3 * $Id: bres.c,v 1.7 2004/04/08 01:36:11 mdw Exp $
5 * Background reverse name resolution
7 * (c) 1999 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of the mLib utilities library.
14 * mLib is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU Library General Public License as
16 * published by the Free Software Foundation; either version 2 of the
17 * License, or (at your option) any later version.
19 * mLib is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 * GNU Library General Public License for more details.
24 * You should have received a copy of the GNU Library General Public
25 * License along with mLib; if not, write to the Free
26 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
30 /*----- Header files ------------------------------------------------------*/
40 #include <sys/types.h>
45 #include <sys/socket.h>
46 #include <netinet/in.h>
47 #include <arpa/inet.h>
55 /*----- Magic numbers -----------------------------------------------------*/
57 #define BRES_MAX 15 /* Maximum number of resolvers */
58 #define BRES_IDLE 60 /* Lifetime of an idle resolver */
60 /*----- Static variables --------------------------------------------------*/
62 #ifndef BRES_STANDALONE
64 static bres_server servers[BRES_MAX]; /* Statically allocated servers */
66 #define FREE ((bres_server *)&freelist)
67 static struct { bres_server *next, *prev; } freelist = { FREE, FREE };
69 #define QUEUE ((bres_client *)&queue)
70 static struct { bres_client *next, *prev; } queue = { QUEUE, QUEUE };
72 static sel_state *sel;
74 static const char *server = 0;
78 /*----- Background resolver protocol --------------------------------------*/
80 /* --- Requests and responses --- *
82 * There are two types of requests: name and addr, corresponding to the
83 * standard @gethostbyname@ and @gethostbyaddr@ calls. There are two types
84 * of responses too: a positive response consists of an encoded equivalent of
85 * a @struct hostent@ structure containing the requested information; a
86 * negative response consists of an @h_errno@ value explaining the problem.
89 #define BRES_BYNAME 0 /* Request: resolve given name */
90 #define BRES_BYADDR 1 /* Request: resolve given address */
92 #define BRES_HOSTENT 0 /* Response: resolved ok */
93 #define BRES_ERROR 1 /* Response: resolution failed */
95 /* --- Encodings --- *
97 * A string is encoded as a @size_t@ length followed by the actual data. The
98 * null terminator is not transmitted.
100 * Addresses for resolution are transmitted as raw @struct in_addr@
103 * A @hostent@ structure is transmitted as a header containing fixed-size
104 * information, followed by the official name, an array of aliases, and an
105 * array of addresses. The number of items in the arrays is specified in the
108 * The implementation assumes that a complete request or reply is always
109 * sent. Undesirable blocking will occur if this is not the case. Both ends
110 * are assumed to trust each other. A protocol failure results in the child
111 * in question being terminated.
114 typedef struct hostskel {
121 /* --- @doread@, @dowrite@ --- *
123 * Arguments: @int fd@ = file descriptor
124 * @void *buf@ = buffer for data
125 * @size_t sz@ = size of data
127 * Returns: Zero if successful, nonzero otherwise.
129 * Use: Reads or writes a chunk of data. @EINTR@ errors are retried;
130 * incomplete reads and writes are continued from where they
131 * left off. End-of-file is considered an I/O error.
134 static int doread(int fd, void *buf, size_t sz)
138 int r = read(fd, p, sz);
153 static int dowrite(int fd, const void *buf, size_t sz)
157 int r = write(fd, p, sz);
172 /* --- @getstring@ --- *
174 * Arguments: @int fd@ = file descriptor to read
176 * Returns: String in heap-allocated block, or a null pointer.
178 * Use: Decodes a string.
181 static char *getstring(int fd)
186 if (doread(fd, &sz, sizeof(sz)) || (p = malloc(sz + 1)) == 0)
188 if (doread(fd, p, sz)) {
196 /* --- @putstring@ --- *
198 * Arguments: @int fd@ = file descriptor to write on
199 * @const char *p@ = pointer to string to write
201 * Returns: Zero if successful.
203 * Use: Encodes a string.
206 static int putstring(int fd, const char *p)
208 size_t sz = strlen(p);
209 if (dowrite(fd, &sz, sizeof(sz)) || dowrite(fd, p, sz))
214 /* --- @gethost@ --- *
216 * Arguments: @int fd@ = file descriptor to read
218 * Returns: Pointer to heap-allocated @struct hostent@, or null.
220 * Use: Decodes a host structure. The resulting structure is all in
221 * one big heap block.
