Taskflow: Learn Backend Engineering From Scratch

Welcome! Taskflow teaches backend engineering fundamentals using only Node.js—no frameworks, no magic.

You'll build a real task queue system step-by-step, learning core concepts as you go.

Why Learn This Way?

Frameworks hide how things work. This project shows you exactly what happens:

• How HTTP requests are parsed
• How data is stored and retrieved
• How middleware chains work
• How to handle errors and scale efficiently
• How real-time updates work with WebSockets

By the end, you'll understand backend systems deeply and be able to debug or build anything.

What You'll Build

A real-time task management app with:

• Task creation, updates, deletion
• Priority-based scheduling
• Dependency tracking between tasks
• Parallel job processing with Worker Threads
• Memory management and monitoring
• Live updates via WebSockets
• Data streaming (CSV/NDJSON export)

Quick Start (5 minutes)

1. Install Node.js

You need Node.js 18+. Download from nodejs.org.

Check you have it:

node --version

2. Clone or Navigate to This Folder

cd se-taskflow-nodejs

3. Setup Environment

cp .env.example .env

This file stores your API tokens (used for testing authentication).

4. Start the Server

node server.js

You should see:

Environment variables loaded natively.
[timestamp] TaskFlow server started on http://localhost:3000
Listening for requests...

5. Open Another Terminal and Try It

Create a task:

curl -X POST http://localhost:3000/tasks \
  -H "Authorization: Bearer secret-admin-123" \
  -H "Content-Type: application/json" \
  -d '{"title":"Learn backend","priority":9}'

List all tasks:

curl http://localhost:3000/tasks \
  -H "Authorization: Bearer secret-user-123"

10-Step Learning Path

Start at Step 1 and progress sequentially. Each step builds on the previous one.

Step	Topic	What You Learn
1	Raw HTTP Server	How Node's http module works, routing, request/response
2	In-Memory Storage	Hash maps, O(1) lookups, the singleton pattern
3	Priority Queues	Heaps, O(log N) operations, scheduling algorithms
4	Dependency Chains	Linked lists, O(N) traversal, recursive resolution
5	Middleware Chains	The Chain of Responsibility pattern, authentication
6	Error Handling	Structured error responses, request correlation
7	Memory Management	Heap vs stack, garbage collection, memory leaks
8	Worker Threads	Parallelism, offloading CPU work, avoiding blocking
9	Streaming Data	Readable streams, backpressure, chunked responses
10	WebSockets	Real-time two-way communication, frame encoding

→ Start with Step 1

Run the Full Learning Demo

After understanding the concepts, run everything together:

# Terminal 1: Start the server
node server.js

# Terminal 2 (optional): Watch live task events
node scripts/websocket-client.js

# Terminal 3: Run the full demo
bash scripts/full-demo.sh

This script demonstrates all 10 concepts in action.

File Organization

server.js                     # The main HTTP server
.env.example                  # Copy to .env before running

learner/                      # 10 step-by-step guides
├── 01-http-server.md        # Start here!
├── 02-task-store.md
├── ...
└── 10-websockets.md

src/                          # Implementation code
├── store/                    # Data structures
├── middleware/               # Request handlers
├── services/                 # Worker pools, WebSockets, memory
├── workers/                  # CPU-heavy background jobs
└── utils/                    # Logging, errors

scripts/                      # Demo and benchmark scripts
├── full-demo.sh             # Run this after learning
├── dependency-resolver-demo.sh
├── websocket-client.js
└── benchmarks/

docs/                         # API reference and operation guides

Key Concepts at a Glance

Data Structures:

• Map (hash table): O(1) lookups
• Max-Heap: O(log N) priority ordering
• Linked List: O(1) append, O(N) traversal

Patterns:

• Middleware Chain of Responsibility
• Singleton (shared state)
• Worker pools (task queues)

Operations:

• HTTP routing with manual parsing
• WebSocket frame protocol
• Request/response correlation
• Memory bounded caches

Common Commands

# Start server
node server.js

# Run full demo (all 10 concepts at once)
bash scripts/full-demo.sh

# Benchmark: Map vs Array lookup speed
node scripts/map-vs-array-benchmark.js

# Benchmark: Main thread vs worker threads
node scripts/worker-benchmark.js

# Dependency resolver demo
bash scripts/dependency-resolver-demo.sh

# Live WebSocket client
node scripts/websocket-client.js

API Quick Reference

All endpoints require authentication header:

