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Date:: Mon Feb 1 11:11:43 2021 UTC
Message:: bring the CGI implementation in par with GLV-1.12556
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1 /*
2  * Copyright (c) 2021 Omar Polo <op@omarpolo.com>
3  *
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose with or without fee is hereby granted, provided that the above
6  * copyright notice and this permission notice appear in all copies.
7  *
8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15  */
16 
17 #include <sys/mman.h>
18 #include <sys/stat.h>
19 
20 #include <netdb.h>
21 
22 #include <assert.h>
23 #include <errno.h>
24 #include <fcntl.h>
25 #include <fnmatch.h>
26 #include <limits.h>
27 #include <string.h>
28 
29 #include "gmid.h"
30 
31 int connected_clients;
32 
33 const char *
34 vhost_lang(struct vhost *v, const char *path)
35 {
36 	struct location *loc;
37 
38 	if (v == NULL || path == NULL)
39 		return NULL;
40 
41 	for (loc = &v->locations[1]; loc->match != NULL; ++loc) {
42 		if (!fnmatch(loc->match, path, 0)) {
43 			if (loc->lang != NULL)
44 				return loc->lang;
45 		}
46 	}
47 
48 	return v->locations[0].lang;
49 }
50 
51 const char *
52 vhost_default_mime(struct vhost *v, const char *path)
53 {
54 	struct location *loc;
55 	const char *default_mime = "application/octet-stream";
56 
57 	if (v == NULL || path == NULL)
58 		return default_mime;
59 
60 	for (loc = &v->locations[1]; loc->match != NULL; ++loc) {
61 		if (!fnmatch(loc->match, path, 0)) {
62 			if (loc->default_mime != NULL)
63 				return loc->default_mime;
64 		}
65 	}
66 
67 	if (v->locations[0].default_mime != NULL)
68 		return v->locations[0].default_mime;
69 	return default_mime;
70 }
71 
72 const char *
73 vhost_index(struct vhost *v, const char *path)
74 {
75 	struct location *loc;
76 	const char *index = "index.gmi";
77 
78 	if (v == NULL || path == NULL)
79 		return index;
80 
81 	for (loc = &v->locations[1]; loc->match != NULL; ++loc) {
82 		if (!fnmatch(loc->match, path, 0)) {
83 			if (loc->index != NULL)
84 				return loc->index;
85 		}
86 	}
87 
88 	if (v->locations[0].index != NULL)
89 		return v->locations[0].index;
90 	return index;
91 }
92 
93 int
94 vhost_auto_index(struct vhost *v, const char *path)
95 {
96 	struct location *loc;
97 
98 	if (v == NULL || path == NULL)
99 		return 0;
100 
101 	for (loc = v->locations; loc->match != NULL; ++loc) {
102 		if (!fnmatch(loc->match, path, 0)) {
103 			if (loc->auto_index != 0)
104 				return loc->auto_index == 1;
105 		}
106 	}
107 
108 	return v->locations[0].auto_index == 1;
109 }
110 
111 int
112 check_path(struct client *c, const char *path, int *fd)
113 {
114 	struct stat sb;
115 	const char *p;
116 	int flags;
117 
118 	assert(path != NULL);
119 
120 	if (*path == '\0')
121 		p = ".";
122 	else if (*path == '/')
123 		/* in send_dir we add an initial / (to be
124 		 * redirect-friendly), but here we want to skip it */
125 		p = path+1;
126 	else
127 		p = path;
128 
129 	flags = O_RDONLY | O_NOFOLLOW;
130 
131 	if (*fd == -1 && (*fd = openat(c->host->dirfd, p, flags)) == -1)