224 #ifndef BRES_STANDALONE
226 static struct hostent *gethost(int fd)
233 /* --- Read the skeleton structure --- */
235 if (doread(fd, &hsk, sizeof(hsk)))
238 /* --- Read the hostname and alias strings --- *
240 * Count the length of the strings as we go.
245 sizeof(struct hostent) +
246 hsk.naddr * hsk.addrsz +
247 (hsk.naddr + hsk.nalias + 2) * sizeof(char *);
249 /* --- Read the primary host name --- */
251 if ((name = getstring(fd)) == 0)
253 sz += strlen(name) + 1;
255 /* --- Read in the alias names --- */
259 if ((alias = malloc(hsk.nalias * sizeof(char *))) == 0)
261 for (i = 0; i < hsk.nalias; i++)
263 for (i = 0; i < hsk.nalias; i++) {
264 if ((alias[i] = getstring(fd)) == 0)
266 sz += strlen(alias[i]) + 1;
270 /* --- Allocate the output structure --- */
272 if ((h = malloc(sz)) == 0)
276 /* --- Fill in the base structure --- */
278 h->h_addrtype = hsk.addrtype;
279 h->h_length = hsk.addrsz;
281 /* --- Start putting everything else in --- */
284 char **p = (char **)(h + 1);
285 char *a = (char *)(p + hsk.nalias + hsk.naddr + 2);
288 /* --- Start with the address table --- */
291 if (doread(fd, a, hsk.naddr * hsk.addrsz))
293 for (i = 0; i < hsk.naddr; i++) {
299 /* --- Finally copy the strings over --- */
301 #define PUT(_p) do { \
302 size_t _len = strlen(_p) + 1; \
303 memcpy(a, (_p), _len); \
311 for (i = 0; i < hsk.nalias; i++) {
324 /* --- Tidy up after various types of failure --- */
329 for (i = 0; i < hsk.nalias && alias[i]; i++)
341 /* --- @puthost@ --- *
343 * Arguments: @int fd@ = file descriptor
344 * @struct hostent *h@ = pointer to host structure
346 * Returns: Zero if successful.
348 * Use: Encodes a host structure.
351 static int puthost(int fd, struct hostent *h)
356 /* --- Fill in and send the skeleton structure --- */
358 for (i = 0; h->h_aliases[i]; i++)
361 for (i = 0; h->h_addr_list[i]; i++)
364 hsk.addrtype = h->h_addrtype;
365 hsk.addrsz = h->h_length;
366 if (dowrite(fd, &hsk, sizeof(hsk)))
369 /* --- Send the name and alias strings --- */
371 if (putstring(fd, h->h_name))
373 for (i = 0; h->h_aliases[i]; i++) {
374 if (putstring(fd, h->h_aliases[i]))
378 /* --- Send the address data --- */
380 for (i = 0; h->h_addr_list[i]; i++) {
381 if (dowrite(fd, h->h_addr_list[i], hsk.addrsz))
385 /* --- OK, done --- */
390 /*----- Resolver server ---------------------------------------------------*/
394 * Arguments: @int rfd@ = output file descriptor for resolved hostnames
395 * @int cfd@ = input file descriptor for raw addresses
399 * Use: Asynchronous name resolving process.
402 static void child(int rfd, int cfd)
404 /* --- Close other file descriptors --- */
408 #if defined(_SC_OPEN_MAX)
409 int maxfd = sysconf(_SC_OPEN_MAX);
410 #elif defined(OPEN_MAX)
411 int maxfd = OPEN_MAX;
417 maxfd = 256; /* Fingers crossed... */
418 for (i = 0; i < maxfd; i++) {
419 if (i != rfd && i != cfd && i != 1)
424 signal(SIGTERM, SIG_DFL);
425 signal(SIGHUP, SIG_DFL);
426 signal(SIGQUIT, SIG_DFL);
427 signal(SIGALRM, SIG_DFL);
428 signal(SIGINT, SIG_DFL);
430 /* --- Main request/response loop --- */
436 /* --- Read the request --- */
438 if (doread(cfd, &req, sizeof(req)))
441 /* --- Process it into a host structure --- */
445 /* --- Normal forward lookup --- */
448 char *name = getstring(cfd);
451 h = gethostbyname(name);
455 /* --- Reverse lookup --- */
460 if (doread(cfd, &addr, sizeof(addr)))
462 if ((h = gethostbyaddr((char *)&addr, sizeof(addr), AF_INET)) == 0)
465 /* --- Do a forward lookup to confirm --- */
468 size_t sz = strlen(h->h_name) + 1;
469 if ((p = malloc(sz)) == 0)
471 memcpy(p, h->h_name, sz);
474 h = gethostbyname(p);
481 for (pp = h->h_addr_list; *pp; pp++) {
483 memcpy(&a, *pp, sizeof(a));
484 if (a.s_addr == addr.s_addr) {
492 h_errno = NO_RECOVERY;
497 /* --- Unknown request -- may have lost sync --- */
503 /* --- Transmit the response --- */
507 if (dowrite(rfd, &resp, sizeof(resp)) || puthost(rfd, h))
511 if (dowrite(rfd, &resp, sizeof(resp)) ||
512 dowrite(rfd, &h_errno, sizeof(h_errno)))
523 * Arguments: @int argc@ = number of command line arguments
524 * @char *argv[]@ = array of arguments
526 * Returns: Runs until killed or an error occurs.