-H "Authorization: Bearer secret-admin-123"   # Admin (can create/update/delete)
-H "Authorization: Bearer secret-user-123"    # User (can only view)

Tasks:

POST /tasks                   # Create a task
GET /tasks                    # List all tasks
GET /tasks/:id                # Get one task
PUT /tasks/:id                # Update a task
DELETE /tasks/:id             # Delete a task
GET /tasks/next               # Get highest priority task
GET /tasks/resolve            # Resolve full dependency order
GET /tasks/:id/resolve        # Resolve dependencies for one task

Real-Time:

WS /ws/tasks                  # Connect for live updates

Monitoring:

GET /tasks/system/memory      # Memory usage stats
GET /tasks/system/ws          # WebSocket connection count
GET /tasks/reports/stats      # Worker pool statistics

Streaming:

GET /tasks/export.csv         # Download tasks as CSV
GET /tasks/stream.ndjson      # Stream tasks as NDJSON

For full API details, see docs/api-reference.md.

Troubleshooting

Port already in use?

# Kill the process using port 3000
lsof -ti:3000 | xargs kill -9

Getting 401 Unauthorized? Add the auth header:

-H "Authorization: Bearer secret-admin-123"

Server crashes on startup? Make sure your node --version shows 18+:

node --version

Next Steps

1. Read Step 1: Raw HTTP Server
2. Build it: Follow the exercises in each guide
3. Run scripts: Use the demo scripts to see it all working
4. Experiment: Modify the code and see what breaks—that's learning!

Questions or Stuck?

• Re-read the specific guide for that concept
• Look at the working code in src/
• Run a demo script to see the live behavior
• Add console.log() statements to trace execution

Technology Stack

• Runtime: Node.js (no TypeScript, no Babel)
• Database: In-memory hash map (resets on restart)
• Real-time: Native WebSocket protocol (no external library)
• External packages: None (everything from Node.js stdlib)

This is intentional—you'll see exactly what you're using and why.

License

Open source, learn freely.

---

Ready? → Start with Step 1: Raw HTTP Server

Taskflow

Taskflow is a real-time, collaborative task queue system built to teach backend engineering from first principles.

This repository intentionally avoids backend frameworks so learners can understand exactly what happens under the hood in production systems. Routing, request parsing, state management, and API behavior are implemented manually using core Node.js APIs.

Why This Repository Exists

Most tutorials start with frameworks and hide core mechanics. Taskflow does the opposite:

• Build with core Node.js first.
• Understand architecture and tradeoffs before abstractions.
• Learn data structures and algorithmic complexity in context.
• Introduce advanced capabilities (streaming, worker threads, WebSockets) progressively.

The result is a learning-first codebase that teaches both implementation and reasoning.

Current Implementation Status

The code now includes Parts 1 through 10:

• Step 1: Raw Node.js HTTP server with manual routing
• Step 2: In-memory task store using JavaScript Map (O(1) Hash Map) and Singleton export
• Step 3: Priority Queue (Max-Heap) for O(log N) prioritized scheduling
• Step 4: Linked-List Task Dependency Chains with O(N) automated garbage collection (sweep)
• Step 5: OOP Middleware Chain of Responsibility (Authentication, Roles, Data Validation)
• Step 6: Global error handling with structured logging and request correlation
• Step 7: Memory leak detection, bounded caches, and memory observability
• Step 8: Worker Thread CPU offloading with a reusable worker pool
• Step 9: Streaming CSV / NDJSON exports with backpressure-safe pipelines
• Step 10: WebSocket live updates with heartbeats and task broadcast

Planned parts are documented in the roadmap below and expanded in the learner guides.

Technology Constraints

• Runtime: Node.js (No Babel, No TypeScript)
• Current external npm packages: none (zero-dependency design)
• WebSocket support is implemented natively with the Node.js upgrade path and manual frame handling

Everything else is built natively.