132 		return FILE_MISSING;
133 
134 	if (fstat(*fd, &sb) == -1) {
135 		LOGN(c, "failed stat for %s: %s", path, strerror(errno));
136 		return FILE_MISSING;
137 	}
138 
139 	if (S_ISDIR(sb.st_mode))
140 		return FILE_DIRECTORY;
141 
142 	if (sb.st_mode & S_IXUSR)
143 		return FILE_EXECUTABLE;
144 
145 	return FILE_EXISTS;
146 }
147 
148 void
149 open_file(struct pollfd *fds, struct client *c)
150 {
151 	switch (check_path(c, c->iri.path, &c->fd)) {
152 	case FILE_EXECUTABLE:
153 		if (starts_with(c->iri.path, c->host->cgi)) {
154 			start_cgi(c->iri.path, "", fds, c);
155 			return;
156 		}
157 
158 		/* fallthrough */
159 
160 	case FILE_EXISTS:
161 		load_file(fds, c);
162 		return;
163 
164 	case FILE_DIRECTORY:
165 		open_dir(fds, c);
166 		return;
167 
168 	case FILE_MISSING:
169 		if (c->host->cgi != NULL && starts_with(c->iri.path, c->host->cgi)) {
170 			check_for_cgi(fds, c);
171 			return;
172 		}
173 		start_reply(fds, c, NOT_FOUND, "not found");
174 		return;
175 
176 	default:
177 		/* unreachable */
178 		abort();
179 	}
180 }
181 
182 void
183 load_file(struct pollfd *fds, struct client *c)
184 {
185 	if ((c->len = filesize(c->fd)) == -1) {
186 		LOGE(c, "failed to get file size for %s", c->iri.path);
187 		start_reply(fds, c, TEMP_FAILURE, "internal server error");
188 		return;
189 	}
190 
191 	if ((c->buf = mmap(NULL, c->len, PROT_READ, MAP_PRIVATE,
192 		    c->fd, 0)) == MAP_FAILED) {
193 		LOGW(c, "mmap: %s: %s", c->iri.path, strerror(errno));
194 		start_reply(fds, c, TEMP_FAILURE, "internal server error");
195 		return;
196 	}
197 	c->i = c->buf;
198 	c->next = S_SENDING_FILE;
199 	start_reply(fds, c, SUCCESS, mime(c->host, c->iri.path));
200 }
201 
202 /*
203  * the inverse of this algorithm, i.e. starting from the start of the
204  * path + strlen(cgi), and checking if each component, should be
205  * faster.  But it's tedious to write.  This does the opposite: starts
206  * from the end and strip one component at a time, until either an
207  * executable is found or we emptied the path.
208  */
209 void
210 check_for_cgi(struct pollfd *fds, struct client *c)
211 {
212 	char path[PATH_MAX];
213 	char *end;
214 
215 	strlcpy(path, c->iri.path, sizeof(path));
216 	end = strchr(path, '\0');
217 
218 	/* NB: assume CGI is enabled and path matches cgi */
219 
220 	while (end > path) {
221 		/* go up one level.  UNIX paths are simple and POSIX
222 		 * dirname, with its ambiguities on if the given path
223 		 * is changed or not, gives me headaches. */
224 		while (*end != '/')
225 			end--;
226 		*end = '\0';
227 
228 		switch (check_path(c, path, &c->fd)) {
229 		case FILE_EXECUTABLE:
230 			start_cgi(path, end+1, fds, c);
231 			return;
232 		case FILE_MISSING:
233 			break;
234 		default:
235 			goto err;
236 		}
237 
238 		*end = '/';
239 		end--;
240 	}
241 
242 err:
243 	start_reply(fds, c, NOT_FOUND, "not found");
244 	return;
245 }
246 
247 void
248 mark_nonblock(int fd)
249 {
250 	int flags;
251 
252 	if ((flags = fcntl(fd, F_GETFL)) == -1)
253 		fatal("fcntl(F_GETFL): %s", strerror(errno));
