prepend cord to self
     absl::Cord self(a);
     MaybeHarden(self);
     self.Prepend(self);
     EXPECT_EQ(a + a, std::string(self)) << "'" << a << "' + '" << a << "'";
   }

   // Try to append/prepend others
   for (size_t j = 0; j < d.size(); j++) {
     std::string b = d.data(j);

     {  // CopyFrom Cord
       absl::Cord x(a);
       absl::Cord y(b);
       MaybeHarden(x);
       x = y;
       EXPECT_EQ(b, std::string(x)) << "'" << a << "' + '" << b << "'";
     }

     {  // CopyFrom absl::string_view
       absl::Cord x(a);
       MaybeHarden(x);
       x = b;
       EXPECT_EQ(b, std::string(x)) << "'" << a << "' + '" << b << "'";
     }

     {  // Cord::Append(Cord)
       absl::Cord x(a);
       absl::Cord y(b);
       MaybeHarden(x);
       x.Append(y);
       EXPECT_EQ(a + b, std::string(x)) << "'" << a << "' + '" << b << "'";
     }

     {  // Cord::Append(absl::string_view)
       absl::Cord x(a);
       MaybeHarden(x);
       x.Append(b);
       EXPECT_EQ(a + b, std::string(x)) << "'" << a << "' + '" << b << "'";
     }

     {  // Cord::Prepend(Cord)
       absl::Cord x(a);
       absl::Cord y(b);
       MaybeHarden(x);
       x.Prepend(y);
       EXPECT_EQ(b + a, std::string(x)) << "'" << b << "' + '" << a << "'";
     }

     {  // Cord::Prepend(absl::string_view)
       absl::Cord x(a);
       MaybeHarden(x);
       x.Prepend(b);
       EXPECT_EQ(b + a, std::string(x)) << "'" << b << "' + '" << a << "'";
     }
   }
 }
}

namespace {

TEST_P(CordTest, RemoveSuffixWithExternalOrSubstring) {
 absl::Cord cord = absl::MakeCordFromExternal(
     "foo bar baz", [](absl::string_view s) { DoNothing(s, nullptr); });
 EXPECT_EQ("foo bar baz", std::string(cord));

 MaybeHarden(cord);

 // This RemoveSuffix() will wrap the EXTERNAL node in a SUBSTRING node.
 cord.RemoveSuffix(4);
 EXPECT_EQ("foo bar", std::string(cord));

 MaybeHarden(cord);

 // This RemoveSuffix() will adjust the SUBSTRING node in-place.
 cord.RemoveSuffix(4);
 EXPECT_EQ("foo", std::string(cord));
}

TEST_P(CordTest, RemoveSuffixMakesZeroLengthNode) {
 absl::Cord c;
 c.Append(absl::Cord(std::string(100, 'x')));
 absl::Cord other_ref = c;  // Prevent inplace appends
 EXPECT_THAT(other_ref, testing::Eq(c));
 MaybeHarden(c);
 c.Append(absl::Cord(std::string(200, 'y')));
 c.RemoveSuffix(200);
 EXPECT_EQ(std::string(100, 'x'), std::string(c));
}

}  // namespace

// CordSpliceTest contributed by hendrie.
namespace {

// Create a cord with an external memory block filled with 'z'
absl::Cord CordWithZedBlock(size_t size) {
 char* data = new char[size];
 if (size > 0) {
   memset(data, 'z', size);
 }
 absl::Cord cord = absl::MakeCordFromExternal(
     absl::string_view(data, size),
     [](absl::string_view s) { delete[] s.data(); });
 return cord;
}

// Establish that ZedBlock does what we think it does.
TEST_P(CordTest, CordSpliceTestZedBlock) {
 absl::Cord blob = CordWithZedBlock(10);
 MaybeHarden(blob);
 EXPECT_EQ(10, blob.size());
 std::string s;
 absl::CopyCordToString(blob, &s);
 EXPECT_EQ("zzzzzzzzzz", s);
}

TEST_P(CordTest, CordSpliceTestZedBlock0) {
 absl::Cord blob = CordWithZedBlock(0);
 MaybeHarden(blob);
 EXPECT_EQ(0, blob.size());
 std::string s;
 absl::CopyCordToString(blob, &s);
 EXPECT_EQ("", s);
}

TEST_P(CordTest, CordSpliceTestZedBlockSuffix1) {
 absl::Cord blob = CordWithZedBlock(10);
 MaybeHarden(blob);
 EXPECT_EQ(10, blob.size());
 absl::Cord suffix(blob);
 suffix.RemovePrefix(9);
 EXPECT_EQ(1, suffix.size());
 std::string s;
 absl::CopyCordToString(suffix, &s);
 EXPECT_EQ("z", s);
}

// Remove all of a prefix block
TEST_P(CordTest, CordSpliceTestZedBlockSuffix0) {
 absl::Cord blob = CordWithZedBlock(10);
 MaybeHarden(blob);
 EXPECT_EQ(10, blob.size());
 absl::Cord suffix(blob);
 suffix.RemovePrefix(10);
 EXPECT_EQ(0, suffix.size());
 std::string s;
 absl::CopyCordToString(suffix, &s);
 EXPECT_EQ("", s);
}

absl::Cord BigCord(size_t len, char v) {
 std::string s(len, v);
 return absl::Cord(s);
}

// Splice block into cord.
absl::Cord SpliceCord(const absl::Cord& blob, int64_t offset,
                     const absl::Cord& block) {
 CHECK_GE(offset, 0);
 CHECK_LE(static_cast<size_t>(offset) + block.size(), blob.size());
 absl::Cord result(blob);
 result.RemoveSuffix(blob.size() - offset);
 result.Append(block);
 absl::Cord suffix(blob);
 suffix.RemovePrefix(offset + block.size());
 result.Append(suffix);
 CHECK_EQ(blob.size(), result.size());
 return result;
}

// Taking an empty suffix of a block breaks appending.
TEST_P(CordTest, CordSpliceTestRemoveEntireBlock1) {
 absl::Cord zero = CordWithZedBlock(10);
 MaybeHarden(zero);
 absl::Cord suffix(zero);
 suffix.RemovePrefix(10);
 absl::Cord result;
 result.Append(suffix);
}

TEST_P(CordTest, CordSpliceTestRemoveEntireBlock2) {
 absl::Cord zero = CordWithZedBlock(10);
 MaybeHarden(zero);
 absl::Cord prefix(zero);
 prefix.RemoveSuffix(10);
 absl::Cord suffix(zero);
 suffix.RemovePrefix(10);
 absl::Cord result(prefix);
 result.Append(suffix);
}

TEST_P(CordTest, CordSpliceTestRemoveEntireBlock3) {
 absl::Cord blob = CordWithZedBlock(10);
 absl::Cord block = BigCord(10, 'b');
 MaybeHarden(blob);
 MaybeHarden(block);
 blob = SpliceCord(blob, 0, block);
}

struct CordCompareTestCase {
 template <typename LHS, typename RHS>
 CordCompareTestCase(const LHS& lhs, const RHS& rhs, bool use_crc)
     : lhs_cord(lhs), rhs_cord(rhs) {
   if (use_crc) {
     lhs_cord.SetExpectedChecksum(1);
   }
 }

 absl::Cord lhs_cord;
 absl::Cord rhs_cord;
};

const auto sign = [](int x) { return x == 0 ? 0 : (x > 0 ? 1 : -1); };

void VerifyComparison(const CordCompareTestCase& test_case) {
 std::string lhs_string(test_case.lhs_cord);
 std::string rhs_string(test_case.rhs_cord);
 int expected = sign(lhs_string.compare(rhs_string));
 EXPECT_EQ(expected, test_case.lhs_cord.Compare(test_case.rhs_cord))
     << "LHS=" << lhs_string << "; RHS=" << rhs_string;
 EXPECT_EQ(expected, test_case.lhs_cord.Compare(rhs_string))
     << "LHS=" << lhs_string << "; RHS=" << rhs_string;
 EXPECT_EQ(-expected, test_case.rhs_cord.Compare(test_case.lhs_cord))
     << "LHS=" << rhs_string << "; RHS=" << lhs_string;
 EXPECT_EQ(-expected, test_case.rhs_cord.Compare(lhs_string))
     << "LHS=" << rhs_string << "; RHS=" << lhs_string;
}

TEST_P(CordTest, Compare) {
 absl::Cord subcord("aaaaaBBBBBcccccDDDDD");
 subcord = subcord.Subcord(3, 10);

 absl::Cord tmp("aaaaaaaaaaaaaaaa");
 tmp.Append("BBBBBBBBBBBBBBBB");
 absl::Cord concat = absl::Cord("cccccccccccccccc");
 concat.Append("DDDDDDDDDDDDDDDD");
 concat.Prepend(tmp);

 absl::Cord concat2("aaaaaaaaaaaaa");
 concat2.Append("aaaBBBBBBBBBBBBBBBBccccc");
 concat2.Append("cccccccccccDDDDDDDDDDDDDD");
 concat2.Append("DD");

 const bool use_crc = UseCrc();

 std::vector<CordCompareTestCase> test_cases = {{
     // Inline cords
     {"abcdef", "abcdef", use_crc},
     {"abcdef", "abcdee", use_crc},
     {"abcdef", "abcdeg", use_crc},
     {"bbcdef", "abcdef", use_crc},
     {"bbcdef", "abcdeg", use_crc},
     {"abcdefa", "abcdef", use_crc},
     {"abcdef", "abcdefa", use_crc},

     // Small flat cords
     {"aaaaaBBBBBcccccDDDDD", "aaaaaBBBBBcccccDDDDD", use_crc},
     {"aaaaaBBBBBcccccDDDDD", "aaaaaBBBBBxccccDDDDD", use_crc},
     {"aaaaaBBBBBcxcccDDDDD", "aaaaaBBBBBcccccDDDDD", use_crc},
     {"aaaaaBBBBBxccccDDDDD", "aaaaaBBBBBcccccDDDDX", use_crc},
     {"aaaaaBBBBBcccccDDDDDa", "aaaaaBBBBBcccccDDDDD", use_crc},
     {"aaaaaBBBBBcccccDDDDD", "aaaaaBBBBBcccccDDDDDa", use_crc},

     // Subcords
     {subcord, subcord, use_crc},
     {subcord, "aaBBBBBccc", use_crc},
     {subcord, "aaBBBBBccd", use_crc},
     {subcord, "aaBBBBBccb", use_crc},
     {subcord, "aaBBBBBxcb", use_crc},
     {subcord, "aaBBBBBccca", use_crc},
     {subcord, "aaBBBBBcc", use_crc},

