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<th colspan="3" align="center">LPRng Reference Manual: 24
Sep 2004 (For LPRng-3.8.28)</th>
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<h1 class="SECT1"><a name="SOCKETAPI">11.3. Socket
API</a></h1>
<p>The Socket API is a very flexible job transfer protocol.
It is widely support by most Print Server manufacturers, with
the Hewlett Packard JetDirect setting the <span class=
"emphasis"><i class="EMPHASIS">de facto</i></span> standard.
The Socket API is extremely simple.</p>
<ol type="1">
<li>
<p>The user establishes a connection to TCP/IP port on
the Printer or Network Print spooler. The HP JetDirect
uses port 9100 by default, but other ports are used as
well. This connection may be refused if the printer is
busy printing a job.</p>
</li>
<li>
<p>When the network connection is established to a system
which has an <span class="emphasis"><i class=
"EMPHASIS">internal printer</i></span> or for which the
Network Print Spooler is an integral part of the system,
the printer usually flushes all internal buffers and
readies itself to receive a new job. However, when you
are using an external Print Server box, you may need to
send specific initialization sequences to the printer to
ensure that it is reset correctly and is ready to receive
new jobs.</p>
</li>
<li>
<p>When the connection is made, all bytes sent to the
connection are either transferred to and external
interface to directly to a <span class="emphasis"><i
class="EMPHASIS">print buffer</i></span> used by the
printer's Print Engine.</p>
</li>
<li>
<p>The connection is bidirectional, and information sent
to the external port by an external printer or error
messages and status generated by the printer's Print
Engine will be transferred over the data link to the
user.</p>
</li>
<li>
<p>The Network Print spooler will keep the connection
open until it is closed by the user. During this period
it may continue to report status or other information
such as printer On Line, paper outages, and so forth.</p>
</li>
<li>
<p>If the connection to the printer is <span class=
"emphasis"><i class="EMPHASIS">half-closed</i></span>,
that is, the <code class="FUNCTION">shutdown()</code>
network system call is used to indicate to the remote
printer that no further data will be sent, then the
printer may immediately terminate the network connection.
This means that no further network or status messages
will be sent to the user.</p>
</li>
<li>
<p>If the connection is to a External Print Server, then
usually the connection can be immediately re-established.
It is the responsibility of the user to ensure that a the
printer has finished its work before sending a new
job.</p>
</li>
<li>
<p>If the connection is to an internal Print Server, then
usually the printer will not allow the connection to be
made, or will refuse all data transfers on the connection
until the printer finishes with the previous job and all
internal buffers have been cleared.</p>
</li>
</ol>
<br>
<br>
<p>The following is a sample printcap showing how to use the
Socket API:</p>
<div class="INFORMALEXAMPLE">
<a name="AEN4937"></a>
<pre class="SCREEN">
lp:
# make a socket connection to port 9100
:lp=10.0.0.2%9100
</pre>
</div>
<br>
<br>
<p>You can use the <a href=
"http://www.l0pht.com/~weld/netcat/" target="_top">netcat</a>
utility by Hobbit <code class="EMAIL"><<a href=
"mailto:Hobbit@avian.org">Hobbit@avian.org</a>></code> to
test that the Socket interface is available and working. If
<tt class="FILENAME">ellipse.ps</tt> is a test file, then:
The simplest and easiest way to print a file to a network
printer appears</p>
<div class="INFORMALEXAMPLE">
<a name="AEN4943"></a>
<pre class="SCREEN">
nc printer.ip.addr 9100 < file
Example:
nc 10.0.0.25 9100 < ellipse.ps
</pre>
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