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[fwd] / bres.c

/* -*-c-*-
 *
 * $Id: bres.c,v 1.1 1999/07/01 08:56:23 mdw Exp $
 *
 * Background reverse name resolution
 *
 * (c) 1999 Mark Wooding
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of the `fw' port forwarder.
 *
 * `fw' is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * `fw' is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with `fw'; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------* 
 *
 * $Log: bres.c,v $
 * Revision 1.1  1999/07/01 08:56:23  mdw
 * Initial revision
 *
 */

/*----- Header files ------------------------------------------------------*/

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <sys/wait.h>

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <mLib/report.h>
#include <mLib/sel.h>
#include <mLib/selbuf.h>

#include "bres.h"

/*----- Magic numbers -----------------------------------------------------*/

#define BRES_MAX 5			/* Maximum number of resolvers */
#define BRES_IDLE 60			/* Lifetime of an idle resolver */

/*----- Static variables --------------------------------------------------*/

static bres_server servers[BRES_MAX];	/* Statically allocated servers */

#define FREE ((bres_server *)&freelist)
static struct { bres_server *next, *prev; } freelist = { FREE, FREE };

#define QUEUE ((bres_client *)&queue)
static struct { bres_client *next, *prev; } queue = { QUEUE, QUEUE };

static sel_state *sel;

/*----- Main code ---------------------------------------------------------*/

/* --- @zap@ --- *
 *
 * Arguments:	@bres_server *rs@ = pointer to server block
 *
 * Returns:	---
 *
 * Use:		Kills a server process, reaps the losing child and makes
 *		things generally clean again.
 */

static void zap(bres_server *rs)
{
  /* --- Close the pipes, kill the child, and reap it --- */

  if (rs->kid != -1) {
    selbuf_disable(&rs->b);
    close(rs->fd);
    close(rs->b.reader.fd);
    kill(rs->kid, SIGTERM);
    waitpid(rs->kid, 0, 0);
    rs->kid = -1;
  }

  /* --- Move the server to the back of the list --- */

  rs->next->prev = rs->prev;
  rs->prev->next = rs->next;
  rs->next = FREE;
  rs->prev = FREE->prev;
  FREE->prev->next = rs;
  FREE->prev = rs;
}

/* --- @bres_abort@ --- *
 *
 * Arguments:	@bres_client *rc@ = pointer to client block
 *
 * Returns:	---
 *
 * Use:		Removes a queued job.
 */

void bres_abort(bres_client *rc)
{
  if (rc->rs) {
    zap(rc->rs);
    rc->rs = 0;
  } else {
    rc->next->prev = rc->prev;
    rc->prev->next = rc->next;
  }
}

/* --- @child@ --- *
 *
 * Arguments:	@int rfd@ = output file descriptor for resolved hostnames
 *		@int cfd@ = input file descriptor for raw addresses
 *
 * Returns:	Never.
 *
 * Use:		Asynchronous name resolving process.
 */

static void child(int rfd, int cfd)
{
  struct in_addr addr;
  FILE *fp = fdopen(rfd, "w");

  {
    int i;
    int maxfd = sysconf(_SC_OPEN_MAX);

    for (i = 0; i < maxfd; i++) {
      if (i != rfd && i != cfd)
	close(i);
    }
  }

  for (;;) {
    int r = read(cfd, &addr, sizeof(addr));
    struct hostent *h;
    char *p;

    if (r <= 0)
      break;
    else if (r != sizeof(addr))
      continue;

    h = gethostbyaddr((char *)&addr, sizeof(addr), AF_INET);
    if (h)
      p = h->h_name;
    else
      p = inet_ntoa(addr);
    fprintf(fp, "%s\n", p);
    fflush(fp);
  }
  _exit(0);
}

/* --- @idle@ --- *
 *
 * Arguments:	@struct timeval *tv@ = pointer to the current time
 *		@void *vp@ = pointer to a server block
 *
 * Returns:	---
 *
 * Use:		Kills off a child which has been idle for too long.
 */

static void idle(struct timeval *tv, void *vp)
{
  bres_server *rs = vp;
  zap(rs);
}

/* --- @answer@ --- *
 *
 * Arguments:	@char *p@ = pointer to string read
 *		@void *vp@ = pointer to server block
 *
 * Returns:	---
 *
 * Use:		Retrieves an answer from a name resolver process.
 */

static void attach(bres_client */*rc*/);

static void answer(char *p, void *vp)
{
  bres_server *rs = vp;
  bres_client *rc = rs->rc;

  /* --- Report the result to my client --- */

  if (rc)
    rc->func(p, rc->p);
  if (!p)
    zap(rs);
  if (!rc)
    return;

  /* --- Wrap up the various structures --- */

  rs->rc = 0;
  rc->rs = 0;
  rs->next = FREE->next;
  rs->prev = FREE;
  FREE->next->prev = rs;
  FREE->next = rs;

  /* --- Tie a timer onto the server block --- */

  {
    struct timeval tv;

    gettimeofday(&tv, 0);
    tv.tv_sec += BRES_IDLE;
    sel_addtimer(sel, &rs->t, &tv, idle, rs);
  }

