Command protoc-gen-grpc-gateway is a plugin for Google protocol buffer compiler to generate a reverse-proxy, which converts incoming RESTful HTTP/1 requests gRPC invocation. You rarely need to run this program directly. Instead, put this program into your $PATH with a name "protoc-gen-grpc-gateway" and run
protoc --grpc-gateway_out=output_directory path/to/input.proto
See README.md for more details.