usr/src/lib/libresolv/res_send.c - illumos-gate - Gitiles

 /*
  * CDDL HEADER START
  *
  * The contents of this file are subject to the terms of the
  * Common Development and Distribution License (the "License").
  * You may not use this file except in compliance with the License.
  *
  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
  * or http://www.opensolaris.org/os/licensing.
  * See the License for the specific language governing permissions
  * and limitations under the License.
  *
  * When distributing Covered Code, include this CDDL HEADER in each
  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  * If applicable, add the following below this CDDL HEADER, with the
  * fields enclosed by brackets "[]" replaced with your own identifying
  * information: Portions Copyright [yyyy] [name of copyright owner]
  *
  * CDDL HEADER END
  */

 /*
  * Copyright 2015 Gary Mills
  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */

 /*	Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T	*/
 /*	  All Rights Reserved  	*/

 /*
  * University Copyright- Copyright (c) 1982, 1986, 1988
  * The Regents of the University of California
  * All Rights Reserved
  *
  * University Acknowledgment- Portions of this document are derived from
  * software developed by the University of California, Berkeley, and its
  * contributors.
  */

 /*
  * Send query to name server and wait for reply.
  */

 #include <sys/param.h>
 #include <sys/time.h>
 #include <sys/socket.h>
 #include <sys/uio.h>
 #include <sys/stat.h>
 #include <netinet/in.h>
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
 #include <errno.h>
 #include <arpa/nameser.h>
 #include <arpa/inet.h>
 #include <resolv.h>
 #include "crossl.h"

 /*
  * Undocumented external function in libsocket
  */
 extern int
 _socket(int, int, int);

 static int s = -1;	/* socket used for communications */
 #if	BSD >= 43
 static struct sockaddr no_addr;
 #endif /* BSD */


 #ifndef FD_SET
 #define	NFDBITS		32
 #define	FD_SETSIZE	32
 #define	FD_SET(n, p)	((p)->fds_bits[(n)/NFDBITS] |= (1 << ((n) % NFDBITS)))
 #define	FD_CLR(n, p)	((p)->fds_bits[(n)/NFDBITS] &= ~(1 << ((n) % NFDBITS)))
 #define	FD_ISSET(n, p)	((p)->fds_bits[(n)/NFDBITS] & (1 << ((n) % NFDBITS)))
 #ifdef SYSV
 #define	FD_ZERO(p)	(void) memset((void *)(p), 0, sizeof (*(p)))
 #else
 #define	FD_ZERO(p)	bzero((char *)(p), sizeof (*(p)))
 #endif
 #endif

 /*
  * 1247019: Kludge to time out quickly if there is no /etc/resolv.conf
  * and a TCP connection to the local DNS server fails.
  */

 static int _confcheck()
 {
 	int ns;
 	struct stat rc_stat;
 	struct sockaddr_in ns_sin;


 	/* First, we check to see if /etc/resolv.conf exists.
 	 * If it doesn't, then localhost is mostlikely to be
 	 * the nameserver.
 	 */
 	if (stat(_PATH_RESCONF, &rc_stat) == -1 && errno == ENOENT) {

 		/* Next, we check to see if _res.nsaddr is set to loopback.
 		 * If it isn't, it has been altered by the application
 		 * explicitly and we then want to bail with success.
 		 */
 		if (_res.nsaddr.sin_addr.S_un.S_addr == htonl(INADDR_LOOPBACK)) {

 			/* Lastly, we try to connect to the TCP port of the
 			 * nameserver.  If this fails, then we know that
 			 * DNS is misconfigured and we can quickly exit.
 			 */
 			ns = socket(AF_INET, SOCK_STREAM, 0);
 			IN_SET_LOOPBACK_ADDR(&ns_sin);
 			ns_sin.sin_port = htons(NAMESERVER_PORT);
 			if (connect(ns, (struct sockaddr *) &ns_sin,
 				    sizeof ns_sin) == -1) {
 				close(ns);
 				return(-1);
 			}
 			else {
 				close(ns);
 				return(0);
 			}
 		}

