[asterisk-dev] Ad: Passing Variables to Voicemail's Email Notification

[Matt Fredrickson]

On Fri, Nov 10, 2017 at 2:20 PM, butrus.butrus at gmail.com
<butrus.butrus at gmail.com> wrote:
> Hello!
>
> While playing with Asterisk's voicemail and it's IMAP storage I found
> a bug - and later I realized how old this bug is. The problem is that
> variable substitions in voicemal.conf works only with a few specialized
> VM_* variables set by app_voicemail.so itself. Apparently the bug was
> discussed here a 10 year ago:
> http://lists.digium.com/pipermail/asterisk-users/2007-August/194717.html
>
> I'm currently using Asterisk 11 (latest version which I can get from
> backports in Debian Wheezy - which I'm ATM for a couple of reasons stuck
> with). So I looked into the sources and I think I found the reason and
> it seems to me quite simple to fix this. I checked the current git and
> the same problem remains there
> as well even if a couple of changes were done since Ast11.
>
> I fixed the issue for me (i.e. in the Ast11 tree) and even added some
> small new features (like the possibility to substitute even the "From:"
> email address, so
> that I can lookup in the dialplan my addressbook database and if the
> number is found I can eventually set the email so that the message looks
> like it came from
> the person who called me - later on, I added the possibility to change
> similarly
> the content-type of the message - now I have HTML messages with
> hyperlinks to my web interface - and to change the Reply-To:
> email-header).
>
> Now, this is probably not of use for you anyway, since I'll probably not
> be willing to sign any license agreement with Digum etc (please, do
> respect it).
> I however published the patches on github
> (https://github.com/butrus/asterisk-patches-gpl) so you can take them as
> an inspiration if you want.

Thanks for letting us know!  Sorry to hear that you're not interested
in signing the license agreement, but that is a personal choice and
we'll respect your decision.

> If I understand it well, without the license agreement I cannot even
> open a bug in the tracker, so I'll describe the problem here so that
> anyone interested can
> make a patch against the current HEAD and try to fix it upstreams.

Unfortunately, that is a limitation built into the bug tracker so that
we don't have any mistakes with regards to licensing conflicts or
mismatched assumptions on code contributions.

> As mentioned above, the problem is that only variables which the
> app_voicemail.so itself sets may be substituted. This puzzled me because
> the ast_str_substitute_variables() function actually needs an asterisk
> channel in order to do the substitution - and the channel has all the
> variables you set in the diaplan prior to calling the Voicemail() app.
>
> What I found is that the module simply allocates a new channel each time
> the substitution is done, for example:
>
>         if (!ast_strlen_zero(emailsubject) || !
> ast_strlen_zero(vmu->emailsubject)) {
>                 char *e_subj = !ast_strlen_zero(vmu->emailsubject) ?
> vmu->emailsubject : emailsubject;
>                 struct ast_channel *ast;
>                 if ((ast = ast_dummy_channel_alloc())) {
>                         prep_email_sub_vars(ast, vmu, msgnum + 1,
> context, mailbox, fromfolder, cidnum, cidname, dur, date, category,
> flag);
>                         ast_str_substitute_variables(&str1, 0, ast,
> e_subj);
>
> [.................................]
>
> Here you can see that for each variable-substitution a new channel is
> allocated (and later destroyed) and prep_email_sub_vars() is called -
> which puzzled me a lot because it would be enough to call this function
> once at the beginning (it prepares the VM_* variables). I actually found
> what the reason might have been: sometimes cidnum and cidname were
> passed to prep_email_sub_vars() sometimes it were cidnum_enc and
> cidname_enc which are variants of cidnum and cidname with control chars
> and chars > 7bit stripped off.
>
> But this is apparently wrong because those strings get escaped (quoted)
> anyway so that this is not needed at all! So the solution is very
> simple: just to get
> rid of any new channel allocation and use the channel inherited from the
> dialplan. Anyway I tried it and tested and this works for me well and
> with a little bit of further enhancement to app_voicemail.so this allows
> me even to do a lot of fancy stuff.
>
> So, feel free to take my observations and eventually fix the
> upstream ;-).

Thanks again for letting us know.  The best place to report bugs is on
the issue tracker, so if there isn't an open issue for it, that might
be worth doing as well.

-- 
Matthew Fredrickson
Digium, Inc. | Engineering Manager
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA