I need socket help UDP broadcast, sendbuf

jkirkerx

I copied some sample code from msdn to create a socket, and modified it for testing. I want to broadcast a udp dgram, but I cant figure out what to send. I'm using ethereal to examine what SQL Management sends, and I'm trying to copy the behavior. So it looks like my first send is accurate, but I'm not sending the correct data out for a response back from sqlbrowser. I'm convinced if I send the right stuff, I will get my responses back from all the SQL servers. If i'm in the wrong forum sorry, didn't really know where to post it. I tried 0x02 in the send buffer. iResult = getaddrinfo( "255.255.255.255", "ms-sql-m", &hints, &result ); I think this is what SQL Management sent

0000 ff ff ff ff ff ff 00 13 72 36 67 30 08 00 45 00 ........ r6g0..E.
0010 00 1d 6f 9a 00 00 80 11 07 8a c0 a8 03 04 ff ff ..o..... ........
0020 ff ff 05 8b 05 9a 00 09 2f 0b 02 ........ /..

And this is what I sent

0000 ff ff ff ff ff ff 00 13 72 36 67 30 08 00 45 00 ........ r6g0..E.
0010 00 22 8c 51 00 00 80 11 ea cd c0 a8 03 04 ff ff .".Q.... ........
0020 ff ff 06 bc 05 9a 00 0e 9c 8f 30 78 32 66 30 62 ........ ..0x2f0b

Goto_Label_

Since you got no error messages.. Gee, im not sure.. could you please post more of your code? look here for hints.

Albert Holguin

Is that what's in the UDP data portion of the packet (not sure where UDP header ended and your data started)? If so, then you can just make a buffer that has the same exact data, shouldn't be hard just do something like:

//Only define data here not the UDP header info
const char RequestBuffer[] = {0xff,0xff,...,0x02} //pseudo-code, enter all numbers one byte at a time
//Remember char type is one byte... and one byte is two hex digits

...then just send that... except, if you're not really sure what's being sent, you may not get exactly what you're expecting... there's probably an API that defines the interactions between a "SQL Manager" and other SQL servers. If you're trying to create an application that simulates a manager, you should probably find whatever standard defines those interactions and implement that instead of just trying to blindly copy a data packet. Good luck. :)

jkirkerx

I know the basics, 8 bit makes a byte, and so forth, but I can't read the code I posted. I am however getting better at using the ethereal, and highlighting the portions of the transmission, such as data. The data being sent seems to be just 1 byte, with a value of 02, and is represented as a dot . I was thinking last night that perhaps instead of sending a char, like you would use to request a web page, I need to send a bytes.

jkirkerx

I hard coded the value for experimenting, The sample code I'm using is for sending text like requesting a web page from a server, and I think I need to send hex code, so I'm going to try and figure out how to send data in a different format. I think the other article in Code Project is correct, in which I need to send 0x02. The szSendBuf is where I place the data.

char* szSendBuf = "STX";
char recvbuf[DEFAULT_BUFLEN];
int iResult;
int recvbuflen = DEFAULT_BUFLEN;

// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if (iResult != 0) {
    printf("WSAStartup failed with error: %d\\n", iResult);
    return 1;
}

ZeroMemory( &hints, sizeof(hints) );
hints.ai\_family = AF\_INET;
hints.ai\_socktype = SOCK\_DGRAM;
hints.ai\_protocol = IPPROTO\_UDP;

// Resolve the server address and port
iResult = getaddrinfo(
    "255.255.255.255",
    "ms-sql-m",
    &hints,
    &result
);

if ( iResult != 0 ) {
    printf("getaddrinfo failed with error: %d\\n", iResult);
    WSACleanup();
    //return 1;
}

// Attempt to connect to an address until one succeeds
for(ptr=result; ptr != NULL ;ptr=ptr->ai\_next) {

    // Create a SOCKET for connecting to server
    ConnectSocket = socket(ptr->ai\_family, ptr->ai\_socktype, ptr->ai\_protocol);

    if (ConnectSocket == INVALID\_SOCKET) {
        printf("socket failed with error: %ld\\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    // Connect to server.
    iResult = connect( ConnectSocket, ptr->ai\_addr, (int)ptr->ai\_addrlen);
    if (iResult == SOCKET\_ERROR) {
        closesocket(ConnectSocket);
        ConnectSocket = INVALID\_SOCKET;
        continue;
    }
    break;
}

freeaddrinfo(result);

if (ConnectSocket == INVALID\_SOCKET) {
    printf("Unable to connect to server!\\n");
    WSACleanup();
    return 1;
}

// Send an initial buffer
iResult = send(
    ConnectSocket,
    szSendBuf,
    (int)strlen(szSendBuf),
    0
);