254 	if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
255 		fatal("fcntl(F_SETFL): %s", strerror(errno));
256 }
257 
258 void
259 handle_handshake(struct pollfd *fds, struct client *c)
260 {
261 	struct vhost *h;
262 	const char *servname;
263 	const char *parse_err = "unknown error";
264 
265 	switch (tls_handshake(c->ctx)) {
266 	case 0:  /* success */
267 	case -1: /* already handshaked */
268 		break;
269 	case TLS_WANT_POLLIN:
270 		fds->events = POLLIN;
271 		return;
272 	case TLS_WANT_POLLOUT:
273 		fds->events = POLLOUT;
274 		return;
275 	default:
276 		/* unreachable */
277 		abort();
278 	}
279 
280 	servname = tls_conn_servername(c->ctx);
281 	if (!puny_decode(servname, c->domain, sizeof(c->domain), &parse_err)) {
282 		LOGI(c, "%s", parse_err);
283 		goto err;
284 	}
285 
286 	for (h = hosts; h->domain != NULL; ++h) {
287 		if (!fnmatch(h->domain, c->domain, 0))
288 			break;
289 	}
290 
291 	/* LOGD(c, "handshake: SNI: \"%s\"; decoded: \"%s\"; matched: \"%s\"", */
292 	/*     servname != NULL ? servname : "(null)", */
293 	/*     c->domain, */
294 	/*     h->domain != NULL ? h->domain : "(null)"); */
295 
296 	if (h->domain != NULL) {
297 		c->state = S_OPEN;
298 		c->host = h;
299 		handle_open_conn(fds, c);
300 		return;
301 	}
302 
303 err:
304 	if (servname != NULL)
305 		strncpy(c->req, servname, sizeof(c->req));
306 	else
307 		strncpy(c->req, "null", sizeof(c->req));
308 
309 	start_reply(fds, c, BAD_REQUEST, "Wrong/malformed host or missing SNI");
310 }
311 
312 void
313 handle_open_conn(struct pollfd *fds, struct client *c)
314 {
315 	const char *parse_err = "invalid request";
316 	char decoded[DOMAIN_NAME_LEN];
317 
318 	bzero(c->req, sizeof(c->req));
319 	bzero(&c->iri, sizeof(c->iri));
320 
321 	switch (tls_read(c->ctx, c->req, sizeof(c->req)-1)) {
322 	case -1:
323 		LOGE(c, "tls_read: %s", tls_error(c->ctx));
324 		close_conn(fds, c);
325 		return;
326 
327 	case TLS_WANT_POLLIN:
328 		fds->events = POLLIN;
329 		return;
330 
331 	case TLS_WANT_POLLOUT:
332 		fds->events = POLLOUT;
333 		return;
334 	}
335 
336 	if (!trim_req_iri(c->req, &parse_err)
337 	    || !parse_iri(c->req, &c->iri, &parse_err)
338 	    || !puny_decode(c->iri.host, decoded, sizeof(decoded), &parse_err)) {
339 		LOGI(c, "iri parse error: %s", parse_err);
340 		start_reply(fds, c, BAD_REQUEST, "invalid request");
341 		return;
342 	}
343 
344 	if (c->iri.port_no != conf.port
345 	    || strcmp(c->iri.schema, "gemini")
346 	    || strcmp(decoded, c->domain)) {
347 		start_reply(fds, c, PROXY_REFUSED, "won't proxy request");
348 		return;
349 	}
350 
351 	open_file(fds, c);
352 }
353 
354 void
355 start_reply(struct pollfd *pfd, struct client *c, int code, const char *meta)
356 {
357 	char buf[1030];		/* status + ' ' + max reply len + \r\n\0 */
358 	const char *lang;
359 	size_t len;
360 
361 	c->code = code;
362 	c->meta = meta;
363 	c->state = S_INITIALIZING;
364 
365 	lang = vhost_lang(c->host, c->iri.path);
366 
367 	snprintf(buf, sizeof(buf), "%d ", code);
368 	strlcat(buf, meta, sizeof(buf));
369 	if (!strcmp(meta, "text/gemini") && lang != NULL) {
