POE::Component::Client::HTTP(3)

NAME
POE::Component::Client::HTTP - a HTTP user-agent component

SYNOPSIS
  use POE qw(Component::Client::HTTP);

  POE::Component::Client::HTTP->spawn(
    Agent     => 'SpiffCrawler/0.90',   # defaults to something long
    Alias     => 'ua',                  # defaults to 'weeble'
    From      => 'spiffster@perl.org',  # defaults to undef (no header)
    Protocol  => 'HTTP/0.9',            # defaults to 'HTTP/1.1'
    Timeout   => 60,                    # defaults to 180 seconds
    MaxSize   => 16384,                 # defaults to entire response
    Streaming => 4096,                  # defaults to 0 (off)
    FollowRedirects => 2,               # defaults to 0 (off)
    Proxy     => "http://localhost:80", # defaults to HTTP_PROXY env. variable
    NoProxy   => [ "localhost", "127.0.0.1" ], # defs to NO_PROXY env. variable
    BindAddr  => "12.34.56.78",         # defaults to INADDR_ANY
  );

  $kernel->post(
    'ua',        # posts to the 'ua' alias
    'request',   # posts to ua's 'request' state
    'response',  # which of our states will receive the response
    $request,    # an HTTP::Request object
  );

  # This is the sub which is called when the session receives a
  # 'response' event.
  sub response_handler {
    my ($request_packet, $response_packet) = @_[ARG0, ARG1];

    # HTTP::Request
    my $request_object  = $request_packet->[0];

    # HTTP::Response
    my $response_object = $response_packet->[0];

    my $stream_chunk;
    if (! defined($response_object->content)) {
      $stream_chunk = $response_packet->[1];
    }

    print(
      "*" x 78, "\n",
      "*** my request:\n",
      "-" x 78, "\n",
      $request_object->as_string(),
      "*" x 78, "\n",
      "*** their response:\n",
      "-" x 78, "\n",
      $response_object->as_string(),
    );

    if (defined $stream_chunk) {
      print "-" x 40, "\n", $stream_chunk, "\n";
    }

    print "*" x 78, "\n";
  }

DESCRIPTION
POE::Component::Client::HTTP is an HTTP user-agent for POE. It lets other sessions run while HTTP transactions are being processed, and it lets several HTTP transactions be processed in parallel.

It supports keep-alive through POE::Component::Client::Keepalive, which in turn uses POE::Component::Client::DNS for asynchronous name resolution.

HTTP client components are not proper objects. Instead of being created, as most objects are, they are "spawned" as separate sessions. To avoid confusion (and hopefully not cause other confusion), they must be spawned with a "spawn" method, not created anew with a "new" one.

CONSTRUCTOR

  spawn
PoCo::Client::HTTP's "spawn" method takes a few named parameters:

Agent => $user_agent_string
Agent => \@list_of_agents
    If a UserAgent header is not present in the HTTP::Request, a random one will be used from those specified by the "Agent" parameter. If none are supplied, POE::Component::Client::HTTP will advertise itself to the server.

    "Agent" may contain a reference to a list of user agents. If this is the case, PoCo::Client::HTTP will choose one of them at random for each request.

Alias => $session_alias
    "Alias" sets the name by which the session will be known. If no alias is given, the component defaults to "weeble". The alias lets several sessions interact with HTTP components without keeping (or even knowing) hard references to them. It's possible to spawn several HTTP components with different names.

ConnectionManager => $poco_client_keepalive
    "ConnectionManager" sets this component's connection pool manager. It expects the connection manager to be a reference to a POE::Component::Client::Keepalive object. The HTTP client component will call "allocate()" on the connection manager itself so you should not have done this already.

      my $pool = POE::Component::Client::Keepalive->new(
        keep_alive    => 10, # seconds to keep connections alive
        max_open      => 100, # max concurrent connections - total
        max_per_host  => 20, # max concurrent connections - per host
        timeout       => 30, # max time (seconds) to establish a new connection
      );

      POE::Component::Client::HTTP->spawn(
        # ...
        ConnectionManager => $pool,
        # ...
      );

    See POE::Component::Client::Keepalive for more information.

