feat: pass fullMethodName to GetConnection

This provides a way to make decision on passing requests based on the
method name.

Signed-off-by: Andrey Smirnov <[email protected]>

Author: smira

go.mod

@@ -1,6 +1,6 @@
 module github.com/talos-systems/grpc-proxy
 
-go 1.18
+go 1.19
 
 require (
 	github.com/golang/protobuf v1.5.2

proxy/director.go

@@ -27,7 +27,7 @@ type Backend interface {
 	// The context returned from this function should be the context for the *outgoing* (to backend) call. In case you want
 	// to forward any Metadata between the inbound request and outbound requests, you should do it manually. However, you
 	// *must* propagate the cancel function (`context.WithCancel`) of the inbound context to the one returned.
-	GetConnection(ctx context.Context) (context.Context, *grpc.ClientConn, error)
+	GetConnection(ctx context.Context, fullMethodName string) (context.Context, *grpc.ClientConn, error)
 
 	// AppendInfo is called to enhance response from the backend with additional data.
 	//
@@ -71,7 +71,7 @@ func (sb *SingleBackend) String() string {
 }
 
 // GetConnection returns a grpc connection to the backend.
-func (sb *SingleBackend) GetConnection(ctx context.Context) (context.Context, *grpc.ClientConn, error) {
+func (sb *SingleBackend) GetConnection(ctx context.Context, fullMethodName string) (context.Context, *grpc.ClientConn, error) {
 	return sb.GetConn(ctx)
 }
 
@@ -88,11 +88,11 @@ func (sb *SingleBackend) BuildError(streaming bool, err error) ([]byte, error) {
 // StreamDirector returns a list of Backend objects to forward the call to.
 //
 // There are two proxying modes:
-//   1. one to one: StreamDirector returns a single Backend object - proxying is done verbatim, Backend.AppendInfo might
-//      be used to enhance response with source information (or it might be skipped).
-//   2. one to many: StreamDirector returns more than one Backend object - for unary calls responses from Backend objects
-//      are aggregated by concatenating protobuf responses (requires top-level `repeated` protobuf definition) and errors
-//      are wrapped as responses via BuildError. Responses are potentially enhanced via AppendInfo.
+//  1. one to one: StreamDirector returns a single Backend object - proxying is done verbatim, Backend.AppendInfo might
+//     be used to enhance response with source information (or it might be skipped).
+//  2. one to many: StreamDirector returns more than one Backend object - for unary calls responses from Backend objects
+//     are aggregated by concatenating protobuf responses (requires top-level `repeated` protobuf definition) and errors
+//     are wrapped as responses via BuildError. Responses are potentially enhanced via AppendInfo.
 //
 // 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.

proxy/handler.go

@@ -63,7 +63,7 @@ func (s *handler) handler(srv interface{}, serverStream grpc.ServerStream) error
 
 		// We require that the backend's returned context inherits from the serverStream.Context().
 		var outgoingCtx context.Context
-		outgoingCtx, backendConnections[i].backendConn, backendConnections[i].connError = backends[i].GetConnection(clientCtx)
+		outgoingCtx, backendConnections[i].backendConn, backendConnections[i].connError = backends[i].GetConnection(clientCtx, fullMethodName)
 
 		if backendConnections[i].connError != nil {
 			continue

proxy/handler_one2many_test.go

@@ -152,7 +152,7 @@ func (b *assertingBackend) String() string {
 	return fmt.Sprintf("backend%d", b.i)
 }
 
-func (b *assertingBackend) GetConnection(ctx context.Context) (context.Context, *grpc.ClientConn, error) {
+func (b *assertingBackend) GetConnection(ctx context.Context, fullMethodName string) (context.Context, *grpc.ClientConn, error) {
 	md, _ := metadata.FromIncomingContext(ctx)
 	// Explicitly copy the metadata, otherwise the tests will fail.
 	outCtx := metadata.NewOutgoingContext(ctx, md.Copy())