370 		strlcat(buf, "; lang=", sizeof(buf));
371 		strlcat(buf, lang, sizeof(buf));
372 	}
373 
374 	len = strlcat(buf, "\r\n", sizeof(buf));
375 	assert(len < sizeof(buf));
376 
377 	switch (tls_write(c->ctx, buf, len)) {
378 	case -1:
379 		close_conn(pfd, c);
380 		return;
381 	case TLS_WANT_POLLIN:
382 		pfd->events = POLLIN;
383 		return;
384 	case TLS_WANT_POLLOUT:
385 		pfd->events = POLLOUT;
386 		return;
387 	}
388 
389 	log_request(c, buf, sizeof(buf));
390 
391 	/* we don't need a body */
392 	if (c->code != SUCCESS) {
393 		close_conn(pfd, c);
394 		return;
395 	}
396 
397 	/* advance the state machine */
398 	c->state = c->next;
399 	handle(pfd, c);
400 }
401 
402 void
403 start_cgi(const char *spath, const char *relpath,
404     struct pollfd *fds, struct client *c)
405 {
406 	char addr[NI_MAXHOST];
407 	const char *ruser, *cissuer, *chash;
408 	int e;
409 
410 	e = getnameinfo((struct sockaddr*)&c->addr, sizeof(c->addr),
411 	    addr, sizeof(addr),
412 	    NULL, 0,
413 	    NI_NUMERICHOST);
414 	if (e != 0)
415 		goto err;
416 
417 	if (tls_peer_cert_provided(c->ctx)) {
418 		ruser = tls_peer_cert_subject(c->ctx);
419 		cissuer = tls_peer_cert_issuer(c->ctx);
420 		chash = tls_peer_cert_hash(c->ctx);
421 	} else {
422 		ruser = NULL;
423 		cissuer = NULL;
424 		chash = NULL;
425 	}
426 
427 	if (!send_iri(exfd, &c->iri)
428 	    || !send_string(exfd, spath)
429 	    || !send_string(exfd, relpath)
430 	    || !send_string(exfd, addr)
431 	    || !send_string(exfd, ruser)
432 	    || !send_string(exfd, cissuer)
433 	    || !send_string(exfd, chash)
434 	    || !send_vhost(exfd, c->host))
435 		goto err;
436 
437 	close(c->fd);
438 	if ((c->fd = recv_fd(exfd)) == -1) {
439 		start_reply(fds, c, TEMP_FAILURE, "internal server error");
440 		return;
441 	}
442 	c->state = S_SENDING_CGI;
443 	cgi_poll_on_child(fds, c);
444 	c->code = -1;
445 	/* handle_cgi(fds, c); */
446 	return;
447 
448 err:
449 	/* fatal("cannot talk to the executor process: %s", strerror(errno)); */
450 	fatal("cannot talk to the executor process");
451 }
452 
453 void
454 send_file(struct pollfd *fds, struct client *c)
455 {
456 	ssize_t ret, len;
457 
458 	/* ensure the correct state */
459 	c->state = S_SENDING_FILE;
460 
461 	len = (c->buf + c->len) - c->i;
462 
463 	while (len > 0) {
464 		switch (ret = tls_write(c->ctx, c->i, len)) {
465 		case -1:
466 			LOGE(c, "tls_write: %s", tls_error(c->ctx));
467 			close_conn(fds, c);
468 			return;
469 
470 		case TLS_WANT_POLLIN:
471 			fds->events = POLLIN;
472 			return;
473 
474 		case TLS_WANT_POLLOUT:
475 			fds->events = POLLOUT;
476 			return;
477 
478 		default:
479 			c->i += ret;
480 			len -= ret;
481 			break;
482 		}
483 	}
484 
485 	close_conn(fds, c);
486 }
487 
488 void
489 open_dir(struct pollfd *fds, struct client *c)
490 {
491 	size_t len;
492 	int dirfd;
493 	char *before_file;
494 
495 	len = strlen(c->iri.path);
496 	if (len > 0 && !ends_with(c->iri.path, "/")) {
497 		redirect_canonical_dir(fds, c);
498 		return;
499 	}
500 
501 	strlcpy(c->sbuf, "/", sizeof(c->sbuf));
502 	strlcat(c->sbuf, c->iri.path, sizeof(c->sbuf));
