TCP RECV

[Paulo Ferreira]

In code below:

DO
    'SLEEP 1
    TCP RECV hTCP, 1024, sBuffer
    Buffer=Buffer+sBuffer
    'SLEEP 1
LOOP UNTIL sBuffer="" OR ISTRUE EOF(hTCP) OR ISTRUE ERR

On a very fast machine, the loop exit by sBuffer="", but
one byte more is incoming. Is it possible ?

A false EOF, before the true segment ends : Is it possible ?

[Bud Durland]

As I understand it, if EOF() tests true after TCP RECV, what's happened is that there was not enough data in the TCP buffer to fulfill the request. In your example, this is 1024 bytes. EOF does NOT mean that more data won't be coming in to the TCP buffer. So on a very fast machine, or on a connection with lots of latency, a false EOF is indeed possible.

------------------
"People sleep peacefully at night because rough men stand ready to do violence on their behalf" -- George Orwell

[Paulo Ferreira]

So, may be this is a way:

DO    
  TCP RECV hTCP, 1024, sBuffer    
  Buffer=Buffer+sBuffer    
  IF sBuffer="" OR ISTRUE EOF(hTCP) THEN
     SLEEP 5
     TCP RECV hTCP, 1024, sBuffer
     Buffer=Buffer+sBuffer
  END IF
LOOP UNTIL sBuffer="" OR ISTRUE EOF(hTCP) OR ISTRUE ERR

What do you think about it ?
Thanks.

------------------

[Roger Garstang]

Perhaps a little better. I too had this annoying issue and it caused
me to give up on adding more advanced stuff to the Web Server app I
made. I did buy a TCP pack offered here at a very good price sometime
back though, so I may recode it someday to use it. Another problem
is when IE is used to download a file it sends the request before the user
is finished selecting a location, so it can be canceled...why in the world
didn't they just request the header then the file when the location
is selected?

Main issue even with modified code is going to be timeouts. The wait with
something like your added SLEEP, plus the wait for the connection when
no data. And never knowing if you need another SLEEP or not. Data size
is never a sure thing...unless you make up your own data structure, but then
you can only use it in your own apps or for a file transfer, etc...not internet
type stuff as they all use unknowns.

------------------
If you aim at nothing...you will hit it.

[This message has been edited by Roger Garstang (edited September 04, 2006).]

[Mike Doty]

Having same problem.
Can't get read more than 1460 bytes with reliability.
TCP SEND nSocket, STRING$(%PacketLength,"X") 'send packet
'SLEEP IS REQURED HERE
'SLEEP 104 'SLEEP 104 required after TCP SEND if PacketLength = 8192 (1 thread)
'SLEEP 160 'SLEEP 160 required after TCP SEND if PacketLength = 8192 (2 threads)
'SLEEP 180 'SLEEP 200 required after TCP SEND if PacketLength = 8192 (3 threads)
'SLEEP 210 'SLEEP 210 required after TCP SEND if PacketLength = 8192 (4 threads)
'SLEEP 260 'SLEEP 260 required after TCP SEND if PacketLength = 8192 (5 threads)
'SLEEP 310 'SLEEP 31 required after TCP SEND if PacketLength = 8192 (6 threads)

DO
       TCP RECV nSocket, %PacketLength, sBuffer
       sPacket = sPacket + sBuffer
       IF sBuffer="" OR ISTRUE EOF(nSocket) THEN
           'falls through with sBuffer = 1460
           '? "The length of sBuffer was" + STR$(Len(sBuffer))
           SLEEP 5
           TCP RECV nSocket, %PacketLength, sBuffer  'goes into a wait until timeout
           ? "The length of sBuffer on second recv" + STR$(LEN(sbuffer))
           sPacket = sPacket+ sBuffer
       END IF
     LOOP UNTIL sBuffer="" OR ISTRUE EOF(nSocket) OR ISTRUE ERR
     ? "This doesn't execute until timeout occurs"

[Mike Doty]

Solution by Don Dickinson in Rserver2

FUNCTION tcpSafeReceive(BYVAL hSocket AS LONG, BYVAL iBufferLen AS LONG, _
                        recBuff AS STRING) AS LONG
 
   'tcpSafeReceive is by Don Dickinson  - rated A+  (required)
 
   DIM iLeft AS LONG
   DIM sBuffer AS STRING
   recBuff = ""
   iLeft = iBufferLen
   DO
      sBuffer = SPACE$(iLeft)
      ON ERROR RESUME NEXT
      sBuffer = SPACE$(iBufferLen)
      TCP RECV hSocket, iLeft, sBuffer
      IF ERR THEN
         FUNCTION = %False
         EXIT FUNCTION
      END IF
      recBuff = recBuff + sBuffer
      IF LEN(recBuff) >= iBufferLen THEN
         EXIT DO
      END IF
      iLeft = iBufferLen - LEN(recBuff)
      SLEEP 5
   LOOP
   FUNCTION = %True
END FUNCTION