  /* --- If there are any clients waiting, attach one --- */

  if (QUEUE->next != QUEUE) {
    rc = QUEUE->next;
    QUEUE->next = rc->next;
    rc->next->prev = QUEUE;
    attach(rc);
  }
}

/* --- @start@ --- *
 *
 * Arguments:	@bres_server *rs@ = pointer to a server block
 *
 * Returns:	Zero if OK, nonzero if something failed.
 *
 * Use:		Starts up a child resolver process.
 */

static int start(bres_server *rs)
{
  int rfd[2], cfd[2];
  pid_t kid;

  /* --- Make the pipes --- */

  if (pipe(rfd))
    goto fail_0;
  if (pipe(cfd))
    goto fail_1;

  /* --- Start up the child process --- */

  if ((kid = fork()) < 0)
    goto fail_2;
  if (kid == 0) {
    close(cfd[1]);
    close(rfd[0]);
    child(rfd[1], cfd[0]);
    _exit(1);
  }

  /* --- Fix up everything in the server block --- */

  close(cfd[0]);
  close(rfd[1]);
  rs->fd = cfd[1];
  selbuf_init(&rs->b, sel, rfd[0], answer, rs);
  rs->kid = kid;
  return (0);

  /* --- Fix up after errors --- */

fail_2:
  close(cfd[0]);
  close(cfd[1]);
fail_1:
  close(rfd[0]);
  close(rfd[1]);
fail_0:
  return (-1);
}

/* --- @attach@ --- *
 *
 * Arguments:	@bres_client *rc@ = pointer to a client block
 *
 * Returns:	---
 *
 * Use:		Attaches a client to a spare server (which is assumed to
 *		exist).
 */

static void attach(bres_client *rc)
{
  bres_server *rs;
  int lose = 0;

  /* --- Fix up the server ready for the job --- *
   *
   * If the server has a process, remove its timer.  Otherwise, fork off a
   * new resolver process.  This is also where I go if I find that the child
   * resolver process has lost while I wasn't looking.  Only one attempt at
   * forking is performed.
   */

again:
  rs = FREE->next;
  if (rs->kid != -1)
    sel_rmtimer(&rs->t);
  else {
    if (lose || start(rs))
      goto lost;
    lose = 1;
  }

  /* --- Submit the job to the resolver --- */

  {
    struct sigaction sa, osa;
    int e;

    /* --- Ignore @SIGPIPE@ for now --- *
     *
     * This way I can trap @EPIPE@ and reap a losing child, if there was one.
     */

    sa.sa_handler = SIG_IGN;
    sa.sa_flags = 0;
    sigemptyset(&sa.sa_mask);
    sigaction(SIGPIPE, &sa, &osa);

    /* --- Write the new job to the child --- */

    e = 0;
    if (write(rs->fd, &rc->addr, sizeof(rc->addr)) < 0)
      e = errno;
    sigaction(SIGPIPE, &osa, 0);

    /* --- Sort out various errors --- */

    if (e == EPIPE) {
      zap(rs);
      goto again;
    } else if (e)
      goto lost;
  }

  /* --- Fiddle with lists so that everything's OK --- */

  rs->next->prev = FREE;
  FREE->next = rs->next;
  rs->next = rs->prev = rs;
  rs->rc = rc;
  rc->rs = rs;
  return;

lost:
  rc->func(0, rc->p);
}

/* --- @bres_resolve@ --- *
 *
 * Arguments:	@bres_client *rc@ = pointer to client block
 *		@struct in_addr addr@ = address to resolve
 *		@void (*func)(const char *host, void *p)@ = handler function
 *		@void *p@ = argument for handler function
 *
 * Returns:	---
 *
 * Use:		Adds a resolver job to the queue.  The job will be processed
 *		when there's a spare resolver process to deal with it.
 */

void bres_resolve(bres_client *rc, struct in_addr addr,
		  void (*func)(const char */*host*/, void */*p*/), void *p)
{
  /* --- Fill in the structure --- */

  rc->addr = addr;
  rc->func = func;
  rc->p = p;
  rc->rs = 0;

  /* --- If there's a free server, plug it in --- */

  if (FREE->next == FREE) {
    rc->next = QUEUE;
    rc->prev = QUEUE->prev;
    QUEUE->prev->next = rc;
    QUEUE->prev = rc;
  } else
    attach(rc);
}

/* --- @bres_init@ --- *
 *
 * Arguments:	@sel_state *s@ = pointer to select multiplexor
 *
 * Returns:	---
 *
 * Use:		Initializes the background resolver for use.
 */

void bres_init(sel_state *s)
{
  int i;

  sel = s;
  for (i = 0; i < BRES_MAX; i++) {
    servers[i].next = FREE;
    servers[i].prev = FREE->prev;
    servers[i].kid = -1;
    servers[i].rc = 0;
    FREE->prev->next = &servers[i];
    FREE->prev = &servers[i];
  }
}

/*----- That's all, folks -------------------------------------------------*/