3 * $Id: bres.c,v 1.1 1999/10/04 21:40:42 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 /*----- Revision history --------------------------------------------------*
33 * Revision 1.1 1999/10/04 21:40:42 mdw
34 * Added background resolver from `fw'.
38 /*----- Header files ------------------------------------------------------*/
46 #include <sys/types.h>
51 #include <sys/socket.h>
52 #include <netinet/in.h>
53 #include <arpa/inet.h>
56 #include <mLib/alloc.h>
57 #include <mLib/report.h>
62 /*----- Magic numbers -----------------------------------------------------*/
64 #define BRES_MAX 15 /* Maximum number of resolvers */
65 #define BRES_IDLE 60 /* Lifetime of an idle resolver */
67 /*----- Static variables --------------------------------------------------*/
69 #ifndef BRES_STANDALONE
71 static bres_server servers
[BRES_MAX
]; /* Statically allocated servers */
73 #define FREE ((bres_server *)&freelist)
74 static struct { bres_server
*next
, *prev
; } freelist
= { FREE
, FREE
};
76 #define QUEUE ((bres_client *)&queue)
77 static struct { bres_client
*next
, *prev
; } queue
= { QUEUE
, QUEUE
};
79 static sel_state
*sel
;
81 static const char *server
= 0;
85 /*----- Background resolver protocol --------------------------------------*/
87 /* --- Requests and responses --- *
89 * There are two types of requests: name and addr, corresponding to the
90 * standard @gethostbyname@ and @gethostbyaddr@ calls. There are two types
91 * of responses too: a positive response consists of an encoded equivalent of
92 * a @struct hostent@ structure containing the requested information; a
93 * negative response consists of an @h_errno@ value explaining the problem.
96 #define BRES_BYNAME 0 /* Request: resolve given name */
97 #define BRES_BYADDR 1 /* Request: resolve given address */
99 #define BRES_HOSTENT 0 /* Response: resolved ok */
100 #define BRES_ERROR 1 /* Response: resolution failed */
102 /* --- Encodings --- *
104 * A string is encoded as a @size_t@ length followed by the actual data. The
105 * null terminator is not transmitted.
107 * Addresses for resolution are transmitted as raw @struct in_addr@
110 * A @hostent@ structure is transmitted as a header containing fixed-size
111 * information, followed by the official name, an array of aliases, and an
112 * array of addresses. The number of items in the arrays is specified in the
115 * The implementation assumes that a complete request or reply is always
116 * sent. Undesirable blocking will occur if this is not the case. Both ends
117 * are assumed to trust each other. A protocol failure results in the child
118 * in question being terminated.
121 typedef struct hostskel
{
128 /* --- @doread@, @dowrite@ --- *
130 * Arguments: @int fd@ = file descriptor
131 * @void *buf@ = buffer for data
132 * @size_t sz@ = size of data
134 * Returns: Zero if successful, nonzero otherwise.
136 * Use: Reads or writes a chunk of data. @EINTR@ errors are retried;
137 * incomplete reads and writes are continued from where they
138 * left off. End-of-file is considered an I/O error.
141 static int doread(int fd
, void *buf
, size_t sz
)
145 int r
= read(fd
, p
, sz
);
160 static int dowrite(int fd
, const void *buf
, size_t sz
)
164 int r
= write(fd
, p
, sz
);
179 /* --- @getstring@ --- *
181 * Arguments: @int fd@ = file descriptor to read
183 * Returns: String in heap-allocated block, or a null pointer.
185 * Use: Decodes a string.
188 static char *getstring(int fd
)
193 if (doread(fd
, &sz
, sizeof(sz
)) || (p
= malloc(sz
+ 1)) == 0)
195 if (doread(fd
, p
, sz
)) {
203 /* --- @putstring@ --- *
205 * Arguments: @int fd@ = file descriptor to write on
206 * @const char *p@ = pointer to string to write
208 * Returns: Zero if successful.
210 * Use: Encodes a string.
213 static int putstring(int fd
, const char *p
)
215 size_t sz
= strlen(p
);
216 if (dowrite(fd
, &sz
, sizeof(sz
)) || dowrite(fd
, p
, sz
))
221 /* --- @gethost@ --- *
223 * Arguments: @int fd@ = file descriptor to read
225 * Returns: Pointer to heap-allocated @struct hostent@, or null.
227 * Use: Decodes a host structure. The resulting structure is all in
228 * one big heap block.
231 #ifndef BRES_STANDALONE
233 static struct hostent
*gethost(int fd
)
240 /* --- Read the skeleton structure --- */
242 if (doread(fd
, &hsk
, sizeof(hsk
)))
245 /* --- Read the hostname and alias strings --- *
247 * Count the length of the strings as we go.
