3 * Background reverse name resolution
5 * (c) 1999 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of the mLib utilities library.
12 * mLib is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Library General Public License as
14 * published by the Free Software Foundation; either version 2 of the
15 * License, or (at your option) any later version.
17 * mLib is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Library General Public License for more details.
22 * You should have received a copy of the GNU Library General Public
23 * License along with mLib; if not, write to the Free
24 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
28 /*----- Header files ------------------------------------------------------*/
38 #include <sys/types.h>
43 #include <sys/socket.h>
44 #include <netinet/in.h>
45 #include <arpa/inet.h>
54 /*----- Magic numbers -----------------------------------------------------*/
56 #define BRES_MAX 15 /* Maximum number of resolvers */
57 #define BRES_IDLE 60 /* Lifetime of an idle resolver */
59 /*----- Static variables --------------------------------------------------*/
61 #ifndef BRES_STANDALONE
63 static bres_server servers[BRES_MAX]; /* Statically allocated servers */
65 #define FREE ((bres_server *)&freelist)
66 static struct { bres_server *next, *prev; } freelist = { FREE, FREE };
68 #define QUEUE ((bres_client *)&queue)
69 static struct { bres_client *next, *prev; } queue = { QUEUE, QUEUE };
71 static sel_state *sel;
73 static const char *server = 0;
77 /*----- Background resolver protocol --------------------------------------*/
79 /* --- Requests and responses --- *
81 * There are two types of requests: name and addr, corresponding to the
82 * standard @gethostbyname@ and @gethostbyaddr@ calls. There are two types
83 * of responses too: a positive response consists of an encoded equivalent of
84 * a @struct hostent@ structure containing the requested information; a
85 * negative response consists of an @h_errno@ value explaining the problem.
88 #define BRES_BYNAME 0 /* Request: resolve given name */
89 #define BRES_BYADDR 1 /* Request: resolve given address */
91 #define BRES_HOSTENT 0 /* Response: resolved ok */
92 #define BRES_ERROR 1 /* Response: resolution failed */
94 /* --- Encodings --- *
96 * A string is encoded as a @size_t@ length followed by the actual data. The
97 * null terminator is not transmitted.
99 * Addresses for resolution are transmitted as raw @struct in_addr@
102 * A @hostent@ structure is transmitted as a header containing fixed-size
103 * information, followed by the official name, an array of aliases, and an
104 * array of addresses. The number of items in the arrays is specified in the
107 * The implementation assumes that a complete request or reply is always
108 * sent. Undesirable blocking will occur if this is not the case. Both ends
109 * are assumed to trust each other. A protocol failure results in the child
110 * in question being terminated.
113 typedef struct hostskel {
120 /* --- @doread@, @dowrite@ --- *
122 * Arguments: @int fd@ = file descriptor
123 * @void *buf@ = buffer for data
124 * @size_t sz@ = size of data
126 * Returns: Zero if successful, nonzero otherwise.
128 * Use: Reads or writes a chunk of data. @EINTR@ errors are retried;
129 * incomplete reads and writes are continued from where they
130 * left off. End-of-file is considered an I/O error.
133 static int doread(int fd, void *buf, size_t sz)
137 int r = read(fd, p, sz);
152 static int dowrite(int fd, const void *buf, size_t sz)
156 int r = write(fd, p, sz);
171 /* --- @getstring@ --- *
173 * Arguments: @int fd@ = file descriptor to read
175 * Returns: String in heap-allocated block, or a null pointer.
177 * Use: Decodes a string.
180 static char *getstring(int fd)
185 if (doread(fd, &sz, sizeof(sz)) || (p = malloc(sz + 1)) == 0)
187 if (doread(fd, p, sz)) {
195 /* --- @putstring@ --- *
197 * Arguments: @int fd@ = file descriptor to write on
198 * @const char *p@ = pointer to string to write
200 * Returns: Zero if successful.
202 * Use: Encodes a string.
205 static int putstring(int fd, const char *p)
207 size_t sz = strlen(p);
208 if (dowrite(fd, &sz, sizeof(sz)) || dowrite(fd, p, sz))
213 /* --- @gethost@ --- *
215 * Arguments: @int fd@ = file descriptor to read
217 * Returns: Pointer to heap-allocated @struct hostent@, or null.
219 * Use: Decodes a host structure. The resulting structure is all in
220 * one big heap block.
