Does Rack-servers block until the whole request body has been read?

[Daniel Abrahamsson <hamsson@gmail.com>]

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Hi,

I am working on a server that deals with large file uploads (currently built 
upon Rails, with a Metal taking care of the uploads). According to the 
rack-specification:
"... handler developers must buffer the input data into some rewindable 
object if the underlying input stream is not rewindable".

For Passenger and Mongrel, this means a temp file is created for the request 
(at least for requests as big as those I am dealing with).

Now, my question is, does Rack wait until all data from the client has been 
read to a tempfile before passing on control to the Rack app (in this case, 
Rails)? Or does it pass on control directly, and block if the application 
reads data faster than the client is sending it?

After some initial testing, it appears to me that the former is the case. 
Can anyone give me advice on how to test this? Perhaps it depends on the web 
server used? Perhaps on the framework?

Thank you in advance for any advance or clarification on this matter.

//Daniel

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