AMX DESIGN XPRESS V 1.5 - PROGRAMMER GUIDE User's Guide download pdf (Page 46)

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KwikNet Overview

Client - Server Using UDP Sockets

This example illustrates the use of KwikNet's UDP socket interface to deliver UDP

datagrams between two end points. This data transfer mechanism is not considered

reliable. Furthermore, since TCP is not used, a logical connection between the end points

does not exist. Although the end points happen to be running on the same host computer,

the actions required by each are still the same as would be required if they resided on

separate hosts interconnected by a real network.

The server's second scenario is embodied in function

server2(). The corresponding

function executed by the client is

client2().

The server calls kn_socket() to create a connectionless datagram socket. The server

calls kn_setsockopt() to force its socket to be non-blocking. It then calls kn_bind() to

bind itself to the socket, identifying itself as port 5001, but allowing

KwikNet to assign its

IP address.

KwikNet assigns IP address 192.168.1.73, the IP address of the only network

present in the sample configuration. Once the bind is complete, the server can

immediately receive data directed to IP address 192.168.1.73.

The server then uses procedure kn_select() to wait until some data from a client is

available for reading. The sample illustrates the proper use of the macros FD_ZERO,

FD_SET and FD_ISSET for manipulating socket sets.

Once data from the client is available, the server uses kn_recvfrom() to learn the client's

network address and to receive a 4 byte message, a long value, from the client. The

server then uses kn_connect() to identify the client to which it must send its response.

The server then uses procedure kn_select() to wait until the server's socket is ready to

accept data for transmission. The value received from the client is incremented by two

and echoed to the client using the kn_send() procedure to send the 4 byte long value.

Once the value has been echoed to the client, the server breaks its association with the

client using kn_connect() to identify its peer as port 0 and IP address 0. The server then

uses kn_shutdown() to terminate all send and receive operations on its socket. The

socket is then closed using kn_close().

The client calls

kn_socket() to create a connectionless datagram socket. It then calls

kn_bind() to bind itself to the socket, allowing KwikNet to assign a port number and IP

address.

The client then uses procedure kn_select() to wait until the client's socket is ready to

accept data for transmission. The arbitrary value 8 is sent to the server using the

kn_sendto() procedure to send the 4 byte long value. The value is sent to the server

with port number 5001 and IP address 192.168.1.73.

Note that the client has to know the port number of the server to which it is trying to

connect. The IP address of the server happens to be the IP address assigned to the

Ethernet network predefined in the KwikNet Library. The sample illustrates the use of

procedure kn_inet_addr() to convert an IP address in dotted decimal form to an

equivalent network compatible form.

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