add metadata forwarder server interceptors

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

interceptors/metadata/forward.go

@@ -0,0 +1,53 @@
+package metadata
+
+import (
+	"context"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+
+	"go.linka.cloud/grpc/interceptors"
+)
+
+func NewForwardInterceptors() interceptors.ServerInterceptors {
+	return &forward{}
+}
+
+type forward struct{}
+
+func (f *forward) UnaryServerInterceptor() grpc.UnaryServerInterceptor {
+	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
+		if md, ok := metadata.FromIncomingContext(ctx); ok {
+			ctx = metadata.NewOutgoingContext(ctx, md.Copy())
+		}
+		return handler(ctx, req)
+	}
+}
+
+func (f *forward) StreamServerInterceptor() grpc.StreamServerInterceptor {
+	return func(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
+		ctx := ss.Context()
+		md1, ok := metadata.FromIncomingContext(ctx)
+		if !ok {
+			return handler(srv, ss)
+		}
+		o := md1.Copy()
+		if md2, ok := metadata.FromOutgoingContext(ctx); ok {
+			o = metadata.Join(o, md2.Copy())
+		}
+		return handler(srv, NewContextServerStream(metadata.NewOutgoingContext(ctx, o), ss))
+	}
+}
+
+func NewContextServerStream(ctx context.Context, ss grpc.ServerStream) grpc.ServerStream {
+	return &ContextWrapper{ServerStream: ss, ctx: ctx}
+}
+
+type ContextWrapper struct {
+	grpc.ServerStream
+	ctx context.Context
+}
+
+func (w *ContextWrapper) Context() context.Context {
+	return w.ctx
+}