Repository Structure

• server.js: HTTP server, route handling, JSON parsing, middleware execution, streaming, memory demos, and WebSocket upgrade handling
• scripts/full-demo.sh: Unified end-to-end demo script covering all major concepts
• scripts/demo-live-events.sh: Emits create/update/delete events for live WebSocket observation
• scripts/map-vs-array-benchmark.js: Big O demonstration (Array.find vs Map.get)
• scripts/worker-benchmark.js: Worker Thread benchmark for blocking vs parallel CPU work
• scripts/dependency-resolver-demo.sh: Recursive dependency resolution and cycle detection demo
• scripts/websocket-client.js: Terminal WebSocket client for live update demos
• docs/full-demo.md: Full demo instructions and integrated endpoint map
• src/store/TaskStore.js: Singleton in-memory state engine
• src/store/PriorityQueue.js: Max-Heap Queue data structure for ordering Tasks by priority
• src/store/DependencyList.js: Singly Linked List data structure for Task prerequisite linking
• src/services/MemoryManager.js: Bounded memory tracking, leak demo batches, and cleanup
• src/services/WorkerPool.js: Managed Worker Thread pool for CPU-heavy jobs
• src/services/WebSocketHub.js: Native WebSocket broadcast and heartbeat manager
• src/middleware/: Chain of Responsibility implementation for Auth, Permissions, and Validations
• src/config/env.js: Zero dependency .env parser
• learner/README.md: Learning path and deep-dive documentation index
• docs/full-demo.md: End-to-end terminal demo instructions

Quick Start

1) Prerequisites

• Node.js 18+ recommended (crypto.randomUUID support)

2) Set up Environment Variables

Create your .env file based on the example to supply the API tokens for the Middleware Chain:

cp .env.example .env

3) Start the API Server

node server.js

Expected startup output:

• Environment variables loaded natively.
• TaskFlow server is running on http://localhost:3000
• Listening for requests... (Press Ctrl+C to stop)

4) Run Integrated Demos

Full integrated demo:

bash scripts/full-demo.sh

Dependency resolver focused demo:

bash scripts/dependency-resolver-demo.sh

Data-structure benchmark:

node scripts/map-vs-array-benchmark.js

Worker benchmark:

node scripts/worker-benchmark.js

You should observe significantly faster Map lookup timing compared to Array.find for large collections.

API Reference (Current)

Base URL: http://localhost:3000

GET /tasks

Returns all tasks. Users and Admins can access this.

GET /tasks/queue

Returns the Max-Heap queue array structure highlighting task priority ordering.

GET /tasks/peek

Returns the absolute highest priority task without dequeuing it. O(1) read time.

POST /tasks

Creates a new task. Requires Admin Token.

Request body (title and priority are validated):

{
  "title": "Prepare sprint board",
  "priority": 5,
  "dependencies": []
}

PUT /tasks/:id

Updates an existing task by merging provided fields. Validates the payload and organically updates the Priority Queue and Dependency Linked List. Requires Admin Token.

DELETE /tasks/:id

Deletes a task and performs an O(N) sweep across all other tasks to cleanly remove its ID from their linked list dependencies to prevent ghost links! Requires Admin Token.

GET /tasks/export.csv

Streams all tasks as CSV using backpressure-safe streaming.

GET /tasks/stream.ndjson

Streams all tasks as NDJSON for incremental consumption.

GET /tasks/next

Returns the next highest-priority task candidate from the queue without dequeuing it.

GET /tasks/resolve

Resolves dependency-safe execution order for all tasks using recursive DFS/topological ordering.

GET /tasks/:id/resolve

Resolves dependency-safe execution order for one task subtree. Returns 409 when a cycle is detected.

POST /tasks/reports/start?heavyIterations=...

Starts a Worker Thread powered task analytics report job and returns a jobId.

GET /tasks/reports/:jobId

Fetches report job status and output.

GET /tasks/reports/stats

Returns report worker pool runtime statistics.

GET /tasks/system/memory

Returns current bounded memory manager and process memory statistics.

POST /tasks/memory/leak?count=...&sizeKb=...

Creates an intentional retained batch (for leak demonstration).

POST /tasks/memory/safe?count=...&sizeKb=...

Creates a bounded cache batch that trims automatically.

POST /tasks/memory/clear

Clears memory demo caches.

GET /tasks/system/ws

Returns WebSocket hub statistics.

WS /ws/tasks

Real-time task event stream (task.created, task.updated, task.deleted).

GET /demo/cpu/ping

Lightweight endpoint for latency checks before and after heavy CPU work.

GET /demo/cpu/blocking?iterations=...

Runs CPU work on the main thread so you can demonstrate event loop blocking.

GET /demo/cpu/worker/run?iterations=...

Runs the same CPU work in a Worker Thread and waits for completion.