Albert Holguin

If the actual data that is being sent is a x02 (hex), then that's what you need to send... looking at your packet, it looks like you have something like "0x2f0b" (as text, not bytes)... that seems like you're accidentally sending the address of your buffer instead of the values contained in it.

jkirkerx

ohhhhhhhhhhh. I think I'm closer now. I'm sending cc, but I'm suppose to send 20. I manually altered the buffer size in send to 1, instead of using (int)strlen(sendbuf) So I think I'm building the data too big. This is a lot to learn, but I need to learn it. here's what I'm using now, I think I'm on the right track

BOOL CA_SQLServer_Scan::_socket_Broadcast_SQLServers( void )
{
#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT 1434

int iResult;
WSADATA wsaData;

SOCKET ConnectSocket = INVALID\_SOCKET;
struct sockaddr\_in clientService; 

int recvbuflen = DEFAULT\_BUFLEN;	
char recvbuf\[DEFAULT\_BUFLEN\] = "";

char mac\[5\];
char sendbuf\[1\];

memset(sendbuf, 0x00, sizeof(sendbuf)); // I added this to package the data, 
strcpy(sendbuf, "");
sprintf(sendbuf+strlen(sendbuf), "", strlen(sendbuf), sendbuf);
memcpy(sendbuf+strlen(sendbuf), mac, 5); // 
    
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if (iResult != NO\_ERROR) {
    wprintf(L"WSAStartup failed with error: %d\\n", iResult);
    return 1;
}

ConnectSocket = socket(AF\_INET, SOCK\_DGRAM, IPPROTO\_UDP);
if (ConnectSocket == INVALID\_SOCKET) {
    wprintf(L"socket failed with error: %ld\\n", WSAGetLastError());
    WSACleanup();
    return 1;
}

clientService.sin\_family = AF\_INET;
clientService.sin\_addr.s\_addr = inet\_addr( "255.255.255.255" );
clientService.sin\_port = htons( DEFAULT\_PORT );

iResult = connect( ConnectSocket, (SOCKADDR\*) &clientService, sizeof(clientService) );
if (iResult == SOCKET\_ERROR) {
    wprintf(L"connect failed with error: %d\\n", WSAGetLastError() );
    closesocket(ConnectSocket);
    WSACleanup();
    return 1;

}

iResult = send( ConnectSocket, sendbuf, 1, 0 ); // I altered it to 1 
if (iResult == SOCKET\_ERROR) {
    wprintf(L"send failed with error: %d\\n", WSAGetLastError());
    closesocket(ConnectSocket);
    WSACleanup();
    return 1;
}

printf("Bytes Sent: %d\\n", iResult);
    
iResult = shutdown(ConnectSocket, SD\_SEND);
if (iResult == SOCKET\_ERROR) {
    wprintf(L"shutdown failed with error: %d\\n", WSAGetLastError());
    closesocket(ConnectSocket);
    WSACleanup();
    return 1;
}

do {

    iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
    if ( iResult > 0 )
        wprintf(L"Bytes received: %d\\n", iResult);
    else if ( iResult == 0 )

jkirkerx

Finally figured it out, and got back packets from all the SQL Servers on the network, complete with all the information I need. So now I know how to send a STX command to SQL Browser, to start a conversation. It's sort of like a modem command. Now I have to figure out how and when to release the receive side of the socket, and only capture the packets that I need. So the SendMessage, which is a char string, has to be set with memset, in order to send just the byte.

Albert Holguin

why not just... ???

char sendbuf[] = {0x02};

Albert Holguin

A char* is not necessarily a string... it's just a char pointer... in network programming, character buffers are commonly used to hold the data being transferred to/from a socket because of the size of a char is one byte. It's just convenient to use that since it's the smallest data element used/transferred.

jkirkerx

I tried and sent the actual string 0x02

jkirkerx

I took out the memset and did the straight char, yes it works and it's faster, OK, feel stupid but I did not fully understand the process. I tried it earlier, but got some kind of Int error. Do you know anything about the receive side of the socket? it just sits there and never closes, or transfer data to the receive buffer.

Albert Holguin

I don't remember exactly off hand what it should do... but since UDP is essentially connectionless (meaning no hand-shaking between server and client), I imagine the socket has to be closed explicitly by the application.

jkirkerx wrote:

or transfer data to the receive buffer.

Don't know exactly what you mean by that.

jkirkerx

I took a generic winsock2 sample code and modified it for UDP broadcast. I have come to the same conclusion, in which the socket will never close, because it's not an single machine to machine connection, in which the other side will never send the symbol saying it's done, or simply close it's port. I just need to figure out how to capture the return data. Not sure if I need 2 sockets, one to just send the broadcast, and the other to just listen. If I do that, I'm afraid the listening socket will cause my code to stop, and I won't be able do anything until the socket closes.