On Wed, Jul 20, 2011 at 6:32 PM, Randall Leeds <[email protected]> wrote: > On Wed, Jul 20, 2011 at 15:20, Paul Davis <[email protected]> wrote: >> On Wed, Jul 20, 2011 at 5:15 PM, Randall Leeds <[email protected]> >> wrote: >>> On Wed, Jul 20, 2011 at 15:09, Paul Davis <[email protected]> >>> wrote: >>>> On Wed, Jul 20, 2011 at 5:03 PM, Travis Jensen <[email protected]> >>>> wrote: >>>>> couch_httpd.erl seems to be confused about what it wants to do with HEAD >>>>> requests. >>>>> >>>>> On the one hand, it supports catching {http_head_abort, Resp} and will >>>>> throw >>>>> that in start_response/3 and start_response_length/4 if your method is set >>>>> to HEAD. >>>>> >>>>> On the other hand, it sets all HEAD requests to GET, so no handler can >>>>> ever >>>>> know a HEAD request was made (instead, it lets Mochiweb strip the body). >>>>> >>>>> I can appreciate the simplicity of the latter, but >>>>> the schizophrenic behavior seems odd. I've also got a custom handler that >>>>> would really like to know if it is HEAD or GET (generating the body takes >>>>> a >>>>> lot of CPU, but I know its length because I store it in a document). >>>>> >>>>> First question: should Couch really set all HEAD requests to GET? >>>>> (Personally, I think not) >>>>> Second question: does anybody know how bad it would be to remove that HEAD >>>>> -> GET mapping? >>>>> >>> >>> It would be bad since a lot of the handlers specifically match against >>> the method being GET. >>> I have a ticket open to do smarter things with HEAD in general, >>> especially as it relates to caching proxies and ETags: >>> https://issues.apache.org/jira/browse/COUCHDB-941 >>> >>> It's something we should definitely set about fixing eventually, but I >>> don't know what the priority is. >>> >>>>> Cheers. >>>>> >>>>> tj >>>>> -- >>>>> *Travis Jensen* >>>>> *** >>>>> *Read the Software Maven @ http://softwaremaven.innerbrane.com/ >>>>> Read my LinkedIn profile @ http://www.linkedin.com/in/travisjensen >>>>> Read my Twitter mumblings @ http://twitter.com/SoftwareMaven >>>>> Send me email @ [email protected] >>>>> >>>>> **What kind of guy calls himself the Software Maven???** >>>>> >>>> >>>> I don't have the answer at the tip of my fingers, but IIRC there was a >>>> specific interaction that we had to do that so that something else >>>> didn't break. I wonder if its possible to tag the request with a >>>> special "is actually a HEAD request" thing so users can check. >>> >>> I don't like an "is actually a HEAD request" flag. >>> Adding HEAD handlers is the right approach, but if we want to be lazy >>> we could support a fallback to GET when we get a function_clause error >>> trying to call the handler. >>> >> >> Yeah, its definitely a hack. A fallback on function_clause would >> definitely be much cleaner I think. Only thing is I tend to wonder if >> there'd be a performance hit since our entire HTTP stack currently >> relies on HEAD -> GET, which would be generate a lot of exception >> handling. > > It'd only occur when people do a HEAD request, so normal operation > would be fine? > Clearly we'd want to log a warning or something and start implementing > all the HEAD responses properly. >
Though I think some libraries will use HEAD requests to check if they can short circuit some operations. No idea what sort of density that'd be and it'd obviously be fairly lib/usecase specific. Also true, if we change this, adding real HEAD responses would be useful. Granted in a webmachine world this would all Just Work. >> >>>> >>>> I'd search through the dev@ list for chatter on that mapping around >>>> the time it was made. I'm pretty sure there was a thread that we did >>>> some discussion on that. >>>> >>> >> >
