Chapter 2: Managing Content Policy Language
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<Exception> Layers
<Exception> layers are evaluated when a proxy transaction is terminated by an exception. This could
be caused by a bad request (for example, the request URL names a non-existent server) or by setting
the
deny or exception() properties in policy. Policy in an exception layer can be used to control how
access logging is performed for exceptions, such as
authentication_failed. It can also be used to
modify the HTTP response headers in the exception page that is sent to the client.
The syntax is:
<Exception [label]> [exception_condition][exception_properties] ...
exception_content
where:
• The
<Exception> layer defines the transactions evaluated against this policy, and restricts the
triggers and properties allowed in the rules used in the layer.
• The optional
label, separated from the layer type by space, is a CPL User-defined Identifier.
• The optional
exception_condition is a list of triggers, all of which must evaluate to true before
the layer content is evaluated. For more information on using conditions, see Chapter 3:
"Condition Reference". See also the following Layer Guards section.
• The optional
exception_properties is a list of properties set if any of the rules in the layer
match. These act as defaults, and can be overridden by property settings in specific rules in the
layer. For more information on using properties, see Chapter 4: "Property Reference". See also the
following Layer Guards section.
<Forward> Layers
<Forward> layers are evaluated when the current transaction requires an upstream connection (and
only then: forward policy will not be evaluated for a cache hit).
<Forward> layers use the server_url=
tests rather than the
url= tests so that they are guaranteed to honor any policy that rewrites the URL.
The syntax is:
<Forward [label]> [forward_condition][forward_properties] ...
forward_content
where:
• The
<Forward> layer defines the transactions evaluated against this policy, and restricts the
triggers and properties allowed in the rules used in the layer.
• The optional
label, separated from the layer type by space, is a CPL User-defined Identifier.
• The optional
forward_condition is a list of triggers, all of which must evaluate to true before the
layer content is evaluated. For more information on using conditions, see Chapter 3: "Condition
Reference". See also the following Layer Guards section.
• The optional
forward_properties is a list of properties set if any of the rules in the layer match.
These act as defaults, and can be overridden by property settings in specific rules in the layer. For
more information on using properties, see Chapter 4: "Property Reference". See also the following
Layer Guards section.
