Try alternate addresses more agressively.

Attempt to connect to alternate addresses if the connect doesn't
succeed in 180ms, and cut wait time between connection attempts
in half for each additional, if no connection was established.

Take the first connection to succeed and close the others.

This makes whois more responsive when e.g. IPv6 service took long
time or fail to respond.

PR:		158125
Submitted by:	Mark Andrews <marka isc org> (with changes from me)
MFC after:	2 weeks

usr.bin/whois/whois.c

@@ -1,4 +1,4 @@
-/*
+/*-
  * Copyright (c) 1980, 1993
  *	The Regents of the University of California.  All rights reserved.
  *
@@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <sys/poll.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <ctype.h>
@@ -55,6 +56,8 @@ __FBSDID("$FreeBSD$");
 #include <string.h>
 #include <sysexits.h>
 #include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
 
 #define	ABUSEHOST	"whois.abuse.net"
 #define	NICHOST		"whois.crsnic.net"
@@ -280,21 +283,136 @@ whois(const char *query, const char *hostname, int flags)
 	FILE *fp;
 	struct addrinfo *hostres, *res;
 	char *buf, *host, *nhost, *p;
-	int i, s;
+	int i, j, s = -1, count;
 	size_t c, len;
+	struct pollfd *fds;
+	int timeout = 180;
 
-	s = -1;
 	hostres = gethostinfo(hostname, 1);
-	for (res = hostres; res; res = res->ai_next) {
-		s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
+	for (res = hostres, count = 0; res; res = res->ai_next)
+		count++;
+
+	fds = calloc(count, sizeof(*fds));
+	if (fds == NULL)
+		err(EX_OSERR, "calloc()");
+
+	/*
+	 * Traverse the result list elements and make non-block
+	 * connection attempts.
+	 */
+	count = i = 0;
+	for (res = hostres; res != NULL; res = res->ai_next) {
+		s = socket(res->ai_family, res->ai_socktype | SOCK_NONBLOCK,
+		    res->ai_protocol);
 		if (s < 0)
 			continue;
-		if (connect(s, res->ai_addr, res->ai_addrlen) == 0)
-			break;
-		close(s);
+		if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
+			if (errno == EINPROGRESS) {
+				/* Add the socket to poll list */
+				fds[i].fd = s;
+				fds[i].events = POLLERR | POLLHUP |
+						POLLIN | POLLOUT;
+				count++;
+				i++;
+			} else {
+				close(s);
+				s = -1;
+
+				/*
+				 * Poll only if we have something to poll,
+				 * otherwise just go ahead and try next
+				 * address
+				 */
+				if (count == 0)
+					continue;
+			}
+		} else
+			goto done;
+
+		/*
+		 * If we are at the last address, poll until a connection is
+		 * established or we failed all connection attempts.
+		 */
+		if (res->ai_next == NULL)
+			timeout = INFTIM;
+
+		/*
+		 * Poll the watched descriptors for successful connections:
+		 * if we still have more untried resolved addresses, poll only
+		 * once; otherwise, poll until all descriptors have errors,
+		 * which will be considered as ETIMEDOUT later.
+		 */
+		do {
+			int n;
+
+			n = poll(fds, i, timeout);
+			if (n == 0) {
+				/*
+				 * No event reported in time.  Try with a
+				 * smaller timeout (but cap at 2-3ms)
+				 * after a new host have been added.
+				 */
+				if (timeout >= 3)
+					timeout <<= 1;
+
+				break;
+			} else if (n < 0) {
+				/*
+				 * errno here can only be EINTR which we would want
+				 * to clean up and bail out.
+				 */
+				s = -1;
+				goto done;
+			}
+
+			/*
+			 * Check for the event(s) we have seen.
+			 */
+			for (j = 0; j < i; j++) {
+				if (fds[j].fd == -1 || fds[j].events == 0 ||
+				    fds[j].revents == 0)
+					continue;
+				if (fds[j].revents & ~(POLLIN | POLLOUT)) {
+					close(s);
+					fds[j].fd = -1;
+					fds[j].events = 0;
+					count--;
+					continue;
+				} else if (fds[j].revents & (POLLIN | POLLOUT)) {
+					/* Connect succeeded. */
+					s = fds[j].fd;
+
+					goto done;
+				}
+
+			}
+		} while (timeout == INFTIM && count != 0);
 	}
+
+	/* All attempts were failed */
+	s = -1;
+	if (count == 0)
+		errno = ETIMEDOUT;
+
+done:
+	/* Close all watched fds except the succeeded one */
+	for (j = 0; j < i; j++)
+		if (fds[j].fd != s && fds[j].fd != -1)
+			close(fds[j].fd);
+
+	if (s != -1) {
+                /* Restore default blocking behavior.  */
+                if ((flags = fcntl(s, F_GETFL)) != -1) {
+                        flags &= ~O_NONBLOCK;
+                        if (fcntl(s, F_SETFL, flags) == -1)
+                                err(EX_OSERR, "fcntl()");
+                } else
+			err(EX_OSERR, "fcntl()");
+        }
+
+	free(fds);
 	freeaddrinfo(hostres);
-	if (res == NULL)
+	if (s == -1)
 		err(EX_OSERR, "connect()");
 
 	fp = fdopen(s, "r+");