Allow UDP server to receive datagrams from multiple socket pairs with -k

flag. Prompted by a question from dsp at 2f30 dot org, diff from Lazarom
Koromil with a few tweaks by me, many thanks.

ok mikeb@ nicm@ haesbaert@

2 files changed, 17 insertions, 7 deletions

diff --git a/src/usr.bin/nc/nc.1 b/src/usr.bin/nc/nc.1
index 75d1437580..232b6f5b6e 100644
--- a/src/usr.bin/nc/nc.1
+++ b/src/usr.bin/nc/nc.1
@@ -1,4 +1,4 @@
-.\"     $OpenBSD: nc.1,v 1.60 2012/02/07 12:11:43 lum Exp $
+.\"     $OpenBSD: nc.1,v 1.61 2012/07/07 15:33:02 haesbaert Exp $
 .\"
 .\" Copyright (c) 1996 David Sacerdote
 .\" All rights reserved.
@@ -25,7 +25,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: February 7 2012 $
+.Dd $Mdocdate: July 7 2012 $
 .Dt NC 1
 .Os
 .Sh NAME
@@ -119,6 +119,10 @@ is completed.
 It is an error to use this option without the
 .Fl l
 option.
+When used together with the
+.Fl u
+option, the server socket is not connected and it can receive UDP datagrams from
+multiple hosts.
 .It Fl l
 Used to specify that
 .Nm
diff --git a/src/usr.bin/nc/netcat.c b/src/usr.bin/nc/netcat.c
index 4bef71a7ca..a034bbab8c 100644
--- a/src/usr.bin/nc/netcat.c
+++ b/src/usr.bin/nc/netcat.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: netcat.c,v 1.108 2012/07/07 09:36:30 haesbaert Exp $ */
+/* $OpenBSD: netcat.c,v 1.109 2012/07/07 15:33:02 haesbaert Exp $ */
 /*
  * Copyright (c) 2001 Eric Jackson <ericj@monkey.org>
  *
@@ -345,11 +345,17 @@ main(int argc, char *argv[])
                         if (s < 0)
                                 err(1, NULL);
                         /*
-                         * For UDP, we will use recvfrom() initially
-                         * to wait for a caller, then use the regular
-                         * functions to talk to the caller.
+                         * For UDP and -k, don't connect the socket, let it
+                         * receive datagrams from multiple socket pairs.
                          */
-                        if (uflag) {
+                        if (uflag && kflag)
+                                readwrite(s);
+                        /*
+                         * For UDP and not -k, we will use recvfrom() initially
+                         * to wait for a caller, then use the regular functions
+                         * to talk to the caller.
+                         */
+                        else if (uflag && !kflag) {
                                 int rv, plen;
                                 char buf[16384];
                                 struct sockaddr_storage z;