ProtoBuffers debug with CURL. ProtoBuffers should be installed first: "yum install protobuf" or "brew install protobuf".

proto.msg

key:"string value"
int_key:22

req

#!/bin/bash
URL=full_method_url                # i.e. "http://server.com/my/method" (without quotes)
REQUEST=request_message_name       # i.e. "Request"
RESPONSE=response_message_name     # i.e. "Response"
PROTO=proto_file_name              # i.e. "./Protocol.proto"

cat proto.msg | protoc --encode $REQUEST $PROTO | curl -sS -X POST --data-binary @- $URL | protoc --decode $RESPONSE $PROTO

How do we construct complex request messages with this approach?

There is protocurl - a command line tool specifically created for this purpose of debugging Protobuf endpoints similar to cURL + JSON.

A request would look like this:

protocurl -I path/to/protos -i ..MyRequest -o ..MyResponse \
  -u <URL> -d 'key: "string", int_key: 42'

It also works with JSON input/output and the text format is documented on the README.

(Disclaimer: I am the author of this CLI since I had the same problem and needed a better tool.)

This is amazing. Thanks for sharing @GollyTicker