 		return(0);
 	}

 	return (0);
 }

 int
 res_send(buf, buflen, answer, anslen)
 	char *buf;
 	int buflen;
 	char *answer;
 	int anslen;
 {
 	register int n;
 	int try, v_circuit, resplen, ns;
 	int gotsomewhere = 0;
 #if	BSD >= 43
 	int connected = 0;
 #endif /* BSD */
 	int connreset = 0;
 	u_short id, len;
 	char *cp;
 	fd_set dsmask;
 	struct timeval timeout;
 	HEADER *hp = (HEADER *) buf;
 	HEADER *anhp = (HEADER *) answer;
 	struct iovec iov[2];
 	int terrno = ETIMEDOUT;
 	char junk[512];

 #ifdef DEBUG
 	if (_res.options & RES_DEBUG) {
 		printf("res_send()\n");
 		p_query(buf);
 	}
 #endif
 	if (!(_res.options & RES_INIT))
 		if (res_init() == -1) {
 			return (-1);
 		}

 	/* 1247019: Check to see if we can bailout quickly. */
 	if (_confcheck() == -1)
 	    return(-1);

 	v_circuit = (_res.options & RES_USEVC) || buflen > PACKETSZ;
 	id = hp->id;
 	/*
 	 * Send request, RETRY times, or until successful
 	 */
 	for (try = 0; try < _res.retry; try++) {
 		for (ns = 0; ns < _res.nscount; ns++) {
 #ifdef DEBUG
 			if (_res.options & RES_DEBUG)
 				printf("Querying server (# %d) address = %s\n",
 				ns+1, inet_ntoa(_res.nsaddr_list[ns].sin_addr));
 #endif
 		usevc:
 			if (v_circuit) {
 				int truncated = 0;

 				/*
 				 * Use virtual circuit;
 				 * at most one attempt per server.
 				 */
 				try = _res.retry;
 				if (s < 0) {
 					s = _socket(AF_INET, SOCK_STREAM, 0);
 					if (s < 0) {
 						terrno = errno;
 #ifdef DEBUG
 						if (_res.options & RES_DEBUG) {
 						perror("socket (vc) failed");
 						}
 #endif
 						continue;
 					}
 					if (connect(s, (struct sockaddr *) &_res.nsaddr_list[ns],
 						sizeof (struct sockaddr)) < 0) {
 						terrno = errno;
 #ifdef DEBUG
 						if (_res.options & RES_DEBUG) {
 						perror("connect failed");
 						}
 #endif
 						(void) close(s);
 						s = -1;
 						continue;
 					}
 				}
 				/*
 				 * Send length & message
 				 */
 				len = htons((u_short)buflen);
 				iov[0].iov_base = (caddr_t)&len;
 				iov[0].iov_len = sizeof (len);
 				iov[1].iov_base = buf;
 				iov[1].iov_len = buflen;
 				if (writev(s, iov, 2) != sizeof (len) +
 								buflen) {
 					terrno = errno;
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG)
 						perror("write failed");
 #endif
 					(void) close(s);
 					s = -1;
 					continue;
 				}
 				/*
 				 * Receive length & response
 				 */
 				cp = answer;
 				len = sizeof (short);
 				while (len != 0 && (n = read
 					(s, (char *)cp, (int)len)) > 0) {
 					cp += n;
 					len -= n;
 				}
 				if (n <= 0) {
 					terrno = errno;
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG)
 						perror("read failed");
 #endif
 					(void) close(s);
 					s = -1;
 				/*
 				 * A long running process might get its TCP
 				 * connection reset if the remote server was
 				 * restarted.  Requery the server instead of
 				 * trying a new one.  When there is only one
 				 * server, this means that a query might work
 				 * instead of failing.  We only allow one reset
 				 * per query to prevent looping.
 				 */
 					if (terrno == ECONNRESET &&
 							!connreset) {
 						connreset = 1;
 						ns--;
 					}
 					continue;
 				}
 				cp = answer;
 				if ((resplen = ntohs(*(u_short *)cp)) >
 								anslen) {
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG)
 						fprintf(stderr,
 							"response truncated\n");
 #endif
 					len = anslen;
 					truncated = 1;
 				} else
 					len = resplen;
 				while (len != 0 &&
 					(n = read(s, (char *)cp,
 							(int)len)) > 0) {
 					cp += n;
 					len -= n;
 				}
 				if (n <= 0) {
 					terrno = errno;
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG)
 						perror("read failed");
 #endif
 					(void) close(s);
 					s = -1;
 					continue;
 				}
 				if (truncated) {
 					/*
 					 * Flush rest of answer
 					 * so connection stays in synch.
 					 */
 					anhp->tc = 1;
 					len = resplen - anslen;
 					/*
 					 * set the value of resplen to anslen,
 					 * this is done because the caller
 					 * assumes resplen contains the size of
 					 * message read into the "answer" buffer
 					 * passed in.
 					 */
 					resplen = anslen;

