Variable Length Packets

Hi,

I would like to ask you a question regarding send and read buffers/packet
lengths. I would like to know how I can make this size variable meaning that
it corresponds to the sending message size.

So far, my program works when I force the buffer sizes to be a certain size,
BUFFER_MAX. I would like to have this according to the message size. I have
tried:

Bytes_sent = send(server_socket, sbuffer, *sbuffer, 0);

Where *sbuffer stores the message size, thereby sending the full message.

Let's say that the message is 7 bytes, where the first 2 bytes state the
message size.

On the receiving end I want to read the message size, and then read
according to how many bytes are left. So I have the following:

Bytes_received = read(client_socket, rbuffer, 2);

Size_of_packet = *rbuffer;

Bytes_received += read(client_socket, (rbuffer+2), (Size_of_packet-2));

Now when I try to read the data in rbuffer, I get values that are different
from those sent.

Please could you help.



My second approach is to use MSG_PEEK and MSG_WAITALL for the receiving end.

Bytes_received = recv(client_socket, rbuffer, 2, MSG_PEEK);

Bytes_received += recv(client_socket, rbuffer, *rbuffer, MSG_WAITALL);

Here, I am able to receive the first two bytes from the first call, but all
the other data are zero.



Please help.

Thank you,

Marcia Hon

Marcia Hon wrote:

> Bytes_sent = send(server_socket, sbuffer, *sbuffer, 0);
>
> Where *sbuffer stores the message size, thereby sending the full
> message.
>
> Let's say that the message is 7 bytes, where the first 2 bytes state
> the message size.

Are you really running on a system where sizeof(size_t) == 2 ? In a
normal IA32 Linux system you need 4 bytes for the len parameter of
recv().

--
Markku Kolkka
(E-Mail Removed)