[web-devel] Content-Length on sendFile

Michael Snoyman michael at snoyman.com
Wed Jun 15 04:29:52 CEST 2011

Let me point out one other distinction: sendFile versus yesod-static.
The former is a function you would call from a normal handler, while
yesod-static is the "magical" package which would actually know all of
the stuff about your files at compile time. For the sendFile case, the
only options for getting the file size are (1) the programmer manually
adding the header and (2) Yesod automatically doing a system call to
get it.

As for the behavior of Warp...  while I agree Kazu that we should
reduce system call overhead, it might make sense for Warp to perform
the system call to get file size *if* no content-length header is

And I'm still very uncomfortable setting the content-length header for
static files based on compile-time information. In this case, having
the wrong value (e.g., someone modified a CSS file after compiling)
will completely break things and corrupt an open HTTP connection.


On Wed, Jun 15, 2011 at 5:22 AM, Kazu Yamamoto <kazu at iij.ad.jp> wrote:
> Greg,
>> I apologize for the confusing terminology. I am not differentiating between
>> sending a static file with sendfile and a streaming response. I
>> am differentiating between 2 different use cases for sending static files
>> (with sendfile). For all of my web applications, I know what all the static
>> files are and they will never change until I deploy another web application.
>> That means I can stat the files once when the application is deployed and keep
>> that information in memory. So I already have the file length information to
>> include in the header, even though I don't do a file stat when the file is
>> requested. wai-app-static and yesod-static supports these techniques.
> Thanks. I think I understand. :)
> So, do you support to *not* change the API (apps should add CL: by
> themselves)?
> --Kazu
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