252 sizeof(struct hostent
) +
253 hsk
.naddr
* hsk
.addrsz
+
254 (hsk
.naddr
+ hsk
.nalias
+ 2) * sizeof(char *);
256 /* --- Read the primary host name --- */
258 if ((name
= getstring(fd
)) == 0)
260 sz
+= strlen(name
) + 1;
262 /* --- Read in the alias names --- */
266 if ((alias
= malloc(hsk
.nalias
* sizeof(char *))) == 0)
268 for (i
= 0; i
< hsk
.nalias
; i
++)
270 for (i
= 0; i
< hsk
.nalias
; i
++) {
271 if ((alias
[i
] = getstring(fd
)) == 0)
273 sz
+= strlen(alias
[i
]) + 1;
277 /* --- Allocate the output structure --- */
279 if ((h
= malloc(sz
)) == 0)
283 /* --- Fill in the base structure --- */
285 h
->h_addrtype
= hsk
.addrtype
;
286 h
->h_length
= hsk
.addrsz
;
288 /* --- Start putting everything else in --- */
291 char **p
= (char **)(h
+ 1);
292 char *a
= (char *)(p
+ hsk
.nalias
+ hsk
.naddr
+ 2);
295 /* --- Start with the address table --- */
298 if (doread(fd
, a
, hsk
.naddr
* hsk
.addrsz
))
300 for (i
= 0; i
< hsk
.naddr
; i
++) {
303 memcpy(&in
, a
, sizeof(in
));
307 /* --- Finally copy the strings over --- */
309 #define PUT(_p) do { \
310 size_t _len = strlen(_p) + 1; \
311 memcpy(a, (_p), _len); \
319 for (i
= 0; i
< hsk
.nalias
; i
++) {
332 /* --- Tidy up after various types of failure --- */
337 for (i
= 0; i
< hsk
.nalias
&& alias
[i
]; i
++)
349 /* --- @puthost@ --- *
351 * Arguments: @int fd@ = file descriptor
352 * @struct hostent *h@ = pointer to host structure
354 * Returns: Zero if successful.
356 * Use: Encodes a host structure.
359 static int puthost(int fd
, struct hostent
*h
)
364 /* --- Fill in and send the skeleton structure --- */
366 for (i
= 0; h
->h_aliases
[i
]; i
++)
369 for (i
= 0; h
->h_addr_list
[i
]; i
++)
372 hsk
.addrtype
= h
->h_addrtype
;
373 hsk
.addrsz
= h
->h_length
;
374 if (dowrite(fd
, &hsk
, sizeof(hsk
)))
377 /* --- Send the name and alias strings --- */
379 if (putstring(fd
, h
->h_name
))
381 for (i
= 0; h
->h_aliases
[i
]; i
++) {
382 if (putstring(fd
, h
->h_aliases
[i
]))
386 /* --- Send the address data --- */
388 for (i
= 0; h
->h_addr_list
[i
]; i
++) {
389 if (dowrite(fd
, h
->h_addr_list
[i
], hsk
.addrsz
))
393 /* --- OK, done --- */
398 /*----- Resolver server ---------------------------------------------------*/
402 * Arguments: @int rfd@ = output file descriptor for resolved hostnames
403 * @int cfd@ = input file descriptor for raw addresses
407 * Use: Asynchronous name resolving process.
410 static void child(int rfd
, int cfd
)
412 /* --- Close other file descriptors --- */
416 int maxfd
= sysconf(_SC_OPEN_MAX
);
419 maxfd
= 256; /* Fingers crossed... */
420 for (i
= 0; i
< maxfd
; i
++) {
421 if (i
!= rfd
&& i
!= cfd
&& i
!= 1)
426 /* --- Main request/response loop --- */
432 /* --- Read the request --- */
434 if (doread(cfd
, &req
, sizeof(req
)))
437 /* --- Process it into a host structure --- */
441 /* --- Normal forward lookup --- */
444 char *name
= getstring(cfd
);
447 h
= gethostbyname(name
);
451 /* --- Forward lookup --- */
456 if (doread(cfd
, &addr
, sizeof(addr
)))
458 if ((h
= gethostbyaddr((char *)&addr
, sizeof(addr
), AF_INET
)) == 0)
461 /* --- Do a forward lookup to confirm --- */
464 size_t sz
= strlen(h
->h_name
) + 1;
465 if ((p
= malloc(sz
)) == 0)
467 memcpy(p
, h
->h_name
, sz
);
470 h
= gethostbyname(p
);
477 for (pp
= h
->h_addr_list
; *pp
; pp
++) {
479 memcpy(&a
, *pp
, sizeof(a
));
480 if (a
.s_addr
== addr
.s_addr
) {
488 h_errno
= NO_RECOVERY
;
493 /* --- Unknown request -- may have lost sync --- */
499 /* --- Transmit the response --- */
503 if (dowrite(rfd
, &resp
, sizeof(resp
)) || puthost(rfd
, h
))
507 if (dowrite(rfd
, &resp
, sizeof(resp
)) ||
508 dowrite(rfd
, &h_errno
, sizeof(h_errno
)))
519 * Arguments: @int argc@ = number of command line arguments
520 * @char *argv[]@ = array of arguments
522 * Returns: Runs until killed or an error occurs.
