gmid/gmid.c

/*
 * Copyright (c) 2020 Omar Polo <op@omarpolo.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/stat.h>

#include <assert.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <string.h>

#include "gmid.h"

#define LOG(priority, c, fmt, ...)					\
	do {								\
		char buf[INET_ADDRSTRLEN];				\
		if (inet_ntop((c)->af, &(c)->addr,			\
		    buf, sizeof(buf)) == NULL)				\
			FATAL("inet_ntop: %s", strerror(errno));	\
		if (foreground)						\
			fprintf(stderr,					\
			    "%s " fmt "\n", buf, __VA_ARGS__);		\
		else							\
			syslog((priority) | LOG_DAEMON,			\
			    "%s " fmt, buf, __VA_ARGS__);		\
	} while (0)

#define LOGE(c, fmt, ...) LOG(LOG_ERR,    c, fmt, __VA_ARGS__)
#define LOGN(c, fmt, ...) LOG(LOG_NOTICE, c, fmt, __VA_ARGS__)
#define LOGI(c, fmt, ...) LOG(LOG_INFO,   c, fmt, __VA_ARGS__)
#define LOGD(c, fmt, ...) LOG(LOG_DEBUG,  c, fmt, __VA_ARGS__)

#define FATAL(fmt, ...)							\
	do {								\
		if (foreground)						\
			fprintf(stderr, fmt "\n", __VA_ARGS__);		\
		else							\
			syslog(LOG_DAEMON | LOG_CRIT,			\
			    fmt, __VA_ARGS__);				\
		exit(1);						\
	} while (0)

const char *dir, *cgi;
int dirfd;
int port;
int foreground;
int connected_clients;

struct etm {			/* file extension to mime */
	const char	*mime;
	const char	*ext;
} filetypes[] = {
	{"application/pdf",	"pdf"},

	{"image/gif",		"gif"},
	{"image/jpeg",		"jpg"},
	{"image/jpeg",		"jpeg"},
	{"image/png",		"png"},
	{"image/svg+xml",	"svg"},

	{"text/gemini",		"gemini"},
	{"text/gemini",		"gmi"},
	{"text/markdown",	"markdown"},
	{"text/markdown",	"md"},
	{"text/plain",		"txt"},
	{"text/xml",		"xml"},

	{NULL, NULL}
};

static inline void
safe_setenv(const char *name, const char *val)
{
	if (val == NULL)
		val = "";
	setenv(name, val, 1);
}

void
sig_handler(int sig)
{
	(void)sig;
}

int
starts_with(const char *str, const char *prefix)
{
	size_t i;

	for (i = 0; prefix[i] != '\0'; ++i)
		if (str[i] != prefix[i])
			return 0;
	return 1;
}

int
start_reply(struct pollfd *pfd, struct client *client, int code, const char *reason)
{
	char buf[1030] = {0}; 	/* status + ' ' + max reply len + \r\n\0 */
	int len;
	int ret;

	client->code = code;
	client->meta = reason;
	client->state = S_INITIALIZING;

	len = snprintf(buf, sizeof(buf), "%d %s\r\n", code, reason);
	assert(len < (int)sizeof(buf));
	ret = tls_write(client->ctx, buf, len);
	if (ret == TLS_WANT_POLLIN) {
		pfd->events = POLLIN;
		return 0;
	}

	if (ret == TLS_WANT_POLLOUT) {
		pfd->events = POLLOUT;
		return 0;
	}

	return 1;
}

ssize_t
filesize(int fd)
{
	ssize_t len;

	if ((len = lseek(fd, 0, SEEK_END)) == -1)
		return -1;
	if (lseek(fd, 0, SEEK_SET) == -1)
		return -1;
	return len;
}

const char *
path_ext(const char *path)
{
	const char *end;

	end = path + strlen(path)-1; /* the last byte before the NUL */
	for (; end != path; --end) {
		if (*end == '.')
			return end+1;
		if (*end == '/')
			break;
	}

