gRPCGateway

gRPCGateway, commonly referred to as grpc-gateway, is an open-source reverse proxy that translates RESTful HTTP/JSON requests into gRPC method invocations. It is part of the grpc-ecosystem and is frequently used to surface a REST API for a gRPC backend, enabling clients that speak HTTP/JSON to interact with services implemented with gRPC.

Operation and architecture: Developers define services in Protocol Buffers and annotate RPC methods with google.api.http rules to specify HTTP endpoints, methods, and parameter mappings. A protoc plugin (protoc-gen-grpc-gateway) generates a Go-based HTTP reverse proxy. At runtime, an incoming HTTP request is matched to a gRPC method, the gateway marshals the JSON payload into a protobuf message, forwards the request to the gRPC server, and then converts the gRPC response back into JSON for the HTTP client. The gateway typically runs as a separate process in front of the gRPC server and can be deployed behind a load balancer or TLS terminator.

Features and scope: The gateway supports REST-to-gRPC mappings with path templates, query parameter binding, and automatic JSON↔protobuf marshaling. It is primarily oriented toward unary RPCs; streaming semantics between HTTP and gRPC are supported to some extent but are more limited compared to direct gRPC usage. It can also generate OpenAPI (Swagger) documentation from protobuf definitions via additional plugins (e.g., protoc-gen-openapiv2).

Usage and requirements: A working gRPC service defined with proper http annotations is required. The protoc plugins must be installed to generate the gateway code, and a running gRPC backend must be available. Deployment typically involves running the gateway alongside the gRPC server, with configurations for security, authentication, and logging.