| |
LWP::UserAgent(3pm) - phpMan
LWP::UserAgent(3pm) User Contributed Perl Documentation LWP::UserAgent(3pm)
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(), post(), put() and delete(). 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
ssl_opts { verify_hostname => 1 }
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 "env_proxy" isn't provided the
"PERL_LWP_ENV_PROXY" environment variable controls if env_proxy() is called during
initialization. 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('gaas AT 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( $cookie_jar_obj )
Get/set the cookie jar object to use. The only requirement is that the cookie jar
object must implement the extract_cookies($response) and add_cookie_header($request)
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 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 environment 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.
"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.
The libwww-perl core no longer bundles protocol plugins for SSL. You will need to
install LWP::Protocol::https separately to enable support for processing https-URLs.
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, $h) = @_; ... }
The handler is called before the "request_prepare" and other standard
initialization of the request. This can be used to set up headers and attributes
that the "request_prepare" handler depends on. Proxy initialization should take
place here; but in general don't register handlers for this phase.
request_prepare => sub { my($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 $_[0] to replace the request that is
sent fully.
The return value from the callback is ignored. If an exception is raised it will
abort the request and make the request method return a "400 Bad request" response.
request_send => sub { my($request, $ua, $h) = @_; ... }
This handler gets a chance of handling requests before they're sent to the
protocol handlers. It should return an HTTP::Response object if it wishes to
terminate the processing; otherwise it should return nothing.
The "response_header" and "response_data" handlers will not be invoked for this
response, but the "response_done" will be.
response_header => sub { my($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, $data) = @_; ... }
This handler is called for each chunk of data received for the response. The
handler might croak to abort the request.
This handler needs to return a TRUE value to be called again for subsequent chunks
for the same request.
response_done => sub { my($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
returns 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 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 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->put( $url, \%form )
$ua->put( $url, \@form )
$ua->put( $url, \%form, $field_name => $value, ... )
$ua->put( $url, $field_name => $value,... Content => \%form )
$ua->put( $url, $field_name => $value,... Content => \@form )
$ua->put( $url, $field_name => $value,... Content => $content )
This method will dispatch a "PUT" 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 PUT() 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->delete( $url )
$ua->delete( $url, $field_name => $value, ... )
This method will dispatch a "DELETE" request on the given $url. Additional headers
and content options are the same as for the get() method.
This method will use the DELETE() 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 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_online
Tries to determine if you have access to the Internet. Returns TRUE if the built-in
heuristics determine that the user agent is able to access the Internet (over HTTP).
See also LWP::Online.
$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 v5.18.2 2014-07-26 LWP::UserAgent(3pm)
|
