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<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D>Hi Lukas, All,<o:p></o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D><o:p> </o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D>I do not have TCP dump, but according to strace, the error is:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Courier New";color:#1F497D"><... writev resumed> ) = -1 ENOTCONN (Transport endpoint is not connected)<o:p></o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D>The error indeed happens on a write, and on the Erlang side this is reported as a normal close, at the next gen_tcp:recv call.<o:p></o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D><o:p> </o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D>Let us not go into discussing what can cause this error on a socket (unix domain BTW). It is irrelevant here.<o:p></o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D>The important here is that this socket error, and any other socket error shall not be confused with an orderly shutdown of the socket.<o:p></o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D><o:p> </o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D>I support the below mentioned proposal of making the default behavior report all errors, and the masking behavior explicitly selected with an option.<o:p></o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D><o:p> </o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D>Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D> Andras<o:p></o:p></span></p>
<p class="MsoNormal"><span style=font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style=font-size:10.0pt;font-family:"Tahoma","sans-serif">From:</span></b><span style=font-size:10.0pt;font-family:"Tahoma","sans-serif"> Lukas Larsson [mailto:lukas@erlang.org]
<br />
<b>Sent:</b> Thursday, August 16, 2018 2:37 PM<br />
<b>To:</b> Bekes, Andras G (IST)<br />
<b>Cc:</b> Erlang Questions<br />
<b>Subject:</b> Re: [erlang-questions] {error,closed} vs. {error,econnreset}<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style=margin-bottom:12.0pt>Hello,<o:p></o:p></p>
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<p class="MsoNormal">On Mon, 6 Aug 2018, 10:49 Bekes, Andras G, wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hi All,<br />
<br />
Reviving this old thread again, because I am getting more and more convinced that we need further changes.<br />
We're still observing connection close events when an error should be reported to gen_tcp level.<br />
It can be a reset error somehow still not reported as 'econnreset', but I suspect it must be some other error.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I suppose that you have not managed to catch the error in a tcp dump as Rory asked for?<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><br />
I checked the code in inet_drv.c. The function<br />
static int tcp_recv(tcp_descriptor* desc, int request_len)<br />
seems to work properly -- a reset is either reported as closed or econnreset, depending on show_econnreset, all other errors are reported as errors.<br />
<br />
However, the function<br />
static int tcp_send_or_shutdown_error(tcp_descriptor* desc, int err)<br />
hides errors. Connection reset errors are properly handled (either reported as closed or econnreset, depending on show_econnreset), but all other errors are just reported as closed.<br />
Active and passive modes have independent code paths, but I think both do the same: all errors are reported as normal close -- except for econnreset.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">There is a merge of error codes happening in tcp_send_error, so some other errors get mapped into econnreset before tcp_send_or_shutdown_error is called.<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><br />
Apparently I need to detect all errors.<br />
Is it possible to implement a show_errors (or show_all_errors) flag, too?<br />
<br />
Actually, this new flag could replace the current show_econnreset flag.<br />
Having two separate flags for econnreset & others requires more complex code, but having a single show_errors flag would simplify the current that provides special treatment for econnreset.<br />
I am not sure if it makes much sense to expose connection reset errors but still mask all other errors as normal close events.<br />
<br />
From a farther point of view, it seems there are network-programming tasks (there is at least one!), for which Erlang seems not suitable. This sounds rather sad.<br />
Luckily the fix doesn't seem difficult.<br />
<br />
What do you think?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I agree that it should be possible to get the original error from the tcp stack. Given the discussions here <a href="https://github.com/erlang/otp/pull/731">https://github.com/erlang/otp/pull/731</a>, maybe it is time to reverse the options
so that returning the original error becomes the default and you have to set an option to get the backwards compatible behaviour?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">We are currently in the process of a major overhaul of gen_tcp and friends, so maybe this can be changed while doing that, as we are bound to break backwards compatibility in various ways during that rewrite anyways.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Lukas<o:p></o:p></p>
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