Fix etcdv3 client won't return error when no endpoint is available

sd/etcdv3/client.go

@@ -8,6 +8,7 @@ import (
 
 	"go.etcd.io/etcd/clientv3"
 	"go.etcd.io/etcd/pkg/transport"
+	"google.golang.org/grpc"
 )
 
 var (
@@ -73,8 +74,14 @@ type ClientOptions struct {
 	CACert        string
 	DialTimeout   time.Duration
 	DialKeepAlive time.Duration
-	Username      string
-	Password      string
+
+	// DialOptions is a list of dial options for the gRPC client (e.g., for interceptors).
+	// For example, pass grpc.WithBlock() to block until the underlying connection is up.
+	// Without this, Dial returns immediately and connecting the server happens in background.
+	DialOptions []grpc.DialOption
+
+	Username string
+	Password string
 }
 
 // NewClient returns Client with a connection to the named machines. It will
@@ -107,6 +114,7 @@ func NewClient(ctx context.Context, machines []string, options ClientOptions) (C
 		Endpoints:         machines,
 		DialTimeout:       options.DialTimeout,
 		DialKeepAliveTime: options.DialKeepAlive,
+		DialOptions:       options.DialOptions,
 		TLS:               tlscfg,
 		Username:          options.Username,
 		Password:          options.Password,

sd/etcdv3/client_test.go

@@ -0,0 +1,80 @@
+package etcdv3
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"google.golang.org/grpc"
+)
+
+const (
+	// irrelevantEndpoint is an address which does not exists.
+	irrelevantEndpoint = "http://irrelevant:12345"
+)
+
+func TestNewClient(t *testing.T) {
+	client, err := NewClient(
+		context.Background(),
+		[]string{irrelevantEndpoint},
+		ClientOptions{
+			DialTimeout:   3 * time.Second,
+			DialKeepAlive: 3 * time.Second,
+		},
+	)
+	if err != nil {
+		t.Fatalf("unexpected error creating client: %v", err)
+	}
+	if client == nil {
+		t.Fatal("expected new Client, got nil")
+	}
+}
+
+func TestClientOptions(t *testing.T) {
+	client, err := NewClient(
+		context.Background(),
+		[]string{},
+		ClientOptions{
+			Cert:          "",
+			Key:           "",
+			CACert:        "",
+			DialTimeout:   3 * time.Second,
+			DialKeepAlive: 3 * time.Second,
+		},
+	)
+	if err == nil {
+		t.Errorf("expected error: %v", err)
+	}
+	if client != nil {
+		t.Fatalf("expected client to be nil on failure")
+	}
+
+	_, err = NewClient(
+		context.Background(),
+		[]string{irrelevantEndpoint},
+		ClientOptions{
+			Cert:          "does-not-exist.crt",
+			Key:           "does-not-exist.key",
+			CACert:        "does-not-exist.CACert",
+			DialTimeout:   3 * time.Second,
+			DialKeepAlive: 3 * time.Second,
+		},
+	)
+	if err == nil {
+		t.Errorf("expected error: %v", err)
+	}
+
+	client, err = NewClient(
+		context.Background(),
+		[]string{irrelevantEndpoint},
+		ClientOptions{
+			DialOptions: []grpc.DialOption{grpc.WithBlock()},
+		},
+	)
+	if err == nil {
+		t.Errorf("expected connection should fail")
+	}
+	if client != nil {
+		t.Errorf("expected client to be nil on failure")
+	}
+}

sd/etcdv3/example_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/sd"
 	"github.com/go-kit/kit/sd/lb"
+	"google.golang.org/grpc"
 )
 
 func Example() {
@@ -44,6 +45,9 @@ func Example() {
 
 		// If DialKeepAlive is 0, it defaults to 3s
 		DialKeepAlive: time.Second * 3,
+
+		// If passing `grpc.WithBlock`, dial connection will block until success.
+		DialOptions: []grpc.DialOption{grpc.WithBlock()},
 	}
 
 	// Build the client.