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<H1><A NAME="SECTION0018120000000000000000"></A>
<A NAME="6290"></A>
<A NAME="6291"></A>
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Higher Level Conventions
</H1>
<P>
Within Bacula, we have established the convention that any time a single
record is passed, it is sent with bnet_send() and read with bnet_recv().
Thus the normal exchange between the server (S) and the client (C) are:
<P>
<PRE>
S: wait for connection C: attempt connection
S: accept connection C: bnet_send() send request
S: bnet_recv() wait for request
S: act on request
S: bnet_send() send ack C: bnet_recv() wait for ack
</PRE>
<P>
Thus a single command is sent, acted upon by the server, and then
acknowledged.
<P>
In certain cases, such as the transfer of the data for a file, all the
information or data cannot be sent in a single packet. In this case, the
convention is that the client will send a command to the server, who knows
that more than one packet will be returned. In this case, the server will
enter a loop:
<P>
<PRE>
while ((n=bnet_recv(bsock)) > 0) {
act on request
}
if (n < 0)
error
</PRE>
<P>
The client will perform the following:
<P>
<PRE>
bnet_send(bsock);
bnet_send(bsock);
...
bnet_sig(bsock, BNET_EOD);
</PRE>
<P>
Thus the client will send multiple packets and signal to the server when all
the packets have been sent by sending a zero length record.
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2012-01-24
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