CookieJar => $cookie_jar
    "CookieJar" sets the component's cookie jar. It expects the cookie jar to be a reference to a HTTP::Cookies object.

From => $admin_address
    "From" holds an e-mail address where the client's administrator and/or maintainer may be reached. It defaults to undef, which means no From header will be included in requests.

MaxSize => OCTETS
    "MaxSize" specifies the largest response to accept from a server. The content of larger responses will be truncated to OCTET octets. This has been used to return the <head></head> section of web pages without the need to wade through <body></body>.

NoProxy => [ $host_1, $host_2, ..., $host_N ]
NoProxy => "host1,host2,hostN"
    "NoProxy" specifies a list of server hosts that will not be proxied. It is useful for local hosts and hosts that do not properly support proxying. If NoProxy is not specified, a list will be taken from the NO_PROXY environment variable.

      NoProxy => [ "localhost", "127.0.0.1" ],
      NoProxy => "localhost,127.0.0.1",

BindAddr => $local_ip
    Specify "BindAddr" to bind all client sockets to a particular local address. The value of BindAddr will be passed through POE::Component::Client::Keepalive to POE::Wheel::SocketFactory (as "bind_address"). See that module's documentation for implementation details.

      BindAddr => "12.34.56.78"

Protocol => $http_protocol_string
    "Protocol" advertises the protocol that the client wishes to see. Under normal circumstances, it should be left to its default value: "HTTP/1.1".

Proxy => [ $proxy_host, $proxy_port ]
Proxy => $proxy_url
Proxy => $proxy_url,$proxy_url,...
    "Proxy" specifies one or more proxy hosts that requests will be passed through. If not specified, proxy servers will be taken from the HTTP_PROXY (or http_proxy) environment variable. No proxying will occur unless Proxy is set or one of the environment variables exists.

    The proxy can be specified either as a host and port, or as one or more URLs. Proxy URLs must specify the proxy port, even if it is 80.

      Proxy => [ "127.0.0.1", 80 ],
      Proxy => "http://127.0.0.1:80/",

    "Proxy" may specify multiple proxies separated by commas. PoCo::Client::HTTP will choose proxies from this list at random. This is useful for load balancing requests through multiple gateways.

      Proxy => "http://127.0.0.1:80/,http://127.0.0.1:81/",

Streaming => OCTETS
    "Streaming" changes allows Client::HTTP to return large content in chunks (of OCTETS octets each) rather than combine the entire content into a single HTTP::Response object.

    By default, Client::HTTP reads the entire content for a response into memory before returning an HTTP::Response object. This is obviously bad for applications like streaming MP3 clients, because they often fetch songs that never end. Yes, they go on and on, my friend.

    When "Streaming" is set to nonzero, however, the response handler receives chunks of up to OCTETS octets apiece. The response handler accepts slightly different parameters in this case. ARG0 is also an HTTP::Response object but it does not contain response content, and ARG1 contains a a chunk of raw response content, or undef if the stream has ended.

      sub streaming_response_handler {
        my $response_packet = $_[ARG1];
        my ($response, $data) = @$response_packet;
        print SAVED_STREAM $data if defined $data;
      }

FollowRedirects => $number_of_hops_to_follow
    "FollowRedirects" specifies how many redirects (e.g. 302 Moved) to follow. If not specified defaults to 0, and thus no redirection is followed. This maintains compatibility with the previous behavior, which was not to follow redirects at all.

    If redirects are followed, a response chain should be built, and can be accessed through $response_object->previous(). See HTTP::Response for details here.

Timeout => $query_timeout
    "Timeout" sets how long POE::Component::Client::HTTP has to process an application's request, in seconds. "Timeout" defaults to 180 (three minutes) if not specified.

    It's important to note that the timeout begins when the component receives an application's request, not when it attempts to connect to the web server.

