##ProtoGen

ProtoGen is a utility to generate mapping functions that easily allow marshalling ProtoBuf structure(s) into a []byte.

ProtoBuf structures are assigned a uint32 value. The protogen tool will generate code that will aid in marshalling from a struct to bytes. It will encode 4 bytes for the proto message id, followed by the bytes from marshalled protobuf struct.

Given the bytes, it will use 4 bytes to extract the message id, then it will attempt to unmarshal the remaining bytes into the associated structure.

The definition of a protocol file should contain an enum with definitions of packet ids. The enum value names should map to various messages defined in the protofile. Value names should match proto messages with the suffix 'Id'. Also the field name should have a comment //@@protogen:SrvReturnCode@@

A proto file should look like the following

file: packets.proto


enum Packet {
    SrvReturnCodeId = 0; //@@protogen:SrvReturnCode@@
}

message SrvReturnCode {
    uint32 event = 1;
    uint32 correlationId = 2;
}

usage: protogen protofile enumNamePacket output_go_file

example: go run protogen /home/alexj/projects/rooms/submodules/protocol-definitions/centralserver/css1erver.proto Packet /home/alexj/projects/rooms/proto/cs/mapping.go

The following go code will be written to the output file

var Mapper ProtobufMessageMapper = &mapper{}

type ProtobufMessageMapper interface {
	MapIDToProto(method uint32) (interface{}, error)
	MapProtoMessageToID(msg interface{}) (uint32, error)
}

type mapper struct{}

func (mapper) MapIDToProto(method uint32) (interface{}, error)     { return MapIDToProto(method) }
func (mapper) MapProtoMessageToID(msg interface{}) (uint32, error) { return MapProtoMessageToID(msg) }

func MapIDToProto(method uint32) (interface{}, error) {...}
func MapProtoMessageToID(msg interface{}) (uint32, error) {...} 
func Parse(data []byte) (interface{}, uint32, error) {...} 
func EncodeMessage(param interface{}) ([]byte, uint32, error) {...} 
func (x Packet) Value() uint32 {...} 
}

Building

go build -o ~/bin/protogen .

or 

make protogen

Example

There is a sample proto file test.proto in the _test directory. If you run make test it will generate the golang code from the proto file. It will also run the protogen tool to generate the utilities for marshalling / unmarshalling from go structs to bytes and vice versa.