223 #ifndef BRES_STANDALONE
225 static struct hostent *gethost(int fd)
232 /* --- Read the skeleton structure --- */
234 if (doread(fd, &hsk, sizeof(hsk)))
237 /* --- Read the hostname and alias strings --- *
239 * Count the length of the strings as we go.
244 sizeof(struct hostent) +
245 hsk.naddr * hsk.addrsz +
246 (hsk.naddr + hsk.nalias + 2) * sizeof(char *);
248 /* --- Read the primary host name --- */
250 if ((name = getstring(fd)) == 0)
252 sz += strlen(name) + 1;
254 /* --- Read in the alias names --- */
258 if ((alias = malloc(hsk.nalias * sizeof(char *))) == 0)
260 for (i = 0; i < hsk.nalias; i++)
262 for (i = 0; i < hsk.nalias; i++) {
263 if ((alias[i] = getstring(fd)) == 0)
265 sz += strlen(alias[i]) + 1;
269 /* --- Allocate the output structure --- */
271 if ((h = malloc(sz)) == 0)
275 /* --- Fill in the base structure --- */
277 h->h_addrtype = hsk.addrtype;
278 h->h_length = hsk.addrsz;
280 /* --- Start putting everything else in --- */
283 char **p = (char **)(h + 1);
284 char *a = (char *)(p + hsk.nalias + hsk.naddr + 2);
287 /* --- Start with the address table --- */
290 if (doread(fd, a, hsk.naddr * hsk.addrsz))
292 for (i = 0; i < hsk.naddr; i++) {
298 /* --- Finally copy the strings over --- */
300 #define PUT(_p) do { \
301 size_t _len = strlen(_p) + 1; \
302 memcpy(a, (_p), _len); \
310 for (i = 0; i < hsk.nalias; i++) {
323 /* --- Tidy up after various types of failure --- */
328 for (i = 0; i < hsk.nalias && alias[i]; i++)
340 /* --- @puthost@ --- *
342 * Arguments: @int fd@ = file descriptor
343 * @struct hostent *h@ = pointer to host structure
345 * Returns: Zero if successful.
347 * Use: Encodes a host structure.
350 static int puthost(int fd, struct hostent *h)
355 /* --- Fill in and send the skeleton structure --- */
357 for (i = 0; h->h_aliases[i]; i++)
360 for (i = 0; h->h_addr_list[i]; i++)
363 hsk.addrtype = h->h_addrtype;
364 hsk.addrsz = h->h_length;
365 if (dowrite(fd, &hsk, sizeof(hsk)))
368 /* --- Send the name and alias strings --- */
370 if (putstring(fd, h->h_name))
372 for (i = 0; h->h_aliases[i]; i++) {
373 if (putstring(fd, h->h_aliases[i]))
377 /* --- Send the address data --- */
379 for (i = 0; h->h_addr_list[i]; i++) {
380 if (dowrite(fd, h->h_addr_list[i], hsk.addrsz))
384 /* --- OK, done --- */
389 /*----- Resolver server ---------------------------------------------------*/
393 * Arguments: @int rfd@ = output file descriptor for resolved hostnames
394 * @int cfd@ = input file descriptor for raw addresses
398 * Use: Asynchronous name resolving process.
401 static void child(int rfd, int cfd)
403 /* --- Close other file descriptors --- */
407 #if defined(_SC_OPEN_MAX)
408 int maxfd = sysconf(_SC_OPEN_MAX);
409 #elif defined(OPEN_MAX)
410 int maxfd = OPEN_MAX;
416 maxfd = 256; /* Fingers crossed... */
417 for (i = 0; i < maxfd; i++) {
418 if (i != rfd && i != cfd && i != 1)
423 signal(SIGTERM, SIG_DFL);
424 signal(SIGHUP, SIG_DFL);
425 signal(SIGQUIT, SIG_DFL);
426 signal(SIGALRM, SIG_DFL);
427 signal(SIGINT, SIG_DFL);
429 /* --- Main request/response loop --- */
435 /* --- Read the request --- */
437 if (doread(cfd, &req, sizeof(req)))
440 /* --- Process it into a host structure --- */
444 /* --- Normal forward lookup --- */
447 char *name = getstring(cfd);
450 h = gethostbyname(name);
454 /* --- Reverse lookup --- */
459 if (doread(cfd, &addr, sizeof(addr)))
461 if ((h = gethostbyaddr((char *)&addr, sizeof(addr), AF_INET)) == 0)
464 /* --- Do a forward lookup to confirm --- */
467 size_t sz = strlen(h->h_name) + 1;
468 if ((p = malloc(sz)) == 0)
470 memcpy(p, h->h_name, sz);
473 h = gethostbyname(p);
480 for (pp = h->h_addr_list; *pp; pp++) {
482 memcpy(&a, *pp, sizeof(a));
483 if (a.s_addr == addr.s_addr) {
491 h_errno = NO_RECOVERY;
496 /* --- Unknown request -- may have lost sync --- */
502 /* --- Transmit the response --- */
506 if (dowrite(rfd, &resp, sizeof(resp)) || puthost(rfd, h))
510 if (dowrite(rfd, &resp, sizeof(resp)) ||
511 dowrite(rfd, &h_errno, sizeof(h_errno)))
522 * Arguments: @int argc@ = number of command line arguments
523 * @char *argv[]@ = array of arguments
525 * Returns: Runs until killed or an error occurs.