 					while (len != 0) {
 						n = (len > sizeof (junk) ?
 							sizeof (junk) : len);
 						if ((n = read(s, junk, n)) > 0)
 							len -= n;
 						else
 							break;
 					}
 				}
 			} else {
 				/*
 				 * Use datagrams.
 				 */
 				if (s < 0) {
 					s = _socket(AF_INET, SOCK_DGRAM, 0);
 					if (s < 0) {
 						terrno = errno;
 #ifdef DEBUG
 						if (_res.options & RES_DEBUG) {
 						perror("socket (dg) failed");
 						}
 #endif
 						continue;
 					}
 				}
 #if	BSD >= 43
 			/*
 			 * I'm tired of answering this question, so:
 			 * On a 4.3BSD+ machine (client and server,
 			 * actually), sending to a nameserver datagram
 			 * port with no nameserver will cause an
 			 * ICMP port unreachable message to be returned.
 			 * If our datagram socket is "connected" to the
 			 * server, we get an ECONNREFUSED error on the next
 			 * socket operation, and select returns if the
 			 * error message is received.  We can thus detect
 			 * the absence of a nameserver without timing out.
 			 * If we have sent queries to at least two servers,
 			 * however, we don't want to remain connected,
 			 * as we wish to receive answers from the first
 			 * server to respond.
 			 */
 				if (_res.nscount == 1 ||
 						(try == 0 && ns == 0)) {
 					/*
 					 * Don't use connect if we might
 					 * still receive a response
 					 * from another server.
 					 */
 					if (connected == 0) {
 						if (connect(s,
 						(struct sockaddr *) &_res.nsaddr_list[ns],
 						sizeof (struct sockaddr)) < 0) {
 #ifdef DEBUG
 							if (_res.options &
 								RES_DEBUG) {
 							perror("connect");
 							}
 #endif
 							continue;
 						}
 						connected = 1;
 					}
 					if (send(s, buf, buflen, 0) != buflen) {
 #ifdef DEBUG
 						if (_res.options & RES_DEBUG)
 							perror("send");
 #endif
 						continue;
 					}
 				} else {
 					/*
 					 * Disconnect if we want to listen for
 					 * responses from more than one server.
 					 */
 					if (connected) {
 						(void) connect(s, &no_addr,
 							sizeof (no_addr));
 						connected = 0;
 					}
 #endif /* BSD */
 					if (sendto(s, buf, buflen, 0,
 						(struct sockaddr *) &_res.nsaddr_list[ns],
 					sizeof (struct sockaddr)) != buflen) {
 #ifdef DEBUG
 						if (_res.options & RES_DEBUG)
 							perror("sendto");
 #endif
 						continue;
 					}
 #if	BSD >= 43
 				}
 #endif