503 	if (!ends_with(c->sbuf, "/"))
504 		strlcat(c->sbuf, "/", sizeof(c->sbuf));
505 	before_file = strchr(c->sbuf, '\0');
506 	len = strlcat(c->sbuf, vhost_index(c->host, c->iri.path),
507 	    sizeof(c->sbuf));
508 	if (len >= sizeof(c->sbuf)) {
509 		start_reply(fds, c, TEMP_FAILURE, "internal server error");
510 		return;
511 	}
512 
513 	c->iri.path = c->sbuf;
514 
515 	/* close later unless we have to generate the dir listing */
516 	dirfd = c->fd;
517 	c->fd = -1;
518 
519 	switch (check_path(c, c->iri.path, &c->fd)) {
520 	case FILE_EXECUTABLE:
521 		if (starts_with(c->iri.path, c->host->cgi)) {
522 			start_cgi(c->iri.path, "", fds, c);
523 			break;
524 		}
525 
526 		/* fallthrough */
527 
528 	case FILE_EXISTS:
529                 load_file(fds, c);
530 		break;
531 
532 	case FILE_DIRECTORY:
533 		start_reply(fds, c, TEMP_REDIRECT, c->sbuf);
534 		break;
535 
536 	case FILE_MISSING:
537 		*before_file = '\0';
538 
539 		if (!vhost_auto_index(c->host, c->iri.path)) {
540 			start_reply(fds, c, NOT_FOUND, "not found");
541 			break;
542 		}
543 
544 		c->fd = dirfd;
545 		c->next = S_SENDING_DIR;
546 
547 		if ((c->dir = fdopendir(c->fd)) == NULL) {
548 			LOGE(c, "can't fdopendir(%d) (vhost:%s) %s: %s",
549 			    c->fd, c->host->domain, c->iri.path, strerror(errno));
550 			start_reply(fds, c, TEMP_FAILURE, "internal server error");
551 			return;
552 		}
553 		c->off = 0;
554 
555                 start_reply(fds, c, SUCCESS, "text/gemini");
556 		return;
557 
558 	default:
559 		/* unreachable */
560 		abort();
561 	}
562 
563 	close(dirfd);
564 }
565 
566 void
567 redirect_canonical_dir(struct pollfd *fds, struct client *c)
568 {
569 	size_t len;
570 
571 	strlcpy(c->sbuf, "/", sizeof(c->sbuf));
572 	strlcat(c->sbuf, c->iri.path, sizeof(c->sbuf));
573 	len = strlcat(c->sbuf, "/", sizeof(c->sbuf));
574 
575 	if (len >= sizeof(c->sbuf)) {
576 		start_reply(fds, c, TEMP_FAILURE, "internal server error");
577 		return;
578 	}
579 
580 	start_reply(fds, c, TEMP_REDIRECT, c->sbuf);
581 }
582 
583 int
584 read_next_dir_entry(struct client *c)
585 {
586 	struct dirent *d;
587 
588 	do {
589 		errno = 0;
590 		if ((d = readdir(c->dir)) == NULL) {
591 			if (errno != 0)
592 				LOGE(c, "readdir: %s", strerror(errno));
593 			return 0;
594 		}
595 	} while (!strcmp(d->d_name, "."));
596 
597 	/* XXX: url escape */
598 	snprintf(c->sbuf, sizeof(c->sbuf), "=> %s %s\n",
599 	    d->d_name, d->d_name);
600 	c->len = strlen(c->sbuf);
601 	c->off = 0;
602 
603 	return 1;
604 }
605 
606 void
607 send_directory_listing(struct pollfd *fds, struct client *c)
608 {
609 	ssize_t r;
610 
611 	while (1) {
612 		if (c->len == 0) {
613 			if (!read_next_dir_entry(c))
614 				goto end;
615 		}
616 
617 		while (c->len > 0) {
618 			switch (r = tls_write(c->ctx, c->sbuf + c->off, c->len)) {
619 			case -1:
620 				goto end;
621 
622 			case TLS_WANT_POLLOUT:
623 				fds->events = POLLOUT;
624 				return;
625 
626 			case TLS_WANT_POLLIN:
627 				fds->events = POLLIN;
628 				return;
629 
630 			default:
631 				c->off += r;
