Are NSStreams or the sockets they use buffered?

FROM : Ryan Homer
DATE : Wed Jan 09 18:02:33 2008

I am using NSStream's getStreamsToHost:port:inputStream:outputStream: 
and sending data over the outputStream to send a file to the receiving 
client.

--- DETAILS ---
On my end, I implement my own buffering in case the packet of data 
that I'm sending can't all be accepted by the recipient. However, if 
another packet of data is "sent" but there is still data queued up, 
I'm queue up this new data elsewhere and waiting for the send queue to 
be emptied.

It may sound a little complicated, but the reason I'm doing it this 
way is because the data is originally tagged with notification 
information and only when the data is actually sent using 
NSOutputStream's write:length: do I post the notification which will 
let me know how much data has been sent thus far. So the backup queue 
can hold the notification information, but the actual send queue is 
just NSMutableData.

Anyway, even if you don't understand the above, the bottom line is 
that I'm trying to send data with as small a buffer as possible so 
that I'm sending data closer to real-time. This is because the 
receiving client will not send any notification that it has received 
the file until it has received the complete file.
--- END DETAILS ---

The end result at the moment is that on my side the file appears to be 
completely sent way before the receiving end gets the complete file. 
So I am wondering if the underlying socket connection that the Cocoa 
framework uses is buffering my data.

Additionally, I am capturing NSStreamEventHasSpaceAvailable event 
codes and I only send data based on this. So does this event code mean 
that the socket can accept more data -- and possible not yet send it 
so it'll buffer it --- OR does it mean that the receiving end of the 
socket can really accept more data?