	return NULL;
}

const char *
mime(const char *path)
{
	const char *ext, *def = "application/octet-stream";
	struct etm *t;

	if ((ext = path_ext(path)) == NULL)
		return def;

	for (t = filetypes; t->mime != NULL; ++t)
		if (!strcmp(ext, t->ext))
			return t->mime;

	return def;
}

int
check_path(struct client *c, const char *path, int *fd)
{
	struct stat sb;

	assert(path != NULL);
	if ((*fd = openat(dirfd, *path ? path : ".",
		    O_RDONLY | O_NOFOLLOW | O_CLOEXEC)) == -1) {
		return FILE_MISSING;
	}

	if (fstat(*fd, &sb) == -1) {
		LOGN(c, "failed stat for %s: %s", path, strerror(errno));
		return FILE_MISSING;
	}

	if (S_ISDIR(sb.st_mode))
		return FILE_DIRECTORY;

	if (sb.st_mode & S_IXUSR)
		return FILE_EXECUTABLE;

	return FILE_EXISTS;
}

/*
 * the inverse of this algorithm, i.e. starting from the start of the
 * path + strlen(cgi), and checking if each component, should be
 * faster.  But it's tedious to write.  This does the opposite: starts
 * from the end and strip one component at a time, until either an
 * executable is found or we emptied the path.
 */
int
check_for_cgi(char *path, char *query, struct pollfd *fds, struct client *c)
{
	char *end;
	end = strchr(path, '\0');

	/* NB: assume CGI is enabled and path matches cgi */

	while (end > path) {
		/* go up one level.  UNIX paths are simple and POSIX
		 * dirname, with its ambiguities on if the given path
		 * is changed or not, gives me headaches. */
		while (*end != '/')
			end--;
		*end = '\0';

		switch (check_path(c, path, &c->fd)) {
		case FILE_EXECUTABLE:
			return start_cgi(path, end+1, query, fds,c);
		case FILE_MISSING:
			break;
		default:
			goto err;
		}

		*end = '/';
		end--;
	}

err:
	if (!start_reply(fds, c, NOT_FOUND, "not found"))
		return 0;
	goodbye(fds, c);
	return 0;
}


int
open_file(char *fpath, char *query, struct pollfd *fds, struct client *c)
{
	switch (check_path(c, fpath, &c->fd)) {
	case FILE_EXECUTABLE:
		if (cgi != NULL && starts_with(fpath, cgi))
			return start_cgi(fpath, "", query, fds, c);

		/* fallthrough */

	case FILE_EXISTS:
		if ((c->len = filesize(c->fd)) == -1) {
			LOGE(c, "failed to get file size for %s", fpath);
			goodbye(fds, c);
			return 0;
		}

		if ((c->buf = mmap(NULL, c->len, PROT_READ, MAP_PRIVATE,
			    c->fd, 0)) == MAP_FAILED) {
			warn("mmap: %s", fpath);
			goodbye(fds, c);
			return 0;
		}
		c->i = c->buf;
		return start_reply(fds, c, SUCCESS, mime(fpath));

	case FILE_DIRECTORY:
		LOGD(c, "%s is a directory, trying %s/index.gmi", fpath, fpath);
		close(c->fd);
		c->fd = -1;
		send_dir(fpath, fds, c);
		return 0;

	case FILE_MISSING:
		if (cgi != NULL && starts_with(fpath, cgi))
			return check_for_cgi(fpath, query, fds, c);

		if (!start_reply(fds, c, NOT_FOUND, "not found"))
			return 0;
		goodbye(fds, c);
		return 0;

	default:
		/* unreachable */
		abort();
	}
}

int
start_cgi(const char *spath, const char *relpath, const char *query,
    struct pollfd *fds, struct client *c)
{
	pid_t pid;
	int p[2]; 		/* read end, write end */

	if (pipe(p) == -1)
		goto err;

	switch (pid = fork()) {
	case -1:
		goto err;

	case 0: { 		/* child */
		char *ex, *requri, *portno;
		char addr[INET_ADDRSTRLEN];
		char *argv[] = { NULL, NULL, NULL };

