protobuf 之 message 接口摘录

// Abstract interface for protocol messages.
//
// See also MessageLite, which contains most every-day operations.  Message
// adds descriptors and reflection on top of that.
//
// The methods of this class that are virtual but not pure-virtual have
// default implementations based on reflection.  Message classes which are
// optimized for speed will want to override these with faster implementations,
// but classes optimized for code size may be happy with keeping them.  See
// the optimize_for option in descriptor.proto.
class LIBPROTOBUF_EXPORT Message : public MessageLite {
 public:
  inline Message() {}
  virtual ~Message();

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

  // Construct a new instance of the same type.  Ownership is passed to the
  // caller.  (This is also defined in MessageLite, but is defined again here
  // for return-type covariance.)
  virtual Message* New() const = 0;

  // Make this message into a copy of the given message.  The given message
  // must have the same descriptor, but need not necessarily be the same class.
  // By default this is just implemented as "Clear(); MergeFrom(from);".
  virtual void CopyFrom(const Message& from);

  // Merge the fields from the given message into this message.  Singular
  // fields will be overwritten, except for embedded messages which will
  // be merged.  Repeated fields will be concatenated.  The given message
  // must be of the same type as this message (i.e. the exact same class).
  virtual void MergeFrom(const Message& from);

  // Verifies that IsInitialized() returns true.  GOOGLE_CHECK-fails otherwise, with
  // a nice error message.
  void CheckInitialized() const;

  // Slowly build a list of all required fields that are not set.
  // This is much, much slower than IsInitialized() as it is implemented
  // purely via reflection.  Generally, you should not call this unless you
  // have already determined that an error exists by calling IsInitialized().
  void FindInitializationErrors(vector<string>* errors) const;

  // Like FindInitializationErrors, but joins all the strings, delimited by
  // commas, and returns them.
  string InitializationErrorString() const;

  // Clears all unknown fields from this message and all embedded messages.
  // Normally, if unknown tag numbers are encountered when parsing a message,
  // the tag and value are stored in the message's UnknownFieldSet and
  // then written back out when the message is serialized.  This allows servers
  // which simply route messages to other servers to pass through messages
  // that have new field definitions which they don't yet know about.  However,
  // this behavior can have security implications.  To avoid it, call this
  // method after parsing.
  //
  // See Reflection::GetUnknownFields() for more on unknown fields.
  virtual void DiscardUnknownFields();

  // Computes (an estimate of) the total number of bytes currently used for
  // storing the message in memory.  The default implementation calls the
  // Reflection object's SpaceUsed() method.
  virtual int SpaceUsed() const;

  // Debugging & Testing----------------------------------------------

  // Generates a human readable form of this message, useful for debugging
  // and other purposes.
  string DebugString() const;
  // Like DebugString(), but with less whitespace.
  string ShortDebugString() const;
  // Like DebugString(), but do not escape UTF-8 byte sequences.
  string Utf8DebugString() const;
  // Convenience function useful in GDB.  Prints DebugString() to stdout.
  void PrintDebugString() const;

  // Heavy I/O -------------------------------------------------------
  // Additional parsing and serialization methods not implemented by
  // MessageLite because they are not supported by the lite library.

  // Parse a protocol buffer from a file descriptor.  If successful, the entire
  // input will be consumed.
  bool ParseFromFileDescriptor(int file_descriptor);
  // Like ParseFromFileDescriptor(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromFileDescriptor(int file_descriptor);
  // Parse a protocol buffer from a C++ istream.  If successful, the entire
  // input will be consumed.
  bool ParseFromIstream(istream* input);
  // Like ParseFromIstream(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromIstream(istream* input);

  // Serialize the message and write it to the given file descriptor.  All
  // required fields must be set.
  bool SerializeToFileDescriptor(int file_descriptor) const;
  // Like SerializeToFileDescriptor(), but allows missing required fields.
  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(ostream* output) const;
  // Like SerializeToOstream(), but allows missing required fields.
  bool SerializePartialToOstream(ostream* output) const;


  // Reflection-based methods ----------------------------------------
  // These methods are pure-virtual in MessageLite, but Message provides
  // reflection-based default implementations.

  virtual string GetTypeName() const;
  virtual void Clear();
  virtual bool IsInitialized() const;
  virtual void CheckTypeAndMergeFrom(const MessageLite& other);
  virtual bool MergePartialFromCodedStream(io::CodedInputStream* input);
  virtual int ByteSize() const;
  virtual void SerializeWithCachedSizes(io::CodedOutputStream* output) const;

 private:
  // This is called only by the default implementation of ByteSize(), to
  // update the cached size.  If you override ByteSize(), you do not need
  // to override this.  If you do not override ByteSize(), you MUST override
  // this; the default implementation will crash.
  //
  // The method is private because subclasses should never call it; only
  // override it.  Yes, C++ lets you do that.  Crazy, huh?
  virtual void SetCachedSize(int size) const;

 public:

  // Introspection ---------------------------------------------------

  // Typedef for backwards-compatibility.
  typedef google::protobuf::Reflection Reflection;

  // Get a Descriptor for this message's type.  This describes what
  // fields the message contains, the types of those fields, etc.
  const Descriptor* GetDescriptor() const { return GetMetadata().descriptor; }

  // Get the Reflection interface for this Message, which can be used to
  // read and modify the fields of the Message dynamically (in other words,
  // without knowing the message type at compile time).  This object remains
  // property of the Message.
  //
  // This method remains virtual in case a subclass does not implement
  // reflection and wants to override the default behavior.
  virtual const Reflection* GetReflection() const {
    return GetMetadata().reflection;
  }

 protected:
  // Get a struct containing the metadata for the Message. Most subclasses only
  // need to implement this method, rather than the GetDescriptor() and
  // GetReflection() wrappers.
  virtual Metadata GetMetadata() const  = 0;


 private:
  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(Message);
};