webserver.c

#include <ctype.h>
#include <fcntl.h>
#include <linux/openat2.h>
#include <netinet/in.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
    if (argc > 2) if (chdir(argv[2])) return 1;

    int listenfd = socket(AF_INET, SOCK_STREAM, 0);

    struct sockaddr_in sock = {
        .sin_family = AF_INET,
        .sin_port = htons(argc > 1 ? atoi(argv[1]) : 80),
    };

    setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int));
    bind(listenfd, (struct sockaddr*)&sock, sizeof(sock));
    listen(listenfd, 10);

    signal(SIGCHLD, SIG_IGN);
    while (1) {
        int fd = accept(listenfd, 0, 0);
        setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &(struct timeval){ .tv_sec = 10 }, sizeof(struct timeval));

        if (!fork()) {
            static char buf[4096];

            read(fd, buf, sizeof buf - 1);
            if (strchr(buf, '\n')) *strchr(buf, '\n') = 0;
            if (strchr(buf, '\r')) *strchr(buf, '\r') = 0;
            if (strrchr(buf, ' ')) *strrchr(buf, ' ') = 0;

            if (!strncmp(buf, "GET ", 4) || !strncmp(buf, "HEAD ", 5)) {
                char *path = buf + 5 + (buf[0] == 'H'), *rptr = path, *wptr = path;

                for ( ; *rptr; rptr++) {
                    if (*rptr != '%') *wptr++ = *rptr;
                    else if (isxdigit(rptr[1]) && isxdigit(rptr[2])) {
#define fromhex(x) (x >= '0' && x <= '9' ? x - '0' : (x|32) - 'a' + 10)
                        *wptr++ = (fromhex(rptr[1]) << 4) | fromhex(rptr[2]);
                        rptr += 2;
                    }
                    else { /* no */ }
                }
                *wptr = 0;
                struct open_how how = {
                    .flags = O_RDONLY,
                    .resolve = RESOLVE_BENEATH,
                };
                int f = syscall(SYS_openat2, AT_FDCWD, path, &how, sizeof how);
                if (f < 0) write(fd, "HTTP/1.0 404 Not Found\r\n\r\n", 26);
                else write(fd, "HTTP/1.0 200 OK\r\n\r\n", 19);

                if (buf[0] == 'G') for (long l; (l = read(f, buf, sizeof buf)) > 0; ) write(fd, buf, l);
            }
            else write(fd, "HTTP/1.0 501 Not Implemented\r\n\r\n", 32);
            break;
        }
        close(fd);
    }
}