		close(p[0]);
		if (dup2(p[1], 1) == -1)
			goto childerr;

		if (inet_ntop(c->af, &c->addr, addr, sizeof(addr)) == NULL)
			goto childerr;

		if (asprintf(&portno, "%d", port) == -1)
			goto childerr;

		if (asprintf(&ex, "%s/%s", dir, spath) == -1)
			goto childerr;

		if (asprintf(&requri, "%s%s%s", spath,
		    *relpath == '\0' ? "" : "/",
		    relpath) == -1)
			goto childerr;

		argv[0] = argv[1] = ex;

		/* fix the env */
		safe_setenv("GATEWAY_INTERFACE", "CGI/1.1");
		safe_setenv("SERVER_SOFTWARE", "gmid");
		safe_setenv("SERVER_PORT", portno);
		/* setenv("SERVER_NAME", "", 1); */
		safe_setenv("SCRIPT_NAME", spath);
		safe_setenv("SCRIPT_EXECUTABLE", ex);
		safe_setenv("REQUEST_URI", requri);
		safe_setenv("REQUEST_RELATIVE", relpath);
		safe_setenv("QUERY_STRING", query);
		safe_setenv("REMOTE_HOST", addr);
		safe_setenv("REMOTE_ADDR", addr);
		safe_setenv("DOCUMENT_ROOT", dir);

		if (tls_peer_cert_provided(c->ctx)) {
			safe_setenv("AUTH_TYPE", "Certificate");
			safe_setenv("REMOTE_USER", tls_peer_cert_subject(c->ctx));
			safe_setenv("TLS_CLIENT_ISSUER", tls_peer_cert_issuer(c->ctx));
			safe_setenv("TLS_CLIENT_HASH", tls_peer_cert_hash(c->ctx));
		}

		execvp(ex, argv);
		goto childerr;
	}

	default:		/* parent */
		close(p[1]);
		close(c->fd);
		c->fd = p[0];
		c->child = pid;
		mark_nonblock(c->fd);
		c->state = S_SENDING;
		handle_cgi(fds, c);
		return 0;
	}

err:
	if (!start_reply(fds, c, TEMP_FAILURE, "internal server error"))
		return 0;
	goodbye(fds, c);
	return 0;

childerr:
	dprintf(p[1], "%d internal server error\r\n", TEMP_FAILURE);
	close(p[1]);
	_exit(1);
}

void
cgi_poll_on_child(struct pollfd *fds, struct client *c)
{
	int fd;

	if (c->waiting_on_child)
		return;
	c->waiting_on_child = 1;

	fds->events = POLLIN;

	fd = fds->fd;
	fds->fd = c->fd;
	c->fd = fd;
}

void
cgi_poll_on_client(struct pollfd *fds, struct client *c)
{
	int fd;

	if (!c->waiting_on_child)
		return;
	c->waiting_on_child = 0;

	fd = fds->fd;
	fds->fd = c->fd;
	c->fd = fd;
}

void
handle_cgi(struct pollfd *fds, struct client *c)
{
	ssize_t r;

	/* ensure c->fd is the child and fds->fd the client */
	cgi_poll_on_client(fds, c);

	while (1) {
		if (c->len == 0) {
			if ((r = read(c->fd, c->sbuf, sizeof(c->sbuf))) == 0)
				goto end;
			if (r == -1) {
				if (errno == EAGAIN || errno == EWOULDBLOCK) {
					cgi_poll_on_child(fds, c);
					return;
				}
                                goto end;
			}
			c->len = r;
			c->off = 0;
		}

		while (c->len > 0) {
			switch (r = tls_write(c->ctx, c->sbuf + c->off, c->len)) {
			case -1:
				goto end;

			case TLS_WANT_POLLOUT:
				fds->events = POLLOUT;
				return;

			case TLS_WANT_POLLIN:
				fds->events = POLLIN;
				return;

			default:
                                c->off += r;
				c->len -= r;
				break;
			}
		}
	}

