Add generic gRPC stream forwarding

MODULE.bazel

@@ -57,6 +57,7 @@ use_repo(
     "com_github_gorilla_mux",
     "com_github_grpc_ecosystem_go_grpc_middleware",
     "com_github_grpc_ecosystem_go_grpc_prometheus",
+    "com_github_jhump_protoreflect_v2",
     "com_github_jmespath_go_jmespath",
     "com_github_klauspost_compress",
     "com_github_lazybeaver_xorshift",

go.mod

@@ -28,6 +28,7 @@ require (
 	github.com/gorilla/mux v1.8.1
 	github.com/grpc-ecosystem/go-grpc-middleware v1.4.0
 	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0
+	github.com/jhump/protoreflect/v2 v2.0.0-beta.2
 	github.com/jmespath/go-jmespath v0.4.0
 	github.com/klauspost/compress v1.18.1
 	github.com/lazybeaver/xorshift v0.0.0-20170702203709-ce511d4823dd

go.sum

@@ -198,6 +198,8 @@ github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 h1:Ovs26xHkKqVztRpIrF/92Bcuy
 github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0/go.mod h1:8NvIoxWQoOIhqOTXgfV/d3M/q6VIi02HzZEHgUlZvzk=
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.27.3 h1:NmZ1PKzSTQbuGHw9DGPFomqkkLWMC+vZCkfs+FHv1Vg=
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.27.3/go.mod h1:zQrxl1YP88HQlA6i9c63DSVPFklWpGX4OWAc9bFuaH4=
+github.com/jhump/protoreflect/v2 v2.0.0-beta.2 h1:qZU+rEZUOYTz1Bnhi3xbwn+VxdXkLVeEpAeZzVXLY88=
+github.com/jhump/protoreflect/v2 v2.0.0-beta.2/go.mod h1:4tnOYkB/mq7QTyS3YKtVtNrJv4Psqout8HA1U+hZtgM=
 github.com/jmespath/go-jmespath v0.4.0 h1:BEgLn5cpjn8UN1mAw4NjwDrS35OdebyEtFe+9YPoQUg=
 github.com/jmespath/go-jmespath v0.4.0/go.mod h1:T8mJZnbsbmF+m6zOOFylbeCJqk5+pHWvzYPziyZiYoo=
 github.com/jmespath/go-jmespath/internal/testify v1.5.1 h1:shLQSRRSCCPj3f2gpwzGwWFoC7ycTf1rcQZHOlsJ6N8=

internal/mock/BUILD.bazel

@@ -260,6 +260,7 @@ gomock(
         "ClientConnInterface",
         "ClientStream",
         "ServerStream",
+        "ServerTransportStream",
         "StreamHandler",
         "Streamer",
         "UnaryHandler",

pkg/grpc/BUILD.bazel

@@ -13,6 +13,7 @@ go_library(
         "client_factory.go",
         "deduplicating_client_factory.go",
         "deny_authenticator.go",
+        "forwarding_stream_handler.go",
         "jmespath_extractor.go",
         "lazy_client_dialer.go",
         "metadata_adding_interceptor.go",
@@ -26,9 +27,12 @@ go_library(
         "peer_transport_credentials_linux.go",
         "proto_trace_attributes_extractor.go",
         "proxy_dialer.go",
+        "reflection_relay.go",
         "request_headers_authenticator.go",
         "request_metadata_tracing_interceptor.go",
+        "routing_stream_handler.go",
         "server.go",
+        "server_transport_stream_context.go",
         "tls_client_certificate_authenticator.go",
     ],
     importpath = "github.com/buildbarn/bb-storage/pkg/grpc",
@@ -49,6 +53,8 @@ go_library(
         "@bazel_remote_apis//build/bazel/remote/execution/v2:remote_execution_go_proto",
         "@com_github_grpc_ecosystem_go_grpc_middleware//:go-grpc-middleware",
         "@com_github_grpc_ecosystem_go_grpc_prometheus//:go-grpc-prometheus",
+        "@com_github_jhump_protoreflect_v2//grpcreflect",
+        "@com_github_jhump_protoreflect_v2//protoresolve",
         "@io_opentelemetry_go_contrib_instrumentation_google_golang_org_grpc_otelgrpc//:otelgrpc",
         "@io_opentelemetry_go_otel//attribute",
         "@io_opentelemetry_go_otel_trace//:trace",
@@ -63,11 +69,15 @@ go_library(
         "@org_golang_google_grpc//metadata",
         "@org_golang_google_grpc//peer",
         "@org_golang_google_grpc//reflection",
+        "@org_golang_google_grpc//reflection/grpc_reflection_v1",
+        "@org_golang_google_grpc//reflection/grpc_reflection_v1alpha",
         "@org_golang_google_grpc//status",
         "@org_golang_google_grpc_security_advancedtls//:advancedtls",
         "@org_golang_google_protobuf//encoding/prototext",
         "@org_golang_google_protobuf//proto",
         "@org_golang_google_protobuf//reflect/protoreflect",
+        "@org_golang_google_protobuf//types/known/emptypb",
+        "@org_golang_x_sync//errgroup",
         "@org_golang_x_sync//semaphore",
     ] + select({
         "@rules_go//go/platform:android": [
@@ -98,6 +108,7 @@ go_test(
         "authenticating_interceptor_test.go",
         "deduplicating_client_factory_test.go",
         "deny_authenticator_test.go",
+        "forwarding_stream_handler_test.go",
         "jmespath_extractor_test.go",
         "lazy_client_dialer_test.go",
         "metadata_adding_interceptor_test.go",
@@ -107,6 +118,7 @@ go_test(
         "proto_trace_attributes_extractor_test.go",
         "request_headers_authenticator_test.go",
         "request_metadata_tracing_interceptor_test.go",
+        "routing_stream_handler_test.go",
     ] + select({
         "@rules_go//go/platform:android": [
             "peer_transport_credentials_test.go",