632 				c->len -= r;
633 				break;
634 			}
635 		}
636 	}
637 
638 end:
639 	close_conn(fds, c);
640 }
641 
642 void
643 cgi_poll_on_child(struct pollfd *fds, struct client *c)
644 {
645 	int fd;
646 
647 	if (c->waiting_on_child)
648 		return;
649 	c->waiting_on_child = 1;
650 
651 	fds->events = POLLIN;
652 
653 	fd = fds->fd;
654 	fds->fd = c->fd;
655 	c->fd = fd;
656 }
657 
658 void
659 cgi_poll_on_client(struct pollfd *fds, struct client *c)
660 {
661 	int fd;
662 
663 	if (!c->waiting_on_child)
664 		return;
665 	c->waiting_on_child = 0;
666 
667 	fd = fds->fd;
668 	fds->fd = c->fd;
669 	c->fd = fd;
670 }
671 
672 /* handle the read from the child process.  Return like read(2) */
673 static ssize_t
674 read_from_cgi(struct client *c)
675 {
676 	void	*buf;
677 	size_t	 len;
678 	ssize_t	 r;
679 
680 	/* if we haven't read a whole response line, we want to
681 	 * continue reading. */
682 
683 	if (c->code == -1) {
684 		buf = c->sbuf + c->len;
685 		len = sizeof(c->sbuf) - c->len;
686 	} else {
687 		buf = c->sbuf;
688 		len = sizeof(c->sbuf);
689 	}
690 
691 	r = read(c->fd, buf, len);
692 	if (r == 0 || r == -1)
693 		return r;
694 
695 	c->len += r;
696 	c->off = 0;
697 
698 	if (c->code != -1)
699 		return r;
700 
701 	if (strchr(c->sbuf, '\n') || c->len == sizeof(c->sbuf)) {
702 		c->code = 0;
703 		log_request(c, c->sbuf, c->len);
704 	}
705 
706 	return r;
707 }
708 
709 void
710 handle_cgi(struct pollfd *fds, struct client *c)
711 {
712 	ssize_t r;
713 
714 	/* ensure c->fd is the child and fds->fd the client */
715 	cgi_poll_on_client(fds, c);
716 
717 	while (1) {
718 		if (c->code == -1 || c->len == 0) {
719 			switch (r = read_from_cgi(c)) {
720 			case 0:
721 				goto end;
722 
723 			case -1:
724 				if (errno == EAGAIN || errno == EWOULDBLOCK) {
725 					cgi_poll_on_child(fds, c);
726 					return;
727 				}
728 				goto end;
729 			}
730 		}
731 
732 		if (c->code == -1) {
733 			cgi_poll_on_child(fds, c);
734 			return;
735 		}
736 
737 		while (c->len > 0) {
738 			switch (r = tls_write(c->ctx, c->sbuf + c->off, c->len)) {
739 			case -1:
740 				goto end;
741 
742 			case TLS_WANT_POLLOUT:
743 				fds->events = POLLOUT;
744 				return;
745 
746 			case TLS_WANT_POLLIN:
747 				fds->events = POLLIN;
748 				return;
749 
750 			default:
751                                 c->off += r;
752 				c->len -= r;
753 				break;
754 			}
755 		}
756 	}
757 
758 end:
759 	close_conn(fds, c);
760 }
761 
762 void
763 close_conn(struct pollfd *pfd, struct client *c)
764 {
765 	c->state = S_CLOSING;
766 
767 	switch (tls_close(c->ctx)) {
768 	case TLS_WANT_POLLIN:
769 		pfd->events = POLLIN;
770 		return;
771 	case TLS_WANT_POLLOUT:
772 		pfd->events = POLLOUT;
773 		return;
774 	}
775 
776 	connected_clients--;
777 
778 	tls_free(c->ctx);
779 	c->ctx = NULL;
780 
781 	if (c->buf != MAP_FAILED)
782 		munmap(c->buf, c->len);
783 
784 	if (c->fd != -1)
785 		close(c->fd);
786 
787 	if (c->dir != NULL)
788 		closedir(c->dir);
789 
790 	close(pfd->fd);
791 	pfd->fd = -1;
792 }
793 
794 void
795 do_accept(int sock, struct tls *ctx, struct pollfd *fds, struct client *clients)
