On Mon, Aug 10, 2009 at 9:11 PM, James Bennett <ubernost...@gmail.com>wrote:
> Earlier today I posted an article on my blog following up on some > discussions of WSGI; one criticism presented was of language in PEP > 333 regarding gzipping of responses by WSGI applications. Ian posted a > comment which stated that the criticism was not correct, but I'm at a > loss to figure out what *is* correct, so I'll bring up the question > here. > > In a parenthetical at the end of the section entitled "Handling the > Content-Length Header", PEP 333 states: > > > Note: applications and middleware must not apply any kind of > > Transfer-Encoding to their output, such as chunking or gzipping; as > > "hop-by-hop" operations, these encodings are the province of the > > actual web server/gateway. See Other HTTP Features below, for more > > details. > > In the section "Other HTTP Features", PEP 333 states, in part: > > > However, because WSGI servers and applications do not communicate > > via HTTP, what RFC 2616 calls "hop-by-hop" headers do not apply to > > WSGI internal communications. WSGI applications must not generate > > any "hop-by-hop" headers [4], attempt to use HTTP features that > > would require them to generate such headers, or rely on the content > > of any incoming "hop-by-hop" headers in the environ dictionary. > > My criticism of this is that this is at best ambiguous, and quite > possibly openly misleading to readers of the PEP. > > The ambiguity here is that "gzip" is a valid value for the > Transfer-Encoding header in HTTP (RFC 2616, Sections 3.6 and 14.41), > but is also a valid value for the Content-Encoding header (RFC 2616, > Sections 3.5 and 14.11). > I just don't get the confusion. Transfer-Encoding is not allowed in WSGI (a hop-by-hop header, like several other Transfer-* headers). Content-Encoding is allowed, because everything not specifically mentioned is allowed. Clearly "Content-Encoding" and "Transfer-Encoding" are different strings. And, as you mention, the normal thing that people currently do is use Content-Encoding anyway, so since people aren't using Transfer-Encoding, why is this controversial? There are some weird implications to using Content-Encoding, specifically ETags and range requests, but eh... those exist in mod_deflate and just about everywhere, and are mostly outside the scope of WSGI. -- Ian Bicking | http://blog.ianbicking.org | http://topplabs.org/civichacker
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