Determining Data Size For Network Send/Rec :: Winsock

Hi.

I am studying networking programming from Network Programming For Microsoft Windows, Second Edition by Anthony Jones and Jim Ohlund. I am just about ready to start on a new product that will be my first real Winsock program. I want to design and implement a simple message program (chat) that work over the IP protocol and TCP protocol.

I have the basic program core design in my mind. However, I am stuck with one problem and it is a problem that even Jones and Ohlund implied could be difficult to overcome for inexperience network programmers.

How do you predetermine the size of the data you receive?

Winsock has two basic functions for receiving data: revc (IPv4 or Winsock 1.1+) and WSARecv (IPv6 or Winsock 2). WSARecv is a powerful tool for *predetermined* data size. You can send multiple packages at one time, but the data size must be predetermined (i.e. 10k, 20k, and finally 30k). I will probably use revc since it is more flexible. Even with recv, however, you must give a specific size (byte) to read. Jones and Ohlund recommend sends the size of the data in the first four byte of the data stream. However, what if the user wants to send something that is larger than what a bour byte char variable can hold?

Please post any possible solutions.

Thanks,
Kuphryn

Then they have done a lot of typing or are going to wait around alot for it to be received (or sent as it would have got a WSAEWOULDBLOCK at the server).

My app sends the size first. Receiving jpg's and data over 52k without problem.

2,147,483,647+ bytes is a lot of data in one send() and a few days on a 56K modem.

The more difficult task is handling WSAEWOULDBLOCK and split recv()
(when all the data does not arrive in the same read or more than one data item arrives in the same read or both)

Thanks.

Can you give me an example?

Let say I want to sent this message:

"Please give an example of how you would receive this message."

// send(socket, &message, sizeof(message), 0);

Kuphryn

iSize=lstrlen(sBuffer);
send(socket,(char*)&iSize ,sizeof(int) ,FLAGS );
send(socket,(char*)sBuffer ,lstrlen(sBuffer) ,FLAGS );

Roughly

Find size recv

Code:

---

While(iUsed<iRecv)
switch(iBuffer)
case READSIZE:
  find expected size //sizeof(int)
  iBuffer++
case READBUFFER
  create new storage to size
  if(Do not have ALL the data)
      copy what you have to storage
      increase iUsed
      increase iOffsetToStorage
  else//have all the data
    copy to storage
    increase iUsed
    iBuffer++
case HAVEALLDATA
  Process
  iBuffer=0
  free storage

---

Remember to use the iOffsetToStorage (this is the amount already in storage) and iUsed (the amount of the buffer processed) when copying from the incomming buffer to the storage buffer.
And that iBuffer is a static (I use a struct for each socket)

Thanks.

Consider these other two techniques by Dire.Wolf:

http://www.gamedev.net/community/for...topic_id=93771

and by Niklas Lindquist

http://www.codeproject.com/script/co...541#xx173653xx

Kuphryn

A full msg is

Size+String

As chat programs receive small amounts of data you need to ensure that if the recv() gets more than a whole msg in one read then you can handle it (and less than a whole msg). I only skimmed the others but do they handle the situation where the recv() gets

Size+String+Size

or worse

Size+String+1/2Size

ect

(NOTE I edited the algy to reflect a better mem handling)

Last one was me not logged in.