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From Fred Toth <ft...@synernet.com>
Subject Re: Byte-serving PDFs unsupported? Or broken?
Date Sun, 14 Sep 2008 18:56:47 GMT
Hello again,

After a bit more looking, I found this discussion in bugzilla from this 
July:

https://issues.apache.org/bugzilla/show_bug.cgi?id=45419

In short, according to the discussion, correct interaction with the
Adobe plugin requires that a server send the "Accept-Ranges" header
in response to the initial request. The Adobe plugin sees this and then
proceeds to read the PDF file in chunks instead of requesting the
whole thing.

Currently, the tomcat DefaultServlet does not set this header, even though
it supports the Content-Range requests.

It appears that I can work around this with a filter. I'll report back 
on that
after I've got one going.

Can anyone comment on the status of this bug?

Many thanks,

Fred Toth

Fred Toth wrote:
> Hi all,
>
> I've been trying to get to the bottom of an old question:
>
> Does tomcat support byte-serving of PDF files? In searching the archives,
> this comes up every few years or so and most responses are confusing
> and inconclusive.
>
> Here's more detail on the question, starting with my symptoms:
>
> For unrelated reasons, I just switched a client's site from using 
> apache to using tomcat 5.
> I immediately starting hearing "PDFs are slower to download". I was 
> able to confirm
> this. For example, a 14mb PDF on my connection using tomcat takes 
> about 45 seconds before
> the first page appears in the browser. On a generic apache install, I 
> see the first page
> in approximately 1 second.
>
> The reason for this is that tomcat, out of the box, does not appear to 
> support "byte serving",
> or, possibly, it doesn't support it in a form that's acceptable to 
> Adobe Acrobat
> browser plug-ins.
>
> To understand this one needs a bit of info on PDF internals:
>
> It is possible to create PDFs that are "optimized for web view". PDFs 
> in this form are
> rearranged internally such that the first page can be delivered more 
> quickly. (Earlier PDFs
> kept all pointer information at the end of the file, which meant the 
> entire file had to
> be downloaded before the reader could find the first page.)
>
> The apache web server supports these "optimized" PDFs with no 
> particular configuration.
> However, tomcat does not.
>
> What I can't seem to find out is if this is just not supported? Or 
> does it require some
> specific tomcat configuration? Or does the Acrobat plug-in bend the 
> specification
> in a way that apache handles, but tomcat does not?
>
> The underlying technology is based on particular HTTP headers. 
> "Accept-Ranges" is used
> by the server to say, "Yes, you can ask me for byte ranges of a file". 
> The browser (or, in
> this case, the Acrobat plug-in) responds with specific Content-Range 
> requests, essentially treating
> the PDF file as a random-access file.
>
> I'm amazed that this doesn't come up more often, considering the 
> prevalence of PDFs
> (and the prevalence of tomcat!)
>
> Also, here are some common discussion comments that are NOT the answer 
> I'm seeking:
>
> 1. Yes, tomcat serves PDFs out of the box quite nicely.
> 2. Yes, one can use apache to serve PDFs instead of tomcat. This is 
> not an option
> in my case because I'm using tomcat to implement access control to 
> those PDFs.
> 3. Yes, I know that one could write code to solve this, but I'm hoping 
> that DefaultServlet
> can do this. It's not trivial to implement.
> 4. I've seen comments that indicate that there is general support in 
> tomcat for Accept-Ranges
> and Content-Range. But I've also seen indications that Acrobat might 
> require some specific
> flow of headers before it does the right thing. I can confirm that 
> neither tomcat 5 nor tomcat 6
> handle this properly (at least with a generic configuration).
> 5. Yes, 14mb is quite large for a PDF and there are ways to make 
> smaller PDFs. This particular
> client has specific reasons for using such large PDFs.
> 6. This has nothing to do with generating PDFs on the fly. These are 
> PDF files sitting
> quietly in the web root.
>
> Thanks for any advice you might have!
>
> Fred Toth
>
>
>
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