use the request context with net/http handler (#1696)

transport/go16.go

@@ -22,6 +22,7 @@ package transport
 
 import (
 	"net"
+	"net/http"
 
 	"google.golang.org/grpc/codes"
 
@@ -43,3 +44,8 @@ func ContextErr(err error) StreamError {
 	}
 	return streamErrorf(codes.Internal, "Unexpected error from context packet: %v", err)
 }
+
+// contextFromRequest returns a background context.
+func contextFromRequest(r *http.Request) context.Context {
+	return context.Background()
+}

transport/go17.go

@@ -23,6 +23,7 @@ package transport
 import (
 	"context"
 	"net"
+	"net/http"
 
 	"google.golang.org/grpc/codes"
 
@@ -44,3 +45,8 @@ func ContextErr(err error) StreamError {
 	}
 	return streamErrorf(codes.Internal, "Unexpected error from context packet: %v", err)
 }
+
+// contextFromRequest returns a context from the HTTP Request.
+func contextFromRequest(r *http.Request) context.Context {
+	return r.Context()
+}

transport/handler_server.go

@@ -284,12 +284,12 @@ func (ht *serverHandlerTransport) WriteHeader(s *Stream, md metadata.MD) error {
 func (ht *serverHandlerTransport) HandleStreams(startStream func(*Stream), traceCtx func(context.Context, string) context.Context) {
 	// With this transport type there will be exactly 1 stream: this HTTP request.
 
-	var ctx context.Context
+	ctx := contextFromRequest(ht.req)
 	var cancel context.CancelFunc
 	if ht.timeoutSet {
-		ctx, cancel = context.WithTimeout(context.Background(), ht.timeout)
+		ctx, cancel = context.WithTimeout(ctx, ht.timeout)
 	} else {
-		ctx, cancel = context.WithCancel(context.Background())
+		ctx, cancel = context.WithCancel(ctx)
 	}
 
 	// requestOver is closed when either the request's context is done