     // Concats
     {concat, concat, use_crc},
     {concat,
      "aaaaaaaaaaaaaaaaBBBBBBBBBBBBBBBBccccccccccccccccDDDDDDDDDDDDDDDD",
      use_crc},
     {concat,
      "aaaaaaaaaaaaaaaaBBBBBBBBBBBBBBBBcccccccccccccccxDDDDDDDDDDDDDDDD",
      use_crc},
     {concat,
      "aaaaaaaaaaaaaaaaBBBBBBBBBBBBBBBBacccccccccccccccDDDDDDDDDDDDDDDD",
      use_crc},
     {concat,
      "aaaaaaaaaaaaaaaaBBBBBBBBBBBBBBBBccccccccccccccccDDDDDDDDDDDDDDD",
      use_crc},
     {concat,
      "aaaaaaaaaaaaaaaaBBBBBBBBBBBBBBBBccccccccccccccccDDDDDDDDDDDDDDDDe",
      use_crc},

     {concat, concat2, use_crc},
 }};

 for (const auto& tc : test_cases) {
   VerifyComparison(tc);
 }
}

TEST_P(CordTest, CompareAfterAssign) {
 absl::Cord a("aaaaaa1111111");
 absl::Cord b("aaaaaa2222222");
 MaybeHarden(a);
 a = "cccccc";
 b = "cccccc";
 EXPECT_EQ(a, b);
 EXPECT_FALSE(a < b);

 a = "aaaa";
 b = "bbbbb";
 a = "";
 b = "";
 EXPECT_EQ(a, b);
 EXPECT_FALSE(a < b);
}

// Test CompareTo() and ComparePrefix() against string and substring
// comparison methods from basic_string.
static void TestCompare(const absl::Cord& c, const absl::Cord& d,
                       RandomEngine* rng) {
 // char_traits<char>::lt is guaranteed to do an unsigned comparison:
 // https://en.cppreference.com/w/cpp/string/char_traits/cmp. We also expect
 // Cord comparisons to be based on unsigned byte comparisons regardless of
 // whether char is signed.
 int expected = sign(std::string(c).compare(std::string(d)));
 EXPECT_EQ(expected, sign(c.Compare(d))) << c << ", " << d;
}

TEST_P(CordTest, CompareComparisonIsUnsigned) {
 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 std::uniform_int_distribution<uint32_t> uniform_uint8(0, 255);
 char x = static_cast<char>(uniform_uint8(rng));
 TestCompare(
     absl::Cord(std::string(GetUniformRandomUpTo(&rng, 100), x)),
     absl::Cord(std::string(GetUniformRandomUpTo(&rng, 100), x ^ 0x80)), &rng);
}

TEST_P(CordTest, CompareRandomComparisons) {
 const int kIters = 5000;
 RandomEngine rng(GTEST_FLAG_GET(random_seed));

 int n = GetUniformRandomUpTo(&rng, 5000);
 absl::Cord a[] = {MakeExternalCord(n),
                   absl::Cord("ant"),
                   absl::Cord("elephant"),
                   absl::Cord("giraffe"),
                   absl::Cord(std::string(GetUniformRandomUpTo(&rng, 100),
                                          GetUniformRandomUpTo(&rng, 100))),
                   absl::Cord(""),
                   absl::Cord("x"),
                   absl::Cord("A"),
                   absl::Cord("B"),
                   absl::Cord("C")};
 for (int i = 0; i < kIters; i++) {
   absl::Cord c, d;
   for (int j = 0; j < (i % 7) + 1; j++) {
     c.Append(a[GetUniformRandomUpTo(&rng, ABSL_ARRAYSIZE(a))]);
     d.Append(a[GetUniformRandomUpTo(&rng, ABSL_ARRAYSIZE(a))]);
   }
   std::bernoulli_distribution coin_flip(0.5);
   MaybeHarden(c);
   MaybeHarden(d);
   TestCompare(coin_flip(rng) ? c : absl::Cord(std::string(c)),
               coin_flip(rng) ? d : absl::Cord(std::string(d)), &rng);
 }
}

template <typename T1, typename T2>
void CompareOperators() {
 const T1 a("a");
 const T2 b("b");

 EXPECT_TRUE(a == a);
 // For pointer type (i.e. `const char*`), operator== compares the address
 // instead of the string, so `a == const char*("a")` isn't necessarily true.
 EXPECT_TRUE(std::is_pointer<T1>::value || a == T1("a"));
 EXPECT_TRUE(std::is_pointer<T2>::value || a == T2("a"));
 EXPECT_FALSE(a == b);

 EXPECT_TRUE(a != b);
 EXPECT_FALSE(a != a);

 EXPECT_TRUE(a < b);
 EXPECT_FALSE(b < a);

 EXPECT_TRUE(b > a);
 EXPECT_FALSE(a > b);

 EXPECT_TRUE(a >= a);
 EXPECT_TRUE(b >= a);
 EXPECT_FALSE(a >= b);

 EXPECT_TRUE(a <= a);
 EXPECT_TRUE(a <= b);
 EXPECT_FALSE(b <= a);
}

TEST_P(CordTest, ComparisonOperators_Cord_Cord) {
 CompareOperators<absl::Cord, absl::Cord>();
}

TEST_P(CordTest, ComparisonOperators_Cord_StringPiece) {
 CompareOperators<absl::Cord, absl::string_view>();
}

TEST_P(CordTest, ComparisonOperators_StringPiece_Cord) {
 CompareOperators<absl::string_view, absl::Cord>();
}

TEST_P(CordTest, ComparisonOperators_Cord_string) {
 CompareOperators<absl::Cord, std::string>();
}

TEST_P(CordTest, ComparisonOperators_string_Cord) {
 CompareOperators<std::string, absl::Cord>();
}

TEST_P(CordTest, ComparisonOperators_stdstring_Cord) {
 CompareOperators<std::string, absl::Cord>();
}

TEST_P(CordTest, ComparisonOperators_Cord_stdstring) {
 CompareOperators<absl::Cord, std::string>();
}

TEST_P(CordTest, ComparisonOperators_charstar_Cord) {
 CompareOperators<const char*, absl::Cord>();
}

TEST_P(CordTest, ComparisonOperators_Cord_charstar) {
 CompareOperators<absl::Cord, const char*>();
}

TEST_P(CordTest, ConstructFromExternalReleaserInvoked) {
 // Empty external memory means the releaser should be called immediately.
 {
   bool invoked = false;
   auto releaser = [&invoked](absl::string_view) { invoked = true; };
   {
     auto c = absl::MakeCordFromExternal("", releaser);
     EXPECT_THAT(c, testing::Eq(""));
     EXPECT_TRUE(invoked);
   }
 }

 // If the size of the data is small enough, a future constructor
 // implementation may copy the bytes and immediately invoke the releaser
 // instead of creating an external node. We make a large dummy std::string to
 // make this test independent of such an optimization.
 std::string large_dummy(2048, 'c');
 {
   bool invoked = false;
   auto releaser = [&invoked](absl::string_view) { invoked = true; };
   {
     auto c = absl::MakeCordFromExternal(large_dummy, releaser);
     EXPECT_THAT(c, testing::Eq(large_dummy));
     EXPECT_FALSE(invoked);
   }
   EXPECT_TRUE(invoked);
 }

 {
   bool invoked = false;
   auto releaser = [&invoked](absl::string_view) { invoked = true; };
   {
     absl::Cord copy;
     {
       auto c = absl::MakeCordFromExternal(large_dummy, releaser);
       copy = c;
       EXPECT_FALSE(invoked);
     }
     EXPECT_FALSE(invoked);
   }
   EXPECT_TRUE(invoked);
 }
}

TEST_P(CordTest, ConstructFromExternalCompareContents) {
 RandomEngine rng(GTEST_FLAG_GET(random_seed));

 for (int length = 1; length <= 2048; length *= 2) {
   std::string data = RandomLowercaseString(&rng, length);
   auto* external = new std::string(data);
   auto cord =
       absl::MakeCordFromExternal(*external, [external](absl::string_view sv) {
         EXPECT_EQ(external->data(), sv.data());
         EXPECT_EQ(external->size(), sv.size());
         delete external;
       });
   MaybeHarden(cord);
   EXPECT_EQ(data, cord);
 }
}

TEST_P(CordTest, ConstructFromExternalLargeReleaser) {
 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 constexpr size_t kLength = 256;
 std::string data = RandomLowercaseString(&rng, kLength);
 std::array<char, kLength> data_array;
 for (size_t i = 0; i < kLength; ++i) data_array[i] = data[i];
 bool invoked = false;
 auto releaser = [data_array, &invoked](absl::string_view data) {
   EXPECT_EQ(data, absl::string_view(data_array.data(), data_array.size()));
   invoked = true;
 };
 (void)MaybeHardened(absl::MakeCordFromExternal(data, releaser));
 EXPECT_TRUE(invoked);
}

TEST_P(CordTest, ConstructFromExternalFunctionPointerReleaser) {
 static absl::string_view data("hello world");
 static bool invoked;
 auto* releaser =
     static_cast<void (*)(absl::string_view)>([](absl::string_view sv) {
       EXPECT_EQ(data, sv);
       invoked = true;
     });
 invoked = false;
 (void)MaybeHardened(absl::MakeCordFromExternal(data, releaser));
 EXPECT_TRUE(invoked);

 invoked = false;
 (void)MaybeHardened(absl::MakeCordFromExternal(data, *releaser));
 EXPECT_TRUE(invoked);
}

TEST_P(CordTest, ConstructFromExternalMoveOnlyReleaser) {
 struct Releaser {
   explicit Releaser(bool* invoked) : invoked(invoked) {}
   Releaser(Releaser&& other) noexcept : invoked(other.invoked) {}
   void operator()(absl::string_view) const { *invoked = true; }

   bool* invoked;
 };

 bool invoked = false;
 (void)MaybeHardened(absl::MakeCordFromExternal("dummy", Releaser(&invoked)));
 EXPECT_TRUE(invoked);
}

TEST_P(CordTest, ConstructFromExternalNoArgLambda) {
 bool invoked = false;
 (void)MaybeHardened(
     absl::MakeCordFromExternal("dummy", [&invoked]() { invoked = true; }));
 EXPECT_TRUE(invoked);
}

TEST_P(CordTest, ConstructFromExternalStringViewArgLambda) {
 bool invoked = false;
 (void)MaybeHardened(absl::MakeCordFromExternal(
     "dummy", [&invoked](absl::string_view) { invoked = true; }));
 EXPECT_TRUE(invoked);
}

TEST_P(CordTest, ConstructFromExternalNonTrivialReleaserDestructor) {
 struct Releaser {
   explicit Releaser(bool* destroyed) : destroyed(destroyed) {}
   ~Releaser() { *destroyed = true; }
   void operator()(absl::string_view) const {}

   bool* destroyed;
 };

 bool destroyed = false;
 Releaser releaser(&destroyed);
 (void)MaybeHardened(absl::MakeCordFromExternal("dummy", releaser));
 EXPECT_TRUE(destroyed);
}

