snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

internal/testutils/pickfirst/pickfirst.go

@@ -0,0 +1,82 @@
+/*
+ *
+ * Copyright 2022 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package pickfirst contains helper functions to check for pickfirst load
+// balancing of RPCs in tests.
+package pickfirst
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/peer"
+	"google.golang.org/grpc/resolver"
+
+	testgrpc "google.golang.org/grpc/interop/grpc_testing"
+	testpb "google.golang.org/grpc/interop/grpc_testing"
+)
+
+// CheckRPCsToBackend makes a bunch of RPCs on the given ClientConn and verifies
+// if the RPCs are routed to a peer matching wantAddr.
+//
+// Returns a non-nil error if context deadline expires before all RPCs begin to
+// be routed to the peer matching wantAddr, or if the backend returns RPC errors.
+func CheckRPCsToBackend(ctx context.Context, cc *grpc.ClientConn, wantAddr resolver.Address) error {
+	client := testgrpc.NewTestServiceClient(cc)
+	peer := &peer.Peer{}
+	// Make sure that 20 RPCs in a row reach the expected backend. Some
+	// tests switch from round_robin back to pick_first and call this
+	// function. None of our tests spin up more than 10 backends. So,
+	// waiting for 20 RPCs to reach a single backend would a decent
+	// indicator of having switched to pick_first.
+	count := 0
+	for {
+		time.Sleep(time.Millisecond)
+		if ctx.Err() != nil {
+			return fmt.Errorf("timeout waiting for RPC to be routed to %s", wantAddr.Addr)
+		}
+		if _, err := client.EmptyCall(ctx, &testpb.Empty{}, grpc.Peer(peer)); err != nil {
+			// Some tests remove backends and check if pick_first is happening across
+			// the remaining backends. In such cases, RPCs can initially fail on the
+			// connection using the removed backend. Just keep retrying and eventually
+			// the connection using the removed backend will shutdown and will be
+			// removed.
+			continue
+		}
+		if peer.Addr.String() != wantAddr.Addr {
+			count = 0
+			continue
+		}
+		count++
+		if count > 20 {
+			break
+		}
+	}
+	// Make sure subsequent RPCs are all routed to the same backend.
+	for i := 0; i < 10; i++ {
+		if _, err := client.EmptyCall(ctx, &testpb.Empty{}, grpc.Peer(peer)); err != nil {
+			return fmt.Errorf("EmptyCall() = %v, want <nil>", err)
+		}
+		if gotAddr := peer.Addr.String(); gotAddr != wantAddr.Addr {
+			return fmt.Errorf("rpc sent to peer %q, want peer %q", gotAddr, wantAddr)
+		}
+	}
+	return nil
+}