 				/*
 				 * Wait for reply
 				 */
 				timeout.tv_sec = (_res.retrans << try);
 				if (try > 0)
 					timeout.tv_sec /= _res.nscount;
 				if (timeout.tv_sec <= 0)
 					timeout.tv_sec = 1;
 				timeout.tv_usec = 0;
 wait:
 				FD_ZERO(&dsmask);
 				FD_SET(s, &dsmask);
 				n = select(s+1, &dsmask, (fd_set *)NULL,
 						(fd_set *)NULL, &timeout);
 				if (n < 0) {
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG)
 						perror("select");
 #endif
 					continue;
 				}
 				if (n == 0) {
 					/*
 					 * timeout
 					 */
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG)
 						printf("timeout\n");
 #endif
 #if BSD >= 43
 					gotsomewhere = 1;
 #endif
 					continue;
 				}
 				if ((resplen = recv(s, answer, anslen, 0))
 									<= 0) {
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG)
 						perror("recvfrom");
 #endif
 					continue;
 				}
 				gotsomewhere = 1;
 				if (id != anhp->id) {
 					/*
 					 * response from old query, ignore it
 					 */
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG) {
 						printf("old answer:\n");
 						p_query(answer);
 					}
 #endif
 					goto wait;
 				}
 				if (!(_res.options & RES_IGNTC) && anhp->tc) {
 					/*
 					 * get rest of answer;
 					 * use TCP with same server.
 					 */
 #ifdef DEBUG
 					if (_res.options & RES_DEBUG)
 						printf("truncated answer\n");
 #endif
 					(void) close(s);
 					s = -1;
 					v_circuit = 1;
 					goto usevc;
 				}
 			}
 #ifdef DEBUG
 			if (_res.options & RES_DEBUG) {
 				printf("got answer:\n");
 				p_query(answer);
 			}
 #endif
 		/*
 		 * If using virtual circuits, we assume that the first server
 		 * is preferred * over the rest (i.e. it is on the local
 		 * machine) and only keep that one open.
 		 * If we have temporarily opened a virtual circuit,
 		 * or if we haven't been asked to keep a socket open,
 		 * close the socket.
 		 */
 			if ((v_circuit &&
 				((_res.options & RES_USEVC) == 0 || ns != 0)) ||
 				(_res.options & RES_STAYOPEN) == 0) {
 				(void) close(s);
 				s = -1;
 			}
 			return (resplen);
 		}
 	}
 	if (s >= 0) {
 		(void) close(s);
 		s = -1;
 	}
 	if (v_circuit == 0)
 		if (gotsomewhere == 0)
 			errno = ECONNREFUSED;	/* no nameservers found */
 		else
 			errno = ETIMEDOUT;	/* no answer obtained */
 	else
 		errno = terrno;
 	return (-1);
 }

 /*
  * This routine is for closing the socket if a virtual circuit is used and
  * the program wants to close it.  This provides support for endhostent()
  * which expects to close the socket.
  *
  * This routine is not expected to be user visible.
  */
 void
 _res_close()
 {
 	if (s != -1) {
 		(void) close(s);
 		s = -1;
 	}
 }
	/*
	* CDDL HEADER START
	*
	* The contents of this file are subject to the terms of the
	* Common Development and Distribution License (the "License").
	* You may not use this file except in compliance with the License.
	*
	* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
	* or http://www.opensolaris.org/os/licensing.
	* See the License for the specific language governing permissions
	* and limitations under the License.
	*
	* When distributing Covered Code, include this CDDL HEADER in each
	* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
	* If applicable, add the following below this CDDL HEADER, with the
	* fields enclosed by brackets "[]" replaced with your own identifying
	* information: Portions Copyright [yyyy] [name of copyright owner]
	*
	* CDDL HEADER END
	*/

	/*
	* Copyright 2015 Gary Mills
	* Copyright 2008 Sun Microsystems, Inc. All rights reserved.
	* Use is subject to license terms.
	*/

	/* Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T */
	/* All Rights Reserved */

	/*
	* University Copyright- Copyright (c) 1982, 1986, 1988
	* The Regents of the University of California
	* All Rights Reserved
	*
	* University Acknowledgment- Portions of this document are derived from
	* software developed by the University of California, Berkeley, and its
	* contributors.
	*/

	/*
	* Send query to name server and wait for reply.
	*/

	#include <sys/param.h>
	#include <sys/time.h>
	#include <sys/socket.h>
	#include <sys/uio.h>
	#include <sys/stat.h>
	#include <netinet/in.h>
	#include <stdio.h>
	#include <string.h>
	#include <unistd.h>
	#include <errno.h>
	#include <arpa/nameser.h>
	#include <arpa/inet.h>
	#include <resolv.h>
	#include "crossl.h"