    Timeouts may result from sending the component too many requests at once. Each request would need to be received and tracked in order. Consider this:

      $_[KERNEL]->post(component => request => ...) for (1..15_000);

    15,000 requests are queued together in one enormous bolus. The component would receive and initialize them in order. The first socket activity wouldn't arrive until the 15,000th request was set up. If that took longer than "Timeout", then the requests that have waited too long would fail.

    "ConnectionManager"'s own timeout and concurrency limits also affect how many requests may be processed at once. For example, most of the 15,000 requests would wait in the connection manager's pool until sockets become available. Meanwhile, the "Timeout" would be counting down.

    Applications may elect to control concurrency outside the component's "Timeout". They may do so in a few ways.

    The easiest way is to limit the initial number of requests to something more manageable. As responses arrive, the application should handle them and start new requests. This limits concurrency to the initial request count.

    An application may also outsource job throttling to another module, such as POE::Component::JobQueue.

    In any case, "Timeout" and "ConnectionManager" may be tuned to maximize timeouts and concurrency limits. This may help in some cases. Developers should be aware that doing so will increase memory usage. POE::Component::Client::HTTP and KeepAlive track requests in memory, while applications are free to keep pending requests on disk.

ACCEPTED EVENTS
Sessions communicate asynchronously with PoCo::Client::HTTP. They post requests to it, and it posts responses back.

  request
Requests are posted to the component's "request" state. They include an HTTP::Request object which defines the request. For example:

  $kernel->post(
    'ua', 'request',           # http session alias & state
    'response',                # my state to receive responses
    GET 'http://poe.perl.org', # a simple HTTP request
    'unique id',               # a tag to identify the request
    'progress',                # an event to indicate progress
    'http://1.2.3.4:80/'       # proxy to use for this request
  );

Requests include the state to which responses will be posted. In the previous example, the handler for a 'response' state will be called with each HTTP response. The "progress" handler is optional and if installed, the component will provide progress metrics (see sample handler below). The "proxy" parameter is optional and if not defined, a default proxy will be used if configured. No proxy will be used if neither a default one nor a "proxy" parameter is defined.

  pending_requests_count
There's also a pending_requests_count state that returns the number of requests currently being processed. To receive the return value, it must be invoked with $kernel->call().

  my $count = $kernel->call('ua' => 'pending_requests_count');

  cancel
Cancel a specific HTTP request. Requires a reference to the original request (blessed or stringified) so it knows which one to cancel. See "progress handler" below for notes on canceling streaming requests.

To cancel a request based on its blessed HTTP::Request object:

  $kernel->post( component => cancel => $http_request );

To cancel a request based on its stringified HTTP::Request object:

  $kernel->post( component => cancel => "$http_request" );

  shutdown
Responds to all pending requests with 408 (request timeout), and then shuts down the component and all subcomponents.

SENT EVENTS

  response handler
In addition to all the usual POE parameters, HTTP responses come with two list references:

  my ($request_packet, $response_packet) = @_[ARG0, ARG1];

$request_packet contains a reference to the original HTTP::Request object. This is useful for matching responses back to the requests that generated them.

  my $http_request_object = $request_packet->[0];
  my $http_request_tag    = $request_packet->[1]; # from the 'request' post

$response_packet contains a reference to the resulting HTTP::Response object.

  my $http_response_object = $response_packet->[0];

Please see the HTTP::Request and HTTP::Response manpages for more information.

  progress handler
The example progress handler shows how to calculate a percentage of download completion.

  sub progress_handler {
    my $gen_args  = $_[ARG0];    # args passed to all calls
    my $call_args = $_[ARG1];    # args specific to the call

    my $req = $gen_args->[0];    # HTTP::Request object being serviced
    my $tag = $gen_args->[1];    # Request ID tag from.
    my $got = $call_args->[0];   # Number of bytes retrieved so far.
    my $tot = $call_args->[1];   # Total bytes to be retrieved.
    my $oct = $call_args->[2];   # Chunk of raw octets received this time.

    my $percent = $got / $tot * 100;

    printf(
      "-- %.0f%% [%d/%d]: %s\n", $percent, $got, $tot, $req->uri()
    );

    # To cancel the request:
    # $_[KERNEL]->post( component => cancel => $req );
  }

DEPRECATION WARNING

The third return argument (the raw octets received) has been deprecated. Instead of it, use the Streaming parameter to get chunks of content in the response handler.

