RE: [libmicrohttpd] Using sendfile for file segment

[Eivind Sarto]

Thanks for the reply.
But, suppose I really, really wanted an API that would allow me to send a 
response with only a segment of a file (and using sendfile).
I have a rather demanding application where I want to store the data in large 
files and serve it to 1000s of clients where each URL
will correspond to a segment of a large file.  I already have written and 
tested modules for standard web servers like Apache and Nginx, but
neither of them have the process model that I need, and will not scale as well. 

If I wanted to hack libmicrohttpd and add my own API, it is not obvious to me 
what that would be (I have only looked at the code for a few
hours).  I cannot add a new function, like
   MHD_create_response_from_fd_and_off(size, off, fd)
because the file offset I need to pass needs to be saved in 
MHD_Connection->response_write_position, and the connection context
is not available when the response is created.

Or, if I simply added an API call
   MHD_set_write_position(connection, offset)
to set the MHD_Connection->response_write_position after I created the 
response, would that work?
There is a lot of code that range checks the response_write_position against 
other fields in the connection and response structures
and since I am not familiar with the logic, I am not sure if it would be that 
easy.
Is it more to it than that?

I would be happy to hack and debug the changes I need, but I would really 
appreciate it if you could point me in the right direction so I
could possibly avoid trying something stupid that will never work.

Thanks,
-eivind
________________________________________
From: address@hidden address@hidden On Behalf Of Christian Grothoff 
address@hidden
Sent: Monday, November 29, 2010 1:47 PM
To: address@hidden
Cc: Eivind Sarto
Subject: Re: [libmicrohttpd] Using sendfile for file segment

You're right that this is currently not possible.  We'd need to extend the API
to allow (additionally) passing an offset / length, then this should be easy
to do.  I'm not opposed to having such a function in principle.

However, as long as you don't require sendfile AND partial sends, you should
be fine with the current API.

Happy hacking,

Christian

On Monday, November 29, 2010 03:16:23 am Eivind Sarto wrote:
> I am looking for a way to use microhttpd to send a response using sendfile,
> but I do not wish to transfer the entire file, just a segment of the file.
>
> I don't see an interface for transferring just a portion of a file (at
> some offset + length)
> and make libmicrohttpd use the linux sendfile system call.
>
> Am I missing something?
>
> -eivind