Blue Coat Systems Proxy SG manual Evaluation Order

ProxySG Content Policy Language Guide

Evaluation Order

CacheOS 4.x filter files have a different order of evaluation than CPL files.

A compiled filter file behaves as if it had a single [Prefix] section, a single [Domain-Suffix]section, and a single [Regular-Expression]section. The filter file is rewritten during file compilation, as follows:

•Any naked filter line that contains regular-expression metacharacters is moved into a virtual

[Regular-Expression] section.

•Any remaining naked filter lines are moved into a virtual [Prefix] section.

•All explicit [Prefix] sections are appended to the virtual [Prefix] section, in the order they are written.

•All explicit [Domain-Suffix]sections are appended to the virtual [Domain-Suffix]section, in the order they are written.

•All explicit [Regular-Expression]sections are appended to the virtual [Regular-Expression]section, in the order they are written.

After all of this rewriting is performed, the filter file has the following order of evaluation:

1.The ALL statements.

2.The virtual [Prefix] section. Within this section, it is the longest match that wins, not the first match.

3.The virtual [Domain-Suffix]section. Within this section, it is the longest match that wins, not the first match.

4.The virtual [Regular-Expression]section. Within this section, it is the first match that wins.

5.The default_filter_properties statements.

Within the above order of evaluation, the first statement that matches wins, or determines how the transaction is handled. At most, one statement is executed. The filter file policy is executed by both proxy and cache transactions, so it is as if the filter file represented a single CPL <Cache> layer.

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