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<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="GENERATOR" CONTENT="Mozilla/4.04 [en] (X11; I; Linux 2.0.32 i486) [Netscape]">
<META NAME="Author" CONTENT="James CE Johnson">
<META NAME="Description" CONTENT="A first step towards using ACE productively">
<TITLE>ACE Tutorial 003</TITLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F">
<CENTER><B><FONT SIZE=+2>ACE Tutorial 003</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>Creating a Simple Client</FONT></B></CENTER>
<P>
<HR WIDTH="100%">
<P>Now that we've seen how to create servers, let's spend just a moment
making a client. Since this is so easy, I'm going to do all of it in this
one page.
<P>
Kirthika says, "Here's an one paragraph abstract for a one page client app:"
<UL>
The server is an Stream object of ACE_SOCK_Stream type. The
ACE_Sock_Connector does the job of actively making a connection with the
listening server. It does so using the server_host_address and port
number which are stored in the ACE_INET_Addr object.Once the
connection has been established, the client begins its interaction
with the server and bombards it with messages.
Note: send_n() call is used since this call sees to the issues of
network buffering and reliably gets the data across to the server.
Also, a timeout value is set to provide fault tolerance if the server
ever dies before the transaction is completed. The server calls a
close() method
once it reads in zero bytes during the Event_Handler::handle_input()
call. This
proves that the client has severed its connection. The server then
shuts down.
</UL>
<HR WIDTH="100%">
<PRE>
<font color=red>// $Id$</font>
<font color=red>/*
To establish a socket connection to a server, we'll need an ACE_SOCK_Connector.
*/</font>
<font color=blue>#include</font> "<font color=green>ace/SOCK_Connector.h</font>"
<font color=red>/*
Unlike the previous two tutorials, we're going to allow the user to provide
command line options this time. Still, we need defaults in case that isn't
done.
*/</font>
static u_short SERVER_PORT = ACE_DEFAULT_SERVER_PORT;
static const char *const SERVER_HOST = ACE_DEFAULT_SERVER_HOST;
static const int MAX_ITERATIONS = 4;
int main (int argc, char *argv[])
{
<font color=red>/*
Accept the users's choice of hosts or use the default. Then do the same
for the TCP/IP port at which the server is listening as well as the
number of iterations to perform.
*/</font>
const char *server_host = argc > 1 ? argv[1] : SERVER_HOST;
u_short server_port = argc > 2 ? <font color=#008888>ACE_OS::atoi</font> (argv[2]) : SERVER_PORT;
int max_iterations = argc > 3 ? <font color=#008888>ACE_OS::atoi</font> (argv[3]) : MAX_ITERATIONS;
<font color=red>/*
Build ourselves a Stream socket. This is a connected socket that provides
reliable end-to-end communications. We will use the server object to send
data to the server we connect to.
*/</font>
ACE_SOCK_Stream server;
<font color=red>/*
And we need a connector object to establish that connection. The ACE_SOCK_Connector
object provides all of the tools we need to establish a connection once we know the
server's network address...
*/</font>
ACE_SOCK_Connector connector;
<font color=red>/*
Which we create with an ACE_INET_Addr object. This object is given the TCP/IP port
and hostname of the server we want to connect to.
*/</font>
ACE_INET_Addr addr (server_port, server_host);
<font color=red>/*
So, we feed the Addr object and the Stream object to the connector's connect() member
function. Given this information, it will establish the network connection to the
server and attach that connection to the server object.
*/</font>
if (connector.connect (server, addr) == -1)
{
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>%p\n</font>", "<font color=green>open</font>"), -1);
}
<font color=red>/*
Just for grins, we'll send the server several messages.
*/</font>
for (int i = 0; i < max_iterations; i++)
{
char buf[BUFSIZ];
<font color=red>/*
Create our message with the message number
*/</font>
<font color=#008888>ACE_OS::sprintf</font> (buf, "<font color=green>message = %d\n</font>", i + 1);
<font color=red>/*
Send the message to the server. We use the server object's send_n() function to
send all of the data at once. There is also a send() function but it may not send
all of the data. That is due to network buffer availability and such. If the send()
doesn't send all of the data, it is up to you to program things such that it will
keep trying until all of the data is sent or simply give up. The send_n() function
already does the "<font color=green>keep trying</font>" option for us, so we use it.
Like the send() method used in the servers we've seen, there are two additional
parameters you can use on the send() and send_n() method calls. The timeout
parameter limits the amount of time the system will attempt to send the data
to the peer. The flags parameter is passed directly to the OS send() system
call. See send(2) for the valid flags values.
*/</font>
if (server.send_n ( buf, strlen(buf) ) == -1)
{
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>%p\n</font>", "<font color=green>send</font>"), -1);
}
else
{
<font color=red>/*
Pause for a second.
*/</font>
<font color=#008888>ACE_OS::sleep</font> (1);
}
}
<font color=red>/*
Close the connection to the server. The servers we've created so far all are based
on the ACE_Reactor. When we close(), the server's reactor will see activity for
the registered event handler and invoke handle_input(). That, in turn, will try
to read from the socket but get back zero bytes. At that point, the server will know
that we've closed from our side.
*/</font>
if (server.close () == -1)
{
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>%p\n</font>", "<font color=green>close</font>"), -1);
}
return 0;
}
</PRE>
<HR WIDTH="100%">
<P>Ok, so that was pretty easy. What would be even easier would be to wrap
all of the connection mess up in an object and overload a couple of basic
operators to make things less network-centric. Perhaps we'll see that in
another tutorial.
<P>If you want to compile it yourself, here's the <A HREF="client.cpp">source</A>,
the <A HREF="Makefile">Makefile</A>,
and <A HREF="00SetEnv">Environment
settings</A>.
<P>
<P><HR WIDTH="100%">
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