|
|
LWP::UserAgent - A WWW UserAgent class
require LWP::UserAgent;
my $ua = LWP::UserAgent->new(env_proxy => 1,
keep_alive => 1,
timeout => 30,
);
$response = $ua->get('http://search.cpan.org/');
# or:
$request = HTTP::Request->new('GET', 'http://search.cpan.org/');
# and then one of these:
$response = $ua->request($request); # or
$response = $ua->request($request, '/tmp/sss'); # or
$response = $ua->request($request, \&callback, 4096);
sub callback { my($data, $response, $protocol) = @_; .... }
The LWP::UserAgent is a class implementing a World-Wide Web
user agent in Perl. It brings together the HTTP::Request,
HTTP::Response and the LWP::Protocol classes that form the rest of the
core of libwww-perl library. For simple uses this class can be used
directly to dispatch WWW requests, alternatively it can be subclassed
for application-specific behaviour.
In normal use the application creates a LWP::UserAgent object, and then
configures it with values for timeouts, proxies, name, etc. It then
creates an instance of HTTP::Request for the request that
needs to be performed. This request is then passed to one of the UserAgent's
request() methods, which dispatches it using the relevant protocol,
and returns a HTTP::Response object.
There are convenience methods for sending the most common request
types; get(), head() and post().
The basic approach of the library is to use HTTP style communication
for all protocol schemes, i.e. you even receive an HTTP::Response
object for gopher or ftp requests. In order to achieve even more
similarity to HTTP style communications, gopher menus and file
directories are converted to HTML documents.
The send_request(), simple_request() and request() methods can process
the content of the response in one of three ways: in core, into a
file, or into repeated calls to a subroutine. You choose which one by
the kind of value passed as the second argument.
The in core variant simply stores the content in a scalar 'content' attribute of the response object and is suitable for small HTML replies that might need further parsing. This variant is used if the second argument is missing (or is undef).
The filename variant requires a scalar containing a filename as the second argument to the request method and is suitable for large WWW objects which need to be written directly to the file without requiring large amounts of memory. In this case the response object returned from the request method will have an empty content attribute. If the request fails, then the content might not be empty, and the file will be untouched.
The subroutine variant requires a reference to callback routine as the second argument to the request method and it can also take an optional chuck size as the third argument. This variant can be used to construct ``pipe-lined'' processing, where processing of received chuncks can begin before the complete data has arrived. The callback function is called with 3 arguments: the data received this time, a reference to the response object and a reference to the protocol object. The response object returned from the request method will have empty content. If the request fails, then the the callback routine is not called, and the response->content might not be empty.
The request can be aborted by calling die() in the callback
routine. The die message will be available as the ``X-Died'' special
response header field.
The library also allows you to use a subroutine reference as content in the request object. This subroutine should return the content (possibly in pieces) when called. It should return an empty string when there is no more content.
The following methods are available:
LWP::UserAgent object and
returns a reference to it.
Key/value pair arguments may be provided to set up the initial state of the user agent. The following options correspond to attribute methods described below:
KEY DEFAULT ----------- -------------------- agent "libwww-perl/#.##" from undef timeout 180 use_eval 1 parse_head 1 max_size undef cookie_jar undef conn_cache undef protocols_allowed undef protocols_forbidden undef requests_redirectable ['GET', 'HEAD']
The followings option are also accepted: If the env_proxy option is
passed in an has a TRUE value, then proxy settings are read from
environment variables. If the keep_alive option is passed in, then
a LWP::ConnCache is set up (see conn_cache() method below). The
keep_alive value is a number and is passed on as the total_capacity
for the connection cache. The keep_alive option also has the
effect of loading and enabling the new experimental HTTP/1.1 protocol
module.
prepare_request().
The $request should be a reference to a HTTP::Request object
with values defined for at least the method() and uri() attributes.
If $arg is a scalar it is taken as a filename where the content of
the response is stored.
If $arg is a reference to a subroutine, then this routine is called
as chunks of the content is received. An optional $size argument
is taken as a hint for an appropriate chunk size.
If $arg is omitted, then the content is stored in the response
object itself.
prepare_request($request)HTTP::Request object by setting up
various headers based on the attributes of the $ua. The headers
affected are; User-Agent, From, Range and Cookie.
The return value is the $request object passed in.
send_request() by
automatically calling the prepare_request() method before the
request is sent.
The arguments are the same as for send_request().
The arguments are the same as for send_request() and
simple_request().
$ua->request(HTTP::Request::Common::GET(
$url, Header =E<gt> Value,... )). See
HTTP::Request::Common.
$ua->request( HTTP::Request::Common::POST(
$url, \%formref, Header =E<gt> Value,... )). Note that the form
reference is optional, and can be either a hashref (\%formdata or {
'key1' = 'val2', 'key2' => 'val2', ...
}>) or an arrayref (\@formdata or
['key1' = 'val2', 'key2' => 'val2', ...]>). See
HTTP::Request::Common.
$ua->request( HTTP::Request::Common::HEAD(
$url, Header =E<gt> Value,... )). See
HTTP::Request::Common.
