[web-devel] Content-Length on sendFile

[David Pollak]

On Tue, Jun 14, 2011 at 12:06 PM, Michael Snoyman <michael at snoyman.com>wrote:

> On Tue, Jun 14, 2011 at 9:55 PM, David Pollak
> <feeder.of.the.bears at gmail.com> wrote:
> >
> >
> > On Tue, Jun 14, 2011 at 11:50 AM, Michael Snoyman <michael at snoyman.com>
> > wrote:
> >>
> >> I think the reason we didn't include the header is because, when I
> >> wrote it, I didn't know of a cross-platform way to get file sizes. Now
> >> that I know about unix-compat, this seems like a reasonable thing to
> >> add. Anyone know a reason we *shouldn't* do this?
> >
> > In Lift, we do not automatically populate the Content-Length for generic
> > BLOB responses because if the response is streaming, then we have to
> > strictly evaluate the stream to determine the length.  For returning
> large
> > items (e.g., a 2 GB AVI), this can cause issues.  We break the Response
> > types into "In Memory" which are strict and we include the Content-Length
> > header, but for responses that are not strict, it's up to the coder.
> >
> > My 2 cents.
>
> Nubis was referring specifically to sending files. Yesod has a similar
> breakdown where some datatypes (strict ByteStrings for instance) have
> a content-length attached, while others (lazy ByteStrings) do not. We
> achieve this via the optional Int argument in the ContentBuilder
> constructor[1]. Various instances of ToContent simply handle this
> differently.
>
> In the case of files, we would either use the length specified by the
> FilePart parameter, or simply get the file size from the file system.
>

Sorry for the newbie mistake and thanks for correction me!

Rock on.


>
> Michael
>
> [1]
> http://hackage.haskell.org/packages/archive/yesod-core/0.8.2/doc/html/Yesod-Content.html
>
> >>
> >> Michael
> >>
> >> On Tue, Jun 14, 2011 at 8:16 PM, Nubis <nubis at woobiz.com.ar> wrote:
> >> > Hi guys,
> >> > Just wanted to give you a heads up that yesod's sendFile is not
> setting
> >> > the
> >> > Content-Length header, which 'breaks' some proxies and load balancers.
> >> > (in
> >> > our case, amazon elastic load balancer).
> >> > I don't know if that's by design, I'm not 100% sure but not setting
> the
> >> > header would be only useful for 'long pooling' of binary files for
> doing
> >> > some sort of hackish http streaming, which I don't think is yesod's
> >> > purpose
> >> > anyways :)
> >> > A workaround is setting the Content-Length header before calling
> >> > sendFile, I
> >> > guess it may be something easy to add, I was going to propose a patch
> >> > that
> >> > just wraps the current implementation in a do block that sets the
> >> > header,
> >> > but then I noticed a number of optimizations being made that hint
> there
> >> > should be a 'better' way.
> >> >
> >> > cheers!
> >> > ----nubis :)
> >> >
> >> > _______________________________________________
> >> > web-devel mailing list
> >> > web-devel at haskell.org
> >> > http://www.haskell.org/mailman/listinfo/web-devel
> >> >
> >> >
> >>
> >> _______________________________________________
> >> web-devel mailing list
> >> web-devel at haskell.org
> >> http://www.haskell.org/mailman/listinfo/web-devel
> >
> >
> >
> > --
> > Lift, the simply functional web framework http://liftweb.net
> > Simply Lift http://simply.liftweb.net
> > Follow me: http://twitter.com/dpp
> > Blog: http://goodstuff.im
> >
> >
>



-- 
Lift, the simply functional web framework http://liftweb.net
Simply Lift http://simply.liftweb.net
Follow me: http://twitter.com/dpp
Blog: http://goodstuff.im
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