Google Protocol Buffers compiler plugin example

demo-output.txt

> protoc --plugin=utils/protoc-gen-demo --demo_out=. demo.proto && \
      cat demo.proto.txt
enum MessageType
	SERVER_SEARCH_CITIES
	CLIENT_FOUND_CITIES
message RPCMessage
	version
	message_id
	body
message MessageBody
	message_type
	city_query
	cities
	client_notification
message CityQuery
	name
message Cities
	cities
message City
	id
	name
	longitude
	latitude

protoc-gen-demo.py

#!/usr/bin/env python
import sys
from google.protobuf.compiler.plugin_pb2 \
    import CodeGeneratorRequest, CodeGeneratorResponse

request = CodeGeneratorRequest()
request.ParseFromString(sys.stdin.read())
response = CodeGeneratorResponse()
for file in request.proto_file:
    out = ''
    for enum in file.enum_type:
        out += 'enum ' + enum.name + '\n'
        for value in enum.value:
            out += '\t' + value.name + '\n'
    for message in file.message_type:
        out += 'message ' + message.name + '\n'
        for field in message.field:
            out += '\t' + field.name + '\n'
    f = response.file.add()
    f.name = file.name + '.txt'
    f.content = out
sys.stdout.write(response.SerializeToString())