luasocket/test/udp-zero-length-send-recv

#!/usr/bin/env 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

]]

socket = 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

assert(r:settimeout(2))

ok, emsg = r:receive()

if not ok or string.len(ok) ~= 0 then
    print("fail - receive of zero failed with:", ok, emsg)
    os.exit(1)
end

print"ok"