sendfile() not detecting closed connections.

Robert Watson rwatson at
Fri Nov 2 13:14:45 PDT 2007

On Fri, 2 Nov 2007, Ian FREISLICH wrote:

> sendfile() reports success for files less than about 64k in size, but I 
> haven't been able to figure out where the threshold is.  It erroneously 
> reports that 41000 of the 64k were sent, but will say the whole file was 
> transferred up to about 64k.  The connection filedescriptor is blocking.

Probably what is happening is that sendfile() is counting bytes successfully 
inserted into the send socket buffer, rather than bytes sent on the wire. 
This is consistent with what happens when you write a file to a TCP socket, 
though, as you only know the bytes made it into the buffer, not to the remote 
destination.  I'd guess the threshold size you're seeing above is the size of 
the default send socket buffer.

Robert N M Watson
Computer Laboratory
University of Cambridge

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