TEST_P(CordTest, ConstructFromExternalReferenceQualifierOverloads) {
 enum InvokedAs { kMissing, kLValue, kRValue };
 enum CopiedAs { kNone, kMove, kCopy };
 struct Tracker {
   CopiedAs copied_as = kNone;
   InvokedAs invoked_as = kMissing;

   void Record(InvokedAs rhs) {
     ASSERT_EQ(invoked_as, kMissing);
     invoked_as = rhs;
   }

   void Record(CopiedAs rhs) {
     if (copied_as == kNone || rhs == kCopy) copied_as = rhs;
   }
 } tracker;

 class Releaser {
  public:
   explicit Releaser(Tracker* tracker) : tr_(tracker) { *tracker = Tracker(); }
   Releaser(Releaser&& rhs) : tr_(rhs.tr_) { tr_->Record(kMove); }
   Releaser(const Releaser& rhs) : tr_(rhs.tr_) { tr_->Record(kCopy); }

   void operator()(absl::string_view) & { tr_->Record(kLValue); }
   void operator()(absl::string_view) && { tr_->Record(kRValue); }

  private:
   Tracker* tr_;
 };

 const Releaser releaser1(&tracker);
 (void)MaybeHardened(absl::MakeCordFromExternal("", releaser1));
 EXPECT_EQ(tracker.copied_as, kCopy);
 EXPECT_EQ(tracker.invoked_as, kRValue);

 const Releaser releaser2(&tracker);
 (void)MaybeHardened(absl::MakeCordFromExternal("", releaser2));
 EXPECT_EQ(tracker.copied_as, kCopy);
 EXPECT_EQ(tracker.invoked_as, kRValue);

 Releaser releaser3(&tracker);
 (void)MaybeHardened(absl::MakeCordFromExternal("", std::move(releaser3)));
 EXPECT_EQ(tracker.copied_as, kMove);
 EXPECT_EQ(tracker.invoked_as, kRValue);

 Releaser releaser4(&tracker);
 (void)MaybeHardened(absl::MakeCordFromExternal("dummy", releaser4));
 EXPECT_EQ(tracker.copied_as, kCopy);
 EXPECT_EQ(tracker.invoked_as, kRValue);

 const Releaser releaser5(&tracker);
 (void)MaybeHardened(absl::MakeCordFromExternal("dummy", releaser5));
 EXPECT_EQ(tracker.copied_as, kCopy);
 EXPECT_EQ(tracker.invoked_as, kRValue);

 Releaser releaser6(&tracker);
 (void)MaybeHardened(absl::MakeCordFromExternal("foo", std::move(releaser6)));
 EXPECT_EQ(tracker.copied_as, kMove);
 EXPECT_EQ(tracker.invoked_as, kRValue);
}

TEST_P(CordTest, ExternalMemoryBasicUsage) {
 static const char* strings[] = {"", "hello", "there"};
 for (const char* str : strings) {
   absl::Cord dst("(prefix)");
   MaybeHarden(dst);
   AddExternalMemory(str, &dst);
   MaybeHarden(dst);
   dst.Append("(suffix)");
   EXPECT_EQ((std::string("(prefix)") + str + std::string("(suffix)")),
             std::string(dst));
 }
}

TEST_P(CordTest, ExternalMemoryRemovePrefixSuffix) {
 // Exhaustively try all sub-strings.
 absl::Cord cord = MakeComposite();
 std::string s = std::string(cord);
 for (int offset = 0; offset <= s.size(); offset++) {
   for (int length = 0; length <= s.size() - offset; length++) {
     absl::Cord result(cord);
     MaybeHarden(result);
     result.RemovePrefix(offset);
     MaybeHarden(result);
     result.RemoveSuffix(result.size() - length);
     EXPECT_EQ(s.substr(offset, length), std::string(result))
         << offset << " " << length;
   }
 }
}

TEST_P(CordTest, ExternalMemoryGet) {
 absl::Cord cord("hello");
 AddExternalMemory(" world!", &cord);
 MaybeHarden(cord);
 AddExternalMemory(" how are ", &cord);
 cord.Append(" you?");
 MaybeHarden(cord);
 std::string s = std::string(cord);
 for (int i = 0; i < s.size(); i++) {
   EXPECT_EQ(s[i], cord[i]);
 }
}

// CordMemoryUsage tests verify the correctness of the EstimatedMemoryUsage()
// We use whiteboxed expectations based on our knowledge of the layout and size
// of empty and inlined cords, and flat nodes.

constexpr auto kFairShare = absl::CordMemoryAccounting::kFairShare;
constexpr auto kTotalMorePrecise =
   absl::CordMemoryAccounting::kTotalMorePrecise;

// Creates a cord of `n` `c` values, making sure no string stealing occurs.
absl::Cord MakeCord(size_t n, char c) {
 const std::string s(n, c);
 return absl::Cord(s);
}

TEST(CordTest, CordMemoryUsageEmpty) {
 absl::Cord cord;
 EXPECT_EQ(sizeof(absl::Cord), cord.EstimatedMemoryUsage());
 EXPECT_EQ(sizeof(absl::Cord), cord.EstimatedMemoryUsage(kFairShare));
 EXPECT_EQ(sizeof(absl::Cord), cord.EstimatedMemoryUsage(kTotalMorePrecise));
}

TEST(CordTest, CordMemoryUsageInlined) {
 absl::Cord a("hello");
 EXPECT_EQ(a.EstimatedMemoryUsage(), sizeof(absl::Cord));
 EXPECT_EQ(a.EstimatedMemoryUsage(kFairShare), sizeof(absl::Cord));
 EXPECT_EQ(a.EstimatedMemoryUsage(kTotalMorePrecise), sizeof(absl::Cord));
}

TEST(CordTest, CordMemoryUsageExternalMemory) {
 absl::Cord cord;
 AddExternalMemory(std::string(1000, 'x'), &cord);
 const size_t expected =
     sizeof(absl::Cord) + 1000 + sizeof(CordRepExternal) + sizeof(intptr_t);
 EXPECT_EQ(cord.EstimatedMemoryUsage(), expected);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kFairShare), expected);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kTotalMorePrecise), expected);
}

TEST(CordTest, CordMemoryUsageFlat) {
 absl::Cord cord = MakeCord(1000, 'a');
 const size_t flat_size =
     absl::CordTestPeer::Tree(cord)->flat()->AllocatedSize();
 EXPECT_EQ(cord.EstimatedMemoryUsage(), sizeof(absl::Cord) + flat_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kFairShare),
           sizeof(absl::Cord) + flat_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) + flat_size);
}

TEST(CordTest, CordMemoryUsageSubStringSharedFlat) {
 absl::Cord flat = MakeCord(2000, 'a');
 const size_t flat_size =
     absl::CordTestPeer::Tree(flat)->flat()->AllocatedSize();
 absl::Cord cord = flat.Subcord(500, 1000);
 EXPECT_EQ(cord.EstimatedMemoryUsage(),
           sizeof(absl::Cord) + sizeof(CordRepSubstring) + flat_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) + sizeof(CordRepSubstring) + flat_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kFairShare),
           sizeof(absl::Cord) + sizeof(CordRepSubstring) + flat_size / 2);
}

TEST(CordTest, CordMemoryUsageFlatShared) {
 absl::Cord shared = MakeCord(1000, 'a');
 absl::Cord cord(shared);
 const size_t flat_size =
     absl::CordTestPeer::Tree(cord)->flat()->AllocatedSize();
 EXPECT_EQ(cord.EstimatedMemoryUsage(), sizeof(absl::Cord) + flat_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) + flat_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kFairShare),
           sizeof(absl::Cord) + flat_size / 2);
}

TEST(CordTest, CordMemoryUsageFlatHardenedAndShared) {
 absl::Cord shared = MakeCord(1000, 'a');
 absl::Cord cord(shared);
 const size_t flat_size =
     absl::CordTestPeer::Tree(cord)->flat()->AllocatedSize();
 cord.SetExpectedChecksum(1);
 EXPECT_EQ(cord.EstimatedMemoryUsage(),
           sizeof(absl::Cord) + sizeof(CordRepCrc) + flat_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kFairShare),
           sizeof(absl::Cord) + sizeof(CordRepCrc) + flat_size / 2);

 absl::Cord cord2(cord);
 EXPECT_EQ(cord2.EstimatedMemoryUsage(),
           sizeof(absl::Cord) + sizeof(CordRepCrc) + flat_size);
 EXPECT_EQ(cord2.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) + sizeof(CordRepCrc) + flat_size);
 EXPECT_EQ(cord2.EstimatedMemoryUsage(kFairShare),
           sizeof(absl::Cord) + (sizeof(CordRepCrc) + flat_size / 2) / 2);
}

TEST(CordTest, CordMemoryUsageBTree) {
 absl::Cord cord1;
 size_t flats1_size = 0;
 absl::Cord flats1[4] = {MakeCord(1000, 'a'), MakeCord(1100, 'a'),
                         MakeCord(1200, 'a'), MakeCord(1300, 'a')};
 for (absl::Cord flat : flats1) {
   flats1_size += absl::CordTestPeer::Tree(flat)->flat()->AllocatedSize();
   cord1.Append(std::move(flat));
 }

 // Make sure the created cord is a BTREE tree. Under some builds such as
 // windows DLL, we may have ODR like effects on the flag, meaning the DLL
 // code will run with the picked up default.
 if (!absl::CordTestPeer::Tree(cord1)->IsBtree()) {
   LOG(WARNING) << "Cord library code not respecting btree flag";
   return;
 }

 size_t rep1_size = sizeof(CordRepBtree) + flats1_size;
 size_t rep1_shared_size = sizeof(CordRepBtree) + flats1_size / 2;

 EXPECT_EQ(cord1.EstimatedMemoryUsage(), sizeof(absl::Cord) + rep1_size);
 EXPECT_EQ(cord1.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) + rep1_size);
 EXPECT_EQ(cord1.EstimatedMemoryUsage(kFairShare),
           sizeof(absl::Cord) + rep1_shared_size);

 absl::Cord cord2;
 size_t flats2_size = 0;
 absl::Cord flats2[4] = {MakeCord(600, 'a'), MakeCord(700, 'a'),
                         MakeCord(800, 'a'), MakeCord(900, 'a')};
 for (absl::Cord& flat : flats2) {
   flats2_size += absl::CordTestPeer::Tree(flat)->flat()->AllocatedSize();
   cord2.Append(std::move(flat));
 }
 size_t rep2_size = sizeof(CordRepBtree) + flats2_size;

 EXPECT_EQ(cord2.EstimatedMemoryUsage(), sizeof(absl::Cord) + rep2_size);
 EXPECT_EQ(cord2.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) + rep2_size);
 EXPECT_EQ(cord2.EstimatedMemoryUsage(kFairShare),
           sizeof(absl::Cord) + rep2_size);

 absl::Cord cord(cord1);
 cord.Append(std::move(cord2));

