PROPOSAL: how extensions should work!

Current Suggestion

Extensions are not implemented. I recommend merely mechanically adding the extension values to the message descriptor before running protoc-c. It works well, and isn't very hard.

Use Cases

VOLUNTEERS? uh, yeah, please write some example use-cases if you are interested

THIS IS AN UNIMPLEMENTED PROPOSAL

Introduction

This is a DRAFT (if that) of the extension API.

The (new as of May 16) plan is to make a MessageDescriptor for every namespace/message combination that has extensions. The lexically-containing message name (if any) may need to be shoved somewhere. We may add an "extends" field to MessageDescriptor to clarify this purpose.

libprotobuf-c functions

ProtobufCMessage *protobuf_c_extension_unpack(ProtobufC_Message *msg,
                                              ProtobufC_MessageDescriptor *extension,
                                              ProtobufC_Allocator *allocator);

If any extension is tagged as "required", its absence will cause the unpacking to fail. You will also get failures on type errors.

For the packing side, you can pack the extensions (using get_packed_size/pack or pack_buffer) and concatenate as binary data. Later, we may add support to generate "UnknownFields" so that you can incorporate them into a message - it's not clear that that's useful.

Generated code

extern ProtobufC_MessageDescriptor extension_namespace___extends___full_message_name;
ExtensionNamespace___extends___FullMessageName *extension_namespace___extends___full_message_name__unpack(FullMessageName *orig_message,
                          ProtobufC_Allocator *allocator);