protobuf 之 MessageLite 接口摘录

class LIBPROTOBUF_EXPORT MessageLite {
 public:
  inline MessageLite() {}
  virtual ~MessageLite();

  // Basic Operations ------------------------------------------------

  // Get the name of this message type, e.g. "foo.bar.BazProto".
  virtual string GetTypeName() const = 0;

  // Construct a new instance of the same type.  Ownership is passed to the
  // caller.
  virtual MessageLite* New() const = 0;

  // Clear all fields of the message and set them to their default values.
  // Clear() avoids freeing memory, assuming that any memory allocated
  // to hold parts of the message will be needed again to hold the next
  // message.  If you actually want to free the memory used by a Message,
  // you must delete it.
  virtual void Clear() = 0;

  // Quickly check if all required fields have values set.
  virtual bool IsInitialized() const = 0;

  // This is not implemented for Lite messages -- it just returns "(cannot
  // determine missing fields for lite message)".  However, it is implemented
  // for full messages.  See message.h.
  virtual string InitializationErrorString() const;

  // If |other| is the exact same class as this, calls MergeFrom().  Otherwise,
  // results are undefined (probably crash).
  virtual void CheckTypeAndMergeFrom(const MessageLite& other) = 0;

  // Parsing ---------------------------------------------------------
  // Methods for parsing in protocol buffer format.  Most of these are
  // just simple wrappers around MergeFromCodedStream().

  // Fill the message with a protocol buffer parsed from the given input
  // stream.  Returns false on a read error or if the input is in the
  // wrong format.
  bool ParseFromCodedStream(io::CodedInputStream* input);
  // Like ParseFromCodedStream(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromCodedStream(io::CodedInputStream* input);
  // Read a protocol buffer from the given zero-copy input stream.  If
  // successful, the entire input will be consumed.
  bool ParseFromZeroCopyStream(io::ZeroCopyInputStream* input);
  // Like ParseFromZeroCopyStream(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromZeroCopyStream(io::ZeroCopyInputStream* 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 ParseFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input, int size);
  // Like ParseFromBoundedZeroCopyStream(), but accepts messages that are
  // missing required fields.
  bool ParsePartialFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input,
                                             int size);
  // Parse a protocol buffer contained in a string.
  bool ParseFromString(const string& data);
  // Like ParseFromString(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromString(const string& data);
  // Parse a protocol buffer contained in an array of bytes.
  bool ParseFromArray(const void* data, int size);
  // Like ParseFromArray(), but accepts messages that are missing
  // required fields.
  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 input overwrite 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().
  virtual bool MergePartialFromCodedStream(io::CodedInputStream* input) = 0;


  // 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;
  // Like SerializeToCodedStream(), but allows missing required fields.
  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;
  // Like SerializeToZeroCopyStream(), but allows missing required fields.
  bool SerializePartialToZeroCopyStream(io::ZeroCopyOutputStream* output) const;
  // Serialize the message and store it in the given string.  All required
  // fields must be set.
  bool SerializeToString(string* output) const;
  // Like SerializeToString(), but allows missing required fields.
  bool SerializePartialToString(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;
  // Like SerializeToArray(), but allows missing required fields.
  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().
  string SerializeAsString() const;
  // Like SerializeAsString(), but allows missing required fields.
  string SerializePartialAsString() const;

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

  // Computes the serialized size of the message.  This recursively calls
  // ByteSize() on all embedded messages.  If a subclass does not override
  // this, it MUST override SetCachedSize().
  virtual int ByteSize() const = 0;

  // Serializes the message without recomputing the size.  The message must
  // not have changed since the last call to ByteSize(); if it has, the results
  // are undefined.
  virtual void SerializeWithCachedSizes(
      io::CodedOutputStream* output) const = 0;

  // 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.
  virtual uint8* SerializeWithCachedSizesToArray(uint8* 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;

 private:
  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageLite);
};