res_send.c

一个C源代码分析器

					_res_close();
					goto next_ns;
				}
				vc = 1;
			}
			/*
			 * Send length & message
			 */
			putshort((u_short)buflen, (u_char*)&len);
			iov[0].iov_base = (caddr_t)&len;
			iov[0].iov_len = INT16SZ;
			iov[1].iov_base = (caddr_t)buf;
			iov[1].iov_len = buflen;
			if (writev(s, iov, 2) != (INT16SZ + buflen)) {
				terrno = errno;
				Perror(stderr, "write failed", errno);
				badns |= (1<<ns);
				_res_close();
				goto next_ns;
			}
			/*
			 * Receive length & response
			 */
			cp = ans;
			len = INT16SZ;
			while ((n = read(s, (char *)cp, (int)len)) > 0) {
				cp += n;
				if ((len -= n) <= 0)
					break;
			}
			if (n <= 0) {
				terrno = errno;
				Perror(stderr, "read failed", errno);
				_res_close();
				/*
				 * 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;
					_res_close();
					goto same_ns;
				}
				_res_close();
				goto next_ns;
			}
			resplen = _getshort(ans);
			if (resplen > anssiz) {
				Dprint(_res.options & RES_DEBUG,
				       (stdout, ";; response truncated\n")
				       );
				truncated = 1;
				len = anssiz;
			} else
				len = resplen;
			cp = ans;
			while (len != 0 &&
			       (n = read(s, (char *)cp, (int)len)) > 0
			       ) {
				cp += n;
				len -= n;
			}
			if (n <= 0) {
				terrno = errno;
				Perror(stderr, "read(vc)", errno);
				_res_close();
				goto next_ns;
			}
			if (truncated) {
				/*
				 * Flush rest of answer
				 * so connection stays in synch.
				 */
				anhp->tc = 1;
				len = resplen - anssiz;
				while (len != 0) {
					char junk[512];

					n = (len > sizeof(junk)
					     ? sizeof(junk)
					     : len);
					if ((n = read(s, junk, n)) > 0)
						len -= n;
					else
						break;
				}
			}
		} else {
			/*
			 * Use datagrams.
			 */
			struct timeval	timeout;
			fd_set		dsmask;
			struct sockaddr_in from;
			int		fromlen;

			if ((s < 0) || vc) {
				if (vc)
					_res_close();
				s = socket(AF_INET, SOCK_DGRAM, PF_UNSPEC);
				if (s < 0) {
 bad_dg_sock:				terrno = errno;
					Perror(stderr, "socket(dg)", errno);
					return (-1);
				}
				connected = 0;
			}
			/*
			 * 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)) {
				/*
				 * Connect only if we are sure we won't
				 * receive a response from another server.
				 */
				if (!connected) {
					if (connect(s,
						    (struct sockaddr *)nsap,
						    sizeof(struct sockaddr)
						    ) < 0
					    ) {
						Aerror(stderr,
						       "connect(dg)",
						       errno, *nsap);
						badns |= (1<<ns);
						_res_close();
						goto next_ns;
					}
					connected = 1;
				}
				if (send(s, buf, buflen, 0) != buflen) {
					Perror(stderr, "send", errno);
					badns |= (1<<ns);
					_res_close();
					goto next_ns;
				}
			} else {
				/*
				 * Disconnect if we want to listen
				 * for responses from more than one server.
				 */
				if (connected) {
#if defined(BSD) && (BSD >= 199103)
					struct sockaddr_in no_addr;

					no_addr.sin_family = AF_INET;
					no_addr.sin_addr.s_addr = INADDR_ANY;
					no_addr.sin_port = 0;
					(void) connect(s,
						       (struct sockaddr *)
						        &no_addr,
						       sizeof(no_addr));
#else
					int s1 = socket(AF_INET, SOCK_DGRAM,
							PF_UNSPEC);
					if (s1 < 0)
						goto bad_dg_sock;
					(void) dup2(s1, s);
					(void) close(s1);
					Dprint(_res.options & RES_DEBUG,
					       (stdout, ";; new DG socket\n"))
#endif
					connected = 0;
					errno = 0;
				}
				if (sendto(s, buf, buflen, 0,
					   (struct sockaddr *)nsap,
					   sizeof(struct sockaddr))
				    != buflen) {
					Aerror(stderr, "sendto", errno, *nsap);
					badns |= (1<<ns);
					_res_close();
					goto next_ns;
				}
			}

