Test showing failure to receive a zero-length packet.

test/udp-zero-length-send-recv

@@ -0,0 +1,35 @@
+#!/usr/bin/lua
+
+--[[
+Show that luasocket returns an error message on zero-length UDP sends,
+even though the send is valid, and in fact the UDP packet is sent
+to the peer:
+
+% sudo tcpdump -i lo -n
+tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
+listening on lo, link-type EN10MB (Ethernet), capture size 65535 bytes
+13:40:16.652808 IP 127.0.0.1.56573 > 127.0.0.1.5432: UDP, length 0
+
+]]
+
+require"socket"
+
+s = assert(socket.udp())
+r = assert(socket.udp())
+assert(r:setsockname("*", 5432))
+assert(s:setpeername("127.0.0.1", 5432))
+
+ok, emsg = s:send("")
+if ok ~= 0 then
+    print("send of zero failed with:", ok, emsg)
+end
+
+ok, emsg = r:receive()
+
+if not ok or string.len(ok) ~= 0 then
+    print("receive of zero failed with:", ok, emsg)
+end
+
+print"ok"
+
+