Blue Coat Systems Proxy SG manual Policy is examined before the requested object is fetched

ProxySG Content Policy Language Guide

Each of the protocol-specific proxy transactions has specific information that can be tested—information that may not be available from or relevant to other protocols. HTTP Headers and Instant Messaging buddy names are two examples of protocol-specific information.

Other key differentiators among the proxy transaction subtypes are the order in which information becomes available and when specific actions must be taken, as dictated by the individual protocols. Variation inherent in the individual protocols determines timing, or the sequence of evaluations that occurs as the transaction is processed.

The following table summarizes the policy evaluation order for each of the protocol-specific proxy transactions.

Table 2.1: When Policy is Evaluated

Transaction Type	Policy is Evaluated....
Tunneled TCP transactions	before the connection is established to the origin server.
HTTP proxy transactions	Before the authentication challenge.
	After the authentication challenge, but before the requested object is fetched.
	Before making an upstream connection, if necessary.
	After the object is fetched
FTP over HTTP transactions:	Before the authentication challenge.
	After the authentication challenge, but before the required FTP commands are
	executed.
	Before making an upstream connection, if necessary.
	After the object is fetched.
Transparent FTP transactions	Policy is examined before the requested object is fetched.
Real Media streaming	Before the authentication challenge.
transactions
	After the authentication challenge, but before getting object information.
	Before making an upstream connection, if necessary.
	After the object information is available, but before streaming begins.
	After streaming begins (this evaluation can be done multiple times, for example
	after playback is paused and restarted).
Windows Media MMS	Before the authentication challenge.
streaming transactions
	Before making an upstream connection, if necessary.
	After the authentication challenge but before getting object information.
	After the object information is available, but before streaming begins.
	After streaming begins (this evaluation can be done multiple times, for example
	after playback is paused and restarted).

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