Web Framework to build REST APIs, Webservices or any HTTP endpoint in C language. Can stream large amount of data, integrate JSON data with Jansson, and create websocket services
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Web Framework to build REST APIs, Webservices or any HTTP endpoint in C language. Can stream large amount of data, integrate JSON data with Jansson, and create websocket services
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Ulfius HTTP Framework

.github/workflows/ccpp.yml CodeQL CII Best Practices

HTTP Framework for REST Applications in C.

Based on GNU Libmicrohttpd for the backend web server, Jansson for the json manipulation library, and Libcurl for the http/smtp client API.

Used to facilitate creation of web applications in C programs with a small memory footprint, as in embedded systems applications.

You can create webservices in HTTP or HTTPS mode, stream data, or implement server websockets.

Hello World! example application

The source code of a hello world using Ulfius is the following:

 * test.c
 * Small Hello World! example
 * to compile with gcc, run the following command
 * gcc -o test test.c -lulfius
#include <stdio.h>
#include <ulfius.h>

#define PORT 8080

 * Callback function for the web application on /helloworld url call
int callback_hello_world (const struct _u_request * request, struct _u_response * response, void * user_data) {
  ulfius_set_string_body_response(response, 200, "Hello World!");

 * main function
int main(void) {
  struct _u_instance instance;

  // Initialize instance with the port number
  if (ulfius_init_instance(&instance, PORT, NULL, NULL) != U_OK) {
    fprintf(stderr, "Error ulfius_init_instance, abort\n");

  // Endpoint list declaration
  ulfius_add_endpoint_by_val(&instance, "GET", "/helloworld", NULL, 0, &callback_hello_world, NULL);

  // Start the framework
  if (ulfius_start_framework(&instance) == U_OK) {
    printf("Start framework on port %d\n", instance.port);

    // Wait for the user to press <enter> on the console to quit the application
  } else {
    fprintf(stderr, "Error starting framework\n");
  printf("End framework\n");


  return 0;

Main features


  • Create a webservice in a separate thread, the endpoint is identified by its method (ex: GET, POST, PUT, DELETE, etc.) and its URL path with its optional parameters (ex: /api/doc/@id). The webservice is executed in a callback function.

  • Stream large amount of data with a reduced memory footprint.

  • Websocket service, the websocket messages exchange is executed in dedicated callback functions.

Client requests

  • Client http[s] and smtp requests execution, the response is parsed in a dedicated structure.

  • Client websocket request execution, the websocket messages exchange is executed in dedicated callback functions.


  • Create a websocket service application

  • Create websocket client application

  • CLI to connect to a remote websocket: uwsc


See INSTALL.md file for installation details


See API.md file for API documentation details

See the online documentation for a doxygen format of the API documentation.

Example programs source code

Example programs are available to understand the different functionalities available, see example_programs folder for detailed sample source codes and documentation.

Example callback functions

Example callback functions are available in the folder example_callbacks. The example callback functions available are:

  • static file server: to provide static files of a specific folder
  • oauth2 bearer: to check the validity of a Oauth2 bearer jwt token. Requires libjwt.

Projects using Ulfius framework

  • Glewlwyd, a lightweight SSO server that provides OAuth2 and OpenID Connect authentication protocols
  • Le Biniou, user-friendly yet powerful music visualization / VJing tool
  • Angharad, House automation system for ZWave and other types of devices
  • Hutch, a safe locker for passwords and other secrets, using JavaScript client side encryption only
  • Taliesin, a lightweight audio streaming server
  • Taulas Raspberry Pi Serial interface, an interface for Arduino devices that implement Taulas protocol, a house automation protocol for Angharad

Questions, problems ?

I'm open for questions and suggestions, feel free to open an issue, a pull request or send me an e-mail if you feel like it!

You can visit the IRC channel #ulfius on the Libera.​Chat network.

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