LWP::UserAgent(3) User Contributed Perl Documentation LWP::UserAgent(3)
NAME
LWP::UserAgent - Web user agent class
SYNOPSIS
require LWP::UserAgent;
my $ua = LWP::UserAgent->new;
$ua->timeout(10);
$ua->env_proxy;
my $response = $ua->get('http://search.cpan.org/');
if ($response->is_success) {
print $response->content; # or whatever
}
else {
die $response->status_line;
}
DESCRIPTION
The "LWP::UserAgent" is a class implementing a web user agent. "LWP::UserAgent" objects can be used
to dispatch web requests.
In normal use the application creates an "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 request method the UserAgent, 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(). When using
these methods then the creation of the request object is hidden as shown in the synopsis above.
The basic approach of the library is to use HTTP style communication for all protocol schemes. This
means that you will construct "HTTP::Request" objects and receive "HTTP::Response" objects even for
non-HTTP resources like gopher and ftp. In order to achieve even more similarity to HTTP style
communications, gopher menus and file directories are converted to HTML documents.
CONSTRUCTOR METHODS
The following constructor methods are available:
$ua = LWP::UserAgent->new( %options )
This method constructs a new "LWP::UserAgent" object and returns it. Key/value pair arguments
may be provided to set up the initial state. The following options correspond to attribute
methods described below:
KEY DEFAULT
----------- --------------------
agent "libwww-perl/#.##"
from undef
conn_cache undef
cookie_jar undef
default_headers HTTP::Headers->new
max_size undef
max_redirect 7
parse_head 1
protocols_allowed undef
protocols_forbidden undef
requests_redirectable ['GET', 'HEAD']
timeout 180
The following additional options are also accepted: If the "env_proxy" option is passed in with a
TRUE value, then proxy settings are read from environment variables (see env_proxy() method
below). 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 passed on as the "total_capacity" for the
connection cache.
$ua->clone
Returns a copy of the LWP::UserAgent object.
ATTRIBUTES
The settings of the configuration attributes modify the behaviour of the "LWP::UserAgent" when it
dispatches requests. Most of these can also be initialized by options passed to the constructor
method.
The following attributes methods are provided. The attribute value is left unchanged if no argument
is given. The return value from each method is the old attribute value.
$ua->agent
$ua->agent( $product_id )
Get/set the product token that is used to identify the user agent on the network. The agent
value is sent as the "User-Agent" header in the requests. The default is the string returned by
the _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
$ua->_agent
Returns the default agent identifier. This is a string of the form "libwww-perl/#.##", where
"#.##" is substituted with the version number of this library.
$ua->from
$ua->from( $email_address )
Get/set the e-mail address for the human user who controls the requesting user agent. The
address should be machine-usable, as defined in RFC 822. The "from" value is send as the "From"
header in the requests. Example:
$ua->from('gaas@cpan.org');
The default is to not send a "From" header. See the default_headers() method for the more
general interface that allow any header to be defaulted.
$ua->cookie_jar
$ua->cookie_jar( $cookie_jar_obj )
Get/set the cookie jar object to use. The only requirement is that the cookie jar object must
implement the extract_cookies($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 initialized 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"));
$ua->default_headers
$ua->default_headers( $headers_obj )
Get/set the headers object that will provide default header values for any requests sent. By
default this will be an empty "HTTP::Headers" object. Example:
$ua->default_headers->push_header('Accept-Language' => "no, en");
$ua->default_header( $field )
$ua->default_header( $field => $value )
This is just a short-cut for $ua->default_headers->header( $field => $value ). Example:
$ua->default_header('Accept-Language' => "no, en");
$ua->conn_cache
$ua->conn_cache( $cache_obj )
Get/set the "LWP::ConnCache" object to use. See LWP::ConnCache for details.
$ua->credentials( $netloc, $realm, $uname, $pass )
Set the user name and password to be used for a realm. It is often more useful to specialize the
get_basic_credentials() method instead.