			/*
			 * Wait for reply
			 */
			timeout.tv_sec = (_res.retrans << try);
			if (try > 0)
				timeout.tv_sec /= _res.nscount;
			if ((long) 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) {
				Perror(stderr, "select", errno);
				_res_close();
				goto next_ns;
			}
			if (n == 0) {
				/*
				 * timeout
				 */
				Dprint(_res.options & RES_DEBUG,
				       (stdout, ";; timeout\n")
				       );
				gotsomewhere = 1;
				_res_close();
				goto next_ns;
			}
			fromlen = sizeof(struct sockaddr_in);
			resplen = recvfrom(s, ans, anssiz, 0,
					   (struct sockaddr *)&from, &fromlen);
			if (resplen <= 0) {
				Perror(stderr, "recvfrom", errno);
				_res_close();
				goto next_ns;
			}
			gotsomewhere = 1;
			if (hp->id != anhp->id) {
				/*
				 * response from old query, ignore it.
				 * XXX - potential security hazard could
				 *	 be detected here.
				 */
				DprintQ((_res.options & RES_DEBUG) ||
					(_res.pfcode & RES_PRF_REPLY),
					(stdout, ";; old answer:\n"),
					ans);
				goto wait;
			}
#if CHECK_SRVR_ADDR
			if (!(_res.options & RES_INSECURE1) &&
			    !our_server(&from)) {
				/*
				 * response from wrong server? ignore it.
				 * XXX - potential security hazard could
				 *	 be detected here.
				 */
				DprintQ((_res.options & RES_DEBUG) ||
					(_res.pfcode & RES_PRF_REPLY),
					(stdout, ";; not our server:\n"),
					ans);
				goto wait;
			}
#endif
			if (!(_res.options & RES_INSECURE2) &&
			    !queries_match(buf, buf + buflen,
					   ans, ans + anssiz)) {
				/*
				 * response contains wrong query? ignore it.
				 * XXX - potential security hazard could
				 *	 be detected here.
				 */
				DprintQ((_res.options & RES_DEBUG) ||
					(_res.pfcode & RES_PRF_REPLY),
					(stdout, ";; wrong query name:\n"),
					ans);
				goto wait;
			}
			if (anhp->rcode == SERVFAIL ||
			    anhp->rcode == NOTIMP ||
			    anhp->rcode == REFUSED) {
				DprintQ(_res.options & RES_DEBUG,
					(stdout, "server rejected query:\n"),
					ans);
				badns |= (1<<ns);
				_res_close();
				goto next_ns;
			}
			if (!(_res.options & RES_IGNTC) && anhp->tc) {
				/*
				 * get rest of answer;
				 * use TCP with same server.
				 */
				Dprint(_res.options & RES_DEBUG,
				       (stdout, ";; truncated answer\n")
				       );
				v_circuit = 1;
				_res_close();
				goto same_ns;
			}
		} /*if vc/dg*/
		DprintQ((_res.options & RES_DEBUG) ||
			(_res.pfcode & RES_PRF_REPLY),
			(stdout, ";; got answer:\n"),
			ans);
		/*
		 * 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) || ns != 0)) ||
		    !(_res.options & RES_STAYOPEN)) {
			_res_close();
		}
		if (Rhook) {
			int done = 0, loops = 0;

			do {
				res_sendhookact act;

				act = (*Rhook)(nsap,
					       buf,
					       buflen,
					       ans,
					       anssiz,
					       &resplen);
				switch (act) {
				case res_goahead:
				case res_done:
					done = 1;
					break;
				case res_nextns:
					_res_close();
					goto next_ns;
				case res_modified:
					/* give the hook another try */
					if (++loops < 42) /*doug adams*/
						break;
					/*FALLTHROUGH*/
				case res_error:
					/*FALLTHROUGH*/
				default:
					return (-1);
				}
			} while (!done);

		}
		return (resplen);
    next_ns: ;
	   } /*foreach ns*/
	} /*foreach retry*/
	_res_close();
	if (!v_circuit) {
		if (!gotsomewhere)
			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 >= 0) {
		(void) close(s);
		s = -1;
		connected = 0;
		vc = 0;
	}
}