GET /demo/cpu/worker/start?iterations=...

Queues a Worker Thread job and returns a job ID for polling.

GET /demo/memory/usage

Returns heap, rss, external, and array buffer memory usage.

POST /demo/memory/leak?count=...&sizeKb=...

Creates an intentional leak batch for demonstration.

POST /demo/memory/safe?count=...&sizeKb=...

Creates a bounded cache batch that gets trimmed automatically.

GET /demo/ws/stats

Returns WebSocket hub statistics.

End-to-End API Walkthrough (Copy/Paste)

Create a Task (Admin Action)

curl -i -X POST http://localhost:3000/tasks \
  -H "Authorization: Bearer secret-admin-123" \
  -H "Content-Type: application/json" \
  -d '{"title":"Implement auth middleware","priority":10}'

Create a Dependent Task

Replace TASK_A_ID with the ID generated in the last command! This automatically injects it into a native Linked List.

curl -i -X POST http://localhost:3000/tasks \
  -H "Authorization: Bearer secret-admin-123" \
  -H "Content-Type: application/json" \
  -d '{"title":"Secondary Task","priority":5,"dependencies":["TASK_A_ID"]}'

List Tasks (User Action)

curl -i -H "Authorization: Bearer secret-user-123" http://localhost:3000/tasks

Update Task

curl -i -X PUT http://localhost:3000/tasks/TASK_A_ID \
  -H "Authorization: Bearer secret-admin-123" \
  -H "Content-Type: application/json" \
  -d '{"priority":100}'

Observe Priority Shift in the Heap

curl -i http://localhost:3000/tasks/peek

Delete Task (Triggers Linked List Sweep)

curl -i -X DELETE http://localhost:3000/tasks/TASK_A_ID \
  -H "Authorization: Bearer secret-admin-123"

Data Model (Current)

Each task currently contains:

• id: UUID string generated by crypto.randomUUID
• title: string
• description: string
• status: string (pending, in-progress, completed)
• priority: integer (higher number = higher execution urgency)
• dependencies: Array serialization of the active DependencyList Singly Linked List
• createdAt: ISO timestamp string
• updatedAt: ISO timestamp string

Internal Architecture & Computer Science

Request Flow

1. Node HTTP server accepts request.
2. src/config/env parses .env manually into global variables.
3. Stream body is read into JSON format globally for mutating requests.
4. Middleware Chain of Responsibility executes: Auth -> Permission -> Validation.
5. If the chain yields, URL/method handles endpoints.
6. TaskStore processes updates:
   • Sets the O(1) Memory map.
   • Safely sweeps and parses arrays to DependencyList.
   • Modifies positions linearly in the PriorityQueue Max Heap.
7. JSON response sent explicitly.

Learning Roadmap (Project Scope)

Taskflow’s intended progression covers:

1. Raw HTTP API in Node.js without frameworks (Done!)
2. In-memory task store with Hash Map and complexity benchmark (Done!)
3. Priority queue for prioritized scheduling (Done!)
4. Linked-list dependency chains and recursive dependency resolution with cycle detection (Done!)
5. Middleware chain (authentication, authorization, validation) (Done!)
6. Global error handling and structured logging (Done!)
7. Intentional memory leak demonstration and remediation (Done!)
8. Worker Thread report generation for CPU-heavy processing (Done!)
9. Streaming CSV export via Node streams (Done!)
10. WebSocket live updates using native Node.js upgrade handling (Done!)

This repository currently has Steps 1 through 10 completely implemented natively!

Concepts Covered in This Repository

• Data Structures: Priority Queues, Binary Heaps, Singly Linked Lists, Hash Maps (O(1) Time vs O(N) vs O(log N)).
• Design Patterns: Singleton State Stores, Object-Oriented Chain of Responsibility, Interceptors.
• Event Loop internals (Timers, Poll, Check phases)
• Call Stack and libuv responsibilities

Detailed guides are available in learner/README.md and docs/full-demo.md.

Troubleshooting

Port 3000 already in use

Run server on a free port by changing PORT in server.js.

Missing or Invalid Tokens

Since Step 5 was introduced, modifying commands explicitly require an ADMIN_TOKEN placed inside the Authorization: Bearer <token> header as seen in the .env file.

Data disappears after restart

Expected behavior. This is currently an in-memory repository designed to teach data structures without database overhead!