Only set sockets to non-blocking mode on the sending side of the

transfer.

Note that the sender can either be the client or the server depending
on whether --reverse is used.

This fixes some problems with UDP transfers getting severely confused
and (wrongly) complaining about packets arriving out of order.

Related to issue #125.

src/iperf_client_api.c

@@ -381,9 +381,12 @@ iperf_run_client(struct iperf_test * test)
 	    if (startup) {
 	        startup = 0;
 
-                SLIST_FOREACH(sp, &test->streams, streams) {
-                    setnonblocking(sp->socket, 1);
-                }
+		// If the client is sending (normal mode) then set nonblocking sockets
+		if (!test->reverse) {
+		    SLIST_FOREACH(sp, &test->streams, streams) {
+			setnonblocking(sp->socket, 1);
+		    }
+		}
 	    }
 
 	    if (test->reverse) {
@@ -406,9 +409,12 @@ iperf_run_client(struct iperf_test * test)
 	         (test->settings->bytes != 0 && test->bytes_sent >= test->settings->bytes) ||
 	         (test->settings->blocks != 0 && test->blocks_sent >= test->settings->blocks))) {
 
-                SLIST_FOREACH(sp, &test->streams, streams) {
-                    setnonblocking(sp->socket, 0);
-                }
+		// If the client is sending (normal mode) then undo nonblocking sockets
+		if (!test->reverse) {
+		    SLIST_FOREACH(sp, &test->streams, streams) {
+			setnonblocking(sp->socket, 0);
+		    }
+		}
 
 		/* Yes, done!  Send TEST_END. */
 		test->done = 1;

src/iperf_server_api.c

@@ -516,7 +516,10 @@ iperf_run_server(struct iperf_test *test)
 			    FD_SET(s, &test->read_set);
 			if (s > test->max_fd) test->max_fd = s;
 
-                        setnonblocking(s, 1);
+			// If the server is sending (reverse mode) then set nonblocking sockets
+			if (test->reverse) {
+			    setnonblocking(s, 1);
+			}
 
                         streams_accepted++;
                         if (test->on_new_stream)