My "rough" explanation below used the header name "Accept-Content" when (as
a coworker pointed out) the correct header name is indeed "Accept-Encoding."

If you're curious to see some evidence of this feature working (after doing
a google search), you can take a look at "about:histograms/Sdch" and you'll
see various stats about its activity (e.g., dictionary sizes and counts; pre
and post compression sizes (excluding gzip); etc.).
The rest of the email is hopefully more factual.

Jim

On Fri, Oct 24, 2008 at 4:01 PM, Jim Roskind <[EMAIL PROTECTED]> wrote:

> I've turned on the experimental SDCH compression protocol by default for
> the ".google.com" domain only.  Currently Google is helping to test
> support by serving some web pages using this protocol (to browsers that
> support it), so this default change will only impact search at google.com If
> things go well, I'll enable it for the entire net in a week or two.
>
> Please report bugs or problems with search if you see any.
>
> The (new/current) default is equivalent to starting chrome via:
>
> ./chrome.exe -enable-sdch=.google.com
>
>
> If this horks your build, and blocks you, you should run with an explicit
> enable supplying a non-existent domain, such as:
>
> ./chrome.exe -enable-sdch=.nonexistantdomainthatyournotworriedabout.com
>
>
> If you're testing out serving the SDCH protocol from your server (other
> than *.google.com), you can fully enable SDCH support in Chromium via:
>
> ./chrome.exe -enable-sdch
>
>
> FAQ
>
> What is SDCH?  It is a delta-compression protocol.  The server provides a
> dictionary, and then can send results "relative" to that dictionary.
>
> Where can I read more about it?  Take a look at
> http://groups.google.com/group/open-vcdiff/browse_thread/thread/8c4bf1dd91a56ac9?pli=1
>
> How does chromium support it (roughly)?  Chromium advertises its support
> of "sdch" in its Accept-Content header (i.e., where it also says it supports
> gzip, deflate, etc.).  A supporting server then sends back (in a response
> header) an URL to get a dictionary "for future use."  Chromium gets the
> dictionary about 15 seconds later (to avoid interfering with the current
> download).  Chromium then advertises both support for "sdch" as well as its
> possession of the dictionary to the appropriate domains.  A domain's server
> that recognizes the dictionary then compresses future payload responses
> using the delta-compression (commonly in concert with gzip compression).
>
>
>
>
>

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