Select hangs after some reads

Steve Holden steve at
Thu Jun 8 20:18:05 CEST 2006

Jon Ribbens wrote:
> In article <mailman.6754.1149779465.27775.python-list at>, Steve Holden wrote:
>>Of course, if the client forces the TCP PSH flag true then the receiver 
>>is guaranteed to debuffer the stream up to that point - this is how FTP 
>>clients work, for example.
> I don't think that's right. You are confusing the PSH flag (which is
> basically unused in Unix networking I think) and the URG flag (which
> is extremely rarely used, but is indeed used by FTP to get abort
> requests to 'jump the queue' as it were).

Nope. The URG flag indicates that a packet contains out-of-band data, 
whihc is what you describe above.

The PSH flag indicates that the data stream must be flushed right 
through to the other end. This is essential for interactive protocols 
such as FTP: without it the server has no way to know that the client 
has sent a complete command, and vice versa.

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