daemoner.c

#define _XOPEN_SOURCE 700

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <netdb.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <spawn.h>
#include <string.h>

extern char **environ;

static void my_perror(char *argv0, char *msg)
{
	char *err = strerror(errno);
	write(2, argv0, strlen(argv0));
	write(2, ": ", 2);
	write(2, msg, strlen(msg));
	write(2, ": ", 2);
	write(2, err, strlen(err));
	write(2, "\n", 1);
}

int main(int argc, char **argv)
{
	int sockfd;
	char *port = 0;

	struct addrinfo hints = {
		.ai_family = AF_UNSPEC,
		.ai_socktype = SOCK_STREAM,
		.ai_flags = AI_PASSIVE
	};
	struct addrinfo *servinfo, *p;

	int rv;
	int opt;

	while((opt = getopt(argc, argv, "tup:")) != -1) {
		switch(opt) {
		case 'p':
			port = optarg;
			break;
		case 't':
			hints.ai_socktype = SOCK_STREAM;
			break;
		case 'u':
			hints.ai_socktype = SOCK_DGRAM;
			break;
		default:
			return 1;
		}
	}
	if(optind >= argc) {
		write(2, argv[0], strlen(argv[0]));
		write(2, ": expected argument\n", strlen(": expected argument\n"));
		return 1;
	}
	if(!port) {
		write(2, argv[0], strlen(argv[0]));
		write(2, ": expected port\n", strlen(": expected port\n"));
		return 1;
	}	

	if((rv = getaddrinfo(NULL, port, &hints, &servinfo)) != 0) {
		const char *err = gai_strerror(rv);
		write(2, argv[0], strlen(argv[0]));
		write(2, ": getaddrinfo: ", strlen(": getaddrinfo :"));
		write(2, err, strlen(err));
		write(2, "\n", 1);
		return 1;
	}

	for(p = servinfo; p != NULL; p = p->ai_next) {
		int flags = 0;
		if((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) {
			my_perror(argv[0], "socket");
			continue;
		}
		if(setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) == -1) {
			my_perror(argv[0], "setsockopt");
			close(sockfd);
			continue;
		}
		if(fcntl(sockfd, F_SETFD, FD_CLOEXEC) == -1) {
			my_perror(argv[0], "fcntl");
			close(sockfd);
			continue;
		}
		if(bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
			my_perror(argv[0], "bind");
			close(sockfd);
			continue;
		}
		break;
	}

	if(!p) return 1;

	if(listen(sockfd, 20) == -1) {
		my_perror(argv[0], "listen");
		return 1;
	}

	close(0);
	close(1);

	signal(SIGCHLD, SIG_IGN);

	while(1) {
		if(accept(sockfd, 0, 0) == -1) {
			my_perror(argv[0], "accept");
			continue;
		}

		if(dup(0) == -1) {
			my_perror(argv[0], "dup");
			close(0);
			continue;
		}
		if(posix_spawnp(&(int){0}, argv[optind], 0, 0, &argv[optind], environ)) {
			my_perror(argv[0], "posix_spawnp");
			close(0);
			close(1);
			continue;
		}
		close(0);
		close(1);
	}
}

http.c

#define _POSIX_C_SOURCE 200809L
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>

static void http_error(int code)
{
	printf("HTTP/1.0 %d Error\r\n"
	       "Content-type: text/plain; charset=UTF-8\r\n"
	       "\r\n"
	       "%d error\r\n", code, code);
	exit(0);
}

static char *fgetline(char *s, int len, FILE *f)
{
	char *ret;

	ret = fgets(s, len, f);

	if(!ret) return ret;

	if(strlen(s) == len - 1 && s[len-1] != '\n') {
		while(!feof(f) && getc(f) != '\n');
	}
	for(; *s; s++)
		if(*s == '\r' || *s == '\n') {
			*s = '\0';
			break;
		}
	return ret;
}

int main(int argc, char **argv)
{
	FILE *f=0;
	char req[4096];
	char junk[4096];
	fgetline(req, sizeof req, stdin);

	while(fgetline(junk, sizeof junk, stdin), strlen(junk) != 0);
	if(strncmp(req, "GET ", 4) != 0) {
		http_error(501);
	}

	for(int i = 4; i < sizeof(req); i++) {
		if(req[i] == ' ') {
			req[i] = '\0';
			break;
		}
	}
	for(int i = 4; i < sizeof(req) - 1; i++) {
		if(req[i] == '.' && req[i+1] == '.') {
			http_error(403);
		}
	}

	f = fopen(req+5, "rb");
	if(!f) {
		if(errno == ENOENT || errno == EISDIR)
			http_error(404);
		else if(errno == EACCES)
			http_error(403);
		else
			http_error(500);
	}
	printf("HTTP/1.0 200 OK\r\n"
	       "\r\n");
	while(!feof(f) && !ferror(f)) {
		size_t len = fread(junk, 1, sizeof(junk), f);
		fwrite(junk, 1, len, stdout);
	}
}