-- import "github.com/mwitkow/grpc-proxy/proxy"

Package proxy provides a reverse proxy handler for gRPC.

The implementation allows a grpc.Server to pass a received ServerStream to a ClientStream without understanding the semantics of the messages exchanged. It basically provides a transparent reverse-proxy.

This package is intentionally generic, exposing a StreamDirector function that allows users of this package to implement whatever logic of backend-picking, dialing and service verification to perform.

See examples on documented functions.

func Codec() grpc.Codec

Codec returns a proxying grpc.Codec with the default protobuf codec as parent.

See CodecWithParent.

func CodecWithParent(fallback grpc.Codec) grpc.Codec

CodecWithParent returns a proxying grpc.Codec with a user provided codec as parent.

This codec is crucial to the functioning of the proxy. It allows the proxy server to be oblivious to the schema of the forwarded messages. It basically treats a gRPC message frame as raw bytes. However, if the server handler, or the client caller are not proxy-internal functions it will fall back to trying to decode the message using a fallback codec.

func RegisterService(server *grpc.Server, director StreamDirector, serviceName string, methodNames ...string)

RegisterService sets up a proxy handler for a particular gRPC service and method. The behaviour is the same as if you were registering a handler method, e.g. from a codegenerated pb.go file.

This can only be used if the server also uses grpcproxy.CodecForServer() ServerOption.

func TransparentHandler(director StreamDirector) grpc.StreamHandler

TransparentHandler returns a handler that attempts to proxy all requests that are not registered in the server. The indented use here is as a transparent proxy, where the server doesn't know about the services implemented by the backends. It should be used as a grpc.UnknownServiceHandler.

This can only be used if the server also uses grpcproxy.CodecForServer() ServerOption.

type StreamDirector func(ctx context.Context, fullMethodName string) (*grpc.ClientConn, error)

StreamDirector returns a gRPC ClientConn to be used to forward the call to.

The presence of the Context allows for rich filtering, e.g. based on Metadata (headers). If no handling is meant to be done, a codes.NotImplemented gRPC error should be returned.

It is worth noting that the StreamDirector will be fired after all server-side stream interceptors are invoked. So decisions around authorization, monitoring etc. are better to be handled there.

See the rather rich example.