源码protobuf 中各个压缩（Serialize）解压缩（Parse）函数辨析

Posted 2022-02-04 看，未来

注释其实很详细。

Parsing

/*
使用从给定输入流解析的协议缓冲区填充消息。读取错误或输入格式错误时返回false。
成功返回并不表示整个输入已使用，请确保调用ConsumedEntireMessage（）检查是否已使用（如果适用）。
*/
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParseFromCodedStream(
      io::CodedInputStream* input);

//跟上面那个功能一样，不过允许 repeated 部分不填充，后面遇到Partial都是这个意思
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParsePartialFromCodedStream(
      io::CodedInputStream* input);
 
 // 从给定的零拷贝输入流读取协议缓冲区。如果成功，将使用整个输入。 
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParseFromZeroCopyStream(
      io::ZeroCopyInputStream* input);

  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParsePartialFromZeroCopyStream(
      io::ZeroCopyInputStream* input);

  // Parse a protocol buffer from a file descriptor.  If successful, the entire
  // input will be consumed.
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParseFromFileDescriptor(
      int file_descriptor);

  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParsePartialFromFileDescriptor(
      int file_descriptor);

  // Parse a protocol buffer from a C++ istream.  If successful, the entire
  // input will be consumed.
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParseFromIstream(std::istream* input);

  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParsePartialFromIstream(
      std::istream* input);

  // Read a protocol buffer from the given zero-copy input stream, expecting
  // the message to be exactly "size" bytes long.  If successful, exactly
  // this many bytes will have been consumed from the input.
  bool MergePartialFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input,
                                             int size);
  // Like ParseFromBoundedZeroCopyStream(), but accepts messages that are
  // missing required fields.
  bool MergeFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input, int size);
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParseFromBoundedZeroCopyStream(
      io::ZeroCopyInputStream* input, int size);
  // Like ParseFromBoundedZeroCopyStream(), but accepts messages that are
  // missing required fields.
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParsePartialFromBoundedZeroCopyStream(
      io::ZeroCopyInputStream* input, int size);

  // Parses a protocol buffer contained in a string. Returns true on success.
  // This function takes a string in the (non-human-readable) binary wire
  // format, matching the encoding output by MessageLite::SerializeToString().
  // If you'd like to convert a human-readable string into a protocol buffer
  // object, see google::protobuf::TextFormat::ParseFromString().
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParseFromString(ConstStringParam data);

  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParsePartialFromString(
      ConstStringParam data);

  // Parse a protocol buffer contained in an array of bytes.
  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParseFromArray(const void* data,
                                                       int size);

  PROTOBUF_ATTRIBUTE_REINITIALIZES bool ParsePartialFromArray(const void* data,
                                                              int size);


  // Reads a protocol buffer from the stream and merges it into this
  // Message.  Singular fields read from the what is
  // already in the Message and repeated fields are appended to those
  // already present.
  //
  // It is the responsibility of the caller to call input->LastTagWas()
  // (for groups) or input->ConsumedEntireMessage() (for non-groups) after
  // this returns to verify that the message's end was delimited correctly.
  //
  // ParseFromCodedStream() is implemented as Clear() followed by
  // MergeFromCodedStream().
  bool MergeFromCodedStream(io::CodedInputStream* input);

  // Like MergeFromCodedStream(), but succeeds even if required fields are
  // missing in the input.
  //
  // MergeFromCodedStream() is just implemented as MergePartialFromCodedStream()
  // followed by IsInitialized().
  bool MergePartialFromCodedStream(io::CodedInputStream* input);

  // Merge a protocol buffer contained in a string.
  bool MergeFromString(ConstStringParam data);

---

Serialization

Methods for serializing in protocol buffer format. Most of these are just simple wrappers around ByteSize() and SerializeWithCachedSizes().

