cri-client: use passthrough resolver for socket endpoints

gRPC defaults to the DNS resolver for bare targets passed to
NewClient. For CRI socket endpoints, GetAddressAndDialer returns a
socket path plus a custom dialer, but handing the bare path to
grpc.NewClient still lets gRPC resolve the target first.

That breaks unix socket clients with errors like "name resolver error:
produced zero addresses" before the custom dialer ever sees the raw
path. Use the passthrough resolver for socket-style addresses so the
runtime and image clients hand the original endpoint directly to the
custom dialer.

Add a regression test for unix sockets, Windows named pipes, and TCP
addresses.

Precedent:
https://github.com/etcd-io/etcd/blob/v3.3.27/clientv3/client.go#L266-L270
https://github.com/grpc/grpc-go/blob/v1.72.2/dialoptions.go#L448-L451

Signed-off-by: Davanum Srinivas <davanum@gmail.com>

staging/src/k8s.io/cri-client/pkg/connection_target.go

@@ -0,0 +1,28 @@
+/*
+Copyright The Kubernetes 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 cri
+
+import "strings"
+
+func clientTargetForAddress(addr string) string {
+	// grpc defaults to the DNS resolver for bare targets. Use the passthrough
+	// resolver for socket-style addresses so the custom dialer gets the raw path.
+	if strings.HasPrefix(addr, "/") {
+		return "passthrough:///" + addr
+	}
+	return addr
+}

staging/src/k8s.io/cri-client/pkg/connection_target_test.go

@@ -0,0 +1,51 @@
+/*
+Copyright The Kubernetes 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 cri
+
+import "testing"
+
+func TestClientTargetForAddress(t *testing.T) {
+	tests := []struct {
+		name string
+		addr string
+		want string
+	}{
+		{
+			name: "unix socket path",
+			addr: "/run/containerd/containerd.sock",
+			want: "passthrough:////run/containerd/containerd.sock",
+		},
+		{
+			name: "windows pipe path",
+			addr: "//./pipe/containerd-containerd",
+			want: "passthrough://///./pipe/containerd-containerd",
+		},
+		{
+			name: "tcp address",
+			addr: "127.0.0.1:1234",
+			want: "127.0.0.1:1234",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := clientTargetForAddress(tc.addr); got != tc.want {
+				t.Fatalf("clientTargetForAddress(%q) = %q, want %q", tc.addr, got, tc.want)
+			}
+		})
+	}
+}

staging/src/k8s.io/cri-client/pkg/remote_image.go

@@ -97,7 +97,7 @@ func NewRemoteImageService(ctx context.Context, endpoint string, connectionTimeo
 		grpc.WithConnectParams(connParams),
 	)
 
-	conn, err := grpc.DialContext(ctx, addr, dialOpts...)
+	conn, err := grpc.NewClient(clientTargetForAddress(addr), dialOpts...)
 	if err != nil {
 		logger.Error(err, "Connect remote image service failed", "address", addr)
 		return nil, err

staging/src/k8s.io/cri-client/pkg/remote_runtime.go

@@ -128,7 +128,7 @@ func NewRemoteRuntimeService(ctx context.Context, endpoint string, connectionTim
 		grpc.WithConnectParams(connParams),
 	)
 
-	conn, err := grpc.DialContext(ctx, addr, dialOpts...)
+	conn, err := grpc.NewClient(clientTargetForAddress(addr), dialOpts...)
 	if err != nil {
 		logger.Error(err, "Connect remote runtime service failed", "address", addr)
 		return nil, err