discard.c

// somewhat performant discard service I guess.
// listens on localhost:1337 (it's not port 9 since I prefer non-priv users)
//
// compile with something like that:
// clang -Wall -Wextra -Werror -pedantic -std=c11 -O2 -o discard discard.c

#include <err.h>
#include <fcntl.h>
#include <netdb.h>
#include <stdlib.h>
#include <string.h>
#include <sys/sendfile.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <unistd.h>

void sigchld(int sig)
{
	(void)sig;

	int status;
	if(waitpid(-1,&status,WNOHANG) == -1)
	{
		err(EXIT_FAILURE,"waitpid");
	}
}

int main(int argc,char **argv)
{
	if(argc > 1)
	{
		errx(EXIT_FAILURE,"Usage: %s",argv[0]);
	}

	struct addrinfo hints;
	struct addrinfo *result,*rp;
	int n;
	pid_t pid;

	memset(&hints,0,sizeof(struct addrinfo));
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_flags = AI_PASSIVE;

	n = getaddrinfo("localhost","1337",&hints,&result);
	if(n != 0)
	{
		errx(EXIT_FAILURE,"getaddrinfo: %s",gai_strerror(n));
	}

	int server;
	for(rp = result;rp != NULL;rp = rp->ai_next)
	{
		server = socket(rp->ai_family,rp->ai_socktype,rp->ai_protocol);
		if(server == -1)
		{
			warn("socket");
			continue;
		}

		int optval = 1;
		setsockopt(server,SOL_SOCKET,SO_REUSEADDR,&optval,sizeof optval);

		if(bind(server,rp->ai_addr,rp->ai_addrlen) == 0)
		{
			break;
		}

		warn("bind");
		close(server);

	}

	if(rp == NULL)
	{
		errx(EXIT_FAILURE,"Could not bind");
	}

	freeaddrinfo(result);

	listen(server,4);
	signal(SIGCHLD,sigchld);

	for(;;)
	{
		int them = accept(server,NULL,NULL);
		if(them < 0)
		{
			warn("accept");
			continue;
		}

		if((pid=fork()))
		{
			if(pid < 0)
			{
				err(EXIT_FAILURE,"fork");
			}
			close(them);
			continue;
		}

		int devnull = open("/dev/null",O_WRONLY);
		while((n = sendfile(devnull,them,0,0x8000000)) > 0);
		if(n < 0)
		{
			warn("sendfile");
		}
		close(them);
		close(devnull);
		err(EXIT_SUCCESS,"prnt");
	}
}