Python Socket Flush

Question

I am trying to make sure that every time I call the socket.send function my buffer is sent (flushed) to my server (which is in C using unix socket).

From my understanding (and from what I see on this board) just disabling the naggle algo. should do it but my server still receive my data in chunk of 4096 bytes (default set)...

Im using the following code in Python v2.5.4:

 self.sck = socket( AF_INET, SOCK_STREAM )

 self.sck.setsockopt( IPPROTO_TCP, TCP_NODELAY, 1 ) # That doesn't seems to work...

 self.sck.connect( ( "127.0.0.1", "12345" ) )

 while( 1 ):
      self.sck.send( "test
" )
      self.sck.send( "" ) # Still trying to flush...

Enabling/Disabling TCP_NODELAY seems that have no effect whatsoever... Is this a bug or I am missing something?

TIA

Answer 1

TCP does not provide any kind of guaranteed "packet" sending to the other end. You are sending data as fast as you can, and TCP is helpfully batching up the data into as much as it can send at once. Your server is receiving data 4096 bytes at a time, probably because that's what it asked for (in a recv() call).

TCP is a stream protocol and therefore you will have to implement some kind of framing yourself. There are no built-in message boundaries.