Authentic Node.js WebSocket Server Workshop
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Authentic Node.js WebSocket Server Workshop
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What you'll learn
Manually implement the WebSocket handshake protocol, including SHA1 and base64 encoding
Parse and process raw WebSocket data frames using buffers and bitwise operations
Construct and send WebSocket messages from server to client with protocol-compliant headers
Handle connection closure, masking issues, and ping/pong logic as per RFC 6455
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There are 6 modules in this course
Updated in May 2025.
This course now features Coursera Coach! A smarter way to learn with interactive, real-time conversations that help you test your knowledge, challenge assumptions, and deepen your understanding as you progress through the course. Unlock the full power of real-time web communication by building a standards-compliant WebSocket server from the ground up. This hands-on course offers an immersive deep dive into the WebSocket protocol using Node.js, helping you truly understand what happens behind the scenes during client-server messaging. By the end of the course, you'll be equipped to implement bidirectional data flow in your own apps with precision and confidence. You'll start by setting up a Node.js HTTP server and enhancing it with custom modules, error handling, and RFC 6455 compliance. Once the foundation is in place, you'll progress to implementing the WebSocket handshake process, parsing headers, and verifying client requests using cryptographic hashing techniques. Debugging and testing are integrated throughout the course to reinforce best practices. In the core modules, you'll master how to receive and decode binary WebSocket frames, handle small to large payloads, and use buffers, bitwise operators, and masking logic for reliable data processing. Then, you'll dive into server-to-client communication, frame construction, and echo responses. The final section focuses on gracefully handling connection closures and error frames, ensuring your implementation is robust and production-ready. This course is ideal for backend developers, full-stack engineers, or anyone looking to gain an authentic understanding of the WebSocket protocol beyond abstractions. A working knowledge of JavaScript and Node.js is required. This is an intermediate-level course designed for those ready to move past high-level libraries and explore the core mechanics of real-time networking.
In this module, we will explore the foundations of WebSocket communication, including how the protocol upgrades from HTTP to enable persistent, two-way connections. We’ll also cover the critical role RFC 6455 plays in ensuring compatibility and protocol integrity. This section sets the groundwork for building an authentic WebSocket server.
What's included
2 videos1 reading
2 videos•Total 10 minutes
- Introduction•6 minutes
- To build a WebSocket server, we need to be RFC compliant•4 minutes
1 reading•Total 10 minutes
- Full Course Resources•10 minutes
In this module, we will build a functional Node.js HTTP server from the ground up. We'll set up the client-side interface, structure our server-side code using custom modules, and implement error handling with debugging support. These steps prepare us for seamlessly introducing WebSocket capabilities.
What's included
6 videos1 assignment
6 videos•Total 34 minutes
- Overview of HTML and CSS•8 minutes
- Setting up our HTTP server•8 minutes
- Creating custom modules and finishing off the HTTP server•4 minutes
- Implementing basic error handling•6 minutes
- Using "Run and Debug" to examine the forEach loop•4 minutes
- Testing our error handling code•5 minutes
1 assignment•Total 15 minutes
- Creating a NodeJS Server - Assessment•15 minutes
In this module, we will focus on initiating a WebSocket connection by listening to the HTTP upgrade event. We’ll break down client headers, use Node’s crypto module to generate a valid Sec-WebSocket-Accept key, and validate the handshake process. Testing ensures our server can establish real-time communication with any compliant client.
What's included
9 videos1 assignment
9 videos•Total 75 minutes
- Using the 'upgrade' event listener to receive three important objects•8 minutes
- Examining the request object in the terminal•6 minutes
- Reading the client's opening handshake request headers•18 minutes
- Sending a "400 Bad Request" response if the client handshake headers fail•12 minutes
- Generate the server response headers object•6 minutes
- Extracting the Sec-WebSocket-Key and using the crypto module•7 minutes
- Timeout! What is SHA-hashing and the crypto module?•4 minutes
- Generate the Sec-WebSocket-Accept value and send back headers to the client•6 minutes
- Testing our code and opening up a valid WebSocket connection•8 minutes
1 assignment•Total 15 minutes
- Establishing a WebSocket Connection - Assessment•15 minutes
In this module, we will dive deep into the anatomy of WebSocket frames. From extracting and unmasking payloads to parsing frame headers with bitwise operations, we’ll cover how the server receives and processes both small and large messages. Debugging tools will assist in refining the logic for real-time, binary-safe communication.
