LWP::UserAgent
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 directo-
ries 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 set-
tings are read from environment variables (see env_proxy() method
below). If the "keep_alive" option is passed in, then a "LWP::Con-
nCache" 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 identi-
fiers with an optional version number separated by the "/" charac-
ter. 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_head-
ers() 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 sev-
enth 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 "proto-
cols_forbidden" list to be ignored.
$ua->protocols_forbidden
$ua->protocols_forbidden( \@protocols )
This reads (or sets) this user agent's list of protocols that the
request method will not allow. The protocol names are case insensi-
tive.
For example: "$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 with-
out 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. Fur-
ther 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 ini-
tialize headers of the request but will determine how the response
content is treated. The following special field names are recog-
nized:
: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 ":con-
tent_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. Oth-
erwise it works like the get() method described above.
$ua->post( $url, \%form )
$ua->post( $url, \@form )
$ua->post( $url, \%form, $field_name => $value, ... )
$ua->post( $url, $field_name => $value,... Content => \%form )
$ua->post( $url, $field_name => $value,... Content => \@form )
$ua->post( $url, $field_name => $value,... Content => $content )
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::Com-
mon" 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 sev-
eral simple requests via the simple_request() method described
below.
The request methods described above; get(), head(), post() and mir-
ror(), 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 sup-
ports 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. Sub-
classes can override this method to prompt the user for the infor-
mation. 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.
$ua->progress( $status, $response )
This is called frequently as the response is received regardless of
how the content is processed. The method is called with $status
"begin" at the start of processing the request and with $state
"end" before the request method returns. In between these $status
will be the fraction of the response currently received or the
string "tick" if the fraction can't be calculated.
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 v5.8.6 2006-06-05 LWP::UserAgent(3)