end:
	goodbye(fds, c);
}

void
send_file(char *path, char *query, struct pollfd *fds, struct client *c)
{
	ssize_t ret, len;

	if (c->fd == -1) {
		if (!open_file(path, query, fds, c))
			return;
		c->state = S_SENDING;
	}

	len = (c->buf + c->len) - c->i;

	while (len > 0) {
		switch (ret = tls_write(c->ctx, c->i, len)) {
		case -1:
			LOGE(c, "tls_write: %s", tls_error(c->ctx));
			goodbye(fds, c);
			return;

		case TLS_WANT_POLLIN:
			fds->events = POLLIN;
			return;

		case TLS_WANT_POLLOUT:
			fds->events = POLLOUT;
			return;

		default:
			c->i += ret;
			len -= ret;
			break;
		}
	}

	goodbye(fds, c);
}

void
send_dir(char *path, struct pollfd *fds, struct client *client)
{
	char fpath[PATHBUF];
	size_t len;

	bzero(fpath, PATHBUF);

	if (path[0] != '.')
		fpath[0] = '.';

	/* this cannot fail since sizeof(fpath) > maxlen of path */
	strlcat(fpath, path, PATHBUF);
	len = strlen(fpath);

	/* add a trailing / in case. */
	if (fpath[len-1] != '/') {
		fpath[len] = '/';
	}

	strlcat(fpath, "index.gmi", sizeof(fpath));

	send_file(fpath, NULL, fds, client);
}

void
handle(struct pollfd *fds, struct client *client)
{
	char buf[GEMINI_URL_LEN];
	const char *parse_err;
	struct uri uri;

	switch (client->state) {
	case S_OPEN:
		bzero(buf, GEMINI_URL_LEN);
		switch (tls_read(client->ctx, buf, sizeof(buf)-1)) {
		case -1:
			LOGE(client, "tls_read: %s", tls_error(client->ctx));
			goodbye(fds, client);
			return;

		case TLS_WANT_POLLIN:
			fds->events = POLLIN;
			return;

		case TLS_WANT_POLLOUT:
			fds->events = POLLOUT;
			return;
		}

		parse_err = "invalid request";
		if (!trim_req_uri(buf) || !parse_uri(buf, &uri, &parse_err)) {
			if (!start_reply(fds, client, BAD_REQUEST, parse_err))
				return;
			goodbye(fds, client);
			return;
		}

		LOGI(client, "GET %s%s%s",
		    *uri.path ? uri.path : "/",
		    *uri.query ? "?" : "",
		    *uri.query ? uri.query : "");

		send_file(uri.path, uri.query, fds, client);
		break;

	case S_INITIALIZING:
		if (!start_reply(fds, client, client->code, client->meta))
			return;

		if (client->code != SUCCESS) {
			/* we don't need a body */
			goodbye(fds, client);
			return;
		}

		client->state = S_SENDING;

		/* fallthrough */

	case S_SENDING:
		if (client->child != -1)
			handle_cgi(fds, client);
		else
			send_file(NULL, NULL, fds, client);
		break;

	case S_CLOSING:
		goodbye(fds, client);
		break;

	default:
		/* unreachable */
		abort();
	}
}

void
mark_nonblock(int fd)
{
	int flags;

	if ((flags = fcntl(fd, F_GETFL)) == -1)
		FATAL("fcntl(F_GETFL): %s", strerror(errno));
	if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
		FATAL("fcntl(F_SETFL): %s", strerror(errno));
}

int
make_socket(int port, int family)
{
	int sock, v;
	struct sockaddr_in addr4;
	struct sockaddr_in6 addr6;
	struct sockaddr *addr;
	socklen_t len;

        switch (family) {
	case AF_INET:
		bzero(&addr4, sizeof(addr4));
		addr4.sin_family = family;
		addr4.sin_port = htons(port);
		addr4.sin_addr.s_addr = INADDR_ANY;
		addr = (struct sockaddr*)&addr4;
		len = sizeof(addr4);
		break;

