HTTP in C

A minimal HTTP/1.1 static file server in a single C file. It accepts TCP connections, parses GET request lines, maps URL paths to the filesystem, and streams file contents back with correct headers. A live access log prints every request with status code, byte count, and response time. Concurrent requests are handled via fork().

Part of the Corg-Labs collection of single-file C programs.

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Features

• TCP socket lifecycle: socket → bind → listen → accept
• GET and HEAD method support; 405 for everything else
• %xx URL decoding and directory-traversal (..) protection
• Automatic index.html serving for directory paths
• MIME type table covering HTML, CSS, JS, JSON, PNG, JPEG, SVG, WASM, and more
• fork()-per-connection concurrency; zombie reaping via SIGCHLD

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Tutorial

1. TCP Socket Setup

int lfd = socket(AF_INET, SOCK_STREAM, 0);

int yes = 1;
setsockopt(lfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));

struct sockaddr_in addr = {
    .sin_family      = AF_INET,
    .sin_port        = htons((uint16_t)port),
    .sin_addr.s_addr = INADDR_ANY,
};
bind(lfd, (struct sockaddr *)&addr, sizeof(addr));
listen(lfd, 64);

SO_REUSEADDR lets the port be rebound immediately after restart.

2. Fork-per-Connection Concurrency

pid_t pid = fork();
if (pid == 0) {
    close(lfd);               /* child doesn't need listener */
    handle_client(cfd, root);
    close(cfd);
    exit(0);
}
close(cfd);                   /* parent closes its copy */

SIGCHLD is caught by a handler that calls waitpid(-1, NULL, WNOHANG) to reap zombies.

3. HTTP Request Parsing

char method[16], raw_path[1024], proto[16];
sscanf(req, "%15s %1023s %15s", method, raw_path, proto);

URL percent-encoding is decoded: %xx hex sequences are converted to their byte values. Any path containing .. is rejected with 403.

4. MIME Type Resolution

static const mime_entry_t MIME_TABLE[] = {
    { "html", "text/html; charset=utf-8" },
    { "js",   "application/javascript"   },
    { "png",  "image/png"                },
    { NULL,   "application/octet-stream" },   /* fallback */
};

strrchr finds the file extension; the table is scanned with strcasecmp.

5. File Streaming

snprintf(hdr, sizeof(hdr),
    "HTTP/1.1 200 OK\r\nContent-Type: %s\r\n"
    "Content-Length: %lld\r\nConnection: close\r\n\r\n",
    mime, (long long)st.st_size);
send_all(cfd, hdr, hlen);

char buf[8192];
while ((n = read(ffd, buf, sizeof(buf))) > 0)
    send_all(cfd, buf, n);

send_all loops until every byte is written, handling short writes.

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Build

gcc http.c -o http

Run

./http                 # port 8080, serve current directory
./http 9090 /var/www   # custom port and root

Open http://localhost:8080/ in a browser. The terminal shows a live access log.

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Concepts Practiced

• TCP socket lifecycle (socket, bind, listen, accept)
• HTTP/1.1 request and response format
• fork()-per-connection concurrency and zombie reaping
• URL percent-decoding and path sanitisation
• MIME type resolution from file extensions
• Reliable write loops for streaming file content

Dependencies

Standard C library + POSIX (sys/socket.h, sys/stat.h, sys/wait.h). No external libraries.