796 {
797 	int i, fd;
798 	struct sockaddr_storage addr;
799 	socklen_t len;
800 
801 	len = sizeof(addr);
802 	if ((fd = accept(sock, (struct sockaddr*)&addr, &len)) == -1) {
803 		if (errno == EWOULDBLOCK)
804 			return;
805 		fatal("accept: %s", strerror(errno));
806 	}
807 
808 	mark_nonblock(fd);
809 
810 	for (i = 0; i < MAX_USERS; ++i) {
811 		if (fds[i].fd == -1) {
812 			bzero(&clients[i], sizeof(struct client));
813 			if (tls_accept_socket(ctx, &clients[i].ctx, fd) == -1)
814 				break; /* goodbye fd! */
815 
816 			fds[i].fd = fd;
817 			fds[i].events = POLLIN;
818 
819 			clients[i].state = S_HANDSHAKE;
820 			clients[i].next = S_SENDING_FILE;
821 			clients[i].fd = -1;
822 			clients[i].waiting_on_child = 0;
823 			clients[i].buf = MAP_FAILED;
824 			clients[i].dir = NULL;
825 			clients[i].addr = addr;
826 
827 			connected_clients++;
828 			return;
829 		}
830 	}
831 
832 	close(fd);
833 }
834 
835 void
836 handle(struct pollfd *fds, struct client *client)
837 {
838 	switch (client->state) {
839 	case S_HANDSHAKE:
840 		handle_handshake(fds, client);
841 		break;
842 
843 	case S_OPEN:
844                 handle_open_conn(fds, client);
845 		break;
846 
847 	case S_INITIALIZING:
848 		start_reply(fds, client, client->code, client->meta);
849                 break;
850 
851 	case S_SENDING_FILE:
852 		send_file(fds, client);
853 		break;
854 
855 	case S_SENDING_DIR:
856 		send_directory_listing(fds, client);
857 		break;
858 
859 	case S_SENDING_CGI:
860 		handle_cgi(fds, client);
861 		break;
862 
863 	case S_CLOSING:
864 		close_conn(fds, client);
865 		break;
866 
867 	default:
868 		/* unreachable */
869 		abort();
870 	}
871 }
872 
873 void
874 loop(struct tls *ctx, int sock4, int sock6)
875 {
876 	int i;
877 	struct client clients[MAX_USERS];
878 	struct pollfd fds[MAX_USERS];
879 
880 	connected_clients = 0;
881 
882 	for (i = 0; i < MAX_USERS; ++i) {
883 		fds[i].fd = -1;
884 		fds[i].events = POLLIN;
885 		bzero(&clients[i], sizeof(struct client));
886 	}
887 
888 	fds[0].fd = sock4;
889 	fds[1].fd = sock6;
890 
891 	for (;;) {
892 		if (poll(fds, MAX_USERS, INFTIM) == -1) {
893 			if (errno == EINTR) {
894                                 fprintf(stderr, "connected clients: %d\n",
895 				    connected_clients);
896 				continue;
897 			}
898 			fatal("poll: %s", strerror(errno));
899 		}
900 
901 		for (i = 0; i < MAX_USERS; i++) {
902 			if (fds[i].revents == 0)
903 				continue;
904 
905 			if (fds[i].revents & (POLLERR|POLLNVAL))
906 				fatal("bad fd %d: %s", fds[i].fd,
907 				    strerror(errno));
908 
909 			if (fds[i].revents & POLLHUP) {
910 				/* fds[i] may be the fd of the stdin
911 				 * of a cgi script that has exited. */
912 				if (!clients[i].waiting_on_child) {
913 					close_conn(&fds[i], &clients[i]);
914 					continue;
915 				}
916 			}
917 
918 			if (fds[i].fd == sock4)
919 				do_accept(sock4, ctx, fds, clients);
920 			else if (fds[i].fd == sock6)
921 				do_accept(sock6, ctx, fds, clients);
922 			else
923 				handle(&fds[i], &clients[i]);
924 		}
925 	}
926 }