	case AF_INET6:
		bzero(&addr6, sizeof(addr6));
		addr6.sin6_family = AF_INET6;
		addr6.sin6_port = htons(port);
		addr6.sin6_addr = in6addr_any;
		addr = (struct sockaddr*)&addr6;
		len = sizeof(addr6);
		break;

	default:
		/* unreachable */
		abort();
	}

	if ((sock = socket(family, SOCK_STREAM, 0)) == -1)
		FATAL("socket: %s", strerror(errno));

	v = 1;
	if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &v, sizeof(v)) == -1)
		FATAL("setsockopt(SO_REUSEADDR): %s", strerror(errno));

	v = 1;
	if (setsockopt(sock, SOL_SOCKET, SO_REUSEPORT, &v, sizeof(v)) == -1)
		FATAL("setsockopt(SO_REUSEPORT): %s", strerror(errno));

	mark_nonblock(sock);

	if (bind(sock, addr, len) == -1)
		FATAL("bind: %s", strerror(errno));

	if (listen(sock, 16) == -1)
		FATAL("listen: %s", strerror(errno));

	return sock;
}

void
do_accept(int sock, struct tls *ctx, struct pollfd *fds, struct client *clients)
{
	int i, fd;
	struct sockaddr_in addr;
	socklen_t len;

	len = sizeof(addr);
	if ((fd = accept(sock, (struct sockaddr*)&addr, &len)) == -1) {
		if (errno == EWOULDBLOCK)
			return;
		FATAL("accept: %s", strerror(errno));
	}

	mark_nonblock(fd);

	for (i = 0; i < MAX_USERS; ++i) {
		if (fds[i].fd == -1) {
			bzero(&clients[i], sizeof(struct client));
			if (tls_accept_socket(ctx, &clients[i].ctx, fd) == -1)
				break; /* goodbye fd! */

			fds[i].fd = fd;
			fds[i].events = POLLIN;

			clients[i].state = S_OPEN;
			clients[i].fd = -1;
			clients[i].child = -1;
			clients[i].buf = MAP_FAILED;
			clients[i].af = AF_INET;
			clients[i].addr = addr.sin_addr;

			connected_clients++;
			return;
		}
	}

	close(fd);
}

void
goodbye(struct pollfd *pfd, struct client *c)
{
	ssize_t ret;

	c->state = S_CLOSING;

	ret = tls_close(c->ctx);
	if (ret == TLS_WANT_POLLIN) {
		pfd->events = POLLIN;
		return;
	}
	if (ret == TLS_WANT_POLLOUT) {
		pfd->events = POLLOUT;
		return;
	}

	connected_clients--;

	tls_free(c->ctx);
	c->ctx = NULL;

	if (c->buf != MAP_FAILED)
		munmap(c->buf, c->len);

	if (c->fd != -1)
		close(c->fd);

	close(pfd->fd);
	pfd->fd = -1;
}

void
loop(struct tls *ctx, int sock)
{
	int i;
	struct client clients[MAX_USERS];
	struct pollfd fds[MAX_USERS];

	for (i = 0; i < MAX_USERS; ++i) {
		fds[i].fd = -1;
		fds[i].events = POLLIN;
		bzero(&clients[i], sizeof(struct client));
	}

	fds[0].fd = sock;

	for (;;) {
		if (poll(fds, MAX_USERS, INFTIM) == -1) {
			if (errno == EINTR) {
                                warnx("connected clients: %d",
				    connected_clients);
				continue;
			}
			FATAL("poll: %s", strerror(errno));
		}

		for (i = 0; i < MAX_USERS; i++) {
			if (fds[i].revents == 0)
				continue;

			if (fds[i].revents & (POLLERR|POLLNVAL))
				FATAL("bad fd %d: %s", fds[i].fd,
				    strerror(errno));

			if (fds[i].revents & POLLHUP) {
				/* fds[i] may be the fd of the stdin
				 * of a cgi script that has exited. */
				if (!clients[i].waiting_on_child) {
					goodbye(&fds[i], &clients[i]);
					continue;
				}
			}

