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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->decoded_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
local_address undef
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 attribute 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('gaasATcpan.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.
$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-Encoding' => scalar HTTP::Message::decodable());
$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 )
$ua->credentials( $netloc, $realm, $uname, $pass )
Get/set the user name and password to be used for a realm.
The $netloc is a string of the form "<host>:<port>". The username and password will only be passed to this server.
Example:
$ua->credentials("www.example.com:80", "Some Realm", "foo", "secret");
$ua->local_address
$ua->local_address( $address )
Get/set the local interface to bind to for network connections. The interface can be specified as a hostname or an
IP address. This value is passed as the "LocalAddr" argument to IO::Socket::INET.
$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->show_progress
$ua->show_progress( $boolean )
Get/set a value indicating whether a progress bar should be displayed on on the terminal as requests are processed.
The default is FALSE.
$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.
$ua->ssl_opts
$ua->ssl_opts( $key )
$ua->ssl_opts( $key => $value )
Get/set the options for SSL connections. Without argument return the list of options keys currently set. With a
single argument return the current value for the given option. With 2 arguments set the option value and return the
old. Setting an option to the value "undef" removes this option.
The options that LWP relates to are:
"verify_hostname" => $bool
When TRUE LWP will for secure protocol schemes ensure it connects to servers that have a valid certificate
matching the expected hostname. If FALSE no checks are made and you can't be sure that you communicate with the
expected peer. The no checks behaviour was the default for libwww-perl-5.837 and earlier releases.
This option is initialized from the PERL_LWP_SSL_VERIFY_HOSTNAME environment variable. If this envirionment
variable isn't set; then "verify_hostname" defaults to 1.
"SSL_ca_file" => $path
The path to a file containing Certificate Authority certificates. A default setting for this option is provided
by checking the environment variables "PERL_LWP_SSL_CA_FILE" and "HTTPS_CA_FILE" in order. Last resort value is
built-in value /etc/pki/tls/certs/ca-bundle.crt.
"SSL_ca_path" => $path
The path to a directory containing files containing Certificate Authority certificates. A default setting for
this option is provided by checking the environment variables "PERL_LWP_SSL_CA_PATH" and "HTTPS_CA_DIR" in order.
Other options can be set and are processed directly by the SSL Socket implementation in use. See IO::Socket::SSL or
Net::SSL for details.
SSL Socket implementation can be selected by environment variable "PERL_NET_HTTPS_SSL_SOCKET_CLASS". IO::Socket::SSL
is preferred by default.
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', 'example.com');
$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,example.com"
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.
Handlers
Handlers are code that injected at various phases during the processing of requests. The following methods are provided
to manage the active handlers:
$ua->add_handler( $phase => \&cb, %matchspec )
Add handler to be invoked in the given processing phase. For how to specify %matchspec see "Matching" in
HTTP::Config.
The possible values $phase and the corresponding callback signatures are:
request_preprepare => sub { my($request, $ua, $h) = @_; ... }
The handler is called before the "request_prepare" and other standard initialization of of the request. This can
be used to set up headers and attributes that the "request_prepare" handler depends on. Proxy initialization
should take place here; but in general don't register handlers for this phase.
request_prepare => sub { my($request, $ua, $h) = @_; ... }
The handler is called before the request is sent and can modify the request any way it see fit. This can for
instance be used to add certain headers to specific requests.
The method can assign a new request object to $_[0] to replace the request that is sent fully.
The return value from the callback is ignored. If an exceptions is raised it will abort the request and make the
request method return a "400 Bad request" response.
request_send => sub { my($request, $ua, $h) = @_; ... }
This handler get a chance of handling requests before it's sent to the protocol handlers. It should return an
HTTP::Response object if it wishes to terminate the processing; otherwise it should return nothing.
The "response_header" and "response_data" handlers will not be invoked for this response, but the "response_done"
will be.
response_header => sub { my($response, $ua, $h) = @_; ... }
This handler is called right after the response headers have been received, but before any content data. The
handler might set up handlers for data and might croak to abort the request.
The handler might set the $response->{default_add_content} value to control if any received data should be added
to the response object directly. This will initially be false if the $ua->request() method was called with a
$content_file or $content_cb argument; otherwise true.
response_data => sub { my($response, $ua, $h, $data) = @_; ... }
This handlers is called for each chunk of data received for the response. The handler might croak to abort the
request.
This handler need to return a TRUE value to be called again for subsequent chunks for the same request.
response_done => sub { my($response, $ua, $h) = @_; ... }
The handler is called after the response has been fully received, but before any redirect handling is attempted.
The handler can be used to extract information or modify the response.
response_redirect => sub { my($response, $ua, $h) = @_; ... }
The handler is called in $ua->request after "response_done". If the handler return an HTTP::Request object we'll
start over with processing this request instead.
$ua->remove_handler( undef, %matchspec )
$ua->remove_handler( $phase, %matchspec )
Remove handlers that match the given %matchspec. If $phase is not provided remove handlers from all phases.
Be careful as calling this function with %matchspec that is not not specific enough can remove handlers not owned by
you. It's probably better to use the set_my_handler() method instead.
The removed handlers are returned.
$ua->set_my_handler( $phase, $cb, %matchspec )
Set handlers private to the executing subroutine. Works by defaulting an "owner" field to the %matchspec that holds
the name of the called subroutine. You might pass an explicit "owner" to override this.
If $cb is passed as "undef", remove the handler.
$ua->get_my_handler( $phase, %matchspec )
$ua->get_my_handler( $phase, %matchspec, $init )
Will retrieve the matching handler as hash ref.
If $init is passed passed as a TRUE value, create and add the handler if it's not found. If $init is a subroutine
reference, then it's called with the created handler hash as argument. This sub might populate the hash with extra
fields; especially the callback. If $init is a hash reference, merge the hashes.
$ua->handlers( $phase, $request )
$ua->handlers( $phase, $response )
Returns the handlers that apply to the given request or response at the given processing phase.
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.
There will still be a response object returned when LWP can't connect to the server specified in the URL or when
other failures in protocol handlers occur. These internal responses use the standard HTTP status codes, so the
responses can't be differentiated by testing the response status code alone. Error responses that LWP generates
internally will have the "Client-Warning" header set to the value "Internal response". If you need to differentiate
these internal responses from responses that a remote server actually generates, you need to test this header value.
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, ... )
$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::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.
$ua->progress( $status, $request_or_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.
When $status is "begin" the second argument is the request object, otherwise it is the response object.
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 1995-2009 Gisle Aas.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl v5.12.4 2011-10-13 LWP::UserAgent(3)