 EXPECT_EQ(cord.EstimatedMemoryUsage(),
           sizeof(absl::Cord) + sizeof(CordRepBtree) + rep1_size + rep2_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) + sizeof(CordRepBtree) + rep1_size + rep2_size);
 EXPECT_EQ(cord.EstimatedMemoryUsage(kFairShare),
           sizeof(absl::Cord) + sizeof(CordRepBtree) + rep1_shared_size / 2 +
               rep2_size);
}

TEST(CordTest, TestHashFragmentation) {
 // Make sure we hit these boundary cases precisely.
 EXPECT_EQ(1024, absl::hash_internal::PiecewiseChunkSize());
 EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly({
     absl::Cord(),
     absl::MakeFragmentedCord({std::string(600, 'a'), std::string(600, 'a')}),
     absl::MakeFragmentedCord({std::string(1200, 'a')}),
     absl::MakeFragmentedCord({std::string(900, 'b'), std::string(900, 'b')}),
     absl::MakeFragmentedCord({std::string(1800, 'b')}),
     absl::MakeFragmentedCord(
         {std::string(2000, 'c'), std::string(2000, 'c')}),
     absl::MakeFragmentedCord({std::string(4000, 'c')}),
     absl::MakeFragmentedCord({std::string(1024, 'd')}),
     absl::MakeFragmentedCord({std::string(1023, 'd'), "d"}),
     absl::MakeFragmentedCord({std::string(1025, 'e')}),
     absl::MakeFragmentedCord({std::string(1024, 'e'), "e"}),
     absl::MakeFragmentedCord({std::string(1023, 'e'), "e", "e"}),
 }));
}

// Regtest for a change that had to be rolled back because it expanded out
// of the InlineRep too soon, which was observable through MemoryUsage().
TEST_P(CordTest, CordMemoryUsageInlineRep) {
 constexpr size_t kMaxInline = 15;  // Cord::InlineRep::N
 const std::string small_string(kMaxInline, 'x');
 absl::Cord c1(small_string);

 absl::Cord c2;
 c2.Append(small_string);
 EXPECT_EQ(c1, c2);
 EXPECT_EQ(c1.EstimatedMemoryUsage(), c2.EstimatedMemoryUsage());
}

TEST_P(CordTest, CordMemoryUsageTotalMorePreciseMode) {
 constexpr size_t kChunkSize = 2000;
 std::string tmp_str(kChunkSize, 'x');
 const absl::Cord flat(std::move(tmp_str));

 // Construct `fragmented` with two references into the same
 // underlying buffer shared with `flat`:
 absl::Cord fragmented(flat);
 fragmented.Append(flat);

 // Memory usage of `flat`, minus the top-level Cord object:
 const size_t flat_internal_usage =
     flat.EstimatedMemoryUsage() - sizeof(absl::Cord);

 // `fragmented` holds a Cord and a CordRepBtree. That tree points to two
 // copies of flat's internals, which we expect to dedup:
 EXPECT_EQ(fragmented.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) +
           sizeof(CordRepBtree) +
           flat_internal_usage);

 // This is a case where kTotal produces an overestimate:
 EXPECT_EQ(fragmented.EstimatedMemoryUsage(),
           sizeof(absl::Cord) +
           sizeof(CordRepBtree) +
           2 * flat_internal_usage);
}

TEST_P(CordTest, CordMemoryUsageTotalMorePreciseModeWithSubstring) {
 constexpr size_t kChunkSize = 2000;
 std::string tmp_str(kChunkSize, 'x');
 const absl::Cord flat(std::move(tmp_str));

 // Construct `fragmented` with two references into the same
 // underlying buffer shared with `flat`.
 //
 // This time, each reference is through a Subcord():
 absl::Cord fragmented;
 fragmented.Append(flat.Subcord(1, kChunkSize - 2));
 fragmented.Append(flat.Subcord(1, kChunkSize - 2));

 // Memory usage of `flat`, minus the top-level Cord object:
 const size_t flat_internal_usage =
     flat.EstimatedMemoryUsage() - sizeof(absl::Cord);

 // `fragmented` holds a Cord and a CordRepBtree. That tree points to two
 // CordRepSubstrings, each pointing at flat's internals.
 EXPECT_EQ(fragmented.EstimatedMemoryUsage(kTotalMorePrecise),
           sizeof(absl::Cord) +
           sizeof(CordRepBtree) +
           2 * sizeof(CordRepSubstring) +
           flat_internal_usage);

 // This is a case where kTotal produces an overestimate:
 EXPECT_EQ(fragmented.EstimatedMemoryUsage(),
           sizeof(absl::Cord) +
           sizeof(CordRepBtree) +
           2 * sizeof(CordRepSubstring) +
           2 * flat_internal_usage);
}
}  // namespace

// Regtest for 7510292 (fix a bug introduced by 7465150)
TEST_P(CordTest, Concat_Append) {
 // Create a rep of type CONCAT
 absl::Cord s1("foobarbarbarbarbar");
 MaybeHarden(s1);
 s1.Append("abcdefgabcdefgabcdefgabcdefgabcdefgabcdefgabcdefg");
 size_t size = s1.size();

 // Create a copy of s1 and append to it.
 absl::Cord s2 = s1;
 MaybeHarden(s2);
 s2.Append("x");

 // 7465150 modifies s1 when it shouldn't.
 EXPECT_EQ(s1.size(), size);
 EXPECT_EQ(s2.size(), size + 1);
}

TEST_P(CordTest, DiabolicalGrowth) {
 // This test exercises a diabolical Append(<one char>) on a cord, making the
 // cord shared before each Append call resulting in a terribly fragmented
 // resulting cord.
 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 const std::string expected = RandomLowercaseString(&rng, 5000);
 absl::Cord cord;
 for (char c : expected) {
   absl::Cord shared(cord);
   EXPECT_THAT(cord, testing::Eq(shared));
   cord.Append(absl::string_view(&c, 1));
   MaybeHarden(cord);
 }
 std::string value;
 absl::CopyCordToString(cord, &value);
 EXPECT_EQ(value, expected);
 LOG(INFO) << "Diabolical size allocated = " << cord.EstimatedMemoryUsage();
}

// The following tests check support for >4GB cords in 64-bit binaries, and
// 2GB-4GB cords in 32-bit binaries.  This function returns the large cord size
// that's appropriate for the binary.

// Construct a huge cord with the specified valid prefix.
static absl::Cord MakeHuge(absl::string_view prefix) {
 absl::Cord cord;
 if (sizeof(size_t) > 4) {
   // In 64-bit binaries, test 64-bit Cord support.
   const size_t size =
       static_cast<size_t>(std::numeric_limits<uint32_t>::max()) + 314;
   cord.Append(absl::MakeCordFromExternal(
       absl::string_view(prefix.data(), size),
       [](absl::string_view s) { DoNothing(s, nullptr); }));
 } else {
   // Cords are limited to 32-bit lengths in 32-bit binaries.  The following
   // tests check for use of "signed int" to represent Cord length/offset.
   // However absl::string_view does not allow lengths >= (1u<<31), so we need
   // to append in two parts;
   const size_t s1 = (1u << 31) - 1;
   // For shorter cord, `Append` copies the data rather than allocating a new
   // node. The threshold is currently set to 511, so `s2` needs to be bigger
   // to not trigger the copy.
   const size_t s2 = 600;
   cord.Append(absl::MakeCordFromExternal(
       absl::string_view(prefix.data(), s1),
       [](absl::string_view s) { DoNothing(s, nullptr); }));
   cord.Append(absl::MakeCordFromExternal(
       absl::string_view("", s2),
       [](absl::string_view s) { DoNothing(s, nullptr); }));
 }
 return cord;
}

TEST_P(CordTest, HugeCord) {
 absl::Cord cord = MakeHuge("huge cord");
 MaybeHarden(cord);

 const size_t acceptable_delta =
     100 + (UseCrc() ? sizeof(absl::cord_internal::CordRepCrc) : 0);
 EXPECT_LE(cord.size(), cord.EstimatedMemoryUsage());
 EXPECT_GE(cord.size() + acceptable_delta, cord.EstimatedMemoryUsage());
}

// Tests that Append() works ok when handed a self reference
TEST_P(CordTest, AppendSelf) {
 // Test the empty case.
 absl::Cord empty;
 MaybeHarden(empty);
 empty.Append(empty);
 ASSERT_EQ(empty, "");

 // We run the test until data is ~16K
 // This guarantees it covers small, medium and large data.
 std::string control_data = "Abc";
 absl::Cord data(control_data);
 while (control_data.length() < 0x4000) {
   MaybeHarden(data);
   data.Append(data);
   control_data.append(control_data);
   ASSERT_EQ(control_data, data);
 }
}

TEST_P(CordTest, MakeFragmentedCordFromInitializerList) {
 absl::Cord fragmented =
     absl::MakeFragmentedCord({"A ", "fragmented ", "Cord"});

 MaybeHarden(fragmented);

 EXPECT_EQ("A fragmented Cord", fragmented);

 auto chunk_it = fragmented.chunk_begin();

 ASSERT_TRUE(chunk_it != fragmented.chunk_end());
 EXPECT_EQ("A ", *chunk_it);

 ASSERT_TRUE(++chunk_it != fragmented.chunk_end());
 EXPECT_EQ("fragmented ", *chunk_it);

 ASSERT_TRUE(++chunk_it != fragmented.chunk_end());
 EXPECT_EQ("Cord", *chunk_it);

 ASSERT_TRUE(++chunk_it == fragmented.chunk_end());
}

TEST_P(CordTest, MakeFragmentedCordFromVector) {
 std::vector<absl::string_view> chunks = {"A ", "fragmented ", "Cord"};
 absl::Cord fragmented = absl::MakeFragmentedCord(chunks);

 MaybeHarden(fragmented);

 EXPECT_EQ("A fragmented Cord", fragmented);

 auto chunk_it = fragmented.chunk_begin();

 ASSERT_TRUE(chunk_it != fragmented.chunk_end());
 EXPECT_EQ("A ", *chunk_it);

 ASSERT_TRUE(++chunk_it != fragmented.chunk_end());
 EXPECT_EQ("fragmented ", *chunk_it);

 ASSERT_TRUE(++chunk_it != fragmented.chunk_end());
 EXPECT_EQ("Cord", *chunk_it);

 ASSERT_TRUE(++chunk_it == fragmented.chunk_end());
}

TEST_P(CordTest, CordChunkIteratorTraits) {
 static_assert(std::is_copy_constructible<absl::Cord::ChunkIterator>::value,
               "");
 static_assert(std::is_copy_assignable<absl::Cord::ChunkIterator>::value, "");

