Richard Russell
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Sending UDP data packets
« Thread started on: Dec 30th, 2015, 1:07pm » |
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There is an ongoing discussion at the Liberty BASIC Yahoo! Group about sending UDP (User Datagram Protocol) packets from an LB program. This is a straightforward thing to do in LB or LBB code (sending UDP packets is probably the simplest of all socket transactions) yet, strangely, the majority of replies there have implied that it is difficult or impossible to achieve without an external 'helper' application!
I have listed below a program to demonstrate just how easy it is to send UDP packets from LB/LBB. For convenience the program goes through the entire startup, open socket, send packet, close socket, shutdown sequence for every packet sent. This should be OK so long as packets are being sent relatively infrequently, but in a program that sends large numbers of packets in quick succession it would be better to keep the socket open for the duration.
Of course I cannot reply to the LB Group myself, which is why I am posting the information here.
Richard.
Code: open "WS2_32" for DLL as #winsock
packet$ = "Hello world!"
ok = UDPsend("127.0.0.1", 12080, packet$)
if ok then print "Packet sent" else print "UDPsend failed"
close #winsock
end
function UDPsend(addr$, port, msg$)
AF.INET = 2
SOCK.DGRAM = 2
IPPROTO.UDP = 17
UDPsend = 0
port = (port and hexdec("FF00")) / 256 + (port and 255) * 256 ' swap bytes
calldll #winsock, "inet_addr", addr$ as ptr, ipaddr as ulong
struct WSAdata, d as char[398]
calldll #winsock, "WSAStartup", 514 as long, WSAdata as struct, ret as long
if ret then exit function
calldll #winsock, "socket", AF.INET as long, SOCK.DGRAM as long, _
IPPROTO.UDP as long, socket as long
if socket = -1 then exit function
struct addr, family as short, port as short, addr as ulong, zero as char[8]
addr.family.struct = AF.INET
addr.port.struct = port
addr.addr.struct = ipaddr
al = len(addr.struct)
ml = len(msg$)
calldll #winsock, "sendto", socket as long, msg$ as ptr, ml as long, _
0 as long, addr as struct, al as long, sent as long
calldll #winsock, "closesocket", socket as long, ret as long
calldll #winsock, "WSACleanup", ret as long
if sent = ml then UDPsend = 1
end function
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