  // Write a protocol buffer of this message to the given output.  Returns
  // false on a write error.  If the message is missing required fields,
  // this may GOOGLE_CHECK-fail.
  bool SerializeToCodedStream(io::CodedOutputStream* output) const;
 
  bool SerializePartialToCodedStream(io::CodedOutputStream* output) const;

  // Write the message to the given zero-copy output stream.  All required
  // fields must be set.
  bool SerializeToZeroCopyStream(io::ZeroCopyOutputStream* output) const;
  
  bool SerializePartialToZeroCopyStream(io::ZeroCopyOutputStream* output) const;
 
  // Serialize the message and store it in the given string.  All required
  // fields must be set.
  bool SerializeToString(std::string* output) const;
  
  bool SerializePartialToString(std::string* output) const;

  // Serialize the message and store it in the given byte array.  All required
  // fields must be set.
  bool SerializeToArray(void* data, int size) const;
  
  bool SerializePartialToArray(void* data, int size) const;

  // Make a string encoding the message. Is equivalent to calling
  // SerializeToString() on a string and using that.  Returns the empty
  // string if SerializeToString() would have returned an error.
  // Note: If you intend to generate many such strings, you may
  // reduce heap fragmentation by instead re-using the same string
  // object with calls to SerializeToString().
  std::string SerializeAsString() const;
  
  std::string SerializePartialAsString() const;

  // Serialize the message and write it to the given file descriptor.  All
  // required fields must be set.
  bool SerializeToFileDescriptor(int file_descriptor) const;
  
  bool SerializePartialToFileDescriptor(int file_descriptor) const;
  
  // Serialize the message and write it to the given C++ ostream.  All
  // required fields must be set.
  bool SerializeToOstream(std::ostream* output) const;
  
  bool SerializePartialToOstream(std::ostream* output) const;

  // Like SerializeToString(), but appends to the data to the string's
  // existing contents.  All required fields must be set.
  bool AppendToString(std::string* output) const;
  // Like AppendToString(), but allows missing required fields.
  bool AppendPartialToString(std::string* output) const;


  // Computes the serialized size of the message.  This recursively calls
  // ByteSizeLong() on all embedded messages.
  //
  // ByteSizeLong() is generally linear in the number of fields defined for the
  // proto.
  virtual size_t ByteSizeLong() const = 0;

  // Legacy ByteSize() API.
  PROTOBUF_DEPRECATED_MSG("Please use ByteSizeLong() instead")
  int ByteSize() const  return internal::ToIntSize(ByteSizeLong()); 

  // Serializes the message without recomputing the size.  The message must not
  // have changed since the last call to ByteSize(), and the value returned by
  // ByteSize must be non-negative.  Otherwise the results are undefined.
  void SerializeWithCachedSizes(io::CodedOutputStream* output) const 
    output->SetCur(_InternalSerialize(output->Cur(), output->EpsCopy()));
  

  // Functions below here are not part of the public interface.  It isn't
  // enforced, but they should be treated as private, and will be private
  // at some future time.  Unfortunately the implementation of the "friend"
  // keyword in GCC is broken at the moment, but we expect it will be fixed.

  // Like SerializeWithCachedSizes, but writes directly to *target, returning
  // a pointer to the byte immediately after the last byte written.  "target"
  // must point at a byte array of at least ByteSize() bytes.  Whether to use
  // deterministic serialization, e.g., maps in sorted order, is determined by
  // CodedOutputStream::IsDefaultSerializationDeterministic().
  uint8_t* SerializeWithCachedSizesToArray(uint8_t* target) const;

  // Returns the result of the last call to ByteSize().  An embedded message's
  // size is needed both to serialize it (because embedded messages are
  // length-delimited) and to compute the outer message's size.  Caching
  // the size avoids computing it multiple times.
  //
  // ByteSize() does not automatically use the cached size when available
  // because this would require invalidating it every time the message was
  // modified, which would be too hard and expensive.  (E.g. if a deeply-nested
  // sub-message is changed, all of its parents' cached sizes would need to be
  // invalidated, which is too much work for an otherwise inlined setter
  // method.)
  virtual int GetCachedSize() const = 0;

---

卷好睡觉。。