facil.io - a mini-framework for C web applications

A Web application in C? It's as easy as:

#include "http.h" /* the HTTP facil.io extension */

// We'll use this callback in `http_listen`, to handles HTTP requests
void on_request(http_s *request);

// These will contain pre-allocated values that we will use often

// Listen to HTTP requests and start facil.io
int main(int argc, char const **argv) {
  // allocating values we use often
  HTTP_HEADER_X_DATA = fiobj_str_new("X-Data", 6);
  // listen on port 3000 and any available network binding (NULL ==
  http_listen("3000", NULL, .on_request = on_request, .log = 1);
  // start the server
  fio_start(.threads = 1);
  // deallocating the common values
  // these can be used, but we're ignoring them here.
  (void)argc; (void)argv;

// Easy HTTP handling
void on_request(http_s *request) {
  http_set_cookie(request, .name = "my_cookie", .name_len = 9, .value = "data",
                  .value_len = 4);
  http_set_header(request, HTTP_HEADER_CONTENT_TYPE,
                  http_mimetype_find("txt", 3));
  http_set_header(request, HTTP_HEADER_X_DATA, fiobj_str_new("my data", 7));
  http_send_body(request, "Hello World!\r\n", 14);

facil.io - more than a powerful HTTP/Websockets server library.

facil.io is an evented Network library written in C. It provides high performance TCP/IP network services by using an evented design that was tested to provide an easy solution to the C10K problem.

facil.io includes a mini-framework for Web Applications, with a fast HTTP / WebSocket server, integrated Pub/Sub, optional Redis connectivity, easy JSON handling, Mustache template rendering and more nifty tidbits.

facil.io powers the HTTP/Websockets Ruby Iodine server and it can easily power your application as well.

facil.io should work on Linux / BSD / macOS (and possibly CYGWIN) and is continuously tested on both Linux and macOS.

facil.io is a source code library, making it easy to incorporate into any project. The API was designed for simplicity and extendability, which means writing new extensions and custom network protocols is easy.

facil.io's core library is a two-file library (fio.h and fio.c), making it easy to incorporate networking solutions into any project.

facil.io supports both single-threaded and multi-threaded operation modes as well as a hybrid mode (multi-process with either a single-threaded or multi-threaded workers).

I used this library (including the HTTP server) on Linux, Mac OS X and FreeBSD (I had to edit the makefile for each environment).

An easy chat-room example

Here's a simple WebSocket chat-room example:

#include "fio_cli.h"
#include "http.h"

/* Chat-room channel name */
static fio_str_info_s CHAT_CHANNEL = {.len = 8, .data = "chatroom"};

/* *****************************************************************************
WebSocket callbacks
***************************************************************************** */

/* We'll subscribe to the channel's chat channel when a new connection opens */
static void on_open_websocket(ws_s *ws) {
  /* subscription - easy as pie */
  websocket_subscribe(ws, .channel = CHAT_CHANNEL, .force_text = 1);
  /* notify everyone about new (named) visitors */
  FIOBJ nickname = (FIOBJ)websocket_udata_get(ws);
  fio_str_info_s n = fiobj_obj2cstr(nickname);
  FIOBJ msg = fiobj_str_new(n.data, n.len);
  fiobj_str_write(msg, " joined the chat.", 17);
  pubsub_publish(.channel = CHAT_CHANNEL, .message = fiobj_obj2cstr(msg));
  /* cleanup */

/* Free the nickname, if any. */
static void on_close_websocket(intptr_t uuid, void *udata) {
  FIOBJ nickname = (FIOBJ)udata;
  fio_str_info_s n = fiobj_obj2cstr(nickname);
  /* send notification */
  FIOBJ msg = fiobj_str_new(n.data, n.len);
  fiobj_str_write(msg, " left the chat.", 15);
  fio_publish(.channel = CHAT_CHANNEL, .message = fiobj_obj2cstr(msg));
  /* cleanup */

/* Received a message from a client, format message for chat . */
static void handle_websocket_messages(ws_s *ws, fio_str_info_s data,
                                      uint8_t is_text) {
  FIOBJ nickname = (FIOBJ)websocket_udata_get(ws);
  fio_str_info_s n = fiobj_obj2cstr(nickname);
  /* allocates a dynamic string. knowing the buffer size is faster */
  FIOBJ msg = fiobj_str_buf(n.len + 2 + data.len);
  fiobj_str_write(msg, n.data, n.len);
  fiobj_str_write(msg, ": ", 2);
  fiobj_str_write(msg, data.data, data.len);
  fio_publish(.channel = CHAT_CHANNEL, .message = fiobj_obj2cstr(msg));

/* *****************************************************************************
HTTP Handling (Upgrading to WebSocket)
***************************************************************************** */

/* Answers simple HTTP requests */
static void answer_http_request(http_s *h) {
  http_set_header2(h, (fio_str_info_s){.data = "Server", .len = 6},
                   (fio_str_info_s){.data = "facil.example", .len = 13});
  http_set_header(h, HTTP_HEADER_CONTENT_TYPE, http_mimetype_find("txt", 3));
  /* this both sends the response and frees the http handler. */
  http_send_body(h, "This is a simple Websocket chatroom example.", 44);

/* tests that the target protocol is "websockets" and upgrades the connection */
static void answer_http_upgrade(http_s *h, char *target, size_t len) {
  /* test for target protocol name */
  if (len != 9 || memcmp(target, "websocket", 9)) {
    http_send_error(h, 400);
  FIOBJ n;
  fio_str_info_s path = fiobj_obj2cstr(h->path);
  if (path.len > 1) {
    n = fiobj_str_new(path.data + 1, path.len - 1);
  } else {
    n = fiobj_str_new("Guest", 5);
  // Websocket upgrade will use our existing response.
  if (http_upgrade2ws(
          h, .on_open = on_open_websocket, .on_close = on_close_websocket,
          .on_message = handle_websocket_messages, .udata = (void *)n))

/* *****************************************************************************
The main function
***************************************************************************** */
int main(int argc, char const *argv[]) {
      argc, argv, 0, 0, "WebSocket chat room example using facil.io",
      FIO_CLI_INT("-t number of threads"),
      FIO_CLI_INT("-w number of workers"),
      FIO_CLI_INT("-p port number to listen on (0 == unix socket)"),
      FIO_CLI_STRING("-b address binding"),
      FIO_CLI_STRING("-www a public folder from which to serve files"),
      FIO_CLI_BOOL("-v logs requests to STDERR"));

  fio_cli_set_default("-p", "3000");

  if (http_listen(fio_cli_get("-p"), fio_cli_get("-b"),
                  .on_request = answer_http_request,
                  .on_upgrade = answer_http_upgrade,
                  .log = fio_cli_get_bool("-v"),
                  .public_folder = fio_cli_get("-www")) == -1) {
    perror("Couldn't listen for HTTP / WebSocket connections");
  fio_start(.threads = fio_cli_get_i("-t"), .workers = fio_cli_get_i("-w"));

Further reading

The code in this project is heavily commented and the header files could (and probably should) be used as the actual documentation.

However, experience shows that a quick reference guide is immensely helpful and that Doxygen documentation is ... well ... less helpful and harder to navigate (I'll leave it at that for now).

I hope you find the documentation on this website helpful.