 // Move semantics to satisfy swappable via std::swap
 static_assert(std::is_move_constructible<absl::Cord::ChunkIterator>::value,
               "");
 static_assert(std::is_move_assignable<absl::Cord::ChunkIterator>::value, "");

 static_assert(
     std::is_same<
         std::iterator_traits<absl::Cord::ChunkIterator>::iterator_category,
         std::input_iterator_tag>::value,
     "");
 static_assert(
     std::is_same<std::iterator_traits<absl::Cord::ChunkIterator>::value_type,
                  absl::string_view>::value,
     "");
 static_assert(
     std::is_same<
         std::iterator_traits<absl::Cord::ChunkIterator>::difference_type,
         ptrdiff_t>::value,
     "");
 static_assert(
     std::is_same<std::iterator_traits<absl::Cord::ChunkIterator>::pointer,
                  const absl::string_view*>::value,
     "");
 static_assert(
     std::is_same<std::iterator_traits<absl::Cord::ChunkIterator>::reference,
                  absl::string_view>::value,
     "");
}

static void VerifyChunkIterator(const absl::Cord& cord,
                               size_t expected_chunks) {
 EXPECT_EQ(cord.chunk_begin() == cord.chunk_end(), cord.empty()) << cord;
 EXPECT_EQ(cord.chunk_begin() != cord.chunk_end(), !cord.empty());

 absl::Cord::ChunkRange range = cord.Chunks();
 EXPECT_EQ(range.begin() == range.end(), cord.empty());
 EXPECT_EQ(range.begin() != range.end(), !cord.empty());

 std::string content(cord);
 size_t pos = 0;
 auto pre_iter = cord.chunk_begin(), post_iter = cord.chunk_begin();
 size_t n_chunks = 0;
 while (pre_iter != cord.chunk_end() && post_iter != cord.chunk_end()) {
   EXPECT_FALSE(pre_iter == cord.chunk_end());   // NOLINT: explicitly test ==
   EXPECT_FALSE(post_iter == cord.chunk_end());  // NOLINT

   EXPECT_EQ(pre_iter, post_iter);
   EXPECT_EQ(*pre_iter, *post_iter);

   EXPECT_EQ(pre_iter->data(), (*pre_iter).data());
   EXPECT_EQ(pre_iter->size(), (*pre_iter).size());

   absl::string_view chunk = *pre_iter;
   EXPECT_FALSE(chunk.empty());
   EXPECT_LE(pos + chunk.size(), content.size());
   EXPECT_EQ(absl::string_view(content.c_str() + pos, chunk.size()), chunk);

   int n_equal_iterators = 0;
   for (absl::Cord::ChunkIterator it = range.begin(); it != range.end();
        ++it) {
     n_equal_iterators += static_cast<int>(it == pre_iter);
   }
   EXPECT_EQ(n_equal_iterators, 1);

   ++pre_iter;
   EXPECT_EQ(*post_iter++, chunk);

   pos += chunk.size();
   ++n_chunks;
 }
 EXPECT_EQ(expected_chunks, n_chunks);
 EXPECT_EQ(pos, content.size());
 EXPECT_TRUE(pre_iter == cord.chunk_end());   // NOLINT: explicitly test ==
 EXPECT_TRUE(post_iter == cord.chunk_end());  // NOLINT
}

TEST_P(CordTest, CordChunkIteratorOperations) {
 absl::Cord empty_cord;
 VerifyChunkIterator(empty_cord, 0);

 absl::Cord small_buffer_cord("small cord");
 MaybeHarden(small_buffer_cord);
 VerifyChunkIterator(small_buffer_cord, 1);

 absl::Cord flat_node_cord("larger than small buffer optimization");
 MaybeHarden(flat_node_cord);
 VerifyChunkIterator(flat_node_cord, 1);

 VerifyChunkIterator(MaybeHardened(absl::MakeFragmentedCord(
                         {"a ", "small ", "fragmented ", "cord ", "for ",
                          "testing ", "chunk ", "iterations."})),
                     8);

 absl::Cord reused_nodes_cord(std::string(40, 'c'));
 reused_nodes_cord.Prepend(absl::Cord(std::string(40, 'b')));
 MaybeHarden(reused_nodes_cord);
 reused_nodes_cord.Prepend(absl::Cord(std::string(40, 'a')));
 size_t expected_chunks = 3;
 for (int i = 0; i < 8; ++i) {
   reused_nodes_cord.Prepend(reused_nodes_cord);
   MaybeHarden(reused_nodes_cord);
   expected_chunks *= 2;
   VerifyChunkIterator(reused_nodes_cord, expected_chunks);
 }

 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 absl::Cord flat_cord(RandomLowercaseString(&rng, 256));
 absl::Cord subcords;
 for (int i = 0; i < 128; ++i) subcords.Prepend(flat_cord.Subcord(i, 128));
 VerifyChunkIterator(subcords, 128);
}


TEST_P(CordTest, AdvanceAndReadOnDataEdge) {
 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 const std::string data = RandomLowercaseString(&rng, 2000);
 for (bool as_flat : {true, false}) {
   SCOPED_TRACE(as_flat ? "Flat" : "External");

   absl::Cord cord =
       as_flat ? absl::Cord(data)
               : absl::MakeCordFromExternal(data, [](absl::string_view) {});
   auto it = cord.Chars().begin();
#if !defined(NDEBUG) || ABSL_OPTION_HARDENED
   EXPECT_DEATH_IF_SUPPORTED(cord.AdvanceAndRead(&it, 2001), ".*");
#endif

   it = cord.Chars().begin();
   absl::Cord frag = cord.AdvanceAndRead(&it, 2000);
   EXPECT_EQ(frag, data);
   EXPECT_TRUE(it == cord.Chars().end());

   it = cord.Chars().begin();
   frag = cord.AdvanceAndRead(&it, 200);
   EXPECT_EQ(frag, data.substr(0, 200));
   EXPECT_FALSE(it == cord.Chars().end());

   frag = cord.AdvanceAndRead(&it, 1500);
   EXPECT_EQ(frag, data.substr(200, 1500));
   EXPECT_FALSE(it == cord.Chars().end());

   frag = cord.AdvanceAndRead(&it, 300);
   EXPECT_EQ(frag, data.substr(1700, 300));
   EXPECT_TRUE(it == cord.Chars().end());
 }
}

TEST_P(CordTest, AdvanceAndReadOnSubstringDataEdge) {
 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 const std::string data = RandomLowercaseString(&rng, 2500);
 for (bool as_flat : {true, false}) {
   SCOPED_TRACE(as_flat ? "Flat" : "External");

   absl::Cord cord =
       as_flat ? absl::Cord(data)
               : absl::MakeCordFromExternal(data, [](absl::string_view) {});
   cord = cord.Subcord(200, 2000);
   const std::string substr = data.substr(200, 2000);

   auto it = cord.Chars().begin();
#if !defined(NDEBUG) || ABSL_OPTION_HARDENED
   EXPECT_DEATH_IF_SUPPORTED(cord.AdvanceAndRead(&it, 2001), ".*");
#endif

   it = cord.Chars().begin();
   absl::Cord frag = cord.AdvanceAndRead(&it, 2000);
   EXPECT_EQ(frag, substr);
   EXPECT_TRUE(it == cord.Chars().end());

   it = cord.Chars().begin();
   frag = cord.AdvanceAndRead(&it, 200);
   EXPECT_EQ(frag, substr.substr(0, 200));
   EXPECT_FALSE(it == cord.Chars().end());

   frag = cord.AdvanceAndRead(&it, 1500);
   EXPECT_EQ(frag, substr.substr(200, 1500));
   EXPECT_FALSE(it == cord.Chars().end());

   frag = cord.AdvanceAndRead(&it, 300);
   EXPECT_EQ(frag, substr.substr(1700, 300));
   EXPECT_TRUE(it == cord.Chars().end());
 }
}

TEST_P(CordTest, CharIteratorTraits) {
 static_assert(std::is_copy_constructible<absl::Cord::CharIterator>::value,
               "");
 static_assert(std::is_copy_assignable<absl::Cord::CharIterator>::value, "");

 // Move semantics to satisfy swappable via std::swap
 static_assert(std::is_move_constructible<absl::Cord::CharIterator>::value,
               "");
 static_assert(std::is_move_assignable<absl::Cord::CharIterator>::value, "");

 static_assert(
     std::is_same<
         std::iterator_traits<absl::Cord::CharIterator>::iterator_category,
         std::input_iterator_tag>::value,
     "");
 static_assert(
     std::is_same<std::iterator_traits<absl::Cord::CharIterator>::value_type,
                  char>::value,
     "");
 static_assert(
     std::is_same<
         std::iterator_traits<absl::Cord::CharIterator>::difference_type,
         ptrdiff_t>::value,
     "");
 static_assert(
     std::is_same<std::iterator_traits<absl::Cord::CharIterator>::pointer,
                  const char*>::value,
     "");
 static_assert(
     std::is_same<std::iterator_traits<absl::Cord::CharIterator>::reference,
                  const char&>::value,
     "");
}

static void VerifyCharIterator(const absl::Cord& cord) {
 EXPECT_EQ(cord.char_begin() == cord.char_end(), cord.empty());
 EXPECT_EQ(cord.char_begin() != cord.char_end(), !cord.empty());

 absl::Cord::CharRange range = cord.Chars();
 EXPECT_EQ(range.begin() == range.end(), cord.empty());
 EXPECT_EQ(range.begin() != range.end(), !cord.empty());

 size_t i = 0;
 absl::Cord::CharIterator pre_iter = cord.char_begin();
 absl::Cord::CharIterator post_iter = cord.char_begin();
 std::string content(cord);
 while (pre_iter != cord.char_end() && post_iter != cord.char_end()) {
   EXPECT_FALSE(pre_iter == cord.char_end());   // NOLINT: explicitly test ==
   EXPECT_FALSE(post_iter == cord.char_end());  // NOLINT

   EXPECT_LT(i, cord.size());
   EXPECT_EQ(content[i], *pre_iter);

   EXPECT_EQ(pre_iter, post_iter);
   EXPECT_EQ(*pre_iter, *post_iter);
   EXPECT_EQ(&*pre_iter, &*post_iter);

   const char* character_address = &*pre_iter;
   absl::Cord::CharIterator copy = pre_iter;
   ++copy;
   EXPECT_EQ(character_address, &*pre_iter);

   int n_equal_iterators = 0;
   for (absl::Cord::CharIterator it = range.begin(); it != range.end(); ++it) {
     n_equal_iterators += static_cast<int>(it == pre_iter);
   }
   EXPECT_EQ(n_equal_iterators, 1);

   absl::Cord::CharIterator advance_iter = range.begin();
   absl::Cord::Advance(&advance_iter, i);
   EXPECT_EQ(pre_iter, advance_iter);

   advance_iter = range.begin();
   EXPECT_EQ(absl::Cord::AdvanceAndRead(&advance_iter, i), cord.Subcord(0, i));
   EXPECT_EQ(pre_iter, advance_iter);

   advance_iter = pre_iter;
   absl::Cord::Advance(&advance_iter, cord.size() - i);
   EXPECT_EQ(range.end(), advance_iter);

   advance_iter = pre_iter;
   EXPECT_EQ(absl::Cord::AdvanceAndRead(&advance_iter, cord.size() - i),
             cord.Subcord(i, cord.size() - i));
   EXPECT_EQ(range.end(), advance_iter);

