working with byte arrays

[Lost User]

Yeah, if you know the data is a char array, pass it to the func as you outineline in your post, and let it do the processing. It is bette to do this, than to proces the data at the level of the code that manages socket communication, it is a more logical split to treat communication at one level, and data processing at another.

============================== Nothing to say.

[jkirkerx]

The sender is microsoft's sql browser. I discovered the return packet data using etherreal, and sending various request to it, until I got the reply I was looking for. Then I wrote the socket program. I have the data packets coming back from all the sql servers on the lan, and they all send the same format back to me. I just need to extract the server name and version number of sql out of the byte array.

[jkirkerx]

I write in vb, and without a doubt, I would pass the data to another function for processing, or just store the data, and process it later. In straight c++, most of the stuff seems pretty easy, but there are some really low level stuff you can get into that gets tricky. I've never asked anyone to write code for me, but I'm really stuck trying to figure out how to pass the data to a another function. I will post my code, and the byte stream I get back, and perhaps someone could can spot the mistake I made, it might be something really small that I didn't get.

BOOL CA_SQLServer_Scan::_socket_Enumerate_SQLServers( void )
{
int iResult;
WSADATA wsaData;

char recvbuf\[256\];
int rv = 0; 
int recvbuflen = 256;
int bytesReceived = 0;
				    
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if (iResult != NO\_ERROR) {
    return FALSE;
}		
//////////////////////////////////////////////////////////////////////////////////////
// Send Data Socket
SOCKET sUDPSocket = INVALID\_SOCKET;
struct sockaddr\_in sTargetDevice;
char cBuffer\[\] = {0x02};

sUDPSocket = socket(AF\_INET, SOCK\_DGRAM, IPPROTO\_UDP);
if (sUDPSocket == INVALID\_SOCKET) {
    int iSocketError = WSAGetLastError();
	goto wsaCleanup;
}

ZeroMemory( &sTargetDevice, sizeof(sTargetDevice));
sTargetDevice.sin\_family = AF\_INET;
sTargetDevice.sin\_addr.s\_addr = inet\_addr( "192.168.3.255" );
sTargetDevice.sin\_port = htons( BROADCAST\_SND\_PORT );

// Try a Connectionless Send Data first
iResult = sendto(sUDPSocket, cBuffer, 1, 0, (SOCKADDR \*) & sTargetDevice, sizeof (sTargetDevice));
if (iResult == SOCKET\_ERROR) {
    goto closeSocket;        
}
    
// Shutdown the send socket for some reason
iResult = shutdown(sUDPSocket, SD\_SEND);
if (iResult == SOCKET\_ERROR) {
    goto closeSocket;
}
// End of Send Data Connection
//////////////////////////////////////////////////////////////////////////////////////
// Enumerate Return Packets	
do {
    bytesReceived = recv(sUDPSocket, recvbuf, recvbuflen, 0);
    if ( bytesReceived > 0 ) {            
		char buf\[256\];
		recvbuf\[bytesReceived\] = '\\0';
		memcpy(buf, recvbuf, bytesReceived);			
		\_process\_SQL\_BufferData(buf, bytesReceived);						
	}
    else if ( bytesReceived == 0 ) {
        printf("Connection closed\\n");
		goto closeSocket;
	}		
	else {
        printf("recv failed: %d\\n", WSAGetLastError());
		goto closeSocket;
	}

[Lost User]

jkirkerx wrote:

I just need to extract the server name and version number of sql out of the byte array.

Given that you have figured out the format and content of the messages, what is the problem?

Unrequited desire is character building. OriginalGriff

[Goto_Label_]

Does this code help point you in the right direction? rcvBuffer is passed to the function processData

#include #include void processData(char &c)
{
char* array = &c;
std::cout << array << std::endl;
}

int main()
{

char\* rcvBuffer = "Hello world";
char& c = rcvBuffer\[0\];
processData(c);

return 0;
}

[Lost User]

assuming this is the format of all messages that you need to process, it looks like the message format is :

Addr Content
0 05
1 0084 (as bytes 8400)
3 "ServerName;DELLC521-01;InstanceName;SQLEXPRESS;IsClustered;No;Version;10.50.1600.1;;"

Byte zero contains some flag or identifier (no idea what)
Bytes 1 & 2 contain a 16-bit integer giving the length of the following data
Bytes 3 - n contain the message data, which in this case is a semi-colon delimited string.

