Implementation:Alibaba MNN Protobuf Descriptor H

Knowledge Sources	Alibaba_MNN Protocol Buffers
Domains	Serialization, Reflection
Last Updated	2026-02-10 12:00 GMT

Overview

Header declaring the Protocol Buffers Descriptor classes for runtime schema reflection, message introspection, and field enumeration.

Description

This header defines the core descriptor class hierarchy: Descriptor (messages), FieldDescriptor (fields), EnumDescriptor (enums), ServiceDescriptor (services), FileDescriptor (files), and DescriptorPool (schema registry). These classes provide a complete runtime representation of .proto schemas, enabling dynamic message creation and reflection-based access. MNN vendors this header because the TensorFlow and Caffe model conversion tools use descriptor-based reflection to navigate model graph structures without hard-coding every message type.

Usage

Vendored dependency used internally by MNN for parsing protobuf-based model formats (TensorFlow, Caffe). Not directly imported by end users.

Code Reference

Source Location

• Repository: Alibaba_MNN
• File: 3rd_party/protobuf/src/google/protobuf/descriptor.h
• Lines: 1-2417

Signature

namespace google {
namespace protobuf {
class Descriptor { int field_count() const; const FieldDescriptor* field(int i) const; };
class FieldDescriptor { FieldDescriptor::Type type() const; int number() const; };
class EnumDescriptor { const EnumValueDescriptor* FindValueByNumber(int n) const; };
class DescriptorPool { const Descriptor* FindMessageTypeByName(const std::string&) const; };
}  // namespace protobuf
}  // namespace google

Import

#include "3rd_party/protobuf/src/google/protobuf/descriptor.h"

I/O Contract

Inputs

Name	Type	Required	Description
N/A	N/A	N/A	Header-only declarations; provides descriptor class interfaces for schema introspection

Outputs

Name	Type	Description
Descriptor	google::protobuf::Descriptor	Message-level schema descriptor with field and nested type access
FieldDescriptor	google::protobuf::FieldDescriptor	Field-level metadata including type, name, number, and label
DescriptorPool	google::protobuf::DescriptorPool	Registry for looking up descriptors by fully qualified name

Usage Examples

// MNN internal usage
#include "google/protobuf/descriptor.h"
const auto* desc = message.GetDescriptor();
for (int i = 0; i < desc->field_count(); ++i) {
  const auto* field = desc->field(i);
}

Related Pages

• Environment:Alibaba_MNN_CPU_Build_Environment