$ua->max_size
$ua->max_size( $bytes )
Get/set the size limit for response content. The default is "undef", which means that there is
no limit. If the returned response content is only partial, because the size limit was exceeded,
then a "Client-Aborted" header will be added to the response. The content might end up longer
than "max_size" as we abort once appending a chunk of data makes the length exceed the limit.
The "Content-Length" header, if present, will indicate the length of the full content and will
normally not be the same as "length($res->content)".
$ua->max_redirect
$ua->max_redirect( $n )
This reads or sets the object's limit of how many times it will obey redirection responses in a
given request cycle.
By default, the value is 7. This means that if you call request() method and the response is a
redirect elsewhere which is in turn a redirect, and so on seven times, then LWP gives up after
that seventh request.
$ua->parse_head
$ua->parse_head( $boolean )
Get/set a value indicating whether we should initialize response headers from the <head> section
of HTML documents. The default is TRUE. Do not turn this off, unless you know what you are
doing.
$ua->protocols_allowed
$ua->protocols_allowed( \@protocols )
This reads (or sets) this user agent's list of protocols that the request methods will
exclusively allow. The protocol names are case insensitive.
For example: "$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->protocols_forbidden
$ua->protocols_forbidden( \@protocols )
This reads (or sets) this user agent's list of protocols that the request method will not allow.
The protocol names are case insensitive.
For example: "$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)"
$ua->requests_redirectable
$ua->requests_redirectable( \@requests )
This reads or sets the object's list of request names that "$ua->redirect_ok(...)" will allow
redirection for. By default, this is "['GET', 'HEAD']", as per RFC 2616. To change to include
'POST', consider:
push @{ $ua->requests_redirectable }, 'POST';
$ua->timeout
$ua->timeout( $secs )
Get/set the timeout value in seconds. The default timeout() value is 180 seconds, i.e. 3 minutes.
The requests is aborted if no activity on the connection to the server is observed for "timeout"
seconds. This means that the time it takes for the complete transaction and the request() method
to actually return might be longer.
Proxy attributes
The following methods set up when requests should be passed via a proxy server.
$ua->proxy(\@schemes, $proxy_url)
$ua->proxy($scheme, $proxy_url)
Set/retrieve proxy URL for a scheme:
$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.
$ua->no_proxy( $domain, ... )
Do not proxy requests to the given domains. Calling no_proxy without any domains clears the list
of domains. Eg:
$ua->no_proxy('localhost', 'no', ...);
$ua->env_proxy
Load proxy settings from *_proxy environment variables. You might specify proxies like this (sh-
syntax):
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.
REQUEST METHODS
The methods described in this section are used to dispatch requests via the user agent. The
following request methods are provided:
$ua->get( $url )
$ua->get( $url , $field_name => $value, ... )
This method will dispatch a "GET" request on the given $url. Further arguments can be given to
initialize the headers of the request. These are given as separate name/value pairs. The return
value is a response object. See HTTP::Response for a description of the interface it provides.
Fields names that start with ":" are special. These will not initialize headers of the request
but will determine how the response content is treated. The following special field names are
recognized:
:content_file => $filename
:content_cb => \&callback
:read_size_hint => $bytes
If a $filename is provided with the ":content_file" option, then the response content will be
saved here instead of in the response object. If a callback is provided with the ":content_cb"
option then this function will be called for each chunk of the response content as it is received
from the server. If neither of these options are given, then the response content will
accumulate in the response object itself. This might not be suitable for very large response
bodies. Only one of ":content_file" or ":content_cb" can be specified. The content of
unsuccessful responses will always accumulate in the response object itself, regardless of the
":content_file" or ":content_cb" options passed in.
The ":read_size_hint" option is passed to the protocol module which will try to read data from
the server in chunks of this size. A smaller value for the ":read_size_hint" will result in a
higher number of callback invocations.
The callback function is called with 3 arguments: a chunk of data, a reference to the response
object, and a reference to the protocol object. The callback can abort the request by invoking
die(). The exception message will show up as the "X-Died" header field in the response returned
by the get() function.
$ua->head( $url )
$ua->head( $url , $field_name => $value, ... )
This method will dispatch a "HEAD" request on the given $url. Otherwise it works like the get()
method described above.
