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Add metadata example
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‎examples/metadata/README.md

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# Metadata example
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This example shows how to set and read metadata in RPC headers and trailers.
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## Start the server
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```
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node server.js
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```
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## Run the client
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```
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node client.js
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```

‎examples/metadata/client.js

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/*
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*
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* Copyright 2023 gRPC authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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*/
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const grpc = require('@grpc/grpc-js');
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const protoLoader = require('@grpc/proto-loader');
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const parseArgs = require('minimist');
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const PROTO_PATH = __dirname + '/../protos/echo.proto';
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const packageDefinition = protoLoader.loadSync(
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PROTO_PATH,
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{keepCase: true,
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longs: String,
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enums: String,
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defaults: true,
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oneofs: true
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});
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const echoProto = grpc.loadPackageDefinition(packageDefinition).grpc.examples.echo;
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const STREAMING_COUNT = 10;
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function unaryCallWithMetadata(client, message) {
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return new Promise((resolve, reject) => {
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console.log('--- unary ---');
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const requestMetadata = new grpc.Metadata();
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requestMetadata.set('timestamp', new Date().toISOString());
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const call = client.unaryEcho({message}, requestMetadata, (error, value) => {
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if (error) {
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console.log(`Received error ${error}`);
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return;
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}
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console.log('Response:');
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console.log(`- ${JSON.stringify(value)}`);
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});
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call.on('metadata', metadata => {
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const timestamps = metadata.get('timestamp');
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if (timestamps.length > 0) {
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console.log('timestamp from header:');
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for (const [index, value] of timestamps.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("timestamp expected but doesn't exist in header");
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}
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const locations = metadata.get('location');
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if (locations.length > 0) {
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console.log('location from header:');
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for (const [index, value] of locations.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("location expected but doesn't exist in header");
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}
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});
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call.on('status', status => {
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const timestamps = status.metadata.get('timestamp');
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if (timestamps.length > 0) {
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console.log('timestamp from trailer:');
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for (const [index, value] of timestamps.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("timestamp expected but doesn't exist in trailer");
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}
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resolve();
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});
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});
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}
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function serverStreamingWithMetadata(client, message) {
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return new Promise((resolve, reject) => {
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console.log('--- server streaming ---');
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const requestMetadata = new grpc.Metadata();
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requestMetadata.set('timestamp', new Date().toISOString());
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const call = client.serverStreamingEcho({message}, requestMetadata);
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call.on('metadata', metadata => {
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const timestamps = metadata.get('timestamp');
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if (timestamps.length > 0) {
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console.log('timestamp from header:');
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for (const [index, value] of timestamps.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("timestamp expected but doesn't exist in header");
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}
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const locations = metadata.get('location');
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if (locations.length > 0) {
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console.log('location from header:');
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for (const [index, value] of locations.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("location expected but doesn't exist in header");
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}
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});
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call.on('data', value => {
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console.log(`Received response ${JSON.stringify(value)}`);
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});
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call.on('status', status => {
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const timestamps = status.metadata.get('timestamp');
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if (timestamps.length > 0) {
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console.log('timestamp from trailer:');
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for (const [index, value] of timestamps.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("timestamp expected but doesn't exist in trailer");
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}
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resolve();
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});
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call.on('error', error => {
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console.log(`Received error ${error}`);
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});
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});
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}
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function clientStreamingWithMetadata(client, message) {
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return new Promise((resolve, reject) => {
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console.log('--- client streaming ---');
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const requestMetadata = new grpc.Metadata();
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requestMetadata.set('timestamp', new Date().toISOString());
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const call = client.clientStreamingEcho(requestMetadata, (error, value) => {
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if (error) {
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console.log(`Received error ${error}`);
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return;
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}
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console.log('Response:');
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console.log(`- ${JSON.stringify(value)}`);
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});
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call.on('metadata', metadata => {
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const timestamps = metadata.get('timestamp');
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if (timestamps.length > 0) {
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console.log('timestamp from header:');
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for (const [index, value] of timestamps.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("timestamp expected but doesn't exist in header");
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}
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const locations = metadata.get('location');
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if (locations.length > 0) {
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console.log('location from header:');
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for (const [index, value] of locations.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("location expected but doesn't exist in header");
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}
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});
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call.on('status', status => {
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const timestamps = status.metadata.get('timestamp');
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if (timestamps.length > 0) {
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console.log('timestamp from trailer:');
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for (const [index, value] of timestamps.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("timestamp expected but doesn't exist in trailer");
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}
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resolve();
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});
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for (let i = 0; i < STREAMING_COUNT; i++) {
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call.write({message});
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}
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call.end();
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});
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}
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function bidirectionalWithMetadata(client, message) {
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return new Promise((resolve, reject) => {
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console.log('--- bidirectional ---');
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const requestMetadata = new grpc.Metadata();
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requestMetadata.set('timestamp', new Date().toISOString());
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const call = client.bidirectionalStreamingEcho(requestMetadata);
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call.on('metadata', metadata => {
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const timestamps = metadata.get('timestamp');
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if (timestamps.length > 0) {
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console.log('timestamp from header:');
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for (const [index, value] of timestamps.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("timestamp expected but doesn't exist in header");
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}
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const locations = metadata.get('location');
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if (locations.length > 0) {
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console.log('location from header:');
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for (const [index, value] of locations.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("location expected but doesn't exist in header");
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}
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});
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call.on('data', value => {
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console.log(`Received response ${JSON.stringify(value)}`);
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});
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call.on('status', status => {
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const timestamps = status.metadata.get('timestamp');
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if (timestamps.length > 0) {
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console.log('timestamp from trailer:');
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for (const [index, value] of timestamps.entries()) {
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console.log(` ${index}. ${value}`);
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}
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} else {
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console.error("timestamp expected but doesn't exist in trailer");
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}
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resolve();
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});
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call.on('error', error => {
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console.log(`Received error ${error}`);
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});
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for (let i = 0; i < STREAMING_COUNT; i++) {
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call.write({message});
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}
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call.end();
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});
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}
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function asyncWait(ms) {
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return new Promise((resolve, reject) => {
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setTimeout(resolve, ms);
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});
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}
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const message = 'this is examples/metadata';
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async function main() {
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let argv = parseArgs(process.argv.slice(2), {
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string: 'target'
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});
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let target;
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if (argv.target) {
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target = argv.target;
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} else {
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target = 'localhost:50051';
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}
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const client = new echoProto.Echo(target, grpc.credentials.createInsecure());
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await unaryCallWithMetadata(client, message);
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await asyncWait(1000);
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await serverStreamingWithMetadata(client, message);
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await asyncWait(1000);
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await clientStreamingWithMetadata(client, message);
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await asyncWait(1000);
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await bidirectionalWithMetadata(client, message);
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client.close();
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}
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main();

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