nginx spdy server hint

CM Fields cmfileds at
Tue Jul 24 21:48:00 UTC 2012

>From what I understand using the "Link" header with the rel=prefetch
directive will download the files once the current page is loaded and
the client connection is idle. This is to pre-load files that the
client may request later on the site. This option seems to be in
Firefox only and available for a few years now.

The Google docs for the "Link" header with the rel=subresource
directive seems to tell the client the files listed are to be
downloaded immediately as they are going to be using on the current
page rendering. In theory the client could ask for the index.html and
the server would send the index.html with the rel=subresource headers
for other jpgs. The client would then immediately ask for the jpgs, if
not already in its cache, instead of decompressing the index.html and
parsing the file to discover the same pictures.

I did a few tests with the following headers which I found searching
the google dev docs. I tested the headers against the latest Firefox
17.0a1 and Chrome 22.0 and nothing seemed to make any difference
according to the browser's development tool timings.

add_header  X-subresource "image/jpeg;/image1.jpg;;
add_header  Link "</image1.jpg>; rel=subresource";

They probably just are not implemented in the browsers at this time.

On Tue, Jul 24, 2012 at 3:33 PM, Valentin V. Bartenev <ne at> wrote:
> On Tuesday 24 July 2012 22:55:57 Valentin V. Bartenev wrote:
>> On Tuesday 24 July 2012 22:36:19 CM Fields wrote:
>> > Thanks for the clarification.
>> >
>> > When I read through the SPDY documents up to version 4 I saw no
>> > mention of server hints at all. I thought I must have missed something
>> > since every news or review article I read mentions SDPY hints, but no
>> > one ever had an example.
>> Seems it's a browser specific feature. It isn't related to SPDY, or nginx.
>>  * http://
>>  *
>> You can try:
>>     add_header Link "</images/big.jpeg>; rel=prefetch";
>> with Firefox.
> I've just test it myself. It works well with my Firefox 14 on both HTTP and
> HTTPS (pure or over SPDY). But I also found that Firebug doesn't show these
> prefetched requests on the Net tab.
> And I had no luck with Chromium 21.
>  wbr, Valentin V. Bartenev
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