527 * Use: A name resolver server process for mLib programs which need
528 * this sort of thing.
531 #ifdef BRES_STANDALONE
533 int main(int argc, char *argv[])
535 if (isatty(STDIN_FILENO)) {
536 char *p = strrchr(argv[0], '/');
542 "%s: don't run this program unless you know what you're doing.\n",
546 child(STDOUT_FILENO, STDIN_FILENO);
552 /*----- Main code ---------------------------------------------------------*/
554 #ifndef BRES_STANDALONE
558 * Arguments: @bres_server *rs@ = pointer to server block
562 * Use: Kills a server process, reaps the losing child and makes
563 * things generally clean again.
566 static void zap(bres_server *rs)
568 /* --- Close the pipes, kill the child, and reap it --- */
573 kill(rs->kid, SIGTERM);
574 waitpid(rs->kid, 0, 0);
578 /* --- Move the server to the back of the list --- */
580 rs->next->prev = rs->prev;
581 rs->prev->next = rs->next;
583 rs->prev = FREE->prev;
584 FREE->prev->next = rs;
588 /* --- @bres_abort@ --- *
590 * Arguments: @bres_client *rc@ = pointer to client block
594 * Use: Removes a queued job.
597 void bres_abort(bres_client *rc)
599 if (rc->q == BRES_BYNAME)
602 sel_rmfile(&rc->rs->f);
606 rc->next->prev = rc->prev;
607 rc->prev->next = rc->next;
613 * Arguments: @struct timeval *tv@ = pointer to the current time
614 * @void *vp@ = pointer to a server block
618 * Use: Kills off a child which has been idle for too long.
621 static void idle(struct timeval *tv, void *vp)
623 bres_server *rs = vp;
627 /* --- @answer@ --- *
629 * Arguments: @int fd@ = file descriptor which is ready
630 * @unsigned mode@ = what it's doing now
631 * @void *vp@ = pointer to server block
635 * Use: Retrieves an answer from a name resolver process.
638 static void attach(bres_client */*rc*/);
640 static void answer(int fd, unsigned mode, void *vp)
642 bres_server *rs = vp;
643 bres_client *rc = rs->rc;
644 struct hostent *h = 0;
648 /* --- Report the result to my client --- */
652 if (doread(fd, &resp, sizeof(resp)) == 0) {
655 doread(fd, &h_errno, sizeof(h_errno));
666 if (rc->q == BRES_BYNAME)
676 /* --- Wrap up the various structures --- */
680 rs->next = FREE->next;
682 FREE->next->prev = rs;
685 /* --- Tie a timer onto the server block --- */
690 gettimeofday(&tv, 0);
691 tv.tv_sec += BRES_IDLE;
692 sel_addtimer(sel, &rs->t, &tv, idle, rs);
695 /* --- If there are any clients waiting, attach one --- */
697 if (QUEUE->next != QUEUE) {
699 QUEUE->next = rc->next;
700 rc->next->prev = QUEUE;
707 * Arguments: @bres_server *rs@ = pointer to a server block
709 * Returns: Zero if OK, nonzero if something failed.
711 * Use: Starts up a child resolver process.
