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Author image Felipe Gasper
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Net::Curl::Promiser - Asynchronous libcurl, the easy way!


Net::Curl::Multi is powerful but tricky to use: polling, callbacks, timers, etc. This module does all of that for you and puts a Promise interface on top of it, so asynchronous I/O becomes almost as simple as synchronous I/O.

Net::Curl::Promiser itself is a base class; you’ll need to use a subclass that works with your chosen event interface.

This distribution provides the following usable subclasses:

If the event interface you want to use isn’t compatible with one of the above, you’ll need to create your own Net::Curl::Promiser subclass. This is undocumented but pretty simple; have a look at the ones above as well as another based on Linux’s epoll(7) in the distribution’s /examples.


This module will, by default, warn() if its objects are DESTROY()ed during Perl’s global destruction phase. To suppress this behavior, set $Net::Curl::Promiser::IGNORE_MEMORY_LEAKS to a truthy value.


This class’s default Promise implementation is Promise::ES6. You can use a different one by overriding the PROMISE_CLASS() method in a subclass, as long as the substitute class’s new() method works the same way as Promise::ES6’s (which itself follows the ECMAScript standard).

(NB: Net::Curl::Promiser::Mojo uses Mojo::Promise instead of Promise::ES6.)

Experimental Promise::XS support

Try out experimental Promise::XS support by running with NET_CURL_PROMISER_PROMISE_ENGINE=Promise::XS in your environment. This will override PROMISE_CLASS().


Internally each instance of this class uses an instance of Net::Curl::Multi and an instance of Net::Curl::Promiser::Backend. (The latter, in turn, is subclassed to provide logic specific to each event interface.) These are kept separate to avoid circular references.


The following are of interest to any code that uses this module:


Instantiates this class, including creation of an underlying Net::Curl::Multi object.

promise($EASY) = OBJ->add_handle( $EASY )

A passthrough to the underlying Net::Curl::Multi object’s method of the same name, but the return is given as a Promise object.

That promise resolves with the passed-in $EASY object. It rejects with either the error given to fail_handle() or the error that Net::Curl::Multi object’s info_read() returns.

IMPORTANT: As with libcurl itself, HTTP-level failures (e.g., 4xx and 5xx responses) are NOT considered failures at this level.

$obj = OBJ->cancel_handle( $EASY )

Prematurely cancels $EASY. The associated promise will be abandoned in pending state, never to resolve nor reject.

Returns OBJ.

$obj = OBJ->fail_handle( $EASY, $REASON )

Like cancel_handle() but rejects $EASY’s associated promise with the given $REASON.

Returns OBJ.

$obj = OBJ->setopt( … )

A passthrough to the underlying Net::Curl::Multi object’s method of the same name. Returns OBJ to facilitate chaining.

This class requires control of certain Net::Curl::Multi options; if you attempt to set one of these here you’ll get an exception.

$obj = OBJ->handles( … )

A passthrough to the underlying Net::Curl::Multi object’s method of the same name.


See the distribution’s /examples directory.


Net::Curl::Simple implements a similar idea to this module but doesn’t return promises. It has a more extensive interface that provides a more “perlish” experience than Net::Curl::Easy.

If you use AnyEvent, then AnyEvent::XSPromises with AnyEvent::YACurl may be a nicer fit for you.




Copyright 2019-2020 Gasper Software Consulting.

This library is licensed under the same terms as Perl itself.