Hi Group,
I am trying to serialize/deserialize a sub message using Protobuf.
The reasons for this is signing. I want to be able to sign part of my
message. To be able to do that, I need to canonicalize it somehow.

If it matters, I use protbuf 3.0.0-alpha (With the proto2 language) with

Example file: testp.proto

    package my_package;

    message my_mess {
      message data {
        optional uint64 x = 1;
        optional uint64 y = 2;
        optional uint64 z = 3;
        optional bytes signature = 4;

In this example, I want to sign the data part of the message. Therefore I
want to serialize only my_mess.data, sign it, put the signature into
my_mess.signature, and then serialize the full message my_mess.

Compiling testp.proto:

    $ protoc -I=. --python_out=. testp.proto
    [libprotobuf WARNING google/protobuf/compiler/parser.cc:471] No syntax
specified for the proto file. Please use 'syntax = "proto2";' or 'syntax =
"proto3";' to specify a syntax version. (Defaulted to proto2 syntax.)

I noticed that mm.data have the methods SerializeToString and
However, it seems like it is not possible to run them directly. Here are my
naive attempts:

    $ ipython

    In [1]: import testp_pb2
    In [2]: mm = testp_pb2.my_mess()
    In [3]: mm.data.x = 1
    In [4]: mm.data.y = 2
    In [5]: mm.data.z = 3
    In [6]: mm.data.SerializeToString()

    TypeError                                 Traceback (most recent call
    <ipython-input-6-faa8e25906ca> in <module>()
    ----> 1 mm.data.SerializeToString()

    TypeError: SerializeToString() missing 1 required positional argument:

    In [7]: mm.data.SerializePartialToString()

    TypeError                                 Traceback (most recent call
    <ipython-input-7-4b2c1ff0b1c9> in <module>()
    ----> 1 mm.data.SerializePartialToString()

    TypeError: SerializePartialToString() missing 1 required positional
argument: 'self'

I was wondering if there is some simple solution I'm missing. I am open to
other suggestions, if you have an idea of signing just a part of the
message in an elegant way.

Note that this question was cross posted at:
However I got no response in there.

Thank you for your help.

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