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From Henrik Nordstrom <>
Subject Re: Reverse proxy mode and DAV protocol
Date Wed, 04 Apr 2007 12:46:19 GMT
ons 2007-04-04 klockan 13:12 +0200 skrev Julian Reschke:

> What I meant by "reason" was the fact that the "Destination" header (and 
> some aspects of the "If" header) require absolute URIs, which is 
> problematic when there's a reverse proxy in the transmission path. All 
> the issues around to rewrite or not to rewrite headers go away once 
> these headers use absolute paths (well, as long as the reverse proxy 
> doesn't also rewrite paths, but I would claim that this is nearly 
> impossible to get right with WebDAV).

Rewriting is nearly impossible to get right. Even when limited to
"simple" rewrites of just the host component.

There is many aspects of HTTP and HTTP applications which depend on the
URIs being known on both sides (client and server), and the more
rewrites you do the higher the risk that some of these is overlooked and
things starts to break.

Most reverse proxies fail even the simple host:port based rewrites,
forgetting or wrongly mapping the internal URIs in some random headers
(i.e. Location, Content-Location, Destination, etc) or generated
response entities. 

WebDAV in particular has a lot of URIs embedded in generated XML
request/response entities.

If you do rewrite then you better make sure you have a clear view of how
the backend URIs should be mapped back to external URIs, and make sure
your rewrites is applied on the complete HTTP messages headers & body,
both requests and responses, and not just the request line.


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