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Reading simple data from a TCP channel

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martinp:
Hello everyone, just a simple question.

I have an incoming TCP data stream I want to capture.  For example port 9004.

I've created a simple incoming server routine.  Not sure if I needed KEEPALIVE but

let TCP=unt; open (TCP,bsz=4096,err=ERR_PORT)"[tcp];9004;KEEPALIVE"
READ_NEXT:
read record (TCP,err=ERR_READ)A$
print "Got: ",A$
goto READ_NEXT


Similarly I ran a linux "nc capture command" capturing data from another port which has the same data being sent to it.


What I am noticing is occasionally the PVX program does something like this:

Almost like a terminator character is received on the port and it registers part of the data then it continues on the next read fine.  So I would have to concatenate the data.

The nc command however does not break apart any data.

I am just wondering if I need to change anything in this routine.  Thanks.

Mike King:
You have specified a blocking factor of 4K so every time you read the most you will get back is 4K regardless of how much has been received.

Your PRINT command will then insert a visible line break on the output -- the line feed is not in the data but simply a result of the PRINT statement not having a trailing comma..

Try:


--- Code: ---  let TCP=unt; open (TCP,bsz=4096,err=ERR_PORT)"[tcp];9004;KEEPALIVE"
READ_NEXT:
  read record (TCP,err=ERR_READ)A$
  print A$,
  goto READ_NEXT
--- End code ---

martinp:
Thanks Mike but this data is coming in very slow like as you can see by the time stamp.  Every few seconds very small data chunks? 

martinp:
Let me resend with this picture I had this code with my time stamp

0040 let TCP=unt; open (TCP,bsz=4096,err=ERR_PORT)"[tcp];9004;KEEPALIVE"
0050 read record (TCP,err=ERR_READ)A$
0060 let TIME$=dte(0:%DATTIM_MSK$)
0070 print TIME$+"   Got: ",A$

Mike King:
Yes but TCP is a streaming transmission so arrival times are never assured.  A transmission error somewhere along the stream can cause a delay/small packet at any time.

Also, if you receiving small intermittent packets I would suggest you add the option NODELAY to disable the Nagles algorithm on the connection, it is normally enabled on TCP. (See Nagles Algorithm at https://en.wikipedia.org/wiki/Nagle%27s_algorithm).  It also possible the sender may need to disable the algorithm to provide an even flow of data.

All that being said, did the example I posted with the trailing comma resolve what you seeing?

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