C / C++ / MFC

Tcp/Ip send() does sometimes not succeed

26-Jan-07 11:21

Maybe I'm way off, but my first thought is that the classes in the DLL aren't exported.

What if you do something like the AFX_EXT_CLASS macro in MFC.

Add something like this to your precompiled header or someplace before every .h file is
compiled:

#if !defined(ZIPIOS_IMP_EXP)
#if defined(ZIPIOS_DLL_BUILD)
#define ZIPIOS_IMP_EXP __declspec(dllexport)
#else
#define ZIPIOS_IMP_EXP __declspec(dllimport)
#endif
#endif

In the zipios source, change the class declarations from

class ZipFile : public FileCollection {
...

to

class ZIPIOS_IMP_EXP ZipFile : public FileCollection {
...

(base classes need to be exported as well)

Define ZIPIOS_DLL_BUILD when building the dll and don't define it when building the app.

Mark

gmon.out File

compmaniac26-Jan-07 8:50

compmaniac

26-Jan-07 8:50

In Dev-C++, I'm compiling a script, and whenever I run the program that's compiled, a file called gmon.out gets outputted. Is it important? If not, how do I make the compiler not create the file while compiling?

(I'm using Dev-C++)

Re: gmon.out File

David Crow26-Jan-07 9:15

David Crow

26-Jan-07 9:15

I'm all for helping out, but wouldn't this be a Dev-C++ question?

"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

"Judge not by the eye but by the heart." - Native American Proverb

Re: gmon.out File

compmaniac26-Jan-07 9:20

compmaniac

26-Jan-07 9:20

Sorry, I'll go post at sourceforge.net

Dee Veloper26-Jan-07 5:48

26-Jan-07 5:48

Hi!

I am currently programming server/client stuff with the c++ functions send and recv. Normally everything works fine but sometimes the client tells me it has sent a message successfully but it is not received by the server. I tracked the packets in the network and no packet had been sent. Documentation says not every successful call to send() guarantees that the data is received by the client. Unfortunately the packet is never sent (waited up to 3 minutes). Since Tcp/Ip is a reliable protocol, I expected the packets to be received by the client as long as the connection is not terminated. How can I make sure that send really sends my data? Is there a flush() command? (using Tcp/Ip non blocking windows socket, checking for send/receive with select).

Any help would be greatly appreciated!!!

Thx
Flo

P.S. Before you ask: it has to be c++ send and recv - no MFC or C# stuff...

Mark Salsbery26-Jan-07 6:05

26-Jan-07 6:05

I would check every send and recv call (breakpoint) and add up the bytes sent/received.
Keep in mind that recv doesn't always give you all the bytes you request in one call and
send doesn't always send the number of bytes you asked it to in one call. Check those return
values!

Mark

Dee Veloper26-Jan-07 6:13

26-Jan-07 6:13

I checked the number of bytes received and sent. The problem is that the send command really does not send anything (I observed my network traffic) but tells me it has sent the correct amount of bytes. I doublechecked with breakpoints and everything I can think of and I have no idea why it does not send anything. The other side is listening with select and no data is to be received. This happens only sometimes. Normally it works fine.

Frustrating Frown | :(

Flo

Mark Salsbery26-Jan-07 6:25

26-Jan-07 6:25

florianhaar wrote:
Frustrating

Indeed!

Which select are you using? Can you post the code you use to receive (it's almost always a
problem on the receiving end)?

Mark

Dee Veloper26-Jan-07 6:39

26-Jan-07 6:39

Thanks for your help so far Mark. I hope this code snippet gives you an idea for a solution:

TIMEVAL tv;
tv.tv_sec=0;
tv.tv_usec=5;
FD_ZERO(&clientSet);
FD_SET(theClient->sock,&clientSet);

if ((errCode=select(0,&clientSet,NULL,NULL,&tv))>0)
{
if ((recvMsgSize=recv(theClient->sock,addBuffer,maxRead,0))<=0)
{
//error handling
...
}
else
message handling...

I do not receive an error or a message. Select() returns only timeout.

Flo

Mark Salsbery26-Jan-07 7:00

26-Jan-07 7:00

if ((recvMsgSize=recv(theClient->sock,addBuffer,maxRead,0))<=0)
...

What is maxRead?
How are you handling if recvMsgSize < maxRead after the call?

Dee Veloper26-Jan-07 7:09

26-Jan-07 7:09

maxRead is the maximum number of bytes the buffer can store. if recvMsgSize is smaller than maxRead (which is normally the case) I copy the data to additional buffers and combine them as soon as all bytes are received. With my problem the data received is always smaller than maxRead.

Mark Salsbery26-Jan-07 7:21

26-Jan-07 7:21

hmmm From what I've seen there shouldn't be a problem.

You've debugged the code? Examining network packets isn't necessarily the way to debug since the
potocol is free to re-packetize your data as needed.

Have you changed any socket options on either end?

There's a bug in the code somewhere Smile | :)

Mark

Dee Veloper26-Jan-07 7:39

26-Jan-07 7:39

I guess I have to think through my code step by step once again. At least I know now, that send() should send after 200ms as long as the connection is established.

Thanks again for your help!

Flo

Mark Salsbery26-Jan-07 7:50

26-Jan-07 7:50

If you'd like to post the send-side code I'd be happy to look at it as well.

Mark

Mike O'Neill26-Jan-07 10:33

Mike O'Neill

26-Jan-07 10:33

I generally agree with Mark's observation that problems like this are almost always caused by code on the receiving side.

Here, you have set the timeout for select() to 5 microseconds. That's way too short.

Your understanding of the send() function is slightly wrong. send() does not actually send bytes out over the wire; that happens later when the winsock TCP stack determines that it's time to send data on the wire, after considertion of things like Nagle, delayed ACK etc. Rather, a successful call to send() only indicates that the winsock stack has successfully transferred data in your user buffer to its internal winsock buffer. The return value from send() tells you exactly how much of your buffer has been accepted; you should therefore inspect the returned value to ensure that winsock transferred everything to its internal buffer.

So, if you are debugging and single-stepping through your code, and you see a successful completion of the call to send(), then it's probably still too early for a sniffer to see the actual data on the wire. That will happen, but it will happen at some indeterminate time in the future.

Mike

Mark Salsbery26-Jan-07 10:42

26-Jan-07 10:42

Thanks Mike!

Maybe you meant to post this to the OP Smile | :)

For some reason I assumed his code was in a loop. If it's not then that 5microsecond timeout is definitely not going to work (well, rarely).

Mark

Mark Salsbery26-Jan-07 10:47