Why Does iOS 6 Safari Cache $.ajax POST Requests Even When Cache is Set to False?

iOS 6 Safari Caching $.ajax POST Requests

Since the release of iOS 6, users have reported an unexpected caching behavior when making $.ajax POST requests within Safari's web view. Despite setting the cache option to false, Safari persistently caches the responses.

Cause

Safari's aggressive caching mechanism specifically targets POST requests that exhibit static function signatures, where the input parameters remain constant and only the returned data varies. By default, Safari considers such requests as cacheable and stores their responses for future retrieval.

Solution

To circumvent this caching issue, modify the function signature to introduce a dynamic parameter. For example, instead of:

getNewRecordID(intRecordType)

Use:

getNewRecordID(intRecordType, strTimestamp)

By incorporating a timestamp or other dynamic parameter into the function signature, Safari recognizes the request as unique and avoids caching the results.

Underlying Reason

Safari's caching behavior stems from an interpretation of the HTTP specification, which allows for caching of POST responses when appropriate Cache-Control or Expires headers are included. However, Apple's implementation extends this caching to scenarios where these headers are absent or set to "max-age=0."

No Cache-Control or Expires headers = iOS6 Safari will cache
Cache-Control max-age=0 and an immediate Expires = iOS6 Safari will cache
Cache-Control: no-cache = iOS6 Safari will NOT cache

Workaround

To disable caching globally for all POST requests, add the following line to the Apache configuration:

Header set Cache-Control "no-cache"

Alternatively, you can limit this behavior specifically to POST requests:

SetEnvIf Request_Method "POST" IS_POST
Header set Cache-Control "no-cache" env=IS_POST

By modifying the function signature and incorporating these caching modifications, you can restore the expected behavior within iOS 6 Safari and ensure that POST requests are not cached.

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