   ++i;
   ++pre_iter;
   post_iter++;
 }
 EXPECT_EQ(i, cord.size());
 EXPECT_TRUE(pre_iter == cord.char_end());   // NOLINT: explicitly test ==
 EXPECT_TRUE(post_iter == cord.char_end());  // NOLINT

 absl::Cord::CharIterator zero_advanced_end = cord.char_end();
 absl::Cord::Advance(&zero_advanced_end, 0);
 EXPECT_EQ(zero_advanced_end, cord.char_end());

 absl::Cord::CharIterator it = cord.char_begin();
 for (absl::string_view chunk : cord.Chunks()) {
   while (!chunk.empty()) {
     EXPECT_EQ(absl::Cord::ChunkRemaining(it), chunk);
     chunk.remove_prefix(1);
     ++it;
   }
 }
}

TEST_P(CordTest, CharIteratorOperations) {
 absl::Cord empty_cord;
 VerifyCharIterator(empty_cord);

 absl::Cord small_buffer_cord("small cord");
 MaybeHarden(small_buffer_cord);
 VerifyCharIterator(small_buffer_cord);

 absl::Cord flat_node_cord("larger than small buffer optimization");
 MaybeHarden(flat_node_cord);
 VerifyCharIterator(flat_node_cord);

 VerifyCharIterator(MaybeHardened(
     absl::MakeFragmentedCord({"a ", "small ", "fragmented ", "cord ", "for ",
                               "testing ", "character ", "iteration."})));

 absl::Cord reused_nodes_cord("ghi");
 reused_nodes_cord.Prepend(absl::Cord("def"));
 reused_nodes_cord.Prepend(absl::Cord("abc"));
 for (int i = 0; i < 4; ++i) {
   reused_nodes_cord.Prepend(reused_nodes_cord);
   MaybeHarden(reused_nodes_cord);
   VerifyCharIterator(reused_nodes_cord);
 }

 RandomEngine rng(GTEST_FLAG_GET(random_seed));
 absl::Cord flat_cord(RandomLowercaseString(&rng, 256));
 absl::Cord subcords;
 for (int i = 0; i < 4; ++i) {
   subcords.Prepend(flat_cord.Subcord(16 * i, 128));
   MaybeHarden(subcords);
 }
 VerifyCharIterator(subcords);
}

TEST_P(CordTest, CharIteratorAdvanceAndRead) {
 // Create a Cord holding 6 flats of 2500 bytes each, and then iterate over it
 // reading 150, 1500, 2500 and 3000 bytes. This will result in all possible
 // partial, full and straddled read combinations including reads below
 // kMaxBytesToCopy. b/197776822 surfaced a bug for a specific partial, small
 // read 'at end' on Cord which caused a failure on attempting to read past the
 // end in CordRepBtreeReader which was not covered by any existing test.
 constexpr int kBlocks = 6;
 constexpr size_t kBlockSize = 2500;
 constexpr size_t kChunkSize1 = 1500;
 constexpr size_t kChunkSize2 = 2500;
 constexpr size_t kChunkSize3 = 3000;
 constexpr size_t kChunkSize4 = 150;
 RandomEngine rng;
 std::string data = RandomLowercaseString(&rng, kBlocks * kBlockSize);
 absl::Cord cord;
 for (int i = 0; i < kBlocks; ++i) {
   const std::string block = data.substr(i * kBlockSize, kBlockSize);
   cord.Append(absl::Cord(block));
 }

 MaybeHarden(cord);

 for (size_t chunk_size :
      {kChunkSize1, kChunkSize2, kChunkSize3, kChunkSize4}) {
   absl::Cord::CharIterator it = cord.char_begin();
   size_t offset = 0;
   while (offset < data.length()) {
     const size_t n = std::min<size_t>(data.length() - offset, chunk_size);
     absl::Cord chunk = cord.AdvanceAndRead(&it, n);
     ASSERT_EQ(chunk.size(), n);
     ASSERT_EQ(chunk.Compare(data.substr(offset, n)), 0);
     offset += n;
   }
 }
}

TEST_P(CordTest, StreamingOutput) {
 absl::Cord c =
     absl::MakeFragmentedCord({"A ", "small ", "fragmented ", "Cord", "."});
 MaybeHarden(c);
 std::stringstream output;
 output << c;
 EXPECT_EQ("A small fragmented Cord.", output.str());
}

TEST_P(CordTest, ForEachChunk) {
 for (int num_elements : {1, 10, 200}) {
   SCOPED_TRACE(num_elements);
   std::vector<std::string> cord_chunks;
   for (int i = 0; i < num_elements; ++i) {
     cord_chunks.push_back(absl::StrCat("[", i, "]"));
   }
   absl::Cord c = absl::MakeFragmentedCord(cord_chunks);
   MaybeHarden(c);

   std::vector<std::string> iterated_chunks;
   absl::CordTestPeer::ForEachChunk(c,
                                    [&iterated_chunks](absl::string_view sv) {
                                      iterated_chunks.emplace_back(sv);
                                    });
   EXPECT_EQ(iterated_chunks, cord_chunks);
 }
}

TEST_P(CordTest, SmallBufferAssignFromOwnData) {
 constexpr size_t kMaxInline = 15;
 std::string contents = "small buff cord";
 EXPECT_EQ(contents.size(), kMaxInline);
 for (size_t pos = 0; pos < contents.size(); ++pos) {
   for (size_t count = contents.size() - pos; count > 0; --count) {
     absl::Cord c(contents);
     MaybeHarden(c);
     absl::string_view flat = c.Flatten();
     c = flat.substr(pos, count);
     EXPECT_EQ(c, contents.substr(pos, count))
         << "pos = " << pos << "; count = " << count;
   }
 }
}

TEST_P(CordTest, Format) {
 absl::Cord c;
 absl::Format(&c, "There were %04d little %s.", 3, "pigs");
 EXPECT_EQ(c, "There were 0003 little pigs.");
 MaybeHarden(c);
 absl::Format(&c, "And %-3llx bad wolf!", 1);
 MaybeHarden(c);
 EXPECT_EQ(c, "There were 0003 little pigs.And 1   bad wolf!");
}

TEST_P(CordTest, Stringify) {
 absl::Cord c =
     absl::MakeFragmentedCord({"A ", "small ", "fragmented ", "Cord", "."});
 MaybeHarden(c);
 EXPECT_EQ(absl::StrCat(c), "A small fragmented Cord.");
}

TEST_P(CordTest, Hardening) {
 absl::Cord cord("hello");
 MaybeHarden(cord);

 // These statement should abort the program in all builds modes.
 EXPECT_DEATH_IF_SUPPORTED(cord.RemovePrefix(6), "");
 EXPECT_DEATH_IF_SUPPORTED(cord.RemoveSuffix(6), "");

 bool test_hardening = false;
 ABSL_HARDENING_ASSERT([&]() {
   // This only runs when ABSL_HARDENING_ASSERT is active.
   test_hardening = true;
   return true;
 }());
 if (!test_hardening) return;

 EXPECT_DEATH_IF_SUPPORTED(cord[5], "");
 EXPECT_DEATH_IF_SUPPORTED(*cord.chunk_end(), "");
 EXPECT_DEATH_IF_SUPPORTED(static_cast<void>(cord.chunk_end()->empty()), "");
 EXPECT_DEATH_IF_SUPPORTED(++cord.chunk_end(), "");
}

// This test mimics a specific (and rare) application repeatedly splitting a
// cord, inserting (overwriting) a string value, and composing a new cord from
// the three pieces. This is hostile towards a Btree implementation: A split of
// a node at any level is likely to have the right-most edge of the left split,
// and the left-most edge of the right split shared. For example, splitting a
// leaf node with 6 edges will result likely in a 1-6, 2-5, 3-4, etc. split,
// sharing the 'split node'. When recomposing such nodes, we 'injected' an edge
// in that node. As this happens with some probability on each level of the
// tree, this will quickly grow the tree until it reaches maximum height.
TEST_P(CordTest, BtreeHostileSplitInsertJoin) {
 absl::BitGen bitgen;

 // Start with about 1GB of data
 std::string data(1 << 10, 'x');
 absl::Cord buffer(data);
 absl::Cord cord;
 for (int i = 0; i < 1000000; ++i) {
   cord.Append(buffer);
 }

 for (int j = 0; j < 1000; ++j) {
   MaybeHarden(cord);
   size_t offset = absl::Uniform(bitgen, 0u, cord.size());
   size_t length = absl::Uniform(bitgen, 100u, data.size());
   if (cord.size() == offset) {
     cord.Append(absl::string_view(data.data(), length));
   } else {
     absl::Cord suffix;
     if (offset + length < cord.size()) {
       suffix = cord;
       suffix.RemovePrefix(offset + length);
     }
     if (cord.size() > offset) {
       cord.RemoveSuffix(cord.size() - offset);
     }
     cord.Append(absl::string_view(data.data(), length));
     if (!suffix.empty()) {
       cord.Append(suffix);
     }
   }
 }
}

class AfterExitCordTester {
public:
 bool Set(absl::Cord* cord, absl::string_view expected) {
   cord_ = cord;
   expected_ = expected;
   return true;
 }

 ~AfterExitCordTester() {
   EXPECT_EQ(*cord_, expected_);
 }
private:
 absl::Cord* cord_;
 absl::string_view expected_;
};

template <typename Str>
void TestAfterExit(Str) {
 const auto expected = Str::value;
 // Defined before `cord` to be destroyed after it.
 static AfterExitCordTester exit_tester;  // NOLINT
 static absl::NoDestructor<absl::Cord> cord_leaker(Str{});
 // cord_leaker is static, so this reference will remain valid through the end
 // of program execution.
 static absl::Cord& cord = *cord_leaker;
 static bool init_exit_tester = exit_tester.Set(&cord, expected);
 (void)init_exit_tester;

 EXPECT_EQ(cord, expected);
 // Copy the object and test the copy, and the original.
 {
   absl::Cord copy = cord;
   EXPECT_EQ(copy, expected);
 }
 // The original still works
 EXPECT_EQ(cord, expected);

 // Try making adding more structure to the tree.
 {
   absl::Cord copy = cord;
   std::string expected_copy(expected);
   for (int i = 0; i < 10; ++i) {
     copy.Append(cord);
     absl::StrAppend(&expected_copy, expected);
     EXPECT_EQ(copy, expected_copy);
   }
 }

