London | 26-SDC-July | Raihan Sharif | Sprint 2 | Chat-app

.gitignore

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+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+lib-cov
+
+# Coverage directory used by tools like istanbul
+coverage
+*.lcov
+
+# nyc test coverage
+.nyc_output
+
+# Grunt intermediate storage (https://gruntjs.com/creating-plugins#storing-task-files)
+.grunt
+
+# Bower dependency directory (https://bower.io/)
+bower_components
+
+# node-waf configuration
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+build/Release
+
+# Dependency directories
+node_modules/
+jspm_packages/
+
+# Snowpack dependency directory (https://snowpack.dev/)
+web_modules/
+
+# TypeScript cache
+*.tsbuildinfo
+
+# Optional npm cache directory
+.npm
+
+# Optional eslint cache
+.eslintcache
+
+# Optional stylelint cache
+.stylelintcache
+
+# Optional REPL history
+.node_repl_history
+
+# Output of 'npm pack'
+*.tgz
+
+# Yarn Integrity file
+.yarn-integrity
+
+# dotenv environment variable files
+.env
+.env.*
+!.env.example
+
+# parcel-bundler cache (https://parceljs.org/)
+.cache
+.parcel-cache
+
+# Next.js build output
+.next
+out
+
+# Nuxt.js build / generate output
+.nuxt
+dist
+.output
+
+# Gatsby files
+.cache/
+# Comment in the public line in if your project uses Gatsby and not Next.js
+# https://nextjs.org/blog/next-9-1#public-directory-support
+# public
+
+# vuepress build output
+.vuepress/dist
+
+# vuepress v2.x temp directory
+.temp
+
+# Sveltekit cache directory
+.svelte-kit/
+
+# vitepress build output
+**/.vitepress/dist
+
+# vitepress cache directory
+**/.vitepress/cache
+
+# Docusaurus cache and generated files
+.docusaurus
+
+# Serverless directories
+.serverless/
+
+# FuseBox cache
+.fusebox/
+
+# DynamoDB Local files
+.dynamodb/
+
+# Firebase cache directory
+.firebase/
+
+# TernJS port file
+.tern-port
+
+# Stores Visual Studio Code versions used for testing Visual Studio Code extensions
+.vscode-test
+
+# pnpm
+.pnpm-store
+
+# yarn v3
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/sdks
+!.yarn/versions
+
+# Vite files
+vite.config.js.timestamp-*
+vite.config.ts.timestamp-*
+.vite/
+
+CORS_ORIGINS
+
+#VS Code
+.vscode

chat-app/backend/.dockerignore

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+.env
+.env.*
+.git
+node_modules
+npm-debug.log

chat-app/backend/Dockerfile

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+FROM node:26.7.0-alpine
+ENV NODE_ENV=production
+WORKDIR /app
+COPY . .
+RUN npm ci --omit=dev
+USER node
+ENTRYPOINT ["node", "pollingApp.js"]

chat-app/backend/EventStream.js

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+class EventStream {
+    constructor() {
+        this.events = [];
+        this.sequence = 0;
+
+        // waiters are HTTP polling requests
+        this.waiters = new Set();
+
+        // subscribers are websocket connections.
+        this.subscribers = new Set();
+    }
+
+    /**
+     * Adds an event to the event stream. {sequnce, type, timestamp, data}.
+     *
+     * @param {"message.liked" | "message.disliked" | "message.created"} type - The type of event (e.g. "like").
+     * @param {*} data - The message that was added or changed, and the changed fields.
+     * @returns The event object, with a sequence number
+     */
+    append(type, data) {
+        const event = {
+            sequence: ++this.sequence,
+            type,
+            timestamp: Date.now(),
+            data,
+        };
+
+        this.events.push(event);
+        this.notifyWaiters();
+        this.notifySubscribers();
+        return event;
+    }
+
+    /**
+     *
+     * @param {number} sequence - returns events with sequence number > given sequence number.
+     * @returns list of events.
+     */
+    getAfter(sequence) {
+        return this.events.filter((event) => event.sequence > sequence);
+    }
+
+    // websocket subscriber
+    subscribe(callback) {
+        const subscriber = {
+            cursor: null,
+            callback: callback,
+        };
+        this.subscribers.add(subscriber);
+        return subscriber;
+    }
+
+    unsubscribe(subscriber) {
+        this.subscribers.delete(subscriber);
+    }
+
+    // WebSocket subscribers
+    notifySubscribers() {
+        for (const subscriber of this.subscribers) {
+            if (subscriber.cursor === null) {
+                continue;
+            }
+
+            const events = this.getAfter(subscriber.cursor);
+
+            if (events.length === 0) {
+                continue;
+            }
+
+            try {
+                subscriber.callback(events);
+            } catch (err) {
+                console.error("subscriber failed", err);
+            }
+        }
+    }
+
+    /**
+     * Polling (HTTP) connections waiting for new events
+     * If no new events are available, keeps connection open for specified time.
+     * @param {number} after - returns events after this sequence number.
+     * @param {*} timeout - How long to wait for a new event before closing the connection.
+     * @returns A promise which resolves with a list of new events or empty list
+     * if timer expires.
+     */
+    waitForEvents(after, timeout = 30_000) {
+        const existing = this.getAfter(after);
+
+        if (existing.length > 0) {
+            return Promise.resolve(existing);
+        }
+
+        return new Promise((resolve) => {
+            const waiter = {
+                after,
+                resolve,
+                timer: setTimeout(() => {
+                    this.waiters.delete(waiter);
+                    resolve([]);
+                }, timeout),
+            };
+
+            this.waiters.add(waiter);
+        });
+    }
+
+    /**
+     * Sends new events for waiting HTTP requests, if there are any events to send.
+     */
+    notifyWaiters() {
+        for (const waiter of this.waiters) {
+            const events = this.getAfter(waiter.after);
+
+            if (events.length === 0) {
+                continue;
+            }
+
+            clearTimeout(waiter.timer);
+            this.waiters.delete(waiter);
+            waiter.resolve(events);
+        }
+    }
+}
+
+export { EventStream };

chat-app/backend/Message.js

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+export class Message {
+    static #nextId = 0;
+
+    /**
+     *
+     * @param {string} username the message sender
+     * @param {*} msg_body text content of the message
+     */
+    constructor(username, msg_body, likes = 0, dislikes = 0) {
+        this.id = Message.#nextId++;
+        this.username = username;
+        this.msg_body = msg_body;
+        this.createdAt = new Date();
+        this.likes = likes;
+        this.dislikes = dislikes;
+    }
+}

chat-app/backend/errorClasses.js

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+class ValidationError extends Error {
+    constructor(message) {
+        super(message);
+        this.name = "ValidationError";
+    }
+}
+
+class NotFoundError extends Error {
+    constructor(message) {
+        super(message);
+        this.name = "NotFoundError";
+    }
+}
+
+export { ValidationError, NotFoundError };