sane-project-website/old-archive/1999-08/0273.html

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<title>sane-devel: Re: net problem</title>
<h1>Re: net problem</h1>
<b>Andreas Beck</b> (<a href="mailto:becka@rz.uni-duesseldorf.de"><i>becka@rz.uni-duesseldorf.de</i></a>)<br>
<i>Sun, 22 Aug 1999 21:01:30 +0200</i>
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<i>&gt; 15526 write(2, "                      Stripes: N"..., 34) = 34</i><br>
<i>&gt; 15526 write(2, "                      Slides: No"..., 33) = 33</i><br>
<i>&gt; 15526 write(2, "  Scan button:        Yes\n", 26) = 26</i><br>
<i>&gt; 15526 write(2, "\nImaging Capabilities...\n", 25) = -1 EPIPE (Broken pipe)</i><br>
<i>&gt; 15526 --- SIGPIPE (Broken pipe) ---</i><br>
<p>
That comes from the remote frontend closing the connection.<br>
<p>
<i>&gt; The SIGPIPE is weird.</i><br>
<i>&gt; The other end of the network (scanimage -L, with just the net driver active):</i><br>
<p>
Here is the network transfer:<br>
<p>
<i>&gt; write(24, "\0\0\0\0\1\0\0\3\0\0\0\4wim\0", 16) = 16</i><br>
A SANE_NET_INIT request.<br>
<p>
<i>&gt; read(24, "\0\0\0\0\1\0\0\3", 8192)      = 8</i><br>
<p>
Answer looks good.<br>
<p>
<i>&gt; write(24, "\0\0\0\1", 4)                = 4</i><br>
<i>&gt; read(24, "\n\nScanner attributes from device"..., 8192) = 43</i><br>
<p>
There we go. For some weird reason the saned sends textual data via the<br>
net stream. That looks like a bug in the backend or the saned.<br>
Seemingly the driver gives additional info to stderr, which gets redirected<br>
over the Network, and causes havoc in the binary protocol.<br>
<p>
<i>&gt; More strangeness: If I do saned -d, it works (just once though)...</i><br>
<p>
<i>&gt; I was just thinking, is this due to the text appearing at startup. </i><br>
<p>
Yes. Definitely. <br>
<p>
<i>&gt; somehow saned started from inetd seems to also send this to the client, </i><br>
<i>&gt; where with saned -d you only get to see the result of the probe, while </i><br>
<i>&gt; the text is on the console where I started saned -d.</i><br>
<p>
O.K.  that indicates, that the backend for some reason sends that diagnostic<br>
stuff to stderr which seems to be mapped to the network connection by inetd<br>
what causes the problem. As a workaround I suggest to use a script saned.in:<br>
<p>
#!/bin/bash<br>
exec saned 2&gt;/dev/null<br>
<p>
which will avoid the stderr stuff to mix up with the net stuff.<br>
<p>
IMHO the backend should be fixed not to spit out such diagnostic stuff<br>
unless told to specifically using a SANE_DEBUG variable or similar.<br>
<p>
CU, ANdy<br>
<p>
<pre>
-- 
= Andreas Beck                    |  Email :  &lt;<a href="mailto:andreas.beck@ggi-project.org">andreas.beck@ggi-project.org</a>&gt; =
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<li> <b>Next message:</b> <a href="0274.html">Bernd Schroeder: "Re: microtek X6 advance and TMA"</a>
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