Executive Summary:
Generalize support for WN's byte range syntax, ";bytes=<start>-<end>".
See http://hopf.math.nwu.edu/docs/range.html for more info.
All comments and feedback are welcome. In particular, if anyone knows of
any other already-deployed 'standards', or a more appropriate forum for
discussion, please say so (and/or forward this message).
Thanks for your time,
dG
David Glazer
dglazer@best.com
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Problem statement:
Define an URL syntax to return a specified byte range from a specified
file living on the server. Servers should be able to support the syntax
via either a built-in extension or a CGI script.
CGI tradeoffs:
Option 1: Use a CGI script
Pros: simple to implement - doesn't require any server code changes
provides the same syntax on all servers that support CGI
Cons: requires an extra system call for each block requested
requires the server to have CGI execution turned on
requires a copy of the CGI script in each served directory
(to avoid some scary security holes)
only works with physical files located on the server's filesystem
Option 2: Build support into the server
Pros: more efficient
easier to administer
leverages all server name-mapping and security features
Cons: requires agreement on syntax to be portable across servers
even after agreement, newly modified servers need to be deployed
Conclusion:
Both options make sense and should be supported, ideally with a single
URL syntax. Hopefully, the CGI version will become less and less
necessary as updated servers are rolled out.
Proposed Syntax:
Given a base URL that identifies a document, append a modifier string to
select a range. The syntax of that string is ";bytes=<start>-<end>",
where <start> and <end> are inclusive byte offsets. The base URL can
either be the normal document URL (for servers with built-in support) or
a CGI URL.
Example:
The file foo.doc is available via URL http://www.a.com/docs/foo.doc
We want to get 512 bytes from foo.doc, starting at offset 1024.
If the server has built-in support, the URL would be
http://www.a.com/docs/foo.doc;bytes=1024-1535
If using a CGI script (installed in foo.doc's directory), the URL would be
http://www.a.com/docs/my.cgi?foo.doc;bytes=1024-1535
Note on Syntax:
We considered several alternative syntaxes, such as:
http://www.a.com/docs/my.cgi?foo.doc;bytes=1024+512
http://www.a.com/docs/my.cgi?foo.doc+1024+1535
http://www.a.com/docs/foo.doc?1024+512
They differ mainly in punctuation and supplying a length instead of an
ending offset. I don't see any intrinsic benefit to most of the choices,
so the facts that WN is shipping with a syntax, and that that syntax can
also be cleanly used in CGI scripts, seem to carry the day.
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