528 * Use: A name resolver server process for mLib programs which need
529 * this sort of thing.
532 #ifdef BRES_STANDALONE
534 int main(int argc, char *argv[])
536 if (isatty(STDIN_FILENO)) {
537 char *p = strrchr(argv[0], '/');
543 "%s: don't run this program unless you know what you're doing.\n",
547 child(STDOUT_FILENO, STDIN_FILENO);
553 /*----- Main code ---------------------------------------------------------*/
555 #ifndef BRES_STANDALONE
559 * Arguments: @bres_server *rs@ = pointer to server block
563 * Use: Kills a server process, reaps the losing child and makes
564 * things generally clean again.
567 static void zap(bres_server *rs)
569 /* --- Close the pipes, kill the child, and reap it --- */
574 kill(rs->kid, SIGTERM);
575 waitpid(rs->kid, 0, 0);
579 /* --- Move the server to the back of the list --- */
581 rs->next->prev = rs->prev;
582 rs->prev->next = rs->next;
584 rs->prev = FREE->prev;
585 FREE->prev->next = rs;
589 /* --- @bres_abort@ --- *
591 * Arguments: @bres_client *rc@ = pointer to client block
595 * Use: Removes a queued job.
598 void bres_abort(bres_client *rc)
600 if (rc->q == BRES_BYNAME)
603 sel_rmfile(&rc->rs->f);
607 rc->next->prev = rc->prev;
608 rc->prev->next = rc->next;
614 * Arguments: @struct timeval *tv@ = pointer to the current time
615 * @void *vp@ = pointer to a server block
619 * Use: Kills off a child which has been idle for too long.
622 static void idle(struct timeval *tv, void *vp)
624 bres_server *rs = vp;
628 /* --- @answer@ --- *
630 * Arguments: @int fd@ = file descriptor which is ready
631 * @unsigned mode@ = what it's doing now
632 * @void *vp@ = pointer to server block
636 * Use: Retrieves an answer from a name resolver process.
639 static void attach(bres_client */*rc*/);
641 static void answer(int fd, unsigned mode, void *vp)
643 bres_server *rs = vp;
644 bres_client *rc = rs->rc;
645 struct hostent *h = 0;
649 /* --- Report the result to my client --- */
653 if (doread(fd, &resp, sizeof(resp)) == 0) {
656 doread(fd, &h_errno, sizeof(h_errno));
667 if (rc->q == BRES_BYNAME)
677 /* --- Wrap up the various structures --- */
681 rs->next = FREE->next;
683 FREE->next->prev = rs;
686 /* --- Tie a timer onto the server block --- */
691 gettimeofday(&tv, 0);
692 tv.tv_sec += BRES_IDLE;
693 sel_addtimer(sel, &rs->t, &tv, idle, rs);
696 /* --- If there are any clients waiting, attach one --- */
698 if (QUEUE->next != QUEUE) {
700 QUEUE->next = rc->next;
701 rc->next->prev = QUEUE;
708 * Arguments: @bres_server *rs@ = pointer to a server block
710 * Returns: Zero if OK, nonzero if something failed.
712 * Use: Starts up a child resolver process.