	/*
	* Undocumented external function in libsocket
	*/
	extern int
	_socket(int, int, int);

	static int s = -1; /* socket used for communications */
	#if BSD >= 43
	static struct sockaddr no_addr;
	#endif /* BSD */


	#ifndef FD_SET
	#define NFDBITS 32
	#define FD_SETSIZE 32
	#define FD_SET(n, p) ((p)->fds_bits[(n)/NFDBITS] \|= (1 << ((n) % NFDBITS)))
	#define FD_CLR(n, p) ((p)->fds_bits[(n)/NFDBITS] &= ~(1 << ((n) % NFDBITS)))
	#define FD_ISSET(n, p) ((p)->fds_bits[(n)/NFDBITS] & (1 << ((n) % NFDBITS)))
	#ifdef SYSV
	#define FD_ZERO(p) (void) memset((void )(p), 0, sizeof ((p)))
	#else
	#define FD_ZERO(p) bzero((char )(p), sizeof ((p)))
	#endif
	#endif

	/*
	* 1247019: Kludge to time out quickly if there is no /etc/resolv.conf
	* and a TCP connection to the local DNS server fails.
	*/

	static int _confcheck()
	{
	int ns;
	struct stat rc_stat;
	struct sockaddr_in ns_sin;


	/* First, we check to see if /etc/resolv.conf exists.
	* If it doesn't, then localhost is mostlikely to be
	* the nameserver.
	*/
	if (stat(_PATH_RESCONF, &rc_stat) == -1 && errno == ENOENT) {

	/* Next, we check to see if _res.nsaddr is set to loopback.
	* If it isn't, it has been altered by the application
	* explicitly and we then want to bail with success.
	*/
	if (_res.nsaddr.sin_addr.S_un.S_addr == htonl(INADDR_LOOPBACK)) {

	/* Lastly, we try to connect to the TCP port of the
	* nameserver. If this fails, then we know that
	* DNS is misconfigured and we can quickly exit.
	*/
	ns = socket(AF_INET, SOCK_STREAM, 0);
	IN_SET_LOOPBACK_ADDR(&ns_sin);
	ns_sin.sin_port = htons(NAMESERVER_PORT);
	if (connect(ns, (struct sockaddr *) &ns_sin,
	sizeof ns_sin) == -1) {
	close(ns);
	return(-1);
	}
	else {
	close(ns);
	return(0);
	}
	}

	return(0);
	}

	return (0);
	}

	int
	res_send(buf, buflen, answer, anslen)
	char *buf;
	int buflen;
	char *answer;
	int anslen;
	{
	register int n;
	int try, v_circuit, resplen, ns;
	int gotsomewhere = 0;
	#if BSD >= 43
	int connected = 0;
	#endif /* BSD */
	int connreset = 0;
	u_short id, len;
	char *cp;
	fd_set dsmask;
	struct timeval timeout;
	HEADER hp = (HEADER ) buf;
	HEADER anhp = (HEADER ) answer;
	struct iovec iov[2];
	int terrno = ETIMEDOUT;
	char junk[512];

	#ifdef DEBUG
	if (_res.options & RES_DEBUG) {
	printf("res_send()\n");
	p_query(buf);
	}
	#endif
	if (!(_res.options & RES_INIT))
	if (res_init() == -1) {
	return (-1);
	}

	/* 1247019: Check to see if we can bailout quickly. */
	if (_confcheck() == -1)
	return(-1);

	v_circuit = (_res.options & RES_USEVC) \|\| buflen > PACKETSZ;
	id = hp->id;
	/*
	* Send request, RETRY times, or until successful
	*/
	for (try = 0; try < _res.retry; try++) {
	for (ns = 0; ns < _res.nscount; ns++) {
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	printf("Querying server (# %d) address = %s\n",
	ns+1, inet_ntoa(_res.nsaddr_list[ns].sin_addr));
	#endif
	usevc:
	if (v_circuit) {
	int truncated = 0;

