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From Michael S├╝dkamp <michael.suedk...@docware.de>
Subject Byte-Range-Serving of DefaultServlet and Acrobat 6
Date Mon, 17 May 2004 11:25:18 GMT
Hello,

I investigated the topic of byte-range-serving from the DefaultServlet with Acrobat 6.

I noticed that Tomcat 4.1.30 did not any byte-range-serving with Acrobat 6.0.0. The entire
file was sent instead.

I compared the HTTP communication with that of Internet Information server where byte-range-serving
of PDF files works.
Here are my results:

1. HTTP header
Acrobat does not request byte-ranges unless the server sends the header "Accept-Ranges: bytes".
Once I added this header, Acrobat requested byte-ranges.
>From the HTTP 1.1 spec I read that sending this header is not required, but Acrobat seems
to need it.

2. blanks in multi-byte-range-requests
After having added the header above, Acrobat sent byte-range-requests. But Acrobat choked.
I did a packet filtering and recognized the following status code sent by Tomcat "416 request
range not satisfiable".
The reason was that Acrobat sent multi-byte-range-request using e.g. the following string
"1000-2000, 3000-3010"
Notice the blank character. It leads to a parsing exception in line 1300 of the DefaultServlet
(Tomcat 4.1.30). If you do a trim() on the rangeDefinition obtained there, this error does
not occur.

3. newline before Mime-separator-string
After fixing step 2 Acrobat did not choke anymore. However, the pdf file was still served
entirely.
Further comparison with the IIS communication revealed that ISS writes the mime-separation-string
("CATALINA_MIME_BOUNDARY" for Tomcat) on a line line, whereas Tomcat does not. After prefixing
the println-commands with "\n" (lines 1910, 1930, 1964, 1984), it finally worked.

I wonder if you would consider to change the DefaultServlet. IMO Acrobat is a very important
application, and unless it doesn't explicitly violate the HTTP spec Tomcat should support
it.

Best regards

Michael


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