.. _xdebug-plugin:

XDebug Plugin
*************

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   http://www.apache.org/licenses/LICENSE-2.0

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The `XDebug` plugin allows HTTP clients to debug the operation of
the Traffic Server cache using the ``X-Debug`` header. The plugin
is triggered by the presence of the ``X-Debug`` header in the client
request. The contents of this header should be the names of the
debug headers that are desired in the response. The `XDebug` plugin
will remove the ``X-Debug`` header from the client request and
inject the desired headers into the client response.

`XDebug` is a global plugin. It is installed by adding it to the
:file:`plugin.config` file.

Debugging Headers
=================

The `XDebug` plugin is able to generate the following debugging headers:

Via
    If the ``Via`` header is requested, the `XDebug` plugin sets the
    :ts:cv:`proxy.config.http.insert_response_via_str` configuration variable
    to ``3`` for the request.

X-Cache-Key
    The ``X-Cache-Key`` header contains the URL that identifies the HTTP object in the
    Traffic Server cache. This header is particularly useful if a custom cache
    key is being used.

X-Cache
    The ``X-Cache`` header contains the results of any cache lookup.

    ==========  ===========
    Value       Description
    ==========  ===========
    none        No cache lookup was attempted.
    miss        The object was not found in the cache.
    hit-stale   The object was found in the cache, but it was stale.
    hit-fresh   The object was fresh in the cache.
    skipped     The cache lookup was skipped.
    ==========  ===========

X-Milestones
    The ``X-Milestones`` header contains detailed information about
    how long the transaction took to traverse portions of the HTTP
    state machine. The timing information is obtained from the
    :c:func:`TSHttpTxnMilestoneGet` API. Each milestone value is a
    fractional number of seconds since the beginning of the
    transaction.
