Implementation:Alibaba MNN Protobuf Message CC

Metadata

Attribute	Value
Implementation File	`3rd_party/protobuf/src/google/protobuf/message.cc`
Line Count	400
Domains	Serialization, Core_API
Key Methods	`Message::SerializeToString`, `Message::ParseFromString`
Created	2026-02-10
Knowledge Sources	Repo, Doc

Overview

Core Message class implementation with reflection support. Contains the runtime implementations of serialization, deserialization, and message utility methods declared in message.h.

Usage note: Vendored dependency used internally by MNN for parsing protobuf-based model formats. Not directly imported by end users.

Description

This source file implements the non-inline methods of the Message base class, including:

Serialization -- SerializeToString, SerializeToArray, SerializeToCodedStream and related overloads that convert a populated message into wire-format bytes.
Deserialization -- ParseFromString, ParseFromArray, ParseFromCodedStream which reconstruct a message from wire-format input.
Reflection-based operations -- CopyFrom, MergeFrom, and DiscardUnknownFields using the Reflection interface.
Message factory -- Default MessageFactory implementation for creating message instances by descriptor.

This file also provides utilities for computing byte sizes, checking initialization status, and debug string generation.

Usage

#include "google/protobuf/message.h"

All generated protobuf message types inherit from Message and rely on the implementations provided in this file.

Code Reference

// Serialize the message to a string in wire format.
bool Message::SerializeToString(std::string* output) const {
  output->clear();
  return AppendToString(output);
}

// Parse a message from a wire-format string.
bool Message::ParseFromString(const std::string& data) {
  return ParseFromArray(data.data(), data.size());
}

// Reflection-based merge from another message of the same type.
void Message::MergeFrom(const Message& from) {
  const Descriptor* descriptor = GetDescriptor();
  const Reflection* reflection = GetReflection();
  // ... field-by-field merge via reflection
}

// Default MessageFactory for creating message instances by Descriptor.
MessageFactory* MessageFactory::generated_factory() {
  static auto* factory = new GeneratedMessageFactory();
  return factory;
}

I/O Contract

Direction	Type	Description
Input	`std::string` / byte array	Wire-format protobuf bytes for deserialization
Output	`std::string` / byte array	Wire-format protobuf bytes from serialization
Input/Output	`Message` object	Populated message fields after parsing or before serialization

Usage Examples

// Serialize a protobuf message to a string
MyProtoMessage msg;
msg.set_name("example");
std::string serialized;
msg.SerializeToString(&serialized);

// Parse a protobuf message from a string
MyProtoMessage parsed;
parsed.ParseFromString(serialized);

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