Construct Header Packet

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Hi All,
Can anyone tell me: "How To Construct A Header?" I am writing a FTP Client-Server Code. And I want to construct a Header for the data packets I have to send to server with information like the size of my data,etc.

Any pointers towards sample/example code would be appreciated.

[edit]
Thanks a lot. Would you please give me some idea on: Follow the code below:

C++

do
{
  dwRecv = recv(SockAccept, pHeader, sizeof(MSG_HEADER), NULL) ;
  if(dwRecv == SOCKET_ERROR)
  {
    printf("Main:: recv Failed: %d\n", WSAGetLastError()) ;
    break ;
  }
}while(dwRecv > 0) ;

Now if I allocate a buffer to read rest of the data, how can I set the buffer in recv in place of pHeader? And is there any solution for large data, so that I can do in recv-allocate-recv loop???
[/edit]

Posted 1-Mar-12 0:29am

Abhineet Ayan Verma

Updated 1-Mar-12 2:48am

Richard MacCutchan

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Richard MacCutchan · Accepted Answer · 2012-03-01T01:23:00

Solution 1

Use a structure[^] and just add the fields you want into it. As long as both client and server use the same structure you should be able to do what you want. The general protocol of your message would then be to send the fixed length structure first, which will contain, at least, the length of the data message, followed by the data.

Posted 1-Mar-12 1:23am

Richard MacCutchan

Comments

Abhineet Ayan Verma 1-Mar-12 7:47am

Can you please give me some code example. Do I have to define two structs with same members at both Client-Server???

Richard MacCutchan 1-Mar-12 8:22am

Just define your struct in a header file which is included into both projects. Try and use as much common code as possible to ensure compatibility at both ends.

Abhineet Ayan Verma 1-Mar-12 8:43am

Thanks a lot. Would you please give me some idea on: Follow the code below:
<pre lang="c++">
do
{
dwRecv = recv(SockAccept, pHeader, sizeof(MSG_HEADER), NULL) ;
if(dwRecv == SOCKET_ERROR)
{
printf("Main:: recv Failed: %d\n", WSAGetLastError()) ;
break ;
}
}while(dwRecv > 0) ;</pre>

Now if I allocate a buffer to read rest of the data, how can I set the buffer in recv in place of pHeader? And is there any solution for large data, so that I can do in recv-allocate-recv loop???

Richard MacCutchan 1-Mar-12 8:50am

Extract the relevant values from the structure, allocate a data buffer and create a new recv() loop to read the message.

Abhineet Ayan Verma 1-Mar-12 9:31am

But what if the data is 500mb or more. I cant allocate that much, that would not be good.

Richard MacCutchan 1-Mar-12 9:49am

As I said, you need to create a recv() loop to read the message. You can either read it in one big block or in lots of small blocks until you have all the data. The actual block size of each segment is for you to decide. Take a look at this wiki entry to see how TCP/IP does it.

Abhineet Ayan Verma 1-Mar-12 10:49am

Thanks man :-)

Construct Header Packet

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