#31 If-Modified-Since support

closed
WebKit (45)
5
2003-02-23
2002-09-13
Ken Lalonde
No

WebKit makes no use of the If-Modified-Since HTTP header,
which makes static content service inefficient.
Of course, you can move your static content to a separate
HTTP server, but adding support for If-Modified-Since
buys most of the benefits and costs little.

The attached patch modifies mod_webkit to pass
the If-Modified-Since header via the request environment
dictionary. While arguably less than elegant,
this does the trick.

The patch to UnknownFileTypeServlet checks the
IMS value against the file's mtime. If it matches,
it sets "Status 304" and sends no content.
(It also corrects some unlikely but possible bugs.)

Discussion

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  • Ken Lalonde
    Ken Lalonde
    2002-09-13

    Patch against today's WebKit CVS

     
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  • Ken Lalonde
    Ken Lalonde
    2002-09-23

    Patch against today's WebKit CVS

     
    Attachments
  • Ken Lalonde
    Ken Lalonde
    2002-09-23

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    Here is an improved version of the above patch.
    This version moves the
    If-Modified-Since logic up to the HTTPServlet level,
    so it may be used by other factories. I've modified PSP
    so that "static" PSP pages may be cached at the client.
    ("Static" pages are those that don't use any dynamic PSP
    hooks.)

    There's also a fix to a typo in Session.py.

     
    • assigned_to: nobody --> stuartd
     
  • Ken Lalonde
    Ken Lalonde
    2003-02-14

    Patch against today's Webware CVS

     
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  • Ken Lalonde
    Ken Lalonde
    2003-02-14

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    Here is a third version of the patch, against today's CVS.
    The PSP caching is now off by default, to avoid breaking
    existing code.
    I've added a patch to mod_webkit2.
    The patch to UnknownFileTypeServlet includes changes made in the
    meantime.

     
  • Logged In: YES
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    Ken,
    Have you any test scripts to verify that the IMS is working
    as expected?

    Also, is there more to the isAuthenticated() method? It
    does not appear to be related to IMS.

    There are some other issues addressed in the
    UnknownFileTypeServlet apparently. Can you provide a
    description of changes in functionality here? It's not
    clear how much of that is needed.

    -- Thanks --

     
  • Ken Lalonde
    Ken Lalonde
    2003-02-22

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    > Have you any test scripts to verify that the IMS
    > is working as expected?

    I've attached a simple script below (test-ims.py)
    that will verify that a given HTTP server is handling
    If-Modified-Since as expected.

    > Also, is there more to the isAuthenticated() method?
    > It does not appear to be related to IMS.

    Dang -- that's an internal thing that shouldn't
    have been part of the patch.
    Just delete the call and definition.

    > There are some other issues addressed in the
    > UnknownFileTypeServlet apparently. Can you provide a
    > description of changes in functionality here?
    > It's not clear how much of that is needed.

    The only essential change to UnknownFileTypeServlet
    for IMS support is the addition of the
    lastModified() method. But I think the other
    changes are worthwhile too:
    - the file in question is now opened exactly once,
    and open() failure is handled correctly.
    - The "CheckDate" config option is no longer used.
    If found in the cache, the file mtime is always
    checked against the cached value. The time
    saved avoiding a stat() call is negligible,
    and certainly not worth the hassle of returning
    stale data.
    - when a cached file changes, the old entry is
    deleted completely. The old code just updated
    the cached mtime and content, so files that grow
    larger than MaxCacheContentSize would still stay
    in the cache.
    - the Content-Length HTTP header is set for all requests,
    not just HEAD.
    - the changes in HTTPServlet remove the need to add
    the Last-Modified header.
    - when sending the data to the client, we send no
    more than the advertized amount (in case the file
    has grown), and never loop on early EOF
    (if it has shrunk). Both cases are unlikely,
    but better safe...

    Also, I recommend changing the default value of the
    CacheContent config setting to 0.
    Caching file data in memory is a waste of time,
    since the memory-to-disk bandwidth isn't the bottleneck.
    The O/S can handle file caching much more efficiently,
    and if speed is really an issue, you're far better off
    serving static data outside of WebKit.

     
  • Ken Lalonde
    Ken Lalonde
    2003-02-22

    Script to verify IMS support

     
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    I have applied this to CVS with the exception of the portion
    which applied to PSP. I took the iconcept from the test
    script and created a WebKit/Testing/TestIMS.py test.

    The PSP patch for IMS still required that the PSP page
    implement a method CachePSPByModTime. It seems if you need
    to implement a method such as that, then you should just be
    able to implement a lastModified method of your own. It
    might be useful to provide a compiled time to the PSP
    servlet to assist in this.

    I am closing this patch, but will pose the question to the
    devel list for comment.

     
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