Page 264 - Asterisk™: The Future of Telephony

else speak "The German office is closed"
end
when US_NUMBER
dial SIP/'us-trunk-out'/extension
when /^\d{11,}$/ # Perl-like regular expression
# Pass any other long numbers straight to our trunk.
dial IAX/'intl-trunk-out'/extension
else
play %w'sorry invalid extension please-try-again'
end
}
With just this small amount of code we accomplish quite a lot. Even with limited or
no knowledge of Ruby, you can probably infer the following things:
• We use a switch-like statement on the “extension” variable (which Adhearsion
creates for us) and branch depending on that.
• Dialing a number between 10 and 99 routes us to the SIP peer with the dialed
numerical username.
• Any number dialed between 6000 and 6200 or between 7000 and 7030 goes to a
MeetMe conference of that same number. This of course requires meetme.conf to
have these conference numbers configured.
• The _'21XX' option comes straight from Asterisk’s pattern style. Prepending a
String with an underscore in Adhearsion secretly invokes a method that returns a
Ruby regular expression. In a Ruby “case” statement, regular expressions can be
used in a “when” statement to check against a pattern. The end effect should be
very familiar to those with extensions.conf writing experience.
• Adhearsion’s syntax for representing channels also comes straight from Asterisk’s
traditional format. SIP/123 can be used verbatim to represent the SIP peer 123. If
a trunk were involved, SIP/trunkname/username would act as you would expect.
• The speak() method abstracts an underlying text-to-speech engine. This can be
configured to use most of the popular engines.
• A full-blown Perl-like regular can be used in a when statement to perform more
sophisticated pattern matching if Asterisk’s patterns do not suffice.
• Adhearsion defines a few constants that may be useful to someone writing dia-
lplans. The US_NUMBER constant here is a regular expression for matching an
American number.
• If you find the need to play several files in sequence, play() accepts an Array of
filenames. By luck, Ruby has a convenient way of creating an Array of Strings.
This is of course just a simple example and covers only the absolute basics of Adhear-
sion’s dialplan authoring capabilities.

236 | Chapter 10: Asterisk Manager Interface (AMI) and Adhearsion