Standalone prototype for serialization of messages for Tribler using Protocol Buffers.

This section will explain how to get your first message compiled.

This is mostly the same as creating a normal Protocol Buffers definition. There are two things you must do however:

1. Put your .proto definition in the src/ folder.
2. Add an import of defaults.proto to your file.

For example src/my_community.proto:

import "defaults.proto";

message Votecast {
  required string cid = 1 [(length) = 8]; // 8 bytes
  required int32 vote = 2 [(length) = 2]; // 2 bytes
  required int64 timestamp = 3;
}

Note that there is a length option specified. This is a custom option to specify the maximum number of bytes a field can maximally occupy. Because values are packed, this will - in almost all cases - never be the actual amount of bytes the field will use on-wire.

To compile your fresh .proto just call the compiler.py script in the src/ folder (make sure to install the protoc compiler first: sudo apt-get install libprotobuf-dev protobuf-compiler). This will create a file called <your_proto_file_name>_pb2.py. In our previous example:

python compiler.py my_community.proto

Now move/copy your compiled package (<your_proto_file_name>_pb2.py) into the messages/ folder. As a final touch edit the __init__.py file in the messages/ folder. You will need to change the definition of MESSAGES to include the __import_handle() of your module. In our example:

MESSAGES = [__import_handle('my_community_pb2')]

Here we assume you have added at least one message to the file tree as described in the previous section. You will also need to have Protocol Buffers installed (sudo apt-get install python-protobuf). To use the Serializer you need to create a Serializer instance (you can have multiple instances if you want):

from serializer import Serializer

s = Serializer()

To serialize a message you need to call the serialize() function. In our running example one would for example to the following:

# By Votecast definition order:
s.serialize("Votecast", "mycid", 15, 12300014)
# By Votecast field names:
s.serialize("Votecast", cid = "mycid", vote = 15, timestamp = 12300014)

To get messages from raw data, you need two things:

1. A handler class (add_package_handler()) or function per message(add_handler()).
2. To call unserialize() on your data.

Several advanced features of unserialize() include the ability to skip unusable bytes and to buffer data for the next call. In our example:

class TestHandler:
    def on_votecast(obj):
        print obj.cid + ", " + str(obj.vote) + ", " + str(obj.timestamp)

def test_handler(obj):
    print obj.cid + ", " + str(obj.vote) + ", " + str(obj.timestamp)
    
s.add_package_handler("my_community", TestHandler())
s.add_handler("Votecast", test_handler)

This is a reference for all source files required for a minimal working example. You will still need to compile src/my_community.proto as described above.

src/my_community.proto:

import "defaults.proto";

message Votecast {
  required string cid = 1 [(length) = 8]; // 8 bytes
  required int32 vote = 2 [(length) = 2]; // 2 bytes
  required int64 timestamp = 3;
}

messages/__init__.py:

def __import_handle(name):
    return __import__(name, globals(), locals(), [], -1)

MESSAGES = [__import_handle('my_community_pb2')]

test.py:

from serializer import Serializer

class TestHandler:
    def on_votecast(obj):
        print "TestHandler received: " + obj.cid + ", " + str(obj.vote) + ", " + str(obj.timestamp)

def test_handler(obj):
    print "test_handler received: " + obj.cid + ", " + str(obj.vote) + ", " + str(obj.timestamp)
    
s = Serializer()
s.add_package_handler("my_community", TestHandler())
s.add_handler("Votecast", test_handler)

# Encode
enc = s.serialize("Votecast", "mycid", 15, 12300014)

# Handle decode
s.unserialize(enc)