How the ProxySG appliance handles byte-range requests

Products

• ProxySG Software - SGOS

Issue/Introduction

When a client makes a byte-range request to the ProxySG appliance, the appliance may or may not respect that part of the request. This article explains how the appliance handles such a request.

Resolution

There are two scenarios depending if the object is cached or not.

If the object is NOT in cache

   If the range requested is less than 14336 bytes (14k), the appliance downloads the entire file and serves the range from cache.

   If the range is more than 14k, the request is treated as non-cacheable and the range is requested from the OCS. The partial file is NOT cached.

If the object is in cache

   If the request did not include a PNC header (Pragma no-cache), the range is served from the cache.

   If the request contains a PNC header and the range is less than 14k, the range is served from cache.

   If the request contains a PNC and the range is greater than 14k, more calculation is done in order to determine if the range will be served from cache or not..

Note: The appliance does not support byte-range requests when the server responds with chunked transfer encoding. When this happens, it results in the appliance serving the entire file with a 200 OK response to the client rather than content-range with only the requested byte-range. 

Workaround

If the caching behavior as described above is causing a problem with a particular server/site and you want the appliance to only send the byte-range as the client has requested, use bypass_cache(yes) in policy for such requests.