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Project: Building a Multi-Threaded HTTP Server in C from Scratch

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Project: Building a Multi-Threaded HTTP Server in C from Scratch
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Project: Building a Multi-Threaded HTTP Server in C from Scratch

Phase 4 Capstone. You've mastered TCP sockets, POSIX threads, and file I/O. Now you'll combine them to build a real HTTP/1.1 server: a program that accepts browser connections, parses HTTP requests, reads HTML/CSS files from disk, and sends proper HTTP responses. This is exactly how the early web worked — and still the foundation of Apache, Nginx, and every C-based web server today.

Table of Contents

HTTP/1.1 Protocol Primer

HTTP is a text-based request-response protocol over TCP. Every browser interaction follows the same pattern:

Request (browser → server):

text


Response (server → browser):


text


Key rules: headers end with \r\n, the header section ends with \r\n\r\n (blank line), then the body follows.




Server Architecture: Thread Pool Model


mermaid




Step 1: Create and Configure the Listening Socket


c




Step 2: Thread Pool Implementation


c




Step 3: HTTP Request Parsing


c




Step 4: MIME Type Detection


c




Step 5: File Serving with sendfile


c




Step 6: HTTP Response Building


c




Step 7: Graceful Shutdown with SIGTERM


c




Testing Your Server


bash




Extension Challenges


    

  1. Keep-Alive: Support Connection: keep-alive — reuse the TCP connection for multiple requests, eliminating per-request TCP handshake overhead.
    2. 

  2. Range requests: Support Range: bytes=0-4095 headers for video streaming (seek without downloading the entire file).
    3. 

  3. epoll-based event loop: Replace the thread-per-request model with a single-thread epoll loop — handle 10,000+ concurrent connections with no context switching overhead.
    4. 

  4. Gzip compression: Compress text files before sending using zlib — reduce bandwidth by 60-80% for HTML/CSS/JS.
    5. 

  5. Virtual hosting: Parse the Host: header; serve from different www/ root directories based on domain name.
    6. 





Phase 4 Reflection


You've just built a significant piece of infrastructure — a real web server that can serve content to a browser. By combining sockets, threads, file I/O, and signal handling, you've touched every layer of the systems stack.


The fundamentals here — listen/accept loop, thread pool, HTTP parsing, file serving — are exactly how Apache httpd was architected in the late 1990s. Nginx replaced the thread model with an event loop (epoll), achieving 10× better concurrency — the extension challenge above is your path to that same transformation.


Read next: C23 Modern Evolution & C Security Hardening →




Part of the C Mastery Course — 30 modules from C basics to production systems engineering.