XDebug Plugin

The XDebug plugin allows HTTP clients to debug the operation of the Traffic Server cache using the default X-Debug header. The plugin is triggered by the presence of the X-Debug or the configured 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 inject the desired headers into the client response. In addition, a value of the form fwd=n may appear in the X-Debug header, where n is a nonnegative number. If n is zero, the X-Debug header will be deleted. Otherwise, n is decremented by 1. =n may be omitted, in which case the X-Debug header will not be modified or deleted.

XDebug is a global plugin. It is installed by adding it to the plugin.config file. It currently takes a single, optional configuration option, --header. E.g.

–header=ATS-My-Debug

This overrides the default X-Debug header name.

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 proxy.config.http.insert_response_via_str configuration variable to 3 for the request.

Diags

If the Diags header is requested, the XDebug plugin enables the transaction specific diagnostics for the transaction. This also requires that proxy.config.diags.debug.enabled is set to 1.

Probe

All request and response headers are written to the response body. Because the body is altered, it disables writing to cache. In conjunction with the fwd tag, the response body will contain a chronological log of all headers for all transactions used for this response.

Layout:

  • Request Headers from Client -> Proxy A

  • Request Headers from Proxy A -> Proxy B

  • Original content body

  • Response Headers from Proxy B -> Proxy A

  • Response Headers from Proxy A -> Client

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 lookups.

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.

If a request goes through multiple proxies, each one appends its X-Cache header content the end of the existing X-Cache header. This is the same order as for the Via header.

X-Cache-Generation

The cache generation ID for this transaction, as specified by the proxy.config.http.cache.generation configuration variable.

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 TSHttpTxnMilestoneGet() API. Each milestone value is a fractional number of seconds since the beginning of the transaction.

X-Transaction-ID

A unique transaction ID, which identifies this request / transaction. This matches the log field format that is also available, %<cruuid>.

X-Remap

If the URL was remapped for a request, this header gives the to and from field from the line in remap.config that caused the URL to be remapped.

X-ParentSelection-Key

The X-ParentSelection-Key header contains the URL that is used to determine parent selection for an object in the Traffic Server. This header is particularly useful if a custom parent selection key is being used.