What's included
34 videos1 assignment
34 videos•Total 266 minutes
- Setting up our file for the next goal•2 minutes
- The socket object inherits from the stream.Duplex class•6 minutes
- Defining our data event handler•5 minutes
- Quick cut - adding the 'end' event listener to our socket object•2 minutes
- Define the processBuffer() function•10 minutes
- The WebSocket binary frame structure•6 minutes
- Coding the task management looping function•9 minutes
- Extract the first 2 bytes of data from the WebSocket data frame•9 minutes
- What are Buffers?•10 minutes
- Why is the letter "a" sent as 7 bytes?•5 minutes
- Using the Debugger tool to analyze code•13 minutes
- Extracting the FIN bit•7 minutes
- Bitwise operators•8 minutes
- Extracting the MASK, OPCODE and initial LENGTH information•4 minutes
- Setting up code to extract the payload length details•4 minutes
- The 3 categories of payload lengths•5 minutes
- Calculating the payload length•15 minutes
- Payload length checks•6 minutes
- Extract the Masking Key•7 minutes
- Define the getPayload() method•14 minutes
- Extract one full frame of data (masked)•14 minutes
- Unmasking the frame payload•7 minutes
- What is the modulus operand?•4 minutes
- Create a persistent fragments array and check for more frames (FIN bit check)•8 minutes
- SMALL payloads - Using the debugger to analyze logic•15 minutes
- Fixing the error in our consumePayload() method•5 minutes
- Adding a prepopulate button to the HTML•8 minutes
- MEDIUM Payloads - Using the debugger to analyze logic•10 minutes
- LARGE Payloads: Part 1 of 3. Understanding getLength() logic•7 minutes
- LARGE Payloads: Part 2 of 3. Waiting for additional chunks•6 minutes
- LARGE Payloads: Part 3 of 3. Processing the entire payload into _fragments•14 minutes
- Improvements, comments, and adding opcode checks•10 minutes
- Advanced - chunk size variation between debugger vs live environment•11 minutes
- Improving our _getInfo() method•4 minutes
1 assignment•Total 15 minutes
- Receiving WebSocket Data - Assessment•15 minutes
In this module, we will construct and send WebSocket frames from server to client. We’ll handle everything from setting FIN and OPCODE bits to encoding payloads and managing variable-length headers. By the end, our server will be capable of echoing messages and handling client responses with precision.
What's included
11 videos1 assignment
11 videos•Total 66 minutes
- Getting project files ready to send data to the client•4 minutes
- Calculating the size of the variable-length header field•10 minutes
- Create the binary frame buffer blueprint•3 minutes
- Creating the first byte of the frame•5 minutes
- Bitwise shift operators•3 minutes
- Populate the frame header with data•11 minutes
- Sending the frame to the client•4 minutes
- Testing whether the client received the frame•6 minutes
- Creating a reset() function•4 minutes
- Using debugger tool to examine code•7 minutes
- Displaying the WebSocket message on the client-side•10 minutes
1 assignment•Total 15 minutes
- Sending WebSocket Data - Assessment•15 minutes
In this module, we will master the process of closing a WebSocket connection. From detecting ping/pong and malformed frames to analyzing closure behavior via the CloseEvent object, we’ll build a fully RFC-compliant server closure workflow. We'll also address edge cases like unmasked data and large payload termination.
What's included
16 videos3 assignments
16 videos•Total 71 minutes
- Setting up project code and defining our mini-goal•5 minutes
- Closing handshake•3 minutes
- Extracting the body (closure code and reason) of the close frame•9 minutes
- Close Frame Structure•3 minutes
- Construct the payload buffer for the close frame•9 minutes
- Completing and sending the final close frame back to the client•5 minutes
- Testing our code•4 minutes
- Using Wireshark to master the TCP closure process•5 minutes
- Checking for "ping" and "pong" data type, and payloads larger than max size•7 minutes
- Extracting the server response from the CloseEvent object•3 minutes
- Sending a closure frame if the masking bit is not set correctly by the client•2 minutes
- Check whether client has sent a closure code•2 minutes
- Displaying default closure message (for normal closure event)•0 minutes
- Fixing comments and removing server response text when a new connection is made•3 minutes
- Server side validation for text•5 minutes
- Fixing the refresh issue killing the server•5 minutes
3 assignments•Total 90 minutes
- Full Course Practice Assessment•15 minutes
- Responding to a Closure Frame - Assessment•15 minutes
- Full Course Assessment•60 minutes
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