tor-browser

Input.h (9085B)

---

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This code is made available to you under your choice of the following sets
* of licensing terms:
*/
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
/* Copyright 2013 Mozilla Contributors
*
* 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
*
*     http://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.
*/

#ifndef mozilla_pkix_Input_h
#define mozilla_pkix_Input_h

#include <algorithm>

#include "mozpkix/Result.h"
#include "stdint.h"

namespace mozilla {
namespace pkix {

class Reader;

// An Input is a safety-oriented immutable weak reference to a array of bytes
// of a known size. The data can only be legally accessed by constructing a
// Reader object, which guarantees all accesses to the data are memory safe.
// Neither Input not Reader provide any facilities for modifying the data
// they reference.
//
// Inputs are small and should usually be passed by value, not by reference,
// though for inline functions the distinction doesn't matter:
//
//    Result GoodExample(Input input);
//    Result BadExample(const Input& input);
//    Result WorseExample(const uint8_t* input, size_t len);
//
// Note that in the example, GoodExample has the same performance
// characteristics as WorseExample, but with much better safety guarantees.
class Input final {
public:
 typedef uint16_t size_type;

 // This constructor is useful for inputs that are statically known to be of a
 // fixed size, e.g.:
 //
 //   static const uint8_t EXPECTED_BYTES[] = { 0x00, 0x01, 0x02 };
 //   const Input expected(EXPECTED_BYTES);
 //
 // This is equivalent to (and preferred over):
 //
 //   static const uint8_t EXPECTED_BYTES[] = { 0x00, 0x01, 0x02 };
 //   Input expected;
 //   Result rv = expected.Init(EXPECTED_BYTES, sizeof EXPECTED_BYTES);
 template <size_type N>
 explicit Input(const uint8_t (&aData)[N]) : data(aData), len(N) {}

 // Construct a valid, empty, Init-able Input.
 Input() : data(nullptr), len(0u) {}

 // This is intentionally not explicit in order to allow value semantics.
 Input(const Input&) = default;

 // Initialize the input. data must be non-null and len must be less than
 // 65536. Init may not be called more than once.
 Result Init(const uint8_t* aData, size_t aLen) {
   if (this->data) {
     // already initialized
     return Result::FATAL_ERROR_INVALID_ARGS;
   }
   if (!aData || aLen > 0xffffu) {
     // input too large
     return Result::ERROR_BAD_DER;
   }

   this->data = aData;
   this->len = aLen;

   return Success;
 }

 // Initialize the input to be equivalent to the given input. Init may not be
 // called more than once.
 //
 // This is basically operator=, but it wasn't given that name because
 // normally callers do not check the result of operator=, and normally
 // operator= can be used multiple times.
 Result Init(Input other) { return Init(other.data, other.len); }

 // Returns the length of the input.
 //
 // Having the return type be size_type instead of size_t avoids the need for
 // callers to ensure that the result is small enough.
 size_type GetLength() const { return static_cast<size_type>(len); }

 // Don't use this. It is here because we have some "friend" functions that we
 // don't want to declare in this header file.
 const uint8_t* UnsafeGetData() const { return data; }

private:
 const uint8_t* data;
 size_t len;

 void operator=(const Input&) = delete;  // Use Init instead.
};

inline bool InputsAreEqual(const Input& a, const Input& b) {
 return a.GetLength() == b.GetLength() &&
        std::equal(a.UnsafeGetData(), a.UnsafeGetData() + a.GetLength(),
                   b.UnsafeGetData());
}

// An Reader is a cursor/iterator through the contents of an Input, designed to
// maximize safety during parsing while minimizing the performance cost of that
// safety. In particular, all methods do strict bounds checking to ensure
// buffer overflows are impossible, and they are all inline so that the
// compiler can coalesce as many of those checks together as possible.
//
// In general, Reader allows for one byte of lookahead and no backtracking.
// However, the Match* functions internally may have more lookahead.
class Reader final {
public:
 Reader() : input(nullptr), end(nullptr) {}

 explicit Reader(Input aInput)
     : input(aInput.UnsafeGetData()),
       end(aInput.UnsafeGetData() + aInput.GetLength()) {}

