RE: Socket receive completely read

["Bartell, Aaron L. (TC)" <ALBartell@xxxxxxxxxxxxxx>]

Good answer Buck, and thanks for the help.

Aaron Bartell


-----Original Message-----
From: Buck Calabro [mailto:Buck.Calabro@commsoft.net]
Sent: Monday, November 25, 2002 2:35 PM
To: rpg400-l@midrange.com
Subject: RE: Socket receive completely read


Aaron,
This is the nature of sockets in general.  Because the network can break
packets up you never really know if the sender is done sending or not.  For
a worse case scenario, consider a chat application.  If you listen for CR/LF
as the 'end of data' marker, what do you do if the typist walks away from
the screen for an hour in the middle of a sentence?

If you program both ends of the connection, there are several ways you can
avoid this problem.  You can have the sender transmit a distinct 'end of
data' marker like $DONE$.  The listener keeps listening until it has
accumulated all of the characters in the delimiter.

You can send a length as the first characters; sort of a 'this message is
THIS long.'  The sender and listener both agree on how many bytes comprise
the length, say 5.  Then the listener keeps listening until it has
accumulated _length_ bytes.

This "chunking" methodology is a variant of the latter.  The sequence you
have is already translated into EBCDIC and I think should be broken down as
follows: "0D 25 F1 0D 25 25 0D 25 F0 0D 25 0D 25"

0D 25 - prev data?
F1 - chunk size (1 byte)
0D 25 -chunk size terminator
25 - the chunk
0D 25 - end of chunk
F0 - chunk size (0 bytes - final chunk)
0D 25 - end of chunk size
0D 25 - end of chunk trailer (empty line)

So the algorithm you need to implement for this seems to be:
1) Accumulate "chuck size" bytes until CRLF
1a) If "chunk size" = 0, exit to (3)
2) Read "chunk size" bytes
2a) Read CRLF
2b) Repeat to (1)
3) Read CRLF
4) Exit
  --buck
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