	/*
	* Use virtual circuit;
	* at most one attempt per server.
	*/
	try = _res.retry;
	if (s < 0) {
	s = _socket(AF_INET, SOCK_STREAM, 0);
	if (s < 0) {
	terrno = errno;
	#ifdef DEBUG
	if (_res.options & RES_DEBUG) {
	perror("socket (vc) failed");
	}
	#endif
	continue;
	}
	if (connect(s, (struct sockaddr *) &_res.nsaddr_list[ns],
	sizeof (struct sockaddr)) < 0) {
	terrno = errno;
	#ifdef DEBUG
	if (_res.options & RES_DEBUG) {
	perror("connect failed");
	}
	#endif
	(void) close(s);
	s = -1;
	continue;
	}
	}
	/*
	* Send length & message
	*/
	len = htons((u_short)buflen);
	iov[0].iov_base = (caddr_t)&len;
	iov[0].iov_len = sizeof (len);
	iov[1].iov_base = buf;
	iov[1].iov_len = buflen;
	if (writev(s, iov, 2) != sizeof (len) +
	buflen) {
	terrno = errno;
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	perror("write failed");
	#endif
	(void) close(s);
	s = -1;
	continue;
	}
	/*
	* Receive length & response
	*/
	cp = answer;
	len = sizeof (short);
	while (len != 0 && (n = read
	(s, (char *)cp, (int)len)) > 0) {
	cp += n;
	len -= n;
	}
	if (n <= 0) {
	terrno = errno;
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	perror("read failed");
	#endif
	(void) close(s);
	s = -1;
	/*
	* A long running process might get its TCP
	* connection reset if the remote server was
	* restarted. Requery the server instead of
	* trying a new one. When there is only one
	* server, this means that a query might work
	* instead of failing. We only allow one reset
	* per query to prevent looping.
	*/
	if (terrno == ECONNRESET &&
	!connreset) {
	connreset = 1;
	ns--;
	}
	continue;
	}
	cp = answer;
	if ((resplen = ntohs((u_short )cp)) >
	anslen) {
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	fprintf(stderr,
	"response truncated\n");
	#endif
	len = anslen;
	truncated = 1;
	} else
	len = resplen;
	while (len != 0 &&
	(n = read(s, (char *)cp,
	(int)len)) > 0) {
	cp += n;
	len -= n;
	}
	if (n <= 0) {
	terrno = errno;
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	perror("read failed");
	#endif
	(void) close(s);
	s = -1;
	continue;
	}
	if (truncated) {
	/*
	* Flush rest of answer
	* so connection stays in synch.
	*/
	anhp->tc = 1;
	len = resplen - anslen;
	/*
	* set the value of resplen to anslen,
	* this is done because the caller
	* assumes resplen contains the size of
	* message read into the "answer" buffer
	* passed in.
	*/
	resplen = anslen;

	while (len != 0) {
	n = (len > sizeof (junk) ?
	sizeof (junk) : len);
	if ((n = read(s, junk, n)) > 0)
	len -= n;
	else
	break;
	}
	}
	} else {
	/*
	* Use datagrams.
	*/
	if (s < 0) {
	s = _socket(AF_INET, SOCK_DGRAM, 0);
	if (s < 0) {
	terrno = errno;
	#ifdef DEBUG
	if (_res.options & RES_DEBUG) {
	perror("socket (dg) failed");
	}
	#endif
	continue;
	}
	}
	#if BSD >= 43
	/*
	* I'm tired of answering this question, so:
	* On a 4.3BSD+ machine (client and server,
	* actually), sending to a nameserver datagram
	* port with no nameserver will cause an
	* ICMP port unreachable message to be returned.
	* If our datagram socket is "connected" to the
	* server, we get an ECONNREFUSED error on the next
	* socket operation, and select returns if the
	* error message is received. We can thus detect
	* the absence of a nameserver without timing out.
	* If we have sent queries to at least two servers,
	* however, we don't want to remain connected,
	* as we wish to receive answers from the first
	* server to respond.
	*/
	if (_res.nscount == 1 \|\|
	(try == 0 && ns == 0)) {
	/*
	* Don't use connect if we might
	* still receive a response
	* from another server.
	*/
	if (connected == 0) {
	if (connect(s,
	(struct sockaddr *) &_res.nsaddr_list[ns],
	sizeof (struct sockaddr)) < 0) {
	#ifdef DEBUG
	if (_res.options &
	RES_DEBUG) {
	perror("connect");
	}
	#endif
	continue;
	}
	connected = 1;
	}
	if (send(s, buf, buflen, 0) != buflen) {
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	perror("send");
	#endif
	continue;
	}
	} else {
	/*
	* Disconnect if we want to listen for
	* responses from more than one server.
	*/
	if (connected) {
	(void) connect(s, &no_addr,
	sizeof (no_addr));
	connected = 0;
	}
	#endif /* BSD */
	if (sendto(s, buf, buflen, 0,
	(struct sockaddr *) &_res.nsaddr_list[ns],
	sizeof (struct sockaddr)) != buflen) {
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	perror("sendto");
	#endif
	continue;
	}
	#if BSD >= 43
	}
	#endif