715 static int start(bres_server *rs)
720 /* --- Make the pipes --- */
727 /* --- Start up the child process --- */
729 if ((kid = fork()) < 0)
736 dup2(cfd[0], STDIN_FILENO);
737 dup2(rfd[1], STDOUT_FILENO);
740 execlp(server, server, (char *)0);
741 child(STDOUT_FILENO, STDIN_FILENO);
743 child(rfd[1], cfd[0]);
747 /* --- Fix up everything in the server block --- */
752 sel_initfile(sel, &rs->f, rfd[0], SEL_READ, answer, rs);
756 /* --- Fix up after errors --- */
768 /* --- @attach@ --- *
770 * Arguments: @bres_client *rc@ = pointer to a client block
774 * Use: Attaches a client to a spare server (which is assumed to
778 static void attach(bres_client *rc)
783 /* --- Fix up the server ready for the job --- *
785 * If the server has a process, remove its timer. Otherwise, fork off a
786 * new resolver process. This is also where I go if I find that the child
787 * resolver process has lost while I wasn't looking. Only one attempt at
788 * forking is performed.
796 if (lose || start(rs))
801 /* --- Submit the job to the resolver --- */
804 struct sigaction sa, osa;
807 /* --- Ignore @SIGPIPE@ for now --- *
809 * This way I can trap @EPIPE@ and reap a losing child, if there was one.
812 sa.sa_handler = SIG_IGN;
814 sigemptyset(&sa.sa_mask);
815 sigaction(SIGPIPE, &sa, &osa);
817 /* --- Write the new job to the child --- */
820 if (dowrite(rs->fd, &rc->q, sizeof(rc->q)))
822 else switch (rc->q) {
824 if (dowrite(rs->fd, &rc->u.addr, sizeof(rc->u.addr)))
828 if (putstring(rs->fd, rc->u.name))
832 sigaction(SIGPIPE, &osa, 0);
834 /* --- Sort out various errors --- *
836 * This was once more complicated, handling @EPIPE@ separately from other
837 * errors. Now everything's handled the same way.
846 /* --- Fiddle with lists so that everything's OK --- */
849 rs->next->prev = FREE;
850 FREE->next = rs->next;
851 rs->next = rs->prev = rs;
858 if (rc->q == BRES_BYNAME)
862 /* --- @resolve@ --- *
864 * Arguments: @bres_client *rc@ = pointer to filled-in client block
868 * Use: Dispatcher for incoming resolution jobs.
871 static void resolve(bres_client *rc)
873 /* --- If there's a free server, plug it in --- */
876 if (FREE->next == FREE) {
878 rc->prev = QUEUE->prev;
879 QUEUE->prev->next = rc;
885 /* --- @bres_byaddr@ --- *
887 * Arguments: @bres_client *rc@ = pointer to client block
888 * @struct in_addr addr@ = address to resolve
889 * @void (*func)(struct hostent *h, void *p)@ = handler function
890 * @void *p@ = argument for handler function
894 * Use: Adds an address lookup job to the queue. The job will be
895 * processed when there's a spare resolver process to deal with
899 void bres_byaddr(bres_client *rc, struct in_addr addr,
900 void (*func)(struct hostent */*h*/, void */*p*/),
910 /* --- @bres_byname@ --- *
912 * Arguments: @bres_client *rc@ = pointer to client block
913 * @const char *name@ = name to resolve
914 * @void (*func)(struct hostent *h, void *p)@ = handler function
915 * @void *p@ = argument for handler function
919 * Use: Adds a name lookup job to the queue. The job will be
920 * processed when there's a spare resolver process to deal with
924 void bres_byname(bres_client *rc, const char *name,
925 void (*func)(struct hostent */*h*/, void */*p*/),
929 rc->u.name = xstrdup(name);
935 /* --- @bres_exec@ --- *
937 * Arguments: @const char *file@ = file containing server code or null
941 * Use: Makes `bres' use a standalone server rather than copies of
942 * the current process. This can reduce memory consumption for
943 * large processes, at the expense of startup time (which
944 * shouldn't be too bad anyway, because of the resolver design).
945 * If the filename is null, a default set up at install time is
946 * used. It's probably a good idea to leave it alone.
949 void bres_exec(const char *file)
954 server = BRES_SERVER;
957 /* --- @bres_init@ --- *
959 * Arguments: @sel_state *s@ = pointer to select multiplexor
963 * Use: Initializes the background resolver for use.
966 void bres_init(sel_state *s)
971 for (i = 0; i < BRES_MAX; i++) {
972 servers[i].next = FREE;
973 servers[i].prev = FREE->prev;
976 FREE->prev->next = &servers[i];
977 FREE->prev = &servers[i];
983 /*----- That's all, folks -------------------------------------------------*/