 Result Init(Input aInput) {
   if (this->input) {
     return Result::FATAL_ERROR_INVALID_ARGS;
   }
   this->input = aInput.UnsafeGetData();
   this->end = aInput.UnsafeGetData() + aInput.GetLength();
   return Success;
 }

 bool Peek(uint8_t expectedByte) const {
   return input < end && *input == expectedByte;
 }

 Result Read(uint8_t& out) {
   Result rv = EnsureLength(1);
   if (rv != Success) {
     return rv;
   }
   out = *input++;
   return Success;
 }

 Result Read(uint16_t& out) {
   Result rv = EnsureLength(2);
   if (rv != Success) {
     return rv;
   }
   out = *input++;
   out <<= 8u;
   out |= *input++;
   return Success;
 }

 template <Input::size_type N>
 bool MatchRest(const uint8_t (&toMatch)[N]) {
   // Normally we use EnsureLength which compares (input + len < end), but
   // here we want to be sure that there is nothing following the matched
   // bytes
   if (static_cast<size_t>(end - input) != N) {
     return false;
   }
   if (!std::equal(input, end, toMatch)) {
     return false;
   }
   input = end;
   return true;
 }

 bool MatchRest(Input toMatch) {
   // Normally we use EnsureLength which compares (input + len < end), but
   // here we want to be sure that there is nothing following the matched
   // bytes
   size_t remaining = static_cast<size_t>(end - input);
   if (toMatch.GetLength() != remaining) {
     return false;
   }
   if (!std::equal(input, end, toMatch.UnsafeGetData())) {
     return false;
   }
   input = end;
   return true;
 }

 Result Skip(Input::size_type len) {
   Result rv = EnsureLength(len);
   if (rv != Success) {
     return rv;
   }
   input += len;
   return Success;
 }

 Result Skip(Input::size_type len, Reader& skipped) {
   Result rv = EnsureLength(len);
   if (rv != Success) {
     return rv;
   }
   rv = skipped.Init(input, len);
   if (rv != Success) {
     return rv;
   }
   input += len;
   return Success;
 }

 Result Skip(Input::size_type len, /*out*/ Input& skipped) {
   Result rv = EnsureLength(len);
   if (rv != Success) {
     return rv;
   }
   rv = skipped.Init(input, len);
   if (rv != Success) {
     return rv;
   }
   input += len;
   return Success;
 }

 void SkipToEnd() { input = end; }

 Result SkipToEnd(/*out*/ Input& skipped) {
   return Skip(static_cast<Input::size_type>(end - input), skipped);
 }

 Result EnsureLength(Input::size_type len) {
   if (static_cast<size_t>(end - input) < len) {
     return Result::ERROR_BAD_DER;
   }
   return Success;
 }

 bool AtEnd() const { return input == end; }

 class Mark final {
  public:
   Mark(const Mark&) = default;  // Intentionally not explicit.
  private:
   friend class Reader;
   Mark(const Reader& aInput, const uint8_t* aMark)
       : input(aInput), mark(aMark) {}
   const Reader& input;
   const uint8_t* const mark;
   void operator=(const Mark&) = delete;
 };

 Mark GetMark() const { return Mark(*this, input); }

 Result GetInput(const Mark& mark, /*out*/ Input& item) {
   if (&mark.input != this || mark.mark > input) {
     return NotReached("invalid mark", Result::FATAL_ERROR_INVALID_ARGS);
   }
   return item.Init(mark.mark,
                    static_cast<Input::size_type>(input - mark.mark));
 }

private:
 Result Init(const uint8_t* data, Input::size_type len) {
   if (input) {
     // already initialized
     return Result::FATAL_ERROR_INVALID_ARGS;
   }
   input = data;
   end = data + len;
   return Success;
 }

 const uint8_t* input;
 const uint8_t* end;

 Reader(const Reader&) = delete;
 void operator=(const Reader&) = delete;
};

inline bool InputContains(const Input& input, uint8_t toFind) {
 Reader reader(input);
 for (;;) {
   uint8_t b;
   if (reader.Read(b) != Success) {
     return false;
   }
   if (b == toFind) {
     return true;
   }
 }
}
}  // namespace pkix
}  // namespace mozilla

#endif  // mozilla_pkix_Input_h