Make the example command buildable on macOS

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

example/cmd/handshaker_linux.go

@@ -0,0 +1,23 @@
+/*
+   Copyright The containerd 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 main
+
+import ttrpc "github.com/containerd/ttrpc"
+
+func defaultHandshaker() ttrpc.Handshaker {
+	return ttrpc.UnixSocketRequireSameUser()
+}

example/cmd/handshaker_other.go

@@ -0,0 +1,25 @@
+// +build !linux
+
+/*
+   Copyright The containerd 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 main
+
+import ttrpc "github.com/containerd/ttrpc"
+
+func defaultHandshaker() ttrpc.Handshaker {
+	return nil
+}

example/cmd/main.go

@@ -73,7 +73,7 @@ func dumpMetadata(ctx context.Context) {
 
 func server() error {
 	s, err := ttrpc.NewServer(
-		ttrpc.WithServerHandshaker(ttrpc.UnixSocketRequireSameUser()),
+		ttrpc.WithServerHandshaker(defaultHandshaker()),
 		ttrpc.WithUnaryServerInterceptor(serverIntercept),
 	)
 	if err != nil {