Documentation has always been Protobuf‘s weakest area. Proto source files are expected to be used like an IDL. This works for simple interfaces, but falls apart as the interface increases in complexity with multiple layers of source files.
With the latest update Protobuf from 2.5.0, protobuf compiler is finally preserving the comments within the proto source files in its Descriptor definition. This opens a door to documenting proto files.
I spent a week or so writing a protobuf compiler plugin that will convert a proto source file into DocBook and PDF. The plugin is called protoc-gen-docbook, following the protobuf compiler’s plugin naming convention.
Here are the shortcut links to the project homepage. It contains much more details on the project.
As usual, feedback is always welcomed.