Using Content-MD5 header

[Matthijs Langenberg]

Igor Sysoev wrote:
> On Mon, Jul 21, 2008 at 01:37:56PM +0200, Matthijs Langenberg wrote:
> 
>> I would like to use the Content-MD5 header from a HTTP response, does
>> Nginx provide a way to add the 'Content-MD5' header to the response for
>> a static file request?
> 
> No, nginx does not support Content-MD5 header.
> Calculating MD5 means that nginx must read whole file before sending it
> to client.
> 
> What purpose of this header ?

Igor,

I'm writing an app that handles file uploads (assets storage) from other 
machines in the network, mostly done by batch processing. I'm using a 
HEAD request to check if a file already is uploaded, but it's hard to 
monitor which files already have been edited and need to be uploaded 
again.
By using the Content-MD5 header and a locally calculated MD5 checksum, I 
can easily check if a file is outdated.
Ofcourse there are other solutions to this problem:
I could also do a GET request to http://some/image.gif/md5, to hit an 
app which calculates the MD5 on request, so nginx doesn't need to 
calculate the MD5 all the time, even for requests that don't use it.
Or I could prepend the filename with (a part) of the MD5 hash. This 
means that I could do a cheap HEAD to http://some/a34sdfs3-image.gif to 
see if my image already exists.

Would it be expensive to add a md5 calculation for static files?
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