On Tue, Jun 30, 2009 at 11:04 AM, Damien Katz<dam...@apache.org> wrote: > Definitely don't buffer the whole thing. Footers are the way to go for > efficiency reasons, but if there is a problem supporting them the > alternative is to just read over the section of file and compute the MD5 > hash, then read it again and stream it to the client. It sounds more > expensive to do it that way, but double reading eliminates double caching as > file system cache will keep it in memory most of the time anyway. And the FS > cache is smarter about not swapping out more important data if the section > is large. >
This works fine when the range isn't expensive to calculate. In the end I'd agree that prohibiting an MD5 purely because its a range request seems silly when it should more likely be an implementation decision. > But footers are definitely the way to go for efficiency. Which brings up a > good question, are there known problems with footer support? > The only problem I can think of is that I can't think of anyone that supports them. That could just be because I've also never seen anything that actually sends them and thus not had to look for client support. > -Damien > > > On Jun 30, 2009, at 10:44 AM, Paul Davis wrote: > >> On Tue, Jun 30, 2009 at 7:12 AM, Damien Katz<dam...@apache.org> wrote: >>> >>> On Jun 30, 2009, at 12:17 AM, Noah Slater wrote: >>> >>>> On Fri, Jun 26, 2009 at 07:08:32AM -0400, Damien Katz wrote: >>>>> >>>>> Md5 here is for integrity purposes, not security, so manufactured >>>>> collisions aren't a problem we are worried about. And I don't think >>>>> there is standard SHA1 header, not that I could find anyway. >>>> >>>> I've been seeing some unrelated emails go past on the W3C HTTP WG >>>> mailing >>>> list >>>> about Content-MD5 header which reminded me of this thread. It seems that >>>> this >>>> value must be calculated from the MIME canonical response body, which >>>> means a >>>> different value for content ranges. This presumably means that CouchDB >>>> must >>>> refuse content range requests, send an MD5 value that does not match the >>>> document revision, or break RFC 1864. >>> >>> Im not sure I understand why we can't just calculate and send the MD5 >>> header >>> for the content range. >>> >> >> I reckon you'd have to buffer the response no? Hard to know the MD5 of >> an a priori unknown set of bytes until the end of the range which >> kinda conflicts with sending the MD5 as a header. Technically there >> are HTTP Footers, but i've never actually seen them used. >> >>> -Damien >>> >>>> >>>> Best, >>>> >>>> -- >>>> Noah Slater, http://tumbolia.org/nslater >>> >>> > >
