packet help

[mickey911]

hi community

my first post.

i have been developing a yahoo messenger client for nintendo ds hand held console utilizing its wifi functionality.I finished laying out the user interface.
i am left with the yahoo protocol.

I want to do some test programs using sockets before actually coding it into my program.
I want to know how to create a packet in c language with the following structure



<------- 4B -------><------- 4B -------><---2B--->
+-------------------+-------------------+---------+
| Y M S G | version | pkt_len |
+---------+---------+---------+---------+---------+
| service | status | session_id |
+---------+-------------------+-------------------+
| |
: D A T A :
| 0 - 65535* |
+-------------------------------------------------+

the library which i use for ds has all the commands for sending and receiving information through sockets.So i just need to know how packets are made or represented in c

[Banfa]

You just need to put the byte values for the various Fields into an array of char (or unsigned char) this could be allocated dynamically.

char *pPacket;
 
pPacket = malloc( <TotalLengthOfPacket> );
 
pPacket[0] = 'Y';
pPacket[1] = 'M';
pPacket[2] = 'S';
pPacket[3] = 'G';
 
...
 
send(pPacket, <TotalLengthOfPacket>);
 

[mickey911]

thanks banfa.

the lib i am using is called palib.it has the following functions.
Supposing
i want to see a network path is available to yahoo server then i have to send the following packet


YMSG --------version 12-----------0
verify(76)-----available----------null


supposing i have to send that to the yahoo server i will first declare a char buffer to store in the packet contents.










char *pPacket;


pPacket = malloc( <TotalLengthOfPacket> );

pPacket[0] = 'Y';
pPacket[1] = 'M';
pPacket[2] = 'S';
pPacket[3] = 'G';

..........


YMSG //this one is clear

version valuue is a 4 byte value '0x09 0x00 0x00 0x0'
0
verify
available
null

so how do i store thse values into the array???
the byte values?

palib has the following handy command once i am able to finish the packet


int sock;
char *pPacket;//create buffer

PA_InitSocket(&sock,"scs.msg.yahoo.com",5050,PA_NO RMAL_TCP); //open socket on yahoo server on port 5050

char *strcpy ( char *pPacket, const char *src ); //i need help with this command too i am not sure if its correct


send(sock,pPacket,256,0); //send the buffered arrayu to yahoo server


this is how it is but as you can see i have a few doubts with strcpy usage and packet representation.Can you help me pout?

[Banfa]

pPacket[0] = 'Y';
pPacket[1] = 'M';
pPacket[2] = 'S';
pPacket[3] = 'G';

..........


YMSG //this one is clear

version valuue is a 4 byte value '0x09 0x00 0x00 0x0'

pPacket[0] = 'Y';
pPacket[1] = 'M';
pPacket[2] = 'S';
pPacket[3] = 'G';
pPacket[4] = 0x09;
pPacket[5] = 0x00;
pPacket[6] = 0x00;
pPacket[7] = 0x00;
 
...
 

But make sure you have the bytes in the right order, bytes 4 - 7 are the value 9 if the byte order is little endian(least significant byte first) but value 150994944 if the byte order is big endian (most significant byte first).