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

[butrus.butrus at gmail.com]

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.

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. 

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 ;-).

P.