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LSValue.h (3950B)

      1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this
      5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 #ifndef mozilla_dom_localstorage_LSValue_h
      8 #define mozilla_dom_localstorage_LSValue_h
      9 
     10 #include <cstdint>
     11 
     12 #include "ErrorList.h"
     13 #include "SnappyUtils.h"
     14 #include "nsString.h"
     15 #include "nsStringFwd.h"
     16 #include "nsTStringRepr.h"
     17 
     18 class mozIStorageStatement;
     19 
     20 namespace IPC {
     21 template <typename>
     22 struct ParamTraits;
     23 }
     24 
     25 namespace mozilla::dom {
     26 
     27 /**
     28 * Represents a LocalStorage value. From content's perspective, values (if
     29 * present) are always DOMStrings. This is also true from a quota-tracking
     30 * perspective. However, for memory and disk efficiency it's preferable to store
     31 * the value in alternate compressed or utf-8 encoding representations. The
     32 * LSValue type exists to support these alternate representations, dynamically
     33 * decompressing/re-encoding to utf-16 while still tracking value size on a
     34 * utf-16 basis for quota purposes.
     35 */
     36 class LSValue final {
     37  friend struct IPC::ParamTraits<LSValue>;
     38 
     39 public:
     40  enum class ConversionType : uint8_t {
     41    NONE = 0u,
     42    UTF16_UTF8 = 1u,
     43    NUM_TYPES = 2u
     44  };
     45 
     46  enum class CompressionType : uint8_t {
     47    UNCOMPRESSED = 0u,
     48    SNAPPY = 1u,
     49    NUM_TYPES = 2u
     50  };
     51 
     52  nsCString mBuffer;
     53  uint32_t mUTF16Length;
     54  ConversionType mConversionType;
     55  CompressionType mCompressionType;
     56 
     57  explicit LSValue()
     58      : mUTF16Length(0u),
     59        mConversionType(ConversionType::NONE),
     60        mCompressionType(CompressionType::UNCOMPRESSED) {
     61    SetIsVoid(true);
     62  }
     63 
     64  bool InitFromString(const nsAString& aBuffer);
     65 
     66  nsresult InitFromStatement(mozIStorageStatement* aStatement, uint32_t aIndex);
     67 
     68  bool IsVoid() const { return mBuffer.IsVoid(); }
     69 
     70  void SetIsVoid(bool aVal) { mBuffer.SetIsVoid(aVal); }
     71 
     72  /**
     73   * This represents the "physical" length that the parent process uses for
     74   * the size of value/item computation. This can also be used to see how much
     75   * memory the value is using at rest or what the cost is for sending the value
     76   * over IPC.
     77   */
     78  uint32_t Length() const { return mBuffer.Length(); }
     79 
     80  /*
     81   * This represents the "logical" length that content sees and that is also
     82   * used for quota management purposes.
     83   */
     84  uint32_t UTF16Length() const { return mUTF16Length; }
     85 
     86  ConversionType GetConversionType() const { return mConversionType; }
     87 
     88  CompressionType GetCompressionType() const { return mCompressionType; }
     89 
     90  bool Equals(const LSValue& aOther) const {
     91    return mBuffer == aOther.mBuffer &&
     92           mBuffer.IsVoid() == aOther.mBuffer.IsVoid() &&
     93           mUTF16Length == aOther.mUTF16Length &&
     94           mConversionType == aOther.mConversionType &&
     95           mCompressionType == aOther.mCompressionType;
     96  }
     97 
     98  bool operator==(const LSValue& aOther) const { return Equals(aOther); }
     99 
    100  bool operator!=(const LSValue& aOther) const { return !Equals(aOther); }
    101 
    102  constexpr const nsCString& AsCString() const { return mBuffer; }
    103 
    104  class Converter {
    105    nsString mBuffer;
    106 
    107   public:
    108    explicit Converter(const LSValue& aValue);
    109    Converter(Converter&& aOther) = default;
    110    ~Converter() = default;
    111 
    112    operator const nsString&() const { return mBuffer; }
    113 
    114   private:
    115    Converter() = delete;
    116    Converter(const Converter&) = delete;
    117    Converter& operator=(const Converter&) = delete;
    118    Converter& operator=(const Converter&&) = delete;
    119  };
    120 
    121  Converter AsString() const { return Converter{*this}; }
    122 };
    123 
    124 const LSValue& VoidLSValue();
    125 
    126 /**
    127 * XXX: This function doesn't have to be public
    128 * once the support for shadow writes is removed.
    129 */
    130 bool PutCStringBytesToString(const nsACString& aSrc, nsString& aDest);
    131 
    132 }  // namespace mozilla::dom
    133 
    134 #endif  // mozilla_dom_localstorage_LSValue_h