[rancid] [PATCH] clogin default prompt matches Extreme XOS banner (was: Re: Extreme XOS (etc.) slow buffered output & clogin)

[Zenon Mousmoulas]

Re-posting the patch with one minor correction.

On Wed, 06 Jun 2012 20:54:27 +0300, Zenon Mousmoulas <zmousm at noc.grnet.gr>
wrote:
> Hi again,
> 
> Taking a closer look, the particular issue is due to '>' appearing in
the
> banner XOS sends (by default) after login. The attached patch takes care
of
> this. I can not recall if this appeared in XOS 12.5 or earlier.
> 
> I understand there is a timeout pattern, implicitly added by a previous
> expect_after command, therefore slow/late output should never be an
issue.
> As mentioned previously, I have also seen this issue on Cisco switches
with
> similarly large post-login banners (banner motd). However I can't
reproduce
> this currently, so let me take this back and the suggested ugly
workaround.
> Sorry for the noise.
> 
> Best regards,
> Z.
> 
> On Wed, 06 Jun 2012 11:52:55 +0300, Zenon Mousmoulas
<zmousm at noc.grnet.gr>
> wrote:
>> Hi,
>> 
>> There is an issue with clogin and buffered output, easily reproducible
>> with Extreme XOS devices, which by default show a sizable banner
>> post-login, but I have also been able to reproduce it with Cisco
> switches,
>> when a large banner is displayed:
>> 
>> On Thu, 01 Dec 2011 03:44:32 +0200, Zenon Mousmoulas
> <zmousm at noc.grnet.gr>
>> wrote:
>>> [...]
>>> However there's still a problem in this version with buffered output
>> from
>>> the extreme. After login, when you send "\r", the following expect
>>> catches the first prompt, not the one after "\r". This becomes evident
>>> later on, when the expect statement in the loop within run_commands
>>> catches
>>> "disable clipaging\r\n\<prompt>" rather than the command echoed and
>>> its' output. So you're always one step behind, until the end, where
you
>>> erroneously see a prompt after sending "quit\r" so you also
>>> send -h "exit\r". This obviously messes up xrancid parsing as
>>> well. See the attached clogin log for more evidence (with exp_internal
>>> added after login).
>> 
>> Some time ago I had posted a patch which tried to address this, among
>> other things related to XOS & rancid. Other changes were accepted in
> 2.3.7
>> (thanks for that), however this issue is still present in 2.3.8.
>> My rather ugly workaround was to add this code after login and before
>> prompt detection:
>> 
>> diff -ru rancid-2.3.8/bin/clogin.in rancid-2.3.8-zmousm/bin/clogin.in
>> --- rancid-2.3.8/bin/clogin.in	2012-02-01 00:42:14.000000000 +0200
>> +++ rancid-2.3.8-zmousm/bin/clogin.in	2012-06-06 09:00:59.000000000
> +0300
>> @@ -858,6 +858,16 @@
>>  	# if login failed or rsh was unsuccessful, move on to the next device
>>  	continue
>>      }
>> +    # Get all (output after login) you can eat in 1s
>> +    # (hopefully up to and including the first prompt).
>> +    # This is mostly necessary to work around
>> +    # stoopid extreme output buffering.
>> +    expect {
>> +	-timeout 1
>> +	-re "\[\n\r]+"	{ exp_continue }
>> +	-re "\[^\n\r]+"	{ exp_continue -continue_timer }
>> +	timeout		{}
>> +    }
>>      # Figure out the prompt.
>>      if { [regexp -- "(#| \\(enable\\))" $prompt_match junk] == 1 } {
>>  	set enable 0
>> 
>> Unfortunately this introduces a 1 second delay for all (not just XOS)
>> clogin-controlled devices, but there is no obvious way to avoid this,
> since
>> we haven't done prompt detection yet and haven't set $platform.
>> Furthermore, this issue is not strictly limited to XOS devices, as
noted
>> previously, therefore a slightly different approach would be perhaps to
>> trigger this delay when the output received after login exceeds some
>> conservative threshold, but I'm not really sure if and how one could do
>> such a thing.
>> 
>> I can send again (off-list) clogin output with expect debugging
enabled,
>> depicting the issue described above, as well as the correct output of
>> clogin patched with the code above.
>> While going through the list archives, I also found this post which
> shows
>> how xrancid parsing (see: missed cmds) and output is messed up exactly
> due
>> to this issue:
>>
http://www.shrubbery.net/pipermail/rancid-discuss/2012-April/006308.html
>> 
>> Please advise how this issue can be addressed.
>> 
>> Thanks,
>> Zenon Mousmoulas
-------------- next part --------------
diff -ru rancid-2.3.8/bin/clogin.in rancid-2.3.8-zmousm/bin/clogin.in
--- rancid-2.3.8/bin/clogin.in	2012-02-01 00:42:14.000000000 +0200
+++ rancid-2.3.8-zmousm/bin/clogin.in	2012-06-06 21:00:05.000000000 +0300
@@ -567,8 +567,22 @@
 				  }
 				  exp_continue
 				}
-	-re "$prompt"		{
+	-indices -re "$prompt"	{
 				  set prompt_match $expect_out(0,string);
+				  if {"$prompt_match" == ">"} {
+					# Extreme XOS >= 12.5 by default sends a banner after login
+				        # including this line:
+				        # "Press the <tab> or '?' key at any time for completions."
+				        # Match and discard it, as it is not a prompt.
+				        if [string match "\r\nPress the <tab>" \
+						[string range $expect_out(buffer) \
+						     [expr $expect_out(0,start) - 16] \
+						     $expect_out(0,start) \
+						]
+					   ] {
+					    exp_continue
+					}
+				  }
 				  break;
 				}
 	"Login invalid"		{