tcp send/recv ?

[mark smit]

Hello all...

Is there any possiblility that a string sent with "tcp send hsock, buffer", could become fragmented so that ONE read with "tcp recv, hsock, 8000, buffer" would not receive the whole contents of the string ?


here is an example...

tcp send hsock, "mark smit"

tcp recv hsock, 8000, buff1
tcp recv hsock, 8000, buff2

buff1 = "mar"
buff2 = "k smit"

Could this happen ?

Cheers!

[Scott Turchin]

I would believe this COULD happen in fact.
TCP/IP is a byte oriented protocol, it does not care waht the data does on the wire and is almost ALWAYS fragmented in one way or another..
Although this may cure your problem, you will have the same issue I had in that you have to parse your buffer to separate it:

Do
  Tcp Recv #hTcp,4096, buffer
  WebIn = WebIn + buffer
Loop While Len(buffer)
Tcp Close hTcp

lCount = Tally(WebIn,$CR) 
For lLoop = 1 To 10
    sInArray = Parse$(WebIn,$CR,lLoop) 
    'Do whatever

Next

That should solve your problem, but you will have to parse based on whatever the expected string is AFTER you do that, ie mark smit would be parsed by the " " (name=parse$(buffer," ",1)


PS, Lance, Jim, I learn quick eh? LOL
Scott

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Scott
mailto:[email protected][email protected]</A>

[This message has been edited by Scott Turchin (edited May 10, 2000).]

[Lance Edmonds]

Where possible, it is always a good idea to build in your own form of data validation, so that if a data packet does manage to go astray, your code will be able to handle it without crashing.



------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[mark smit]

Hello again...

I have already tried your example code above to ensure that the FULL data packet has been read in.

do
tcp recv hsock, 2048, buffer
packet = (packet & buffer)
loop while len(buffer)

On my machine the above loop hangs up on the last read. The only way to break to loop was to "Task Manager it to death" or close the hsock connection via the sending program. I have tried the above example in a modified way so that i could see what was happening.

do
tcp recv hsock, 8, buffer
packet = (packet & buffer)
msgbox "[" & buffer & "]"
loop while len(buffer)

note: the brackets are just to show any white space...

This example displays "[]" on the last read and then when I close the connection another %FD_READ message seems to be sent because another "MSGBOX" pops up with the full message packet in brackets "[]".

Cheers!

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[Semen Matusovski]

mark --
try this. if you haven't dial-up, you should correct port and name of server in tcp open (be careful here).
<font face="courier new, courier" size="3"><pre>
#compile exe
#register none
#dim all
#include "win32api.inc"

function pbmain
dim buffer as string, kbuffer as long, i as long
tcp open port 80 at "www.powerbasic.com" as #1 timeout 5000
tcp print #1, "get http://www.powerbasic.com/support/pb...ead.php?t=2199 http/1.0"
tcp print #1, "
kbuffer = 2048: buffer$ = space$(kbuffer)
open "tmp.html" for output as #2
do
tcp recv #1, kbuffer, buffer
if len(buffer) = 0 then exit do
print #2, buffer;
loop
close #2
tcp close #1
open "tmp.html" for binary as #2: get$ #2, lof(2), buffer: close #2
open "tmp.html" for output as #2
print #2, "------------- this web-page was downloaded by pb at " + time$ + " ----------<br><br>"
print #2, "
i = instr(buffer, $crlf + $crlf)
if ucase$(left$(buffer, 5)) = "http/" and i then print #2, mid$(buffer, i + 4); else _
print #2, buffer;
close #2
shellexecute %hwnd_desktop, "open", "tmp.html", byval 0, byval 0, %sw_shownormal
end function
[/CODE]



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[mark smit]

Hello Semen !

Thank you for your reply but I am having a hard time understanding why the port and address would be my problem. reason being that I do have the right port and address and I am able to retreive a partial message but on the last read (ie the end of the message) my program gets stuck in the loop until the connection is closed.

Cheers !

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

[Semen Matusovski]

Mark --
post not workable fragment from your program (but from Compile Exe to End Function of PbMain).
Perhaps, your done something wrong somewhere or do not use Register None.
I use PB/TCP-based utility in commercial program w/o problem.

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

[mark smit]

Hello Again Semen !

Here is my code that did not work, in fact it causes a general protection fault. I hope i've posted the code write...

