HTTP From TCP

Building an HTTP/1.1 server from scratch using raw TCP sockets. This is course code from Boot.dev, developed in WSL Alpine.

What's This About

Instead of using Go's net/http package like a normal person, this project implements HTTP from the ground up. We're talking raw TCP connections, manually parsing request lines, headers, bodies - the whole thing. It's a great way to actually understand what's happening under the hood when you make an HTTP request.

Project Structure

cmd/
  httpserver/    - The main HTTP server
  tcplistener/   - Simple TCP listener for debugging requests
  udplistener/   - UDP listener (because why not)
  udpsender/     - UDP sender for testing

internal/
  headers/       - HTTP header parsing and management
  request/       - HTTP request parsing (state machine style)
  response/      - HTTP response writing
  server/        - TCP server with connection handling

The HTTP Server

Runs on port 42069 (obviously). Handles a few routes:

• / - Returns a success page
• /yourproblem - Returns 400 Bad Request (your fault)
• /myproblem - Returns 500 Internal Server Error (my fault)
• /video - Serves assets/vim.mp4 if it exists
• /httpbin/* - Proxies to httpbin.org with chunked transfer encoding and trailers

The proxy endpoint is the interesting one - it streams responses using chunked transfer encoding and adds SHA256 and content length trailers at the end.

How It Works

Request Parsing

The request parser is a state machine that processes incoming bytes:

1. Parse the request line (method, target, HTTP version)
2. Parse headers until we hit the empty line
3. Read the body based on Content-Length

It handles partial reads and buffer management properly, so it works with real TCP connections where data arrives in chunks.

Response Writing

The response writer can:

• Write status lines (200, 400, 500)
• Write headers
• Write regular bodies
• Write chunked bodies (for streaming)
• Write trailers (metadata after the body)

Headers

Case-insensitive header storage with support for:

• Getting/setting/replacing/deleting headers
• Parsing raw header bytes
• Iterating over all headers
• Comma-separated values for duplicate headers

Running It

# Build and run the HTTP server
go run ./cmd/httpserver

# Test it
curl http://localhost:42069/
curl http://localhost:42069/yourproblem
curl http://localhost:42069/video

Or use netcat for raw requests:

echo -e "GET /httpbin/html HTTP/1.1\r\nHost: localhost\r\nConnection: close\r\n\r\n" | nc localhost 42069

The Other Tools

tcplistener - Just accepts TCP connections and prints the parsed HTTP request. Useful for debugging.

udplistener/udpsender - UDP tools for messing around with datagrams. Not really HTTP-related but they were part of the learning process.

Dependencies

• Go 1.22+
• testify (for tests)

Notes

This was built as a learning exercise. The error messages in the HTML responses are intentionally cheeky. The port number is also intentionally immature. It's fine.