pkg/grpc/forwarding_stream_handler.go

@@ -0,0 +1,91 @@
+package grpc
+
+import (
+	"io"
+
+	"golang.org/x/sync/errgroup"
+	"google.golang.org/grpc"
+	"google.golang.org/protobuf/types/known/emptypb"
+)
+
+// NewForwardingStreamHandler creates a grpc.StreamHandler that forwards gRPC
+// calls to a grpc.ClientConnInterface backend.
+func NewForwardingStreamHandler(client grpc.ClientConnInterface) grpc.StreamHandler {
+	forwarder := &forwardingStreamHandler{
+		backend: client,
+	}
+	return forwarder.HandleStream
+}
+
+type forwardingStreamHandler struct {
+	backend grpc.ClientConnInterface
+}
+
+// HandleStream creates a new stream to the backend. Requests from
+// incomingStream are forwarded to the backend stream and responses from the
+// backend stream are sent back in the incomingStream.
+func (s *forwardingStreamHandler) HandleStream(srv any, incomingStream grpc.ServerStream) error {
+	method := MustStreamMethodFromContext(incomingStream.Context())
+	desc := grpc.StreamDesc{
+		// According to grpc.StreamDesc documentation, StreamName and Handler
+		// are only used when registering handlers on a server.
+		StreamName: "",
+		Handler:    nil,
+		// Streaming behaviour is wanted, single message is treated the same on
+		// transport level, the application just closes the stream after the
+		// first message.
+		ServerStreams: true,
+		ClientStreams: true,
+	}
+	group, groupCtx := errgroup.WithContext(incomingStream.Context())
+	group.Go(func() error {
+		// groupCtx is guaranteed to be canceled before returning from this method, so outgoingStream will not leak resources.
+		outgoingStream, err := s.backend.NewStream(groupCtx, &desc, method)
+		if err != nil {
+			return err
+		}
+		// Avoid group.Go because incomingStream.RecvMsg might block returning
+		// an error from the outgoingStream and getting the context for
+		// incomingStream canceled.
+		go func() {
+			for {
+				msg := &emptypb.Empty{}
+				if err := incomingStream.RecvMsg(msg); err != nil {
+					if err == io.EOF {
+						// Let's continue to receive on outgoingStream, so don't
+						// cancel grouptCtx.
+						outgoingStream.CloseSend()
+						return
+					}
+					// Cancel groupCtx immediately.
+					group.Go(func() error { return err })
+					return
+				}
+				if err := outgoingStream.SendMsg(msg); err != nil {
+					if err == io.EOF {
+						// The error will be returned by outgoingStream.RecvMsg(),
+						// no need to cancel groupCtx now.
+						return
+					}
+					// Cancel groupCtx immediately.
+					group.Go(func() error { return err })
+					return
+				}
+			}
+		}()
+
+		for {
+			msg := &emptypb.Empty{}
+			if err := outgoingStream.RecvMsg(msg); err != nil {
+				if err == io.EOF {
+					return nil
+				}
+				return err
+			}
+			if err := incomingStream.SendMsg(msg); err != nil {
+				return err
+			}
+		}
+	})
+	return group.Wait()
+}