Add cancellation example

Author: murgatroid99

examples/cancellation/README.md

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+# Cancellation
+
+This example shows how clients can cancel in-flight RPCs by cancelling the
+call object returned by the method invocation. The client will receive a status
+with code `CANCELLED` and the server handler's call object will emit a
+`'cancelled'` event.
+
+## Start the server
+
+```
+node server.js
+```
+
+## Run the client
+
+```
+node client.js
+```

examples/cancellation/client.js

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+/*
+ *
+ * Copyright 2023 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.
+ *
+ */
+
+const grpc = require('@grpc/grpc-js');
+const protoLoader = require('@grpc/proto-loader');
+const parseArgs = require('minimist');
+
+const PROTO_PATH = __dirname + '/../protos/echo.proto';
+
+const packageDefinition = protoLoader.loadSync(
+  PROTO_PATH,
+  {keepCase: true,
+   longs: String,
+   enums: String,
+   defaults: true,
+   oneofs: true
+  });
+const echoProto = grpc.loadPackageDefinition(packageDefinition).grpc.examples.echo;
+
+function main() {
+  let argv = parseArgs(process.argv.slice(2), {
+    string: 'target',
+    default: {target: 'localhost:50052'}
+  });
+  const client = new echoProto.Echo(argv.target, grpc.credentials.createInsecure());
+  const call = client.bidirectionalStreamingEcho();
+  const EXPECTED_MESSAGES = 2;
+  let receivedMessages = 0;
+  call.on('data', value => {
+    console.log(`received message "${value.message}"`)
+    receivedMessages += 1;
+    if (receivedMessages >= EXPECTED_MESSAGES) {
+      console.log('cancelling call');
+      call.cancel();
+    }
+  });
+  call.on('status', statusObject => {
+    console.log(`received call status with code ${grpc.status[statusObject.code]}`);
+  });
+  call.on('error', error => {
+    console.log(`received error ${error}`);
+  })
+  console.log('sending message "hello"');
+  call.write({message: 'hello'});
+  console.log('sending message "world"')
+  call.write({message: 'world'});
+}
+
+main();

examples/cancellation/server.js

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+/*
+ *
+ * Copyright 2023 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.
+ *
+ */
+
+const grpc = require('@grpc/grpc-js');
+const protoLoader = require('@grpc/proto-loader');
+const parseArgs = require('minimist');
+
+const PROTO_PATH = __dirname + '/../protos/echo.proto';
+
+const packageDefinition = protoLoader.loadSync(
+  PROTO_PATH,
+  {keepCase: true,
+   longs: String,
+   enums: String,
+   defaults: true,
+   oneofs: true
+  });
+const echoProto = grpc.loadPackageDefinition(packageDefinition).grpc.examples.echo;
+
+function bidirectionalStreamingEcho(call) {
+  call.on('data', value => {
+    const message = value.message;
+    console.log(`echoing message "${message}"`);
+    call.write({message: message});
+  });
+  call.on('end', () => {
+    call.end();
+  });
+  call.on('cancelled', () => {
+    console.log('received cancelled event');
+  });
+}
+
+const serviceImplementation = {
+  bidirectionalStreamingEcho
+}
+
+function main() {
+  const argv = parseArgs(process.argv.slice(2), {
+    string: 'port',
+    default: {port: '50052'}
+  });
+  const server = new grpc.Server();
+  server.addService(echoProto.Echo.service, serviceImplementation);
+  server.bindAsync(`0.0.0.0:${argv.port}`, grpc.ServerCredentials.createInsecure(), () => {
+    server.start();
+  });
+  client = new echoProto.Echo(`localhost:${argv.port}`, grpc.credentials.createInsecure());
+}
+
+main();