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CRut, a ReST application framework

CRut is web application framework for services written in C. It is realized so to save the more resources as possible and to be run on Internet-of-Things devices. It has been developed for the PeerStreamer-ng web application, a service for real-time P2P streaming.

Developers are asked to define and couple HTTP request patterns (i.e., URI) and methods. CRut also serves the files placed in the Public/ folder.

By default, CRut runs on port 3000.

Compile and run

make
./crut

Point your web browser at http://localhost:3000.

Create your routes

The HTTP request patters comprise of

  • an HTTP method;
  • a regex for the URL.

HTTP methods are: GET, PUT, POST, UPDATE, DELETE, OPTION, HEAD. Regex allows the specification of a broad range of HTTP resource patters; for example, if you want to match the resource with URL /channels/BBC, you can write: "/channels/[A-z0-9]+$". The previous regex will match all the URLs of the form /channels/ where is any string comprising of lower and upper case letters and numbers.

A path handler is a C function pointer with type

void (*path_handler)(struct mg_connection *nc, struct http_message *hm);

A route is the triple HTTP method, URL regex, path handler. Routes are defined so to react to specific HTTP requests with some C code. Routes can be defined in the src/routes.c file with the following line:

res |= router_add_route(r, "POST", "^[/]+channels/[A-z0-9]+$", path_handler); 

where res and r are scope specific variable to be used as-is.

Define your handlers

Defining a path handler is easy as opening src/path_handlers.c and writing:

void path_handler(struct mg_connection *nc, struct http_message *hm)
{
		mg_http_short_answer(nc, 200);
}

The example code above will answer to incoming HTTP requests with a polite "HTTP 200 OK" message.

Handlers can take advantage from some helpers for getting request variable values;

  • mg_uri_field(hm, pos) returns a char array pointer with the value of the URI field specified by pos; for example, for the request /channels/BBC, with pos=1 it will return "BBC".
  • mg_get_http_var(&hm->body, "data", buff, BUFF_LENGTH) stores in the buffer pointed by buff the value of the HTTP variable "data" encoded in the request.

The helpers also include some functions for answering:

  • mg_http_short_answer(nc, code); will send the HTTP request with the status code code and the brief corresponding message;
  • mg_http_text_answer(nc, code, body); adds the possibility to also specify the response message;
  • mg_http_json_answer(nc, code, body); adds the possibility to specify a JSON body (it automatically set the Content-type header).
  • mg_http_answer(nc, code, content_type, body); sends an HTTP requests setting the content type and the response body.

SSL

CRut supports SSL, just enable it at compilation time:

ENABLE_SSL=1 make

Tests

CRut comes with a unit-test suite (in /Test). To run all of them at once type:

make tests

It requires valgrind to be installed and present in the PATH.

CRut can also be compiled in debug mode for enabling extra output:

DEBUG=1 make

Tutorials

A tutorial about using CRut to create a web app turning Raspberry pi leds on and off is avaiable.

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