Initial addition to CVS. The dnsserver process is a child executable that

handle DNS resolving.

src/dnsserver.c

@@ -0,0 +1,242 @@
+/* $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 */
+	}
+}