/*
 * simple and trivial SCGI server with hard-coded results for use in unit tests
 * - listens on STDIN_FILENO (socket on STDIN_FILENO must be set up by caller)
 * - processes a single SCGI request at a time
 * - arbitrary limitation: reads request headers netstring up to 64k in size
 * - expect recv data for request headers netstring every 10ms or less
 * - no read timeouts for request body; might block reading request body
 * - no write timeouts; might block writing response
 *
 * Copyright(c) 2017 Glenn Strauss gstrauss()gluelogic.com  All rights reserved
 * License: BSD 3-clause (same as lighttpd)
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <poll.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#ifndef MSG_DONTWAIT
#define MSG_DONTWAIT 0
#endif

static int finished;
static char buf[65536];


static char *
scgi_getenv(char *r, const unsigned long rlen, const char * const name)
{
    /* simple search;
     * if many lookups are done, then should use more efficient data structure*/
    char * const end = r+rlen;
    char *z;
    const size_t len = strlen(name);
    do {
        if (0 == strcmp(r, name)) return r+len+1;

        z = memchr(r, '\0', (size_t)(end-r));
        if (NULL == z) return NULL;
        z = memchr(z+1, '\0', (size_t)(end-r));
        if (NULL == z) return NULL;
        r = z+1;
    } while (r < end);
    return NULL;
}


static void
scgi_process (const int fd)
{
    ssize_t rd = 0, offset = 0;
    char *p = NULL, *r;
    unsigned long rlen;
    long long cl;

    assert(fd == STDOUT_FILENO); /*(required for response sent with printf())*/
    fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);

    do {
        struct pollfd pfd = { fd, POLLIN, 0 };
        switch (poll(&pfd, 1, 10)) { /* 10ms timeout */
          default: /* 1; the only pfd has revents */
            break;
          case -1: /* error */
          case  0: /* timeout */
            pfd.revents |= POLLERR;
            break;
        }
        if (!(pfd.revents & POLLIN))
            break;
        do {
            rd = recv(fd, buf+offset, sizeof(buf)-offset, MSG_DONTWAIT);
        } while (rd < 0 && errno == EINTR);
        if (rd > 0)
            offset += rd;
        else if (0 == rd) {
            p = memchr(buf, ':', offset);
            break;
        }
        else if (errno == EAGAIN || errno == EWOULDBLOCK)
            continue;
        else
            break;
    } while (NULL == (p = memchr(buf,':',offset)) && offset < 21);
    if (NULL == p)
        return; /* timeout or error receiving start of netstring */
    rlen = strtoul(buf, &p, 10);
    if (*buf == '-' || *p != ':' || p == buf || rlen == ULONG_MAX)
        return; /* invalid netstring (and rlen == ULONG_MAX is too long)*/
    if (rlen > sizeof(buf) - (p - buf) - 2)
        return; /* netstring longer than arbitrary limit we accept here */
    rlen += (p - buf) + 2;

    while ((ssize_t)rlen < offset) {
        struct pollfd pfd = { fd, POLLIN, 0 };
        switch (poll(&pfd, 1, 10)) { /* 10ms timeout */
          default: /* 1; the only pfd has revents */
            break;
          case -1: /* error */
          case  0: /* timeout */
            pfd.revents |= POLLERR;
            break;
        }
        if (!(pfd.revents & POLLIN))
            break;
        do {
            rd = recv(fd, buf+offset, sizeof(buf)-offset, MSG_DONTWAIT);
        } while (rd < 0 && errno == EINTR);
        if (rd > 0)
            offset += rd;
        else if (0 == rd)
            break;
        else if (errno == EAGAIN || errno == EWOULDBLOCK)
            continue;
        else
            break;
    }
    if (offset < (ssize_t)rlen)
        return; /* timeout or error receiving netstring */
    if (buf[rlen-1] != ',')
        return; /* invalid netstring */
    rlen -= (p - buf) + 2;
    r = p+1;

    /* not checking for empty headers in SCGI request (empty values allowed) */

    /* SCGI request must contain "SCGI" header with value "1" */
    p = scgi_getenv(r, rlen, "SCGI");
    if (NULL == p || p[0] != '1' || p[1] != '\0')
        return; /* missing or invalid SCGI header */

    /* CONTENT_LENGTH must be first header in SCGI request; always required */
    if (0 != strcmp(r, "CONTENT_LENGTH"))
        return; /* missing CONTENT_LENGTH */

    errno = 0;
    cl = strtoll(r+sizeof("CONTENT_LENGTH"), &p, 10);
    if (*p != '\0' || p == r+sizeof("CONTENT_LENGTH") || cl < 0 || 0 != errno)
        return; /* invalid CONTENT_LENGTH */

    fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) & ~O_NONBLOCK);

    /* read,discard request body (currently ignored in these SCGI unit tests)
     * (make basic effort to read body; ignore any timeouts or errors here) */
    cl -= (offset - (r+rlen+1 - buf));
    while (cl > 0) {
        char x[8192];
        do {
            rd = recv(fd, x, (cl>(long long)sizeof(x)?sizeof(x):(size_t)cl), 0);
        } while (rd < 0 && errno == EINTR);
        if (rd <= 0)
            break;
        cl -= rd;
    }

    /*(similar to fcgi-responder.c:fcgi_process_params())*/
    const char *cdata = NULL;
    if (NULL != (p = scgi_getenv(r, rlen, "QUERY_STRING"))) {
        if (0 == strcmp(p, "lf"))
            cdata = "Status: 200 OK\n\n";
        else if (0 == strcmp(p, "crlf"))
            cdata = "Status: 200 OK\r\n\r\n";
        else if (0 == strcmp(p, "slow-lf")) {
            printf("Status: 200 OK\n");
            fflush(stdout);
            cdata = "\n";
        }
        else if (0 == strcmp(p,"slow-crlf")) {
            printf("Status: 200 OK\r\n");
            fflush(stdout);
            cdata = "\r\n";
        }
        else if (0 == strcmp(p, "die-at-end")) {
            cdata = "Status: 200 OK\r\n\r\n";
            finished = 1;
        }
        else
            cdata = "Status: 200 OK\r\n\r\n";
    }
    else {
        cdata = "Status: 500 Internal Foo\r\n\r\n";
        p = NULL;
    }

    if (cdata) printf("%s", cdata);

    if (NULL == p)
        cdata = NULL;
    else if (0 == strncmp(p, "env=", 4))
        cdata = scgi_getenv(r, rlen, p+4);
    else
        cdata = "test123";

    if (cdata) printf("%s", cdata);

    fflush(stdout);
}


int
main (void)
{
    int fd;
    fcntl(STDIN_FILENO, F_SETFL, fcntl(STDIN_FILENO, F_GETFL) & ~O_NONBLOCK);
    close(STDOUT_FILENO); /*(so that accept() returns fd to STDOUT_FILENO)*/

    do {
        fd = accept(STDIN_FILENO, NULL, NULL);
        if (fd < 0)
            continue;
        assert(fd == STDOUT_FILENO);
        scgi_process(fd);
    } while (fd > 0 ? 0 == close(fd) && !finished : errno == EINTR);

    return 0;
}