524 * Use: A name resolver server process for mLib programs which need
525 * this sort of thing.
528 #ifdef BRES_STANDALONE
530 int main(int argc
, char *argv
[])
532 if (isatty(STDIN_FILENO
)) {
533 char *p
= strrchr(argv
[0], '/');
539 "%s: don't run this program unless you know what you're doing.\n",
543 child(STDOUT_FILENO
, STDIN_FILENO
);
549 /*----- Main code ---------------------------------------------------------*/
551 #ifndef BRES_STANDALONE
555 * Arguments: @bres_server *rs@ = pointer to server block
559 * Use: Kills a server process, reaps the losing child and makes
560 * things generally clean again.
563 static void zap(bres_server
*rs
)
565 /* --- Close the pipes, kill the child, and reap it --- */
570 kill(rs
->kid
, SIGTERM
);
571 waitpid(rs
->kid
, 0, 0);
575 /* --- Move the server to the back of the list --- */
577 rs
->next
->prev
= rs
->prev
;
578 rs
->prev
->next
= rs
->next
;
580 rs
->prev
= FREE
->prev
;
581 FREE
->prev
->next
= rs
;
585 /* --- @bres_abort@ --- *
587 * Arguments: @bres_client *rc@ = pointer to client block
591 * Use: Removes a queued job.
594 void bres_abort(bres_client
*rc
)
596 if (rc
->q
== BRES_BYNAME
)
599 sel_rmfile(&rc
->rs
->f
);
603 rc
->next
->prev
= rc
->prev
;
604 rc
->prev
->next
= rc
->next
;
610 * Arguments: @struct timeval *tv@ = pointer to the current time
611 * @void *vp@ = pointer to a server block
615 * Use: Kills off a child which has been idle for too long.
618 static void idle(struct timeval
*tv
, void *vp
)
620 bres_server
*rs
= vp
;
624 /* --- @answer@ --- *
626 * Arguments: @int fd@ = file descriptor which is ready
627 * @unsigned mode@ = what it's doing now
628 * @void *vp@ = pointer to server block
632 * Use: Retrieves an answer from a name resolver process.
635 static void attach(bres_client */
*rc*/
);
637 static void answer(int fd
, unsigned mode
, void *vp
)
639 bres_server
*rs
= vp
;
640 bres_client
*rc
= rs
->rc
;
641 struct hostent
*h
= 0;
645 /* --- Report the result to my client --- */
649 if (doread(fd
, &resp
, sizeof(resp
)) == 0) {
652 doread(fd
, &h_errno
, sizeof(h_errno
));
663 if (rc
->q
== BRES_BYNAME
)
673 /* --- Wrap up the various structures --- */
677 rs
->next
= FREE
->next
;
679 FREE
->next
->prev
= rs
;
682 /* --- Tie a timer onto the server block --- */
687 gettimeofday(&tv
, 0);
688 tv
.tv_sec
+= BRES_IDLE
;
689 sel_addtimer(sel
, &rs
->t
, &tv
, idle
, rs
);
692 /* --- If there are any clients waiting, attach one --- */
694 if (QUEUE
->next
!= QUEUE
) {
696 QUEUE
->next
= rc
->next
;
697 rc
->next
->prev
= QUEUE
;
704 * Arguments: @bres_server *rs@ = pointer to a server block
706 * Returns: Zero if OK, nonzero if something failed.
708 * Use: Starts up a child resolver process.
