Add Express ALS example

express-als/app.js

@@ -0,0 +1,30 @@
+const express = require('express');
+const app = express();
+const logic = require('./logic');
+const { v4: uuidv4 } = require('uuid');
+const logger = require('./logger');
+const {asyncLocalStorage} = require('./async-storage');
+
+app.use((req, res, next) => {
+    const traceId = req.headers['x-request-id'] || uuidv4();
+    asyncLocalStorage.run(new Map(), () => {
+        logger.init(traceId)
+        next();
+    })
+});
+
+app.use((req, res, next) => {
+    logger.get().info('Middleware');
+    next();
+});
+
+app.get('/', (req, res) => {
+    logger.get().info('start request');
+    logic.foo();
+    logger.get().info('end request');
+    res.end('ok');
+});
+
+app.listen(8800, () => {
+    logger.get().info('Application Start...')
+});

express-als/async-storage.js

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+const { AsyncLocalStorage } = require('async_hooks');
+const asyncLocalStorage = new AsyncLocalStorage();
+
+module.exports = {
+    asyncLocalStorage
+}

express-als/logger.js

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+const logger = require('pino')({
+    prettyPrint: true
+});
+const {asyncLocalStorage} = require('./async-storage');
+
+module.exports = {
+    init(traceId) {
+        const store = asyncLocalStorage.getStore();
+        const childLogger = logger.child({
+            traceId
+        })
+        store.set('logger', childLogger);
+    },
+    get() {
+        const store = asyncLocalStorage.getStore();
+        const childLogger = store?.get('logger');
+        return childLogger ? childLogger : logger;
+    }
+}

express-als/logic.js

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+const logger = require('./logger');
+
+module.exports = {
+    foo() {
+        logger.get().info('foo')
+    }
+}