LWP::RobotUA − a class for well−behaved Web robots
use
LWP::RobotUA;
my $ua = LWP::RobotUA−>new('my−robot/0.1',
'[email protected]');
$ua−>delay(10); # be very nice −− max
one hit every ten minutes!
...
# Then just use it just like a normal LWP::UserAgent:
my $response = $ua−>get('http://whatever.int/...');
...
This class implements a user agent that is suitable for robot applications. Robots should be nice to the servers they visit. They should consult the /robots.txt file to ensure that they are welcomed and they should not make requests too frequently.
But before you consider writing a robot, take a look at <http://www.robotstxt.org/>.
When you use an LWP::RobotUA object as your user agent, then you do not really have to think about these things yourself; "robots.txt" files are automatically consulted and obeyed, the server isn’t queried too rapidly, and so on. Just send requests as you do when you are using a normal LWP::UserAgent object (using "$ua−>get(...)", "$ua−>head(...)", "$ua−>request(...)", etc.), and this special agent will make sure you are nice.
The LWP::RobotUA is a sub-class of LWP::UserAgent and implements the same methods. In addition the following methods are provided:
my $ua =
LWP::RobotUA−>new( %options )
my $ua = LWP::RobotUA−>new( $agent, $from )
my $ua = LWP::RobotUA−>new( $agent, $from, $rules
)
The LWP::UserAgent options "agent" and "from" are mandatory. The options "delay", "use_sleep" and "rules" initialize attributes private to the RobotUA. If "rules" are not provided, then WWW::RobotRules is instantiated providing an internal database of robots.txt.
It is also possible to just pass the value of "agent", "from" and optionally "rules" as plain positional arguments.
my $delay =
$ua−>delay;
$ua−>delay( $minutes );
Get/set the minimum delay between requests to the same server, in minutes. The default is 1 minute. Note that this number doesn’t have to be an integer; for example, this sets the delay to 10 seconds:
$ua−>delay(10/60);
my $bool =
$ua−>use_sleep;
$ua−>use_sleep( $boolean );
Get/set a value indicating whether the UA should "sleep" in LWP::RobotUA if requests arrive too fast, defined as "$ua−>delay" minutes not passed since last request to the given server. The default is true. If this value is false then an internal "SERVICE_UNAVAILABLE" response will be generated. It will have a "Retry−After" header that indicates when it is OK to send another request to this server.
my $rules =
$ua−>rules;
$ua−>rules( $rules );
Set/get which WWW::RobotRules object to use.
my $num = $ua−>no_visits( $netloc )
Returns the number of documents fetched from this server host. Yeah I know, this method should probably have been named "num_visits" or something like that. :−(
my $num = $ua−>host_wait( $netloc )
Returns the number of seconds (from now) you must wait before you can make a new request to this host.
my $string = $ua−>as_string;
Returns a string that describes the state of the UA. Mainly useful for debugging.
LWP::UserAgent, WWW::RobotRules
Copyright 1996−2004 Gisle Aas.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.