REQUEST CALLBACKS
The HTTP::Request object passed to the request event can contain a CODE reference as "content". This allows for sending large files without wasting memory. Your callback should return a chunk of data each time it is called, and an empty string when done. Don't forget to set the Content-Length header correctly. Example:

  my $request = HTTP::Request->new( PUT => 'http://...' );

  my $file = '/path/to/large_file';

  open my $fh, '<', $file;

  my $upload_cb = sub {
    if ( sysread $fh, my $buf, 4096 ) {
      return $buf;
    }
    else {
      close $fh;
      return '';
    }
  };

  $request->content_length( -s $file );

  $request->content( $upload_cb );

  $kernel->post( ua => request, 'response', $request );

CONTENT ENCODING AND COMPRESSION
Transparent content decoding has been disabled as of version 0.84. This also removes support for transparent gzip requesting and decompression.

To re-enable gzip compression, specify the gzip Content-Encoding and use HTTP::Response's decoded_content() method rather than content():

  my $request = HTTP::Request->new(
    GET => "http://www.yahoo.com/", [
      'Accept-Encoding' => 'gzip'
    ]
  );

  # ... time passes ...

  my $content = $response->decoded_content();

The change in POE::Component::Client::HTTP behavior was prompted by changes in HTTP::Response that surfaced a bug in the component's transparent gzip handling.

Allowing the application to specify and handle content encodings seems to be the most reliable and flexible resolution.

For more information about the problem and discussions regarding the solution, see: <http://www.perlmonks.org/?node_id=683833> and <http://rt.cpan.org/Ticket/Display.html?id=35538>

ENVIRONMENT
POE::Component::Client::HTTP uses two standard environment variables: HTTP_PROXY and NO_PROXY.

HTTP_PROXY sets the proxy server that Client::HTTP will forward requests through. NO_PROXY sets a list of hosts that will not be forwarded through a proxy.

See the Proxy and NoProxy constructor parameters for more information about these variables.

SEE ALSO
This component is built upon HTTP::Request, HTTP::Response, and POE. Please see its source code and the documentation for its foundation modules to learn more. If you want to use cookies, you'll need to read about HTTP::Cookies as well.

Also see the test program, t/01_request.t, in the PoCo::Client::HTTP distribution.

BUGS
There is no support for CGI_PROXY or CgiProxy.

Secure HTTP (https) proxying is not supported at this time.

There is no object oriented interface. See POE::Component::Client::Keepalive and POE::Component::Client::DNS for examples of a decent OO interface.

AUTHOR, COPYRIGHT, & LICENSE
POE::Component::Client::HTTP is

•   Copyright 1999-2006 Rocco Caputo

•   Copyright 2004 Rob Bloodgood

•   Copyright 2004-2005 Martijn van Beers

All rights are reserved. POE::Component::Client::HTTP is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

CONTRIBUTORS
Joel Bernstein solved some nasty race conditions. Portugal Telecom <http://www.sapo.pt/> was kind enough to support his contributions.

Jeff Bisbee added POD tests and documentation to pass several of them to version 0.79. He's a kwalitee-increasing machine!

CONTACT
Rocco may be contacted by e-mail via <mailto:rcaputo@cpan.org>, and Martijn may be contacted by email via <mailto:martijn@cpan.org>.

The preferred way to report bugs or requests is through RT though. See <http://rt.cpan.org/NoAuth/Bugs.html?Dist=POE-Component-Client-HTTP> or mail <mailto:bug-POE-Component-Client-HTTP@rt.cpan.org>

For questions, try the POE mailing list (poe@perl.org)