[asterisk-bugs] [Asterisk 0017450]: [patch] "setvar" can add multiple variables with the same name to a channel, and has a mismatch between his behaviour and his do

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=17450 
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Reported By:                nahuelgreco
Assigned To:                
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Project:                    Asterisk
Issue ID:                   17450
Category:                   Channels/chan_dahdi
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
Asterisk Version:           SVN 
JIRA:                        
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases):  trunk 
SVN Revision (number only!): 267095 
Request Review:              
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Date Submitted:             2010-06-02 17:28 CDT
Last Modified:              2010-06-03 01:33 CDT
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Summary:                    [patch] "setvar" can add multiple variables with the
same name to a channel, and has a mismatch between his behaviour and his do
Description: 
Suppose the following piece of chan_dahdi.conf:

  setvar=V1=foo
  channel => 1

  setvar=V2=bar
  channel => 2

  setvar=V1=baz
  channel => 3

In the current trunk version, each channel (dahdi_pvt structure) will have
his own copies of the variables (after
https://issues.asterisk.org/view.php?id=16359 fix). For example, the
ast_variables linked list for channel 3 will have the following form:

  channel 3:   V1=foo -> V2=bar -> V1=baz

When a call is made and dahdi_new(...) is executed, dahdi_new(...) will
processes the variables list left-to-right, so for a call in channel 3 the
value of V1 for that call will be finally "baz" because is the last one to
be set by dahdi_new(...). This makes the bug benevolous, the call variables
will be ok, but if you do a "dahdi show channel 3" you will see the two
versions of V1, and that's wrong. Before the
https://issues.asterisk.org/view.php?id=16359 fix the bug was worse,
because the call in channel 3 got V1=foo.

A patch against trunk removing the duplicates is attached.

Also, there is a conceptual mismatch. The documentation in
chan_dahdi.conf.sample states that "setvar" defines a "Channel variable to
be set for all calls from this channel". Maybe the correct behaviour is to
get only V1 defined for channel 3 and not V2, by resetting the setvar list
(confp->chan.vars) after each "channel" statement. 

I also think the linked list built at confp->chan.vars is probably leaking
across reloads.

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 (0122864) tilghman (administrator) - 2010-06-03 01:33
 https://issues.asterisk.org/view.php?id=17450#c122864 
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1) I agree on the leak, and I'm uploading a fix for that.
2) I don't agree on skipping variables and here's why:  we have dialplan
functions which may be set with this method, and those don't have a
particular problem with being set more than once.  In fact, each setting
may depend upon the previous value internally, which makes skipping
variables problematic.
3) Inheritance of previous values is a feature, not a bug.  If you'd like
an explicit "clearvars" command, as we have in chan_mgcp, I'm open to that. 

Issue History 
Date Modified    Username       Field                    Change               
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2010-06-03 01:33 tilghman       Note Added: 0122864                          
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