Net::WebSocket - WebSocket in Perl


    use Net::WebSocket::Handshake::Client ();
    use Net::WebSocket::HTTP_R ();

    my $handshake = Net::WebSocket::Handshake::Client->new(
        uri => $uri,

    syswrite $inet, $handshake->to_string() or die $!;

    #You can parse HTTP headers however you want;
    #Net::WebSocket makes no assumptions about this.
    my $resp = HTTP::Response->parse($hdrs_txt);

    #If you use an interface that’s compatible with HTTP::Response,
    #then you can take advantage of this convenience function;
    #otherwise you’ll need to do a bit more work.
    Net::WebSocket::HTTP_R::handshake_parse_response( $handshake, $resp );

    #See below about IO::Framed
    my $iof = IO::Framed->new($inet);

    my $parser = Net::WebSocket::Parser->new($iof);

    my $ept = Net::WebSocket::Endpoint::Client->new(
        parser => $parser,
        out => $iof,

        $ept->create_message( 'text', 'Hello, world' )->to_bytes()

    #Determine that $inet can be read from …

    my $msg = $ept->get_next_message();

    #… or, if we timeout while waiting for $inet to be ready for reading:

    exit if $ept->is_closed();


This is a beta release. It should be safe for production, but there could still be small changes to the API. Please check the changelog before upgrading.


This distribution provides a set of fundamental tools for communicating via WebSocket. It is only concerned with the protocol itself; the underlying transport mechanism is up to you: it could be a file, a UNIX socket, ordinary TCP/IP, some funky tie()d object, or whatever.

Net::WebSocket also “has no opinions” about how you should do I/O or HTTP headers. There are too many different ways to accomplish HTTP header management in particular for it to be sensible for a WebSocket library to impose any one approach. As a result of this, Net::WebSocket can probably fit your project with minimal overhead. There are some examples of how you might write complete applications (client or server) in the distribution’s demo/ directory.

Net::WebSocket emphasizes flexibility and lightness rather than the more monolithic approach in modules like Mojolicious. Net::WebSocket should support anything that the WebSocket protocol itself can do, as lightly as possible and without prejudice as to how you want to do it: extensions, streaming, blocking or non-blocking I/O, arbitrary HTTP headers, etc. The end result should be a clean, light implementation that will grow (or shrink!) as your needs dictate.


Here are the main modules:


Logic for handshakes. Every application needs one of these. This handles all headers and can also negotiate subprotocols and extensions for you.


A thin convenience wrapper for HTTP::Request and HTTP::Response, CPAN’s “standard” classes to represent HTTP requests and responses. Net::WebSocket::HTTP_R should also work with other classes whose interfaces are compatible with these “standard” ones.


A high-level abstraction to parse input and respond to control frames and timeouts. You can use this to receive streamed (i.e., fragmented) transmissions as well. You don’t have to use this module, but it will make your life easier.


Translate WebSocket frames out of a filehandle into useful data for your application.


Useful for sending streamed (fragmented) data rather than a full message in a single frame.


Useful for creating raw frames. You probably shouldn’t call these classes directly; instead, use Endpoint’s create_message() method. But if you want to dig deeply, these will be your bread and butter. See Net::WebSocket::Frame::text for sample usage.



WebSocket uses regular HTTP headers for its handshakes. Because there are many different solutions around for parsing HTTP headers, Net::WebSocket is “agnostic” about how that’s done. The advantage is that if you’ve got a custom solution for parsing headers then Net::WebSocket can fit into that quite easily.

The liability of this is that you, the library user, must give headers directly to your Handshake object. (NB: Net::WebSocket::HTTP_R might be able to do this for you.)


As per the specification, client serializers “MUST” mask the data randomly, whereas server serializers “MUST NOT” do this. Net::WebSocket does this for you automatically, but you need to distinguish between client serializers—which mask their payloads—and server serializers, which don’t mask.

This module used to do this with Bytes::Random::Secure::Tiny, but that seems like overkill given that the masking is only there to accommodate peculiarities of certain proxies. Moreover, TLS is widely available and free now besides, and it will randomize the data stream anyway. So, nowadays we just use Perl’s rand() built-in.

Text vs. Binary

Recall that in some languages—like JavaScript!—the difference between “text” and “binary” is much more significant than for us in Perl.

Use of IO::Framed

CPAN’s IO::Framed provides a straightforward interface for chunking up data from byte streams into frames. It also provides a write buffer for non-blocking writes, and it (by default) retries on EINTR. You don’t have to use it (which is why it’s not listed as a requirement), but you’ll need to provide a compatible interface if you don’t.

See the demo scripts that use IO::Framed for an example of when you may need a different solution here.


The WebSocket specification describes several methods of extending the protocol, all of which Net::WebSocket supports:

  • The three reserved bits in each frame’s header. (See Net::WebSocket::Frame.) This is used, e.g., in the permessage-deflate extension. (See below for its implementation in Net::WebSocket.)

  • Additional opcodes: 3-7 and 11-15. You’ll need to subclass Net::WebSocket::Frame for this, and you will likely want to subclass Net::WebSocket::Parser. If you’re using the custom classes for streaming, then you can also subclass Net::WebSocket::Streamer. See each of those modules for more information on doing this.

    THIS IS NOT WELL TESTED. Proceed with caution, and please file bug reports as needed. (I personally don’t know of any applications that actually use this.)

  • Apportion part of the payload data for the extension. This you can do in your application.


Net::WebSocket fully supports the permessage-deflate (compression) extension. See Net::WebSocket::PMCE::deflate for details.


At this point Net::WebSocket seems to support everything the WebSocket protocol can (usefully) do, including compression. Please file bug reports for any issues that may crop up.

  • Add more tests.


Mojolicious has a WebSocket implementation. It’s not as complete as Net::WebSocket, but if you’re using Mojolicious, you might try this first.

Protocol::WebSocket is an older module that supports pre-standard versions of the WebSocket protocol. It’s similar to this one in that it gives you just the protocol itself, but it doesn’t give you things like automatic ping/pong/close, classes for each message type, etc.

Net::WebSocket::Server implements only server behaviors and gives you more automation than P::WS.

Net::WebSocket::EV uses XS to call wslay. As of this writing it lacks support for handshake logic.



Felipe Gasper (FELIPE)


Copyright 2018-2019 by Gasper Software Consulting


This distribution is released under the same license as Perl.