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2008-04-22 10:43:24
LWP::UserAgent - Web user agent class
require LWP::UserAgent;
my $ua = LWP::UserAgent->new;
$ua->timeout(10);
$ua->env_proxy;
my $response = $ua->get('');
if ($response->is_success) {
print $response->content; # or whatever
}
else {
die $response->status_line;
}
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.
The following constructor methods are available:
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.
Returns a copy of the LWP::UserAgent object.
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.
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
Returns the default agent identifier. This is a string of the form "libwww-perl/#.##", where "#.##" is substituted with the version number of this library.
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:
$ua->from('gaas@cpan.org');
The default is to not send a "From" header. See the default_headers() method for the more general interface that allow any header to be defaulted.
Get/set the cookie jar object to use. The only requirement is that
the cookie jar object must implement the extract_cookies($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"));
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");
This is just a short-cut for $ua->default_headers->header( $field => $value ). Example:
$ua->default_header('Accept-Language' => "no, en");
Get/set the LWP::ConnCache object to use. See for details.
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.
The $netloc a string of the form "
$ua->credenticals("", "Some Realm", "foo", "secret");
Get/set the size limit for response content. The default is undef,
which means that there is no limit. If the returned response content is
only partial, because the size limit was exceeded, then a
"Client-Aborted" header will be added to the response. The content
might end up longer than max_size as we abort once
appending a chunk of data makes the length exceed the limit. The
"Content-Length" header, if present, will indicate the length of the
full content and will normally not be the same as length($res->content).
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.
Get/set a value indicating whether we should initialize response headers from the
section of HTML documents. The default is TRUE. Do not turn this off, unless you know what you are doing.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.
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)
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';
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.
The following methods set up when requests should be passed via a proxy server.
Set/retrieve proxy URL for a scheme:
$ua->proxy(['http', 'ftp'], '');
$ua->proxy('gopher', '');
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.
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', ...);
Load proxy settings from *_proxy environment variables. You might specify proxies like this (sh-syntax):
gopher_proxy=
wais_proxy=
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.
The methods described in this section are used to dispatch requests via the user agent. The following request methods are provided:
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 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.
This method will dispatch a HEAD request on the given $url. Otherwise it works like the get() method described above.
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 for a details on how to pass form content and other advanced features.
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.
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 and 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.
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.
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.
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.
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".
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.
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.
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 for a complete overview of libwww-perl5. See and the scripts lwp-request and lwp-download for examples of usage.
See and for a description of the message objects dispatched and received. See and for other ways to build request objects.
See and for examples of more specialized user agents based on .
Copyright 1995-2008 Gisle Aas.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.