Question

I’m trying to talk to a C# program that uses protobuf-net from an iphone using http://code.google.com/p/metasyntactic/wiki/ProtocolBuffers

Unfortunately the .proto file I’ve been given (generated from the C# source code) includes an a line that protoc is rejecting:

repeated Pair_Guid_List`1 Local = 6;

It appears that this is because the source data is a C# Dictionary, with a Guid key and a class as the value. Is there a way to cope with this better?

The protobuf-net version in use is r278.zip.

(The C# sending and receiving these protobufs all works fine, it’s just when we add the iphone into the mix that this becomes an issue.)

UPDATE: all working now thanks to Marc!

The object on the C# side turned out to be:

[ProtoMember(7)]
public Dictionary<Guid, List<Pages>> ReceivedPages { get; set; }

which worked fine using the following in the .proto:

message PagesDict {
  required bcl.Guid guid = 1;
  repeated Pages Pages = 2;
}

with the message in question containing:

  repeated PagesDict ReceivedPages = 7;

Answer 1

Firstly – are you trying to use protobuf-net on the iPhone? v1 is not expected to work via monotouch; v2 does work (that was a big driver for the v2 work), but is not yet released (it is usable but incomplete at the moment). Let me know if you are trying to do this, as it would matter ;-p

I expect they’ve obtained that .proto by calling Serializer.GetProto<T>, which is unfortunately not fool-proof, especially when things like Dictionary<,> are involved (I’ll add a TODO to try to fix that in v2).

The good news is that it models Dictionary<TKey,TValue> as repeated someType, where someType should be:

message someType {
    required keyType key = 1;
    required valueType value = 2;
}

And Guid is modelled as bcl.Guid (bcl.proto), which is:

message Guid {
  optional fixed64 lo = 1; // the first 8 bytes of the guid
  optional fixed64 hi = 2; // the second 8 bytes of the guid
}

Note, however, that no “proto” is needed at all if working .NET-to-.NET; just compatible types.