			if (i == 0) { /* new client */
				do_accept(sock, ctx, fds, clients);
				continue;
			}

			handle(&fds[i], &clients[i]);
		}
	}
}

char *
absolutify_path(const char *path)
{
	char *wd, *r;

	if (*path == '/')
		return strdup(path);

	wd = getwd(NULL);
	if (asprintf(&r, "%s/%s", wd, path) == -1)
		err(1, "asprintf");
	free(wd);
	return r;
}

void
usage(const char *me)
{
	fprintf(stderr,
	    "USAGE: %s [-h] [-c cert.pem] [-d docs] [-k key.pem] "
	    "[-l logfile] [-p port] [-x cgi-bin]\n",
	    me);
}

int
main(int argc, char **argv)
{
	const char *cert = "cert.pem", *key = "key.pem";
	struct tls *ctx = NULL;
	struct tls_config *conf;
	int sock, ch;
	connected_clients = 0;

	if ((dir = absolutify_path("docs")) == NULL)
		err(1, "absolutify_path");

	cgi = NULL;
	port = 1965;
	foreground = 0;

	while ((ch = getopt(argc, argv, "c:d:fhk:p:x:")) != -1) {
		switch (ch) {
		case 'c':
			cert = optarg;
			break;

		case 'd':
			free((char*)dir);
			if ((dir = absolutify_path(optarg)) == NULL)
				err(1, "absolutify_path");
			break;

		case 'f':
			foreground = 1;
			break;

		case 'h':
			usage(*argv);
			return 0;

		case 'k':
			key = optarg;
			break;

		case 'p': {
			char *ep;
			long lval;

			errno = 0;
			lval = strtol(optarg, &ep, 10);
			if (optarg[0] == '\0' || *ep != '\0')
				err(1, "not a number: %s", optarg);
			if (lval < 0 || lval > UINT16_MAX)
				err(1, "port number out of range: %s", optarg);
			port = lval;
			break;
		}

		case 'x':
			cgi = optarg;
			break;

		default:
			usage(*argv);
			return 1;
		}
	}

	signal(SIGPIPE, SIG_IGN);
	signal(SIGCHLD, SIG_IGN);

#ifdef SIGINFO
	signal(SIGINFO, sig_handler);
#endif
	signal(SIGUSR2, sig_handler);

	if (!foreground)
		signal(SIGHUP, SIG_IGN);

	if ((conf = tls_config_new()) == NULL)
		err(1, "tls_config_new");

	/* optionally accept client certs, but don't try to verify them */
	tls_config_verify_client_optional(conf);
	tls_config_insecure_noverifycert(conf);

	if (tls_config_set_protocols(conf,
	    TLS_PROTOCOL_TLSv1_2 | TLS_PROTOCOL_TLSv1_3) == -1)
		err(1, "tls_config_set_protocols");

	if (tls_config_set_cert_file(conf, cert) == -1)
		err(1, "tls_config_set_cert_file: %s", cert);

	if (tls_config_set_key_file(conf, key) == -1)
		err(1, "tls_config_set_key_file: %s", key);

	if ((ctx = tls_server()) == NULL)
		err(1, "tls_server");

	if (tls_configure(ctx, conf) == -1)
		errx(1, "tls_configure: %s", tls_error(ctx));

	sock = make_socket(port, AF_INET);

	if ((dirfd = open(dir, O_RDONLY | O_DIRECTORY)) == -1)
		err(1, "open: %s", dir);

	if (!foreground && daemon(0, 1) == -1)
		exit(1);

	if (unveil(dir, "rx") == -1)
		err(1, "unveil");

	if (pledge("stdio rpath inet proc exec", NULL) == -1)
		err(1, "pledge");

	/* drop proc and exec if cgi isn't enabled */
	if (cgi == NULL && pledge("stdio rpath inet", NULL) == -1)
		err(1, "pledge");

	loop(ctx, sock);

	close(sock);
	tls_free(ctx);
	tls_config_free(conf);
}