$ua->post( $url, \%form )
$ua->post( $url, \@form )
$ua->post( $url, \%form, $field_name => $value, ... )
This method will dispatch a "POST" request on the given $url, with %form or @form providing the
key/value pairs for the fill-in form content. Additional headers and content options are the same
as for the get() method.
This method will use the POST() function from "HTTP::Request::Common" to build the request. See
HTTP::Request::Common for a details on how to pass form content and other advanced features.
$ua->mirror( $url, $filename )
This method will get the document identified by $url and store it in file called $filename. If
the file already exists, then the request will contain an "If-Modified-Since" header matching the
modification time of the file. If the document on the server has not changed since this time,
then nothing happens. If the document has been updated, it will be downloaded again. The
modification time of the file will be forced to match that of the server.
The return value is the the response object.
$ua->request( $request )
$ua->request( $request, $content_file )
$ua->request( $request, $content_cb )
$ua->request( $request, $content_cb, $read_size_hint )
This method will dispatch the given $request object. Normally this will be an instance of the
"HTTP::Request" class, but any object with a similar interface will do. The return value is a
response object. See HTTP::Request and HTTP::Response for a description of the interface
provided by these classes.
The request() method will process redirects and authentication responses transparently. This
means that it may actually send several simple requests via the simple_request() method described
below.
The request methods described above; get(), head(), post() and mirror(), will all dispatch the
request they build via this method. They are convenience methods that simply hides the creation
of the request object for you.
The $content_file, $content_cb and $read_size_hint all correspond to options described with the
get() method above.
You are allowed to use a CODE reference as "content" in the request object passed in. The
"content" function should return the content when called. The content can be returned in chunks.
The content function will be invoked repeatedly until it return an empty string to signal that
there is no more content.
$ua->simple_request( $request )
$ua->simple_request( $request, $content_file )
$ua->simple_request( $request, $content_cb )
$ua->simple_request( $request, $content_cb, $read_size_hint )
This method dispatches a single request and returns the response received. Arguments are the
same as for request() described above.
The difference from request() is that simple_request() will not try to handle redirects or
authentication responses. The request() method will in fact invoke this method for each simple
request it sends.
$ua->is_protocol_supported( $scheme )
You can use this method to test whether this user agent object supports the specified "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 the user agent'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.
Callback methods
The following methods will be invoked as requests are processed. These methods are documented here
because subclasses of "LWP::UserAgent" might want to override their behaviour.
$ua->prepare_request( $request )
This method is invoked by simple_request(). Its task is to modify the given $request object by
setting up various headers based on the attributes of the user agent. The return value should
normally be the $request object passed in. If a different request object is returned it will be
the one actually processed.
The headers affected by the base implementation are; "User-Agent", "From", "Range" and "Cookie".
$ua->redirect_ok( $prospective_request, $response )
This method is called by request() before it tries to follow a redirection to the request in
$response. This should return a TRUE value if this redirection is permissible. The
$prospective_request will be the request to be sent if this method returns TRUE.
The base 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.
$ua->get_basic_credentials( $realm, $uri, $isproxy )
This is called by request() to retrieve credentials for documents protected by Basic or Digest
Authentication. The arguments passed in is the $realm provided by the server, the $uri requested
and a boolean flag to indicate if this is authentication against a proxy server.
The method should return a username and password. It should return an empty list to abort the
authentication resolution attempt. Subclasses can override this method to prompt the user for
the information. An example of this can be found in "lwp-request" program distributed with this
library.
The base implementation simply checks a set of pre-stored member variables, set up with the
credentials() method.
SEE ALSO
See LWP for a complete overview of libwww-perl5. See lwpcook and the scripts lwp-request and lwp-
download for examples of usage.
See HTTP::Request and HTTP::Response for a description of the message objects dispatched and
received. See HTTP::Request::Common and HTML::Form for other ways to build request objects.
See WWW::Mechanize and WWW::Search for examples of more specialized user agents based on
"LWP::UserAgent".
COPYRIGHT
Copyright 1995-2004 Gisle Aas.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.
perl v5.8.8 2004-11-12 LWP::UserAgent(3)
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