So given the above information your message processor can copy the characters (using the length information) into a proper null-terminated string buffer. That string may then be split into tokens and each required value can be found by comparing the keywords with known tokens. Something like:

int msgLength = buffer[2] << 8 + buffer[1];
char* szWords = new char[msgLength + 1];
strncpy(szWords, buffer + 3, msgLength);
// remainder of code left as an exercise for the reader
// use strtok() to extract each token
// strcmp() to look for keywords
//
// alternatively use std::string to parse and extract

Unrequited desire is character building. OriginalGriff I'm sitting here giving you a standing ovation - Len Goodman

[App_]

:thumbsup:

[App_]

is done like this:

#include <iostream>
using namespace std;

void charray(char test[]) {
strncpy(test,"test",sizeof(test));
}

int main() {
char test[256]={' '};
charray(test);
printf("Text in %s!\n", test);
return 0;
}

[jkirkerx]

I experimented with that Friday night, and only the first byte copied over in strncpy. I think the 2nd byte bombed in the copy. The same thing happens when I pass the byte array to a function. It must be the 2nd byte, so perhaps I need to cut off the header of the byte array, and then do the copy and pass.

[jkirkerx]

Give me an hour to digest the knowledge you presented, looks very helpful and promising. perhaps in words, get the message length the packet declared make a new byte array copy the message only to the new byte array, leaving the packet header behind then pass the message to the function, and extract the ; delimited data.

[jkirkerx]

Didn't work at first, then I hardcoded the message length just for testing, and everything worked, including passing the string to the function. I need to figure out the length calculation. Working on that now, almost there, wow

int msgLength = 80;
char* szWords = new char[msgLength + 1];
strncpy(szWords, recvbuf + 3, msgLength);

This is the szWords,

szWords 0x003e8f10 "ServerName;DELLC521-01;InstanceName;SQLEXPRESS;IsClustered;No;Version;10.50.1600Íýýýý««««««««þîþ"

[Lost User]

You cannot use sizeof() in the function above, because the array size is not known at that point.

Unrequited desire is character building. OriginalGriff I'm sitting here giving you a standing ovation - Len Goodman

[Lost User]

jkirkerx wrote:

I need to figure out the length calculation.

I gave you the code for that in my previous message; and I missed a line of code, so it should read:

int msgLength = buffer[2] << 8 + buffer[1];
char* szWords = new char[msgLength + 1];
strncpy(szWords, buffer + 3, msgLength);
szWords[msgLength] = '\0';

Unrequited desire is character building. OriginalGriff I'm sitting here giving you a standing ovation - Len Goodman

[jkirkerx]

So I still need to terminate the string with \0 Having trouble with the length, I did quick cheat with

int msgLength = bytesReceived - 3;
//int msgLength = recvbuf[2] << 8 + recvbuf[1];
char* szWords = new char[msgLength + 1];
strncpy(szWords, recvbuf + 3, msgLength);

int msgLength with is an integer, I keep getting 0, is it because recvbuf[2] is returning the string, but wait, it's a byte representing a number. hmm

[Lost User]

Sorry, I really need to test my code before posting here, and check my operator precedence rules. In my defence, it is getting late and I'm half way through a nice bottle of Merlot :-D Try:

int msgLength = (recvbuf[2] << 8) + recvbuf[1];

Unrequited desire is character building. OriginalGriff I'm sitting here giving you a standing ovation - Len Goodman

[jkirkerx]

Hey no problem, I thought perhaps I had to solve it as a test of some sort. I answer asp.net server control questions on my last beer before I turn off the computer at night. I want to thank you for helping me. It was really bring me down, and everyone just sort of gave me a blank look, "Its so easy, come on, that c++ 101". Words cannot express the gratitude for the help. I really appreciate it, and yes, code project pulls through with expert help.

[Goto_Label_]

:laugh: great fun but we didnt solve the passing of byte arrays

[jkirkerx]

oh no, it got solved! Richard wrote some code to extract the message size from byte 2, copy just the message to a new char array, termintate it with \0, and pass it to my function for processing I'm stoked, surfer happiness, yeah! I've been banging my head for days on this, feeling pretty stupid about it. Thanks for watching the show! msgLength = (recvbuf[2] << 8) + recvbuf[1]; szWords = new char[msgLength + 1]; strncpy(szWords, recvbuf + 3, msgLength); szWords[msgLength] = '\0'; _process_SQL_BufferData(szWords, bytesReceived);

[Lost User]

Happy to help, it's what makes CodeProject fun! That and your appreciation.

Unrequited desire is character building. OriginalGriff I'm sitting here giving you a standing ovation - Len Goodman

[jschell]

jkirkerx wrote:

When I pass it to a function, the data is lost.

What does that mean exactly? One possibility is that you are misusing the buffer. If so that has nothing to do with sockets nor with how you chose to process the data.