	/*
	* Wait for reply
	*/
	timeout.tv_sec = (_res.retrans << try);
	if (try > 0)
	timeout.tv_sec /= _res.nscount;
	if (timeout.tv_sec <= 0)
	timeout.tv_sec = 1;
	timeout.tv_usec = 0;
	wait:
	FD_ZERO(&dsmask);
	FD_SET(s, &dsmask);
	n = select(s+1, &dsmask, (fd_set *)NULL,
	(fd_set *)NULL, &timeout);
	if (n < 0) {
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	perror("select");
	#endif
	continue;
	}
	if (n == 0) {
	/*
	* timeout
	*/
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	printf("timeout\n");
	#endif
	#if BSD >= 43
	gotsomewhere = 1;
	#endif
	continue;
	}
	if ((resplen = recv(s, answer, anslen, 0))
	<= 0) {
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	perror("recvfrom");
	#endif
	continue;
	}
	gotsomewhere = 1;
	if (id != anhp->id) {
	/*
	* response from old query, ignore it
	*/
	#ifdef DEBUG
	if (_res.options & RES_DEBUG) {
	printf("old answer:\n");
	p_query(answer);
	}
	#endif
	goto wait;
	}
	if (!(_res.options & RES_IGNTC) && anhp->tc) {
	/*
	* get rest of answer;
	* use TCP with same server.
	*/
	#ifdef DEBUG
	if (_res.options & RES_DEBUG)
	printf("truncated answer\n");
	#endif
	(void) close(s);
	s = -1;
	v_circuit = 1;
	goto usevc;
	}
	}
	#ifdef DEBUG
	if (_res.options & RES_DEBUG) {
	printf("got answer:\n");
	p_query(answer);
	}
	#endif
	/*
	* If using virtual circuits, we assume that the first server
	* is preferred * over the rest (i.e. it is on the local
	* machine) and only keep that one open.
	* If we have temporarily opened a virtual circuit,
	* or if we haven't been asked to keep a socket open,
	* close the socket.
	*/
	if ((v_circuit &&
	((_res.options & RES_USEVC) == 0 \|\| ns != 0)) \|\|
	(_res.options & RES_STAYOPEN) == 0) {
	(void) close(s);
	s = -1;
	}
	return (resplen);
	}
	}
	if (s >= 0) {
	(void) close(s);
	s = -1;
	}
	if (v_circuit == 0)
	if (gotsomewhere == 0)
	errno = ECONNREFUSED; /* no nameservers found */
	else
	errno = ETIMEDOUT; /* no answer obtained */
	else
	errno = terrno;
	return (-1);
	}

	/*
	* This routine is for closing the socket if a virtual circuit is used and
	* the program wants to close it. This provides support for endhostent()
	* which expects to close the socket.
	*
	* This routine is not expected to be user visible.
	*/
	void
	_res_close()
	{
	if (s != -1) {
	(void) close(s);
	s = -1;
	}
	}