manishrjain commented :
You could annotate protobufs with JSON tags, I think, which can then be used to parse directly from JSON byte array. Otherwise, you could create Go structs, with the JSON tags, parse into the Go struct, and then “transfer” over into the PBs.
We had a complicated way to parse responses directly into protobufs, but we got rid of that in favor of JSON, which works for most users. Direct protobuf parsing is not coming back.