{code}
#compile exe
#register none
#include "win32api.inc"
#include "wsock32.inc"

%WM_SERVERNOTIFY = 8000
%IDBUTTON = 9000

function FormatIP(byval IPAddress as long) as string
dim address as string

address = mkl$(IPAddress)
function = format$(asc(address, 1), "#.") & _
format$(asc(address, 2), "#.") & _
format$(asc(address, 3), "#.") & _
format$(asc(address, 4), "#")

end function

callback function dlgproc() as long
dim hserver as static long
dim hsock as static long
dim buffer1 as static string
dim buffer2 as static string

select case cbmsg
case %WM_INITDIALOG
hserver = freefile
tcp open server port 2000 as hserver
tcp notify hserver, accept to cbhndl as %WM_SERVERNOTIFY

case %WM_SERVERNOTIFY
select case lowrd(cblparam)
case %FD_ACCEPT
hsock = freefile
tcp accept hserver as hsock
tcp notify hsock, recv close to cbhndl as %WM_SERVERNOTIFY

case %FD_CLOSE
tcp close hsock

case %FD_READ
'tcp recv hsock, 2048, buffer2

do
tcp recv hsock, 8, buffer1
buffer2 = (buffer2 & buffer1)
msgbox buffer2
loop until buffer1 = ""

msgbox buffer2

end select

end select
end function

callback function dobutton() as long
dim address as long
dim hsock as long


host addr to address

hsock = freefile
tcp open port 2000 at FormatIP(address) as hsock
tcp send hsock, "Hello, this is just a test message"
tcp close hsock
end function

function pbmain() as long
dim hdlg as long

dialog new %HWND_DESKTOP, "Send", %NULL, %NULL, 256, 96, %DS_CENTER or %WS_CAPTION or %WS_SYSMENU to hdlg
control add button, hdlg, %IDBUTTON, "start", 4, 4, 32, 14 call dobutton
dialog show modal hdlg, call dlgproc
end function

{/code}

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

[mark smit]

Ok, posting the code didn't work the way I wanted it to...

how do post code into this forums like you did Semen ?

Cheers !

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


[This message has been edited by mark smit (edited May 10, 2000).]

[Semen Matusovski]

Mark --
1) to post a code you should type
[ code ] <--- without spaces
Text of program
[ /code ] <--- without spaces

2) I guess, that you try to rebuild PBCC EchoServ & Eclient.

Note, should be TWO programs - server & client, started in the same moment.
In your code you try to send a message to yourself. Results you see.
Look PBCC samples once again.

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

[mark smit]

Hello Semen !

I was trying to write a small file transfer program. The program I just sent you was just to try out an experiment. The original program is much bigger. Just for the fun of it could you please copy the example program and run it and tell me what happens on your machine ? I should also tell you that I'm running Windows 2000 Pro here. I still don't know why my program acts as though it is stuck in the "DO" loop until the connection is closed. This only happens if I try to read the TCP stream in small chunks rather than read as much as possible with one "recv" line.

Cheers!

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

[Semen Matusovski]

Mark --
I tested this fragment under Win2000 Pro.
Sometimes I saw Msgbox with some letters, then GPF.
Sometimes - imm. GPF.
After this I encounted that you send message to yourself.
Meanwhile, PBCC samples - server/client - work fine.

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

[mark smit]

Hello again...

Well I'm glad to see that it also happend on your machine. I dont think that its my code because if you comment out the do/loop and uncomment out the single line right after %FD_READ then the program works just fine. I have tried the program with and without static string buffers but both versions do the same.

Uncomment the line "tcp recv hsock, 2048, buffer2"
rem out the "DO WHILE LOOP"

and try it, then it works but this code should work either way. In one method I just read in the full buffer and the other I read in small chunks and add them to the main buffer.

This really should work! (but it doesn't)
I hope lance can have a look at this also...

Cheers Semen!

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


[This message has been edited by mark smit (edited May 10, 2000).]

[Shawn Bever]

Mark -

Just a thought- I noticed that you always read the same number of characters from the stream. In my experience with serial i/o, rarely is the remaining number of characters in the input buffer the same as the rest of the blocks of the incoming data. I have not yet used the TCP calls (have used UDP), but perhaps it is possible that you are reading past the end of the data on the last read. Normally, I test to see how many bytes are in the input buffer prior to performing a read, and if the buffer has fewer bytes than my standard read count, I specify the number that actually exist in the buffer. Hope this helps!

Shawn Bever

[Lance Edmonds]

Mark,

If the problem has not yet been resolved (see related thread on connecting to ftp.powerbasic.com with TCP), then post the current 'version' of your code and I'll try to take a look.

Thanks!

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>