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/* $Id: dnsserver.c,v 1.1 2002-05-23 04:40:42 rjkaes Exp $
*
* This is a DNS resolver program. I've borrowed _liberally_ from
* Squid's dnsserver program. Only one argument is passed to this
* program (the path to the Unix socket.) Additionally, this program
* will be started by tinyproxy itself.
*
* As noted, communication is conducted over a Unix socket. The
* client opens a connection and writes a '\n' terminated string with
* either a domain name (if an address is required) or a
* dotted-decimal IP address (if the domain name is required.) This
* program will then respond with a '\n' terminated string starting
* with either "$addr" if IP addresses are being returned, or "$name"
* if a host name is returned. The connection will remain open until
* the "$shutdown" command is sent by the client.
*
* Copyright (C) 2002 Robert James Kaes (rjkaes@flarenet.com)
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2, or (at your option) any
* later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*/
#include "common.h"
#include "daemon.h"
#include "heap.h"
#include "network.h"
#include "text.h"
/*
* Store a copy of the location of the Unix socket
*/
static char *unix_socket_path;
/*
* Handle SIGCHLD signals so that zombies are reaped.
*/
static void
child_signal_handler(int signo)
{
pid_t pid;
int status;
while ((pid = waitpid(-1, &status, WNOHANG)) > 0)
;
return;
}
/*
* Handle the SIGTERM signal to remove the Unix socket
*/
static void
term_signal_handler(int signo)
{
unlink(unix_socket_path);
return;
}
/*
* Text error messages for DNS problems.
*/
static char*
dns_error_messages(int err)
{
if (err == HOST_NOT_FOUND)
return "Host not found (authoritative)";
else if (err == TRY_AGAIN)
return "Host not found (non-authoritative)";
else if (err == NO_RECOVERY)
return "Non recoverable errors";
else if (err == NO_DATA || err == NO_ADDRESS)
return "Valid name, no data record of requested type";
else
return "Unknown DNS problem";
}
/*
* Lookup and return the information for a host name (or IP address)
*/
static int
lookup_dns(int fd)
{
const struct hostent *result = NULL;
int reverse_lookup = 0;
int retry = 0;
int i;
struct in_addr addr;
char *buf;
ssize_t len;
char address_buf[1024];
len = readline(fd, &buf);
chomp(buf, len);
if (strcmp(buf, "$shutdown") == 0)
return 0;
if (strcmp(buf, "$hello") == 0) {
write_message(fd, "$alive\n");
return 1;
}
/*
* Check to see if the buffer is an IP address in dotted-decimal
* form.
*/
for (;;) {
if (inet_aton(buf, &addr)) {
reverse_lookup = 1;
result = gethostbyaddr((char *)&addr.s_addr, 4, AF_INET);
} else {
result = gethostbyname(buf);
}
if (NULL != result)
break;
if (h_errno != TRY_AGAIN)
break;
if (++retry == 3)
break;
sleep(1);
}
if (NULL == result) {
if (h_errno == TRY_AGAIN) {
write_message(fd, "$fail Name Server for domain '%s' is unavailable.\n", buf);
} else {
write_message(fd, "$fail DNS Domain '%s' is invalid: %s.\n",
buf, dns_error_messages(h_errno));
}
return 1;
}
if (reverse_lookup) {
write_message(fd, "$name %s\n", result->h_name);
return 1;
}
strlcpy(address_buf, "$addr", sizeof(address_buf));
for (i = 0; i < 32; i++) {
if (!result->h_addr_list[i])
break;
memcpy(&addr, result->h_addr_list[i], sizeof(addr));
strlcat(address_buf, " ", sizeof(address_buf));
strlcat(address_buf, inet_ntoa(addr), sizeof(address_buf));
}
write_message(fd, "%s\n", address_buf);
return 1;
}
/*
* Print out a usage message.
*/
static void
usage(void)
{
fprintf(stderr, "usage: dnsserver path\n");
}
/*
* Start up function. Create the sockets and fork() when needed.
*/
int
main(int argc, char **argv)
{
int listenfd, connfd;
pid_t childpid;
socklen_t clilen;
struct sockaddr_un cliaddr, servaddr;
if (--argc != 1) {
usage();
exit(1);
}
/*
* The path for the socket is supplied as the one (and only) command
* line argument.
*/
unix_socket_path = safestrdup(argv[1]);
if (!unix_socket_path) {
fprintf(stderr, "%s: could not allocate memory.\n", argv[0]);
exit(1);
}
/* Create the listening socket */
listenfd = socket(AF_LOCAL, SOCK_STREAM, 0);
if (listenfd < 0) {
fprintf(stderr, "%s: could not create listening socket.\n",
argv[0]);
exit(1);
}
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sun_family = AF_LOCAL;
strcpy(servaddr.sun_path, unix_socket_path);
if (bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0) {
fprintf(stderr, "%s: could not bind socket.\n", argv[0]);
exit(1);
}
if (listen(listenfd, MAXLISTEN) < 0) {
fprintf(stderr, "%s: could not start listening on socket.\n",
argv[0]);
exit(1);
}
set_signal_handler(SIGCHLD, child_signal_handler);
set_signal_handler(SIGTERM, term_signal_handler);
for ( ; ; ) {
clilen = sizeof(cliaddr);
if ((connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen)) < 0) {
if (errno == EINTR)
continue;
else
exit(1);
}
if ((childpid = fork()) == 0) {
/* child process */
close(listenfd);
while (lookup_dns(connfd))
;
close(connfd);
exit(0);
}
close(connfd); /* parent closes connected socket */
}
}
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