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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_static("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
  facil_run(.threads = 1);
  // deallocating the common values

// 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 a C mini-framework for web applications and includes a fast HTTP and Websocket server, a native Pub/Sub solution, an optional Redis pub/sub engine, support for custom protocols and some nifty tidbits.

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

facil.io provides high performance TCP/IP network services to Linux / BSD (and macOS) by using an evented design that was tested to provide an easy solution to the C10K problem.

facil.io prefers a TCP/IP specialized solution over a generic one (although it can be easily adopted for Unix sockets, UDP and other approaches).

facil.io includes a number of libraries that work together for a common goal. Some of the libraries (i.e., some core types the thread-pool library defer, the socket library sock, the evented IO core evio and the parsers can be used independently while others are designed to work together using a modular approach.

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 chatroom example

Here’s a simple Websocket chatroom example:

#include "http.h"
#include "pubsub.h"
#include <string.h>

/* *****************************************************************************
***************************************************************************** */

struct nickname {
  size_t len;
  char nick[];

/* This initalization requires GNU gcc / clang ...
 * ... it's a default name for unimaginative visitors.
static struct nickname MISSING_NICKNAME = {.len = 7, .nick = "unknown"};
/* *****************************************************************************
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 */
  struct nickname *n = websocket_udata(ws);
  if (n) {
    FIOBJ msg = fiobj_str_new(n->nick, n->len);
    fiobj_str_write(msg, " joined the chat.", 17);
    pubsub_publish(.channel = CHAT_CHANNEL, .message = msg);
    /* cleanup */

/* Free the nickname, if any. */
static void on_close_websocket(ws_s *ws) {
  struct nickname *n = websocket_udata(ws);
  if (n) {
    /* send notification */
    FIOBJ msg = fiobj_str_new(n->nick, n->len);
    fiobj_str_write(msg, " left the chat.", 15);
    pubsub_publish(.channel = CHAT_CHANNEL, .message = msg);
    /* cleanup */

/* Received a message from a client, format message for chat . */
static void handle_websocket_messages(ws_s *ws, char *data, size_t size,
                                      uint8_t is_text) {
  struct nickname *n = websocket_udata(ws);
  if (!n)

  /* allocates a dynamic string. knowing the buffer size is faster */
  FIOBJ msg = fiobj_str_buf(n->len + 2 + size);
  fiobj_str_write(msg, n->nick, n->len);
  fiobj_str_write(msg, ": ", 2);
  fiobj_str_write(msg, data, size);
  if (pubsub_publish(.channel = CHAT_CHANNEL, .message = msg))
    fprintf(stderr, "Failed to publish\n");

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

/* Answers simple HTTP requests */
static void answer_http_request(http_s *h) {
  http_set_header2(h, (fio_cstr_s){.name = "Server", .len = 6},
                   (fio_cstr_s){.value = "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);
  struct nickname *n = NULL;
  fio_cstr_s path = fiobj_obj2cstr(h->path);
  if (path.len > 1) {
    n = malloc(path.len + sizeof(*n));
    n->len = path.len - 1;
    memcpy(n->nick, path.data + 1, path.len); /* will copy the NUL byte */
  // Websocket upgrade will use our existing response.
  if (http_upgrade2ws(.http = h, .on_open = on_open_websocket,
                      .on_close = on_close_websocket,
                      .on_message = handle_websocket_messages, .udata = n))

/* Our main function, we'll start up the server */
int main(void) {
  const char *port = "3000";
  const char *public_folder = NULL;
  uint32_t threads = 1;
  uint32_t workers = 1;
  uint8_t print_log = 0;
  CHAT_CHANNEL = fiobj_sym_new("chat", 4);

  if (http_listen(port, NULL, .on_request = answer_http_request,
                  .on_upgrade = answer_http_upgrade, .log = print_log,
                  .public_folder = public_folder))
    perror("Couldn't initiate Websocket service"), exit(1);
  facil_run(.threads = threads, .processes = workers);


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).

The documentation in this folder includes:

Forking, Contributing and all that Jazz

Sure, why not. If you can add Solaris or Windows support to evio, that could mean facil.io would become available for use on these platforms as well (as well as the HTTP protocol implementation and all the niceties that implies).

If you encounter any issues, open an issue (or, even better, a pull request with a fix) - that would be great :-)

Hit me up if you want to: