Order of Content Rules
Content rules are typically processed in the order they appear on a policy route. However, there are certain circumstances where this is not the case.
ICAP Previewing
If previewing is enabled by the ICAP client, a preview of the request or response is sent to the ICAP server. This enables the Gateway to operate more efficiently, as there might be policy rules which can be implemented without the server waiting for a browser request to be satisfied.
However, as a result of previewing, some content rules might not be applied in the order in which they are displayed on the policy route.
| Previewing is recommended in order to maximize the performance of the ICAP Gateway. |
Example: media type rule and filename rule
You configure a policy route to block downloaded Excel files and any downloaded filename with the extension: *.xlsx.
If previewing is enabled, the file headers are downloaded by the proxy first, during the preview. No media type information is initially detected. Content rule 2 is then applied first, while Content Rule 1 requires response data to be downloaded before it can be applied.