What is gRPC gateway and what problem does it solve?

grpc-gateway is a plugin for the protoc compiler that generates a reverse proxy HTTP/JSON gateway from annotated .proto files. It solves the browser/REST client compatibility problem: by adding HTTP annotations to your .proto (using google.api.http options), grpc-gateway generates Go code that translates incoming REST/JSON requests to gRPC calls and translates the gRPC responses back to JSON. Example annotation: rpc GetUser(GetUserRequest) returns (User) { option (google.api.http) = { get: "/v1/users/{id}" }; }. This allows you to maintain a single gRPC service definition and expose it as both a gRPC API (for internal microservices) and a REST/JSON API (for browser clients, external partners, or legacy systems) without maintaining two separate server implementations.