711 static int start(bres_server
*rs
)
716 /* --- Make the pipes --- */
723 /* --- Start up the child process --- */
725 if ((kid
= fork()) < 0)
732 dup2(cfd
[0], STDIN_FILENO
);
733 dup2(rfd
[1], STDOUT_FILENO
);
736 execlp(server
, server
, (char *)0);
737 child(STDOUT_FILENO
, STDIN_FILENO
);
739 child(rfd
[1], cfd
[0]);
743 /* --- Fix up everything in the server block --- */
748 sel_initfile(sel
, &rs
->f
, rfd
[0], SEL_READ
, answer
, rs
);
752 /* --- Fix up after errors --- */
764 /* --- @attach@ --- *
766 * Arguments: @bres_client *rc@ = pointer to a client block
770 * Use: Attaches a client to a spare server (which is assumed to
774 static void attach(bres_client
*rc
)
779 /* --- Fix up the server ready for the job --- *
781 * If the server has a process, remove its timer. Otherwise, fork off a
782 * new resolver process. This is also where I go if I find that the child
783 * resolver process has lost while I wasn't looking. Only one attempt at
784 * forking is performed.
792 if (lose
|| start(rs
))
797 /* --- Submit the job to the resolver --- */
800 struct sigaction sa
, osa
;
803 /* --- Ignore @SIGPIPE@ for now --- *
805 * This way I can trap @EPIPE@ and reap a losing child, if there was one.
808 sa
.sa_handler
= SIG_IGN
;
810 sigemptyset(&sa
.sa_mask
);
811 sigaction(SIGPIPE
, &sa
, &osa
);
813 /* --- Write the new job to the child --- */
816 if (dowrite(rs
->fd
, &rc
->q
, sizeof(rc
->q
)))
818 else switch (rc
->q
) {
820 if (dowrite(rs
->fd
, &rc
->u
.addr
, sizeof(rc
->u
.addr
)))
824 if (putstring(rs
->fd
, rc
->u
.name
))
828 sigaction(SIGPIPE
, &osa
, 0);
830 /* --- Sort out various errors --- *
832 * This was once more complicated, handling @EPIPE@ separately from other
833 * errors. Now everything's handled the same way.
842 /* --- Fiddle with lists so that everything's OK --- */
845 rs
->next
->prev
= FREE
;
846 FREE
->next
= rs
->next
;
847 rs
->next
= rs
->prev
= rs
;
854 if (rc
->q
== BRES_BYNAME
)
858 /* --- @resolve@ --- *
860 * Arguments: @bres_client *rc@ = pointer to filled-in client block
864 * Use: Dispatcher for incoming resolution jobs.
867 static void resolve(bres_client
*rc
)
869 /* --- If there's a free server, plug it in --- */
872 if (FREE
->next
== FREE
) {
874 rc
->prev
= QUEUE
->prev
;
875 QUEUE
->prev
->next
= rc
;
881 /* --- @bres_byaddr@ --- *
883 * Arguments: @bres_client *rc@ = pointer to client block
884 * @struct in_addr addr@ = address to resolve
885 * @void (*func)(struct hostent *h, void *p)@ = handler function
886 * @void *p@ = argument for handler function
890 * Use: Adds an address lookup job to the queue. The job will be
891 * processed when there's a spare resolver process to deal with
895 void bres_byaddr(bres_client
*rc
, struct in_addr addr
,
896 void (*func
)(struct hostent */
*h*/
, void */
*p*/
),
906 /* --- @bres_byname@ --- *
908 * Arguments: @bres_client *rc@ = pointer to client block
909 * @const char *name@ = name to resolve
910 * @void (*func)(struct hostent *h, void *p)@ = handler function
911 * @void *p@ = argument for handler function
915 * Use: Adds a name lookup job to the queue. The job will be
916 * processed when there's a spare resolver process to deal with
920 void bres_byname(bres_client
*rc
, const char *name
,
921 void (*func
)(struct hostent */
*h*/
, void */
*p*/
),
925 rc
->u
.name
= xstrdup(name
);
931 /* --- @bres_exec@ --- *
933 * Arguments: @const char *file@ = file containing server code or null
937 * Use: Makes `bres' use a standalone server rather than copies of
938 * the current process. This can reduce memory consumption for
939 * large processes, at the expense of startup time (which
940 * shouldn't be too bad anyway, because of the resolver design).
941 * If the filename is null, a default set up at install time is
942 * used. It's probably a good idea to leave it alone.
945 void bres_exec(const char *file
)
950 server
= BRES_SERVER
;
953 /* --- @bres_init@ --- *
955 * Arguments: @sel_state *s@ = pointer to select multiplexor
959 * Use: Initializes the background resolver for use.
962 void bres_init(sel_state
*s
)
967 for (i
= 0; i
< BRES_MAX
; i
++) {
968 servers
[i
].next
= FREE
;
969 servers
[i
].prev
= FREE
->prev
;
972 FREE
->prev
->next
= &servers
[i
];
973 FREE
->prev
= &servers
[i
];
979 /*----- That's all, folks -------------------------------------------------*/