$ua->request( HTTP::Request::Common::PUT(
$url, Header =E<gt> Value,... )). See
HTTP::Request::Common.
$ua->request and $ua->simple_request will exclusively
allow.
For example: $ua->protocols_allowed( [ 'http', 'https'] );
means that this user agent will allow only those protocols,
and attempts to use this user-agent to access URLs with any other
schemes (like ``ftp://...'') will result in a 500 error.
To delete the list, call:
$ua->protocols_allowed(undef)
By default, an object has neither a protocols_allowed list, nor a protocols_forbidden list.
Note that having a protocols_allowed list causes any protocols_forbidden list to be ignored.
$ua->request and $ua->simple_request will not allow.
For example: $ua->protocols_forbidden( [ 'file', 'mailto'] );
means that this user-agent will not allow those protocols, and
attempts to use this user-agent to access URLs with those schemes
will result in a 500 error.
To delete the list, call:
$ua->protocols_forbidden(undef)
is_protocol_supported($scheme)scheme. (The scheme might be a string (like 'http' or
'ftp') or it might be an URI object reference.)
Whether a scheme is supported, is determined by $ua's protocols_allowed or protocols_forbidden lists (if any), and by the capabilities of LWP. I.e., this will return TRUE only if LWP supports this protocol and it's permitted for this particular object.
$ua->redirect_ok(...) will allow redirection for. By
default, this is ['GET', 'HEAD'], as per RFC 2068. To
change to include 'POST', consider:
push @{ $ua->requests_redirectable }, 'POST';
redirect_ok($prospective_request)request() before it tries to follow a
redirection to the request in $prospective_request. This
should return a true value if this redirection is
permissible.
The default implementation will return FALSE unless the method
is in the object's requests_redirectable list,
FALSE if the proposed redirection is to a ``file://...''
URL, and TRUE otherwise.
Subclasses might want to override this.
(This method's behavior in previous versions was simply to return TRUE for anything except POST requests).
get_basic_credentials() method instead.
request() to retrieve credentials for a Realm
protected by Basic Authentication or Digest Authentication.
Should return username and password in a list. Return undef to abort the authentication resolution atempts.
This implementation simply checks a set of pre-stored member
variables. Subclasses can override this method to e.g. ask the user
for a username/password. An example of this can be found in
lwp-request program distributed with this library.
agent([$product_id])_agent()
method (see below).
If the $product_id ends with space then the _agent string is
appended to it.
The user agent string should be one or more simple product identifiers with an optional version number separated by the ``/'' character. Examples are:
$ua->agent('Checkbot/0.4 ' . $ua->_agent);
$ua->agent('Checkbot/0.4 '); # same as above
$ua->agent('Mozilla/5.0');
$ua->agent(""); # don't identify
from([$email_address])
$ua->from('gaas@cpan.org');
The default is to not send a ``From'' header.
timeout([$secs])timeout() value is
180 seconds, i.e. 3 minutes.
cookie_jar([$cookie_jar_obj])extract_cookies($request) and
add_cookie_header($response) methods. These methods will then be
invoked by the user agent as requests are sent and responses are
received. Normally this will be a HTTP::Cookies object or some
subclass.
The default is to have no cookie_jar, i.e. never automatically add ``Cookie'' headers to the requests.
Shortcut: If a reference to a plain hash is passed in as the
$cookie_jar_object, then it is replaced with an instance of
HTTP::Cookies that is initalized based on the hash. This form also
automatically loads the HTTP::Cookies module. It means that:
$ua->cookie_jar({ file => "$ENV{HOME}/.cookies.txt" });
is really just a shortcut for:
require HTTP::Cookies;
$ua->cookie_jar(HTTP::Cookies->new(file => "$ENV{HOME}/.cookies.txt"));
conn_cache([$cache_obj])parse_head([$boolean])max_size([$bytes])undef,
which means that there is no limit. If the returned response content
is only partial, because the size limit was exceeded, then a
``Client-Aborted'' header will be added to the response.
proxy(...)
$ua->proxy(['http', 'ftp'], 'http://proxy.sn.no:8001/');
$ua->proxy('gopher', 'http://proxy.sn.no:8001/');
The first form specifies that the URL is to be used for proxying of access methods listed in the list in the first method argument, i.e. 'http' and 'ftp'.
The second form shows a shorthand form for specifying proxy URL for a single access scheme.
env_proxy()gopher_proxy=http://proxy.my.place/ wais_proxy=http://proxy.my.place/ no_proxy="localhost,my.domain" export gopher_proxy wais_proxy no_proxy
Csh or tcsh users should use the setenv command to define these
environment variables.
On systems with case-insensitive environment variables there exists a
name clash between the CGI environment variables and the HTTP_PROXY
environment variable normally picked up by env_proxy(). Because of
this HTTP_PROXY is not honored for CGI scripts. The
CGI_HTTP_PROXY environment variable can be used instead.
no_proxy($domain,...)
$ua->no_proxy('localhost', 'no', ...);
See the LWP manpage for a complete overview of libwww-perl5. See lwp-request and lwp-mirror for examples of usage.
Copyright 1995-2001 Gisle Aas.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.