Logging and debugging
============================

Socket.IO is now completely instrumented by a minimalistic yet
tremendously powerful utility called
`debug <https://github.com/visionmedia/debug>`_ by TJ Holowaychuk.

Before 1.0, the Socket.IO server would default to logging everything out
to the console. This turned out to be annoyingly verbose for many users
(although extremely useful for others), so now we default to being
completely silent by default.

The basic idea is that each module used by Socket.IO provides different
debugging scopes that give you insight into the internals. By default,
all output is suppressed, and you can opt into seeing messages by
supplying the ``DEBUG`` env variable (Node.JS) or the
``localStorage.debug`` property (Browsers).

You can see it in action for example on our homepage:

.. raw:: html

   <video id="debugging-vid" data-setup='{"autoplay":true,"loop":true, "techOrder": ["html5", "flash"], "height": 300}' class="video-js vjs-default-skin" autoplay loop width="100%">

.. raw:: html

   <source src="https://i.cloudup.com/transcoded/IL9alTr0eO.mp4" type="video/mp4">

.. raw:: html

   </video>

Available debugging scopes
--------------------------

The best way to see what information is available is to use the ``*``:

::

   DEBUG=* node yourfile.js

or in the browser:

::

   localStorage.debug = '*';

And then filter by the scopes you’re interested in. You can prefix the
``*`` with scopes, separated by comma if there is more than one. For
example, to only see debug statements from the socket.io client on
Node.js try this:

::

   DEBUG=socket.io:client* node yourfile.js

To see all debug messages from the engine *and* socket.io:

::

   DEBUG=engine,socket.io* node yourfile.js