On 4 January 2011 15:43, James Y Knight <f...@fuhm.net> wrote: > > On Jan 3, 2011, at 10:39 PM, Graham Dumpleton wrote: > >> As documented in: >> >> Â http://blog.dscpl.com.au/2009/10/wsgi-issues-with-http-head-requests.html >> >> the automatic addition of a Content-Length response header where >> len(iterable) is 1, can cause wrong output for cases where WSGI >> application believes that it can itself decide not to return any >> actual content for a HEAD response, ignoring the fact that there could >> be output filters which rely on headers or content being exactly the >> same as for GET. >> >> Do we therefore still want to promote the idea that the optimisation >> is a good idea or even allowed? > > I think it would be nice if it was allowed -- it makes simple apps easier. > Just because some WSGI applications may be broken w.r.t. HEAD, that doesn't > make this optimization undesirable. > > However, the current description does leave things a bit ambiguous. Why, for > example, does it suggest only adding Content-Length if the length of the > iterable is 1? Surely "if type(iterable) in (list, tuple)", the server could > also set the Content-Length header to "sum(len(s) for s in iterable)". Is > that forbidden, or just not explicitly spelled out as allowed?
It just doesn't mention it. From memory it also doesn't mention what to do about case when len(iterable) is 0 either, which presumably if such an optimisation was allowed could allow you to set Content-Length to 0. > If your app *wants* to special-case HEAD handling so as to avoid generating > the body when it doesn't need to, how can it do that correctly/reliably? If > you normally return content with hard-to-determine length, and you want the > HEAD processing to thus also omit Content-Length (and not, say, have the > server decide it should return Content-Length: 0), what do you have to return > to ensure this happens? Which is further support for the WSGI server not making decisions itself to set Content-Length. But then, if an application isn't going to generate Content-Length for HEAD, then it can't by rights do it for GET either for same request else the response headers are different. Graham _______________________________________________ Web-SIG mailing list Web-SIG@python.org Web SIG: http://www.python.org/sigs/web-sig Unsubscribe: http://mail.python.org/mailman/options/web-sig/archive%40mail-archive.com