714 static int start(bres_server *rs)
720 /* --- Make the pipes --- */
727 /* --- Start up the child process --- */
729 if ((kid = fork()) < 0)
736 md[0].cur = cfd[0]; md[0].want = STDIN_FILENO;
737 md[1].cur = rfd[1]; md[1].want = STDOUT_FILENO;
738 if (mdup(md, 2) || execlp(server, server, (char *)0))
739 child(STDOUT_FILENO, STDIN_FILENO);
741 child(rfd[1], cfd[0]);
745 /* --- Fix up everything in the server block --- */
750 sel_initfile(sel, &rs->f, rfd[0], SEL_READ, answer, rs);
754 /* --- Fix up after errors --- */
766 /* --- @attach@ --- *
768 * Arguments: @bres_client *rc@ = pointer to a client block
772 * Use: Attaches a client to a spare server (which is assumed to
776 static void attach(bres_client *rc)
781 /* --- Fix up the server ready for the job --- *
783 * If the server has a process, remove its timer. Otherwise, fork off a
784 * new resolver process. This is also where I go if I find that the child
785 * resolver process has lost while I wasn't looking. Only one attempt at
786 * forking is performed.
794 if (lose || start(rs))
799 /* --- Submit the job to the resolver --- */
802 struct sigaction sa, osa;
805 /* --- Ignore @SIGPIPE@ for now --- *
807 * This way I can trap @EPIPE@ and reap a losing child, if there was one.
810 sa.sa_handler = SIG_IGN;
812 sigemptyset(&sa.sa_mask);
813 sigaction(SIGPIPE, &sa, &osa);
815 /* --- Write the new job to the child --- */
818 if (dowrite(rs->fd, &rc->q, sizeof(rc->q)))
820 else switch (rc->q) {
822 if (dowrite(rs->fd, &rc->u.addr, sizeof(rc->u.addr)))
826 if (putstring(rs->fd, rc->u.name))
830 sigaction(SIGPIPE, &osa, 0);
832 /* --- Sort out various errors --- *
834 * This was once more complicated, handling @EPIPE@ separately from other
835 * errors. Now everything's handled the same way.
844 /* --- Fiddle with lists so that everything's OK --- */
847 rs->next->prev = FREE;
848 FREE->next = rs->next;
849 rs->next = rs->prev = rs;
856 if (rc->q == BRES_BYNAME)
860 /* --- @resolve@ --- *
862 * Arguments: @bres_client *rc@ = pointer to filled-in client block
866 * Use: Dispatcher for incoming resolution jobs.
869 static void resolve(bres_client *rc)
871 /* --- If there's a free server, plug it in --- */
874 if (FREE->next == FREE) {
876 rc->prev = QUEUE->prev;
877 QUEUE->prev->next = rc;
883 /* --- @bres_byaddr@ --- *
885 * Arguments: @bres_client *rc@ = pointer to client block
886 * @struct in_addr addr@ = address to resolve
887 * @void (*func)(struct hostent *h, void *p)@ = handler function
888 * @void *p@ = argument for handler function
892 * Use: Adds an address lookup job to the queue. The job will be
893 * processed when there's a spare resolver process to deal with
897 void bres_byaddr(bres_client *rc, struct in_addr addr,
898 void (*func)(struct hostent */*h*/, void */*p*/),
908 /* --- @bres_byname@ --- *
910 * Arguments: @bres_client *rc@ = pointer to client block
911 * @const char *name@ = name to resolve
912 * @void (*func)(struct hostent *h, void *p)@ = handler function
913 * @void *p@ = argument for handler function
917 * Use: Adds a name lookup job to the queue. The job will be
918 * processed when there's a spare resolver process to deal with
922 void bres_byname(bres_client *rc, const char *name,
923 void (*func)(struct hostent */*h*/, void */*p*/),
927 rc->u.name = xstrdup(name);
933 /* --- @bres_exec@ --- *
935 * Arguments: @const char *file@ = file containing server code or null
939 * Use: Makes `bres' use a standalone server rather than copies of
940 * the current process. This can reduce memory consumption for
941 * large processes, at the expense of startup time (which
942 * shouldn't be too bad anyway, because of the resolver design).
943 * If the filename is null, a default set up at install time is
944 * used. It's probably a good idea to leave it alone.
947 void bres_exec(const char *file)
952 server = BRES_SERVER;
955 /* --- @bres_init@ --- *
957 * Arguments: @sel_state *s@ = pointer to select multiplexor
961 * Use: Initializes the background resolver for use.
964 void bres_init(sel_state *s)
969 for (i = 0; i < BRES_MAX; i++) {
970 servers[i].next = FREE;
971 servers[i].prev = FREE->prev;
974 FREE->prev->next = &servers[i];
975 FREE->prev = &servers[i];
981 /*----- That's all, folks -------------------------------------------------*/