 // Make sure we are using the right branch during constant evaluation.
 EXPECT_EQ(absl::CordTestPeer::IsTree(cord), cord.size() >= 16);

 for (int i = 0; i < 10; ++i) {
   // Make a few more Cords from the same global rep.
   // This tests what happens when the refcount for it gets below 1.
   EXPECT_EQ(expected, absl::Cord(Str{}));
 }
}

constexpr int SimpleStrlen(const char* p) {
 return *p ? 1 + SimpleStrlen(p + 1) : 0;
}

struct ShortView {
 constexpr absl::string_view operator()() const {
   return absl::string_view("SSO string", SimpleStrlen("SSO string"));
 }
};

struct LongView {
 constexpr absl::string_view operator()() const {
   return absl::string_view("String that does not fit SSO.",
                            SimpleStrlen("String that does not fit SSO."));
 }
};


TEST_P(CordTest, AfterExit) {
 TestAfterExit(absl::strings_internal::MakeStringConstant(ShortView{}));
 TestAfterExit(absl::strings_internal::MakeStringConstant(LongView{}));
}

namespace {

// Test helper that generates a populated cord for future manipulation.
//
// By test convention, all generated cords begin with the characters "abcde" at
// the start of the first chunk.
class PopulatedCordFactory {
public:
 constexpr PopulatedCordFactory(absl::string_view name,
                                absl::Cord (*generator)())
     : name_(name), generator_(generator) {}

 absl::string_view Name() const { return name_; }
 absl::Cord Generate() const { return generator_(); }

private:
 absl::string_view name_;
 absl::Cord (*generator_)();
};

// clang-format off
// This array is constant-initialized in conformant compilers.
PopulatedCordFactory cord_factories[] = {
 {"sso", [] { return absl::Cord("abcde"); }},
 {"flat", [] {
   // Too large to live in SSO space, but small enough to be a simple FLAT.
   absl::Cord flat(absl::StrCat("abcde", std::string(1000, 'x')));
   flat.Flatten();
   return flat;
 }},
 {"external", [] {
   // A cheat: we are using a string literal as the external storage, so a
   // no-op releaser is correct here.
   return absl::MakeCordFromExternal("abcde External!", []{});
 }},
 {"external substring", [] {
   // A cheat: we are using a string literal as the external storage, so a
   // no-op releaser is correct here.
   absl::Cord ext = absl::MakeCordFromExternal("-abcde External!", []{});
   return absl::CordTestPeer::MakeSubstring(ext, 1, ext.size() - 1);
 }},
 {"substring", [] {
   absl::Cord flat(absl::StrCat("-abcde", std::string(1000, 'x')));
   flat.Flatten();
   return flat.Subcord(1, 998);
 }},
 {"fragmented", [] {
   std::string fragment = absl::StrCat("abcde", std::string(195, 'x'));
   std::vector<std::string> fragments(200, fragment);
   absl::Cord cord = absl::MakeFragmentedCord(fragments);
   assert(cord.size() == 40000);
   return cord;
 }},
};
// clang-format on

// Test helper that can mutate a cord, and possibly undo the mutation, for
// testing.
class CordMutator {
public:
 constexpr CordMutator(absl::string_view name, void (*mutate)(absl::Cord&),
                       void (*undo)(absl::Cord&) = nullptr)
     : name_(name), mutate_(mutate), undo_(undo) {}

 absl::string_view Name() const { return name_; }
 void Mutate(absl::Cord& cord) const { mutate_(cord); }
 bool CanUndo() const { return undo_ != nullptr; }
 void Undo(absl::Cord& cord) const { undo_(cord); }

private:
 absl::string_view name_;
 void (*mutate_)(absl::Cord&);
 void (*undo_)(absl::Cord&);
};

// clang-format off
// This array is constant-initialized in conformant compilers.
CordMutator cord_mutators[] = {
 {"clear", [](absl::Cord& c) { c.Clear(); }},
 {"overwrite", [](absl::Cord& c) { c = "overwritten"; }},
 {
   "append string",
   [](absl::Cord& c) { c.Append("0123456789"); },
   [](absl::Cord& c) { c.RemoveSuffix(10); }
 },
 {
   "append cord",
   [](absl::Cord& c) {
     c.Append(absl::MakeFragmentedCord({"12345", "67890"}));
   },
   [](absl::Cord& c) { c.RemoveSuffix(10); }
 },
 {
   "append checksummed cord",
   [](absl::Cord& c) {
     absl::Cord to_append = absl::MakeFragmentedCord({"12345", "67890"});
     to_append.SetExpectedChecksum(999);
     c.Append(to_append);
   },
   [](absl::Cord& c) { c.RemoveSuffix(10); }
 },
 {
   "append self",
   [](absl::Cord& c) { c.Append(c); },
   [](absl::Cord& c) { c.RemoveSuffix(c.size() / 2); }
 },
 {
   "append empty string",
   [](absl::Cord& c) { c.Append(""); },
   [](absl::Cord& c) { }
 },
 {
   "append empty cord",
   [](absl::Cord& c) { c.Append(absl::Cord()); },
   [](absl::Cord& c) { }
 },
 {
   "append empty checksummed cord",
   [](absl::Cord& c) {
     absl::Cord to_append;
     to_append.SetExpectedChecksum(999);
     c.Append(to_append);
   },
   [](absl::Cord& c) { }
 },
 {
   "prepend string",
   [](absl::Cord& c) { c.Prepend("9876543210"); },
   [](absl::Cord& c) { c.RemovePrefix(10); }
 },
 {
   "prepend cord",
   [](absl::Cord& c) {
     c.Prepend(absl::MakeFragmentedCord({"98765", "43210"}));
   },
   [](absl::Cord& c) { c.RemovePrefix(10); }
 },
 {
   "prepend checksummed cord",
   [](absl::Cord& c) {
     absl::Cord to_prepend = absl::MakeFragmentedCord({"98765", "43210"});
     to_prepend.SetExpectedChecksum(999);
     c.Prepend(to_prepend);
   },
   [](absl::Cord& c) { c.RemovePrefix(10); }
 },
 {
   "prepend empty string",
   [](absl::Cord& c) { c.Prepend(""); },
   [](absl::Cord& c) { }
 },
 {
   "prepend empty cord",
   [](absl::Cord& c) { c.Prepend(absl::Cord()); },
   [](absl::Cord& c) { }
 },
 {
   "prepend empty checksummed cord",
   [](absl::Cord& c) {
     absl::Cord to_prepend;
     to_prepend.SetExpectedChecksum(999);
     c.Prepend(to_prepend);
   },
   [](absl::Cord& c) { }
 },
 {
   "prepend self",
   [](absl::Cord& c) { c.Prepend(c); },
   [](absl::Cord& c) { c.RemovePrefix(c.size() / 2); }
 },
 {"remove prefix", [](absl::Cord& c) { c.RemovePrefix(c.size() / 2); }},
 {"remove suffix", [](absl::Cord& c) { c.RemoveSuffix(c.size() / 2); }},
 {"remove 0-prefix", [](absl::Cord& c) { c.RemovePrefix(0); }},
 {"remove 0-suffix", [](absl::Cord& c) { c.RemoveSuffix(0); }},
 {"subcord", [](absl::Cord& c) { c = c.Subcord(1, c.size() - 2); }},
 {
   "swap inline",
   [](absl::Cord& c) {
     absl::Cord other("swap");
     c.swap(other);
   }
 },
 {
   "swap tree",
   [](absl::Cord& c) {
     absl::Cord other(std::string(10000, 'x'));
     c.swap(other);
   }
 },
};
// clang-format on
}  // namespace

TEST_P(CordTest, ExpectedChecksum) {
 for (const PopulatedCordFactory& factory : cord_factories) {
   SCOPED_TRACE(factory.Name());
   for (bool shared : {false, true}) {
     SCOPED_TRACE(shared);

     absl::Cord shared_cord_source = factory.Generate();
     auto make_instance = [=] {
       return shared ? shared_cord_source : factory.Generate();
     };

     const absl::Cord base_value = factory.Generate();
     const std::string base_value_as_string(factory.Generate().Flatten());

     absl::Cord c1 = make_instance();
     EXPECT_FALSE(c1.ExpectedChecksum().has_value());

     // Setting an expected checksum works, and retains the cord's bytes
     c1.SetExpectedChecksum(12345);
     EXPECT_EQ(c1.ExpectedChecksum().value_or(0), 12345);
     EXPECT_EQ(c1, base_value);

     // Test that setting an expected checksum again doesn't crash or leak
     // memory.
     c1.SetExpectedChecksum(12345);
     EXPECT_EQ(c1.ExpectedChecksum().value_or(0), 12345);
     EXPECT_EQ(c1, base_value);

     // CRC persists through copies, assignments, and moves:
     absl::Cord c1_copy_construct = c1;
     EXPECT_EQ(c1_copy_construct.ExpectedChecksum().value_or(0), 12345);

     absl::Cord c1_copy_assign;
     c1_copy_assign = c1;
     EXPECT_EQ(c1_copy_assign.ExpectedChecksum().value_or(0), 12345);

     absl::Cord c1_move(std::move(c1_copy_assign));
     EXPECT_EQ(c1_move.ExpectedChecksum().value_or(0), 12345);

     EXPECT_EQ(c1.ExpectedChecksum().value_or(0), 12345);

     // A CRC Cord compares equal to its non-CRC value.
     EXPECT_EQ(c1, make_instance());

     for (const CordMutator& mutator : cord_mutators) {
       SCOPED_TRACE(mutator.Name());

       // Test that mutating a cord removes its stored checksum
       absl::Cord c2 = make_instance();
       c2.SetExpectedChecksum(24680);

       mutator.Mutate(c2);

       if (c1 == c2) {
         // Not a mutation (for example, appending the empty string).
         // Whether the checksum is removed is not defined.
         continue;
       }

       EXPECT_EQ(c2.ExpectedChecksum(), absl::nullopt);

       if (mutator.CanUndo()) {
         // Undoing an operation should not restore the checksum
         mutator.Undo(c2);
         EXPECT_EQ(c2, base_value);
         EXPECT_EQ(c2.ExpectedChecksum(), absl::nullopt);
       }
     }

     absl::Cord c3 = make_instance();
     c3.SetExpectedChecksum(999);
     const absl::Cord& cc3 = c3;

     // Test that all cord reading operations function in the face of an
     // expected checksum.

