1

IPK project 1 - lightweight HTTP server

Assignment

Implement lightweight HTTP server in C/C++ with minimum requirements. Create Makefile to build application. Server should be started with

$ ./hinfosvc [PORT]

And also should support killing by Ctrl+C.
These endpoints are required:

1. GET http://servername:[PORT]/hostname - returns hostname of machine
2. GET http://servername:[PORT]/cpu-name - returns CPU used by machine
3. GET http://servername:[PORT]/load - returns percentage CPU usage

Usage

Compilation

Firstly, the server needs to be compiled. Just use provided Makefile and compile program with:

$ make

Run

After successfully compilation, server could be started with following command:

$ ./hinfosvc [PORT]

Don't forget to replace [PORT] with port you want the server to listen on. For example:

$ ./hinfosvc 12345

Server should listen and accept connections at [PORT] after it prints Listening on [PORT].

Available endpoints

Server supports 3 endpoints, these could be reached using standard web browser or tools like wget or curl. All the examples bellow assumes, that you have server already running.
Personally I prefer to use curl, so these examples uses it.

/hostname

Server returns hostname of machine it runs on.
Program uses gethostname() function to detect actual hostname.

$ curl http://localhost:[PORT]/hostname
merlin.fit.vutbr.cz

/cpu-name

Server returns name of first CPU found in /proc/cpuinfo.

$ curl http://localhost:[PORT]/cpu-name
Intel(R) Xeon(R) Silver 4214R CPU @ 2.40GHz

/load

Server returns CPU usage, calculation is inspired by this algorithm.

$ curl http://localhost:[PORT]/load
7%

Implementation details

Lightweight HTTP server is implemented as modular program, that means you can easily add new endpoints without any refactor.
Server does not support HTTPS nor IPv6.

The entrypoint of program is function main() in main.c file, that function is responsible for starting server, listening at [PORT] and also for accepting new connections.

Connection as file descriptor are then passed to process_connection() function also located in main.c file.
process_connection() is responsible to read connection body, in our case the HTTP header and body. Project does not use the body at all, so only BUFFER_SIZE bytes are read, the rest is just "collected".

Based on the requested endpoint from connection, corresponding endpoint is found in ENDPOINTS array (located in endpoints.c file). If you want to add a new endpoint, just add it there. Registered function (2nd member of struct endpoint_t) should be pointer to the function that "handles" request. It should return pointer to the response_t struct that contains corresponding HTTP status code (response.h/statuses) and string to be sent back to the user.

The response is then send back to the sender using function send_response() located in main.c file. Firstly it sends the headers defined as a macro RESPONSE_HEADER in response.h file, and then it sends the string from content (member of response_t struct defined in response.h).

Connection is then closed.
Anytime during this process could be server killed by SIGINT signal, signal handler (signal_handler() located in main.c) releases all the allocated resources and also closes all the connections.

Author

Samuel Dobron (xdobro23)
Faculty of Information Technology, Brno University of Technology