Re: NSURLRequest conditional GET

FROM : Marc Monguio
DATE : Thu Jun 19 18:42:58 2008

below...

On Jun 19, 2008, at 6:13 PM, Jens Alfke wrote:

>
> On 18 Jun '08, at 3:01 AM, Marc Monguio wrote:
>

>> The documentation I've found about "Conditional GET" in the web 
>> says I should be sending "If-Modified-Since" and "If-None-Match" 
>> headers with the contents of "Last-Modified" and ETag" headers from 
>> the last server's answer. However it doesn't look like a 
>> NSURLRequest with a NSURLRequestUseProtocolCachePolicy is adding 
>> the "If-None-Match" header. Fortunately it adds the "Last-Modified" 
>> header automatically so I've tweaked my server-side to be able to 
>> work just with this header for caching.
>>
>> Is this a bug in NSURLRequestUseProtocolCachePolicy ?

>
> I think so; or at least a case where it's not being as optimal as it 
> could be.


I submitted a bug to Apple's. Id 6021187


>> When debugging the status in the "connection:didReceiveResponse:" 
>> delegate method the statusCode is always 200. I knew for sure than 
>> in fact it was being cached so I ran "tcpdump" and I saw that 
>> except the first call the rest were always Status  Code 304 Not 
>> Modified. Why I can't see what I really get from the server in my 
>> code?

>
> I think the framework does this intentionally since it's hiding the 
> details of the caching from you. Since you didn't explicitly add an 
> if-modified-since header to your request, a 304 response wouldn't be 
> a valid status code for the request as you generated it.


I agree. My concern is that there seems to be no way to know if 
caching is actually working unless you sniff your TCP connections 
which is obviously a workaround.

> When I've implemented conditional requests, I've always added the 
> necessary headers myself. I haven't used the CFNetwork cache at all 
> in these cases; but I think you could do so by first sending the 
> request in use-cache-only mode, checking the mod date and etag of 
> the response, and then sending a request with your own if-none-match 
> and if-modified-since headers, using the ignore-cache mode.


Since my setup works I'll keep using NSURLRequest with 
NSURLRequestUseProtocolCachePolicy. It's always good to know that you 
have actually added the Headers manually and that it works. Thanks.