     // Test data precondition
     ASSERT_TRUE(cc3.StartsWith("abcde"));

     EXPECT_EQ(cc3.size(), base_value_as_string.size());
     EXPECT_FALSE(cc3.empty());
     EXPECT_EQ(cc3.Compare(base_value), 0);
     EXPECT_EQ(cc3.Compare(base_value_as_string), 0);
     EXPECT_EQ(cc3.Compare("wxyz"), -1);
     EXPECT_EQ(cc3.Compare(absl::Cord("wxyz")), -1);
     EXPECT_EQ(cc3.Compare("aaaa"), 1);
     EXPECT_EQ(cc3.Compare(absl::Cord("aaaa")), 1);
     EXPECT_EQ(absl::Cord("wxyz").Compare(cc3), 1);
     EXPECT_EQ(absl::Cord("aaaa").Compare(cc3), -1);
     EXPECT_TRUE(cc3.StartsWith("abcd"));
     EXPECT_EQ(std::string(cc3), base_value_as_string);

     std::string dest;
     absl::CopyCordToString(cc3, &dest);
     EXPECT_EQ(dest, base_value_as_string);

     bool first_pass = true;
     for (absl::string_view chunk : cc3.Chunks()) {
       if (first_pass) {
         EXPECT_TRUE(absl::StartsWith(chunk, "abcde"));
       }
       first_pass = false;
     }
     first_pass = true;
     for (char ch : cc3.Chars()) {
       if (first_pass) {
         EXPECT_EQ(ch, 'a');
       }
       first_pass = false;
     }
     EXPECT_TRUE(absl::StartsWith(*cc3.chunk_begin(), "abcde"));
     EXPECT_EQ(*cc3.char_begin(), 'a');

     auto char_it = cc3.char_begin();
     absl::Cord::Advance(&char_it, 2);
     EXPECT_EQ(absl::Cord::AdvanceAndRead(&char_it, 2), "cd");
     EXPECT_EQ(*char_it, 'e');
     char_it = cc3.char_begin();
     absl::Cord::Advance(&char_it, 2);
     EXPECT_TRUE(absl::StartsWith(absl::Cord::ChunkRemaining(char_it), "cde"));

     EXPECT_EQ(cc3[0], 'a');
     EXPECT_EQ(cc3[4], 'e');
     EXPECT_EQ(absl::HashOf(cc3), absl::HashOf(base_value));
     EXPECT_EQ(absl::HashOf(cc3), absl::HashOf(base_value_as_string));
   }
 }
}

// Test the special cases encountered with an empty checksummed cord.
TEST_P(CordTest, ChecksummedEmptyCord) {
 absl::Cord c1;
 EXPECT_FALSE(c1.ExpectedChecksum().has_value());

 // Setting an expected checksum works.
 c1.SetExpectedChecksum(12345);
 EXPECT_EQ(c1.ExpectedChecksum().value_or(0), 12345);
 EXPECT_EQ(c1, "");
 EXPECT_TRUE(c1.empty());

 // Test that setting an expected checksum again doesn't crash or leak memory.
 c1.SetExpectedChecksum(12345);
 EXPECT_EQ(c1.ExpectedChecksum().value_or(0), 12345);
 EXPECT_EQ(c1, "");
 EXPECT_TRUE(c1.empty());

 // CRC persists through copies, assignments, and moves:
 absl::Cord c1_copy_construct = c1;
 EXPECT_EQ(c1_copy_construct.ExpectedChecksum().value_or(0), 12345);

 absl::Cord c1_copy_assign;
 c1_copy_assign = c1;
 EXPECT_EQ(c1_copy_assign.ExpectedChecksum().value_or(0), 12345);

 absl::Cord c1_move(std::move(c1_copy_assign));
 EXPECT_EQ(c1_move.ExpectedChecksum().value_or(0), 12345);

 EXPECT_EQ(c1.ExpectedChecksum().value_or(0), 12345);

 // A CRC Cord compares equal to its non-CRC value.
 EXPECT_EQ(c1, absl::Cord());

 for (const CordMutator& mutator : cord_mutators) {
   SCOPED_TRACE(mutator.Name());

   // Exercise mutating an empty checksummed cord to catch crashes and exercise
   // memory sanitizers.
   absl::Cord c2;
   c2.SetExpectedChecksum(24680);
   mutator.Mutate(c2);

   if (c2.empty()) {
     // Not a mutation
     continue;
   }
   EXPECT_EQ(c2.ExpectedChecksum(), absl::nullopt);

   if (mutator.CanUndo()) {
     mutator.Undo(c2);
   }
 }

 absl::Cord c3;
 c3.SetExpectedChecksum(999);
 const absl::Cord& cc3 = c3;

 // Test that all cord reading operations function in the face of an
 // expected checksum.
 EXPECT_TRUE(cc3.StartsWith(""));
 EXPECT_TRUE(cc3.EndsWith(""));
 EXPECT_TRUE(cc3.empty());
 EXPECT_EQ(cc3, "");
 EXPECT_EQ(cc3, absl::Cord());
 EXPECT_EQ(cc3.size(), 0);
 EXPECT_EQ(cc3.Compare(absl::Cord()), 0);
 EXPECT_EQ(cc3.Compare(c1), 0);
 EXPECT_EQ(cc3.Compare(cc3), 0);
 EXPECT_EQ(cc3.Compare(""), 0);
 EXPECT_EQ(cc3.Compare("wxyz"), -1);
 EXPECT_EQ(cc3.Compare(absl::Cord("wxyz")), -1);
 EXPECT_EQ(absl::Cord("wxyz").Compare(cc3), 1);
 EXPECT_EQ(std::string(cc3), "");

 std::string dest;
 absl::CopyCordToString(cc3, &dest);
 EXPECT_EQ(dest, "");

 for (absl::string_view chunk : cc3.Chunks()) {  // NOLINT(unreachable loop)
   static_cast<void>(chunk);
   GTEST_FAIL() << "no chunks expected";
 }
 EXPECT_TRUE(cc3.chunk_begin() == cc3.chunk_end());

 for (char ch : cc3.Chars()) {  // NOLINT(unreachable loop)
   static_cast<void>(ch);
   GTEST_FAIL() << "no chars expected";
 }
 EXPECT_TRUE(cc3.char_begin() == cc3.char_end());

 EXPECT_EQ(cc3.TryFlat(), "");
 EXPECT_EQ(absl::HashOf(c3), absl::HashOf(absl::Cord()));
 EXPECT_EQ(absl::HashOf(c3), absl::HashOf(absl::string_view()));
}

// This must not be static to avoid aggressive optimizations.
ABSL_ATTRIBUTE_WEAK
size_t FalseReport(const absl::Cord& a, bool f);

ABSL_ATTRIBUTE_NOINLINE
size_t FalseReport(const absl::Cord& a, bool f) {
 absl::Cord b;
 const absl::Cord& ref = f ? b : a;
 // Test that sanitizers report nothing here. Without
 // InlineData::Rep::annotated_this() compiler can unconditionally load
 // poisoned parts, assuming that local variable is fully accessible.
 return ref.size();
}

TEST(CordSanitizerTest, SanitizesCordFalseReport) {
 absl::Cord c;
 for (int i = 0; i < 1000; ++i) c.Append("a");
 FalseReport(c, false);
}

TEST(CrcCordTest, ChecksummedEmptyCordEstimateMemoryUsage) {
 absl::Cord cord;
 cord.SetExpectedChecksum(0);
 EXPECT_NE(cord.EstimatedMemoryUsage(), 0);
}

TEST(CordThreeWayComparisonTest, CompareCords) {
#ifndef __cpp_impl_three_way_comparison
 GTEST_SKIP() << "C++20 three-way <=> comparison not supported";
#else
 EXPECT_EQ(absl::Cord("a") <=> absl::Cord("a"), std::strong_ordering::equal);
 EXPECT_EQ(absl::Cord("aaaa") <=> absl::Cord("aaab"),
           std::strong_ordering::less);
 EXPECT_EQ(absl::Cord("baaa") <=> absl::Cord("a"),
           std::strong_ordering::greater);
#endif
}

TEST(CordThreeWayComparisonTest, CompareCordsAndStringViews) {
#ifndef __cpp_impl_three_way_comparison
 GTEST_SKIP() << "C++20 three-way <=> comparison not supported";
#else
 EXPECT_EQ(absl::string_view("a") <=> absl::Cord("a"),
           std::strong_ordering::equal);
 EXPECT_EQ(absl::Cord("a") <=> absl::string_view("b"),
           std::strong_ordering::less);
 EXPECT_EQ(absl::string_view("b") <=> absl::Cord("a"),
           std::strong_ordering::greater);
#endif
}

#if defined(GTEST_HAS_DEATH_TEST) && defined(ABSL_INTERNAL_CORD_HAVE_SANITIZER)

// Returns an expected poison / uninitialized death message expression.
const char* MASanDeathExpr() {
 return "(use-after-poison|use-of-uninitialized-value)";
}

TEST(CordSanitizerTest, SanitizesEmptyCord) {
 absl::Cord cord;
 const char* data = cord.Flatten().data();
 EXPECT_DEATH(EXPECT_EQ(data[0], 0), MASanDeathExpr());
}

TEST(CordSanitizerTest, SanitizesSmallCord) {
 absl::Cord cord("Hello");
 const char* data = cord.Flatten().data();
 EXPECT_DEATH(EXPECT_EQ(data[5], 0), MASanDeathExpr());
}

TEST(CordSanitizerTest, SanitizesCordOnSetSSOValue) {
 absl::Cord cord("String that is too big to be an SSO value");
 cord = "Hello";
 const char* data = cord.Flatten().data();
 EXPECT_DEATH(EXPECT_EQ(data[5], 0), MASanDeathExpr());
}

TEST(CordSanitizerTest, SanitizesCordOnCopyCtor) {
 absl::Cord src("hello");
 absl::Cord dst(src);
 const char* data = dst.Flatten().data();
 EXPECT_DEATH(EXPECT_EQ(data[5], 0), MASanDeathExpr());
}

TEST(CordSanitizerTest, SanitizesCordOnMoveCtor) {
 absl::Cord src("hello");
 absl::Cord dst(std::move(src));
 const char* data = dst.Flatten().data();
 EXPECT_DEATH(EXPECT_EQ(data[5], 0), MASanDeathExpr());
}

TEST(CordSanitizerTest, SanitizesCordOnAssign) {
 absl::Cord src("hello");
 absl::Cord dst;
 dst = src;
 const char* data = dst.Flatten().data();
 EXPECT_DEATH(EXPECT_EQ(data[5], 0), MASanDeathExpr());
}

TEST(CordSanitizerTest, SanitizesCordOnMoveAssign) {
 absl::Cord src("hello");
 absl::Cord dst;
 dst = std::move(src);
 const char* data = dst.Flatten().data();
 EXPECT_DEATH(EXPECT_EQ(data[5], 0), MASanDeathExpr());
}

TEST(CordSanitizerTest, SanitizesCordOnSsoAssign) {
 absl::Cord src("hello");
 absl::Cord dst("String that is too big to be an SSO value");
 dst = src;
 const char* data = dst.Flatten().data();
 EXPECT_DEATH(EXPECT_EQ(data[5], 0), MASanDeathExpr());
}

#endif  // GTEST_HAS_DEATH_TEST && ABSL_INTERNAL_CORD_HAVE_SANITIZER