|
I understand now that the data I receive from a socket is a byte array.
But I don't understand how to pass the byte array to a function for further processing. Plus I'm not sure if I should leave it as a byte array, or try to convert it to a string, so I can extract data from it. I'm confused as to whether this buffer is a pointer to data somewhere else, and If I need to make a copy of it, before passing it to a function. When I pass it to a function, the data is lost.
Kind of tired of going around in circles here on this, and I need road map to head in the right direction.
I make my receive buffer
char recvbuf[256];
I get data
0x05 '' 0x54 'T' 0x53 'S' 0x65 'e'
And I try to pass it to a function for processing. Unless just extracting the info I need does not require a function. Suggestion?
void _process(char *pbuffer)
{
}
|
|
|
|
|
I can't speak for your application nor what data you will be receiving from the socket. But if the data is a "protocol", that is, some well defined sequence of bytes with fields, flags, data, etc, then it is most likely that the information is "binary", that is, not all the data maps nicely into printable or viewable characters, all zero bytes comes to mind, your 0x05 example too.
C and C++ "string" variables, whether CString or std::string and their manipulation functions are not really tolerant of nulls intersperced in the data.
C# strings do allow nulls in the data and I have seen many a C / C++ programmer get totally confused by the idea of nulls in strings.
So, I'd say save yourself some future grief and use a byte array. Passing a byte array is no different than passing a char array other than some folks incorrectly equate "char array" with "string" in all cases.
|
|
|
|
|
Great Information!
In this case, the data being received are byte stream?
Header stuff, ServerName:WWW;Custered:false;NamedPipe:\\pipename;Version:1.5.02.23;empty space
Taking into consideration the thread below yours, I will make a copy of the buffer, and pass the copy to the function to fish out the server name, and version.
Thanks for looking at my post, your advice puts back on track.
jkirkerx
|
|
|
|
|
Don't convert it to a string... that's a bad idea... extract whatever data bytes according to whatever API you happen to be using, then cast the converted bytes to whatever type they're supposed to be. As far as whether you need to copy the data before passing it, it depends on where you defined your recvbuff[] and whether it'll be used again, if the buffer is a local variable within your receive method, then it'll automatically go out of scope when the method is finished, so you should copy the data... also, if the buffer is to be used repeatedly (receiving multiple packets), then the data should be copied over to another buffer before moving on, otherwise it might be overwritten before it's used downstream.
|
|
|
|
|
The research I did made it sound like std:string was the swiss army knife or manipulation.
I used memset to copy the data, because I could not figure out how to use strcpy, the copy has the first 2 bytes, and stopped.
I still can't figure out why when I pass the data, I only get the first 2 bytes.
You wisdom gives me a map to use, so I can focus on the copy and pass, then I have to tackle the data extraction.
Thank you very much
jkirkerx
|
|
|
|
|
You seem to be working at this from the wrong direction. The first thing you need to do is work out (or ask the sender) the exact format of the data you are receiving. All data read from sockets is presented as a stream of bytes, and without knowing the significance, format and values of each byte or group of bytes, there is no way you can do anything with the information you receive. Never assume that data is presented as a string unless you are certain that is how it has been sent.
|
|
|
|
|
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 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?
|
|
|
|
|
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.
|
|
|
|
|
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;
}
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 );
iResult = sendto(sUDPSocket, cBuffer, 1, 0, (SOCKADDR *) & sTargetDevice, sizeof (sTargetDevice));
if (iResult == SOCKET_ERROR) {
goto closeSocket;
}
iResult = shutdown(sUDPSocket, SD_SEND);
if (iResult == SOCKET_ERROR) {
goto closeSocket;
}
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;
}
}
while( bytesReceived > 0 );
closeSocket:
iResult = closesocket(sUDPSocket);
if (iResult == SOCKET_ERROR) {
goto wsaCleanup;
}
wsaCleanup:
WSACleanup();
return TRUE;
}
void CA_SQLServer_Scan::_process_SQL_BufferData( char pBuffer[256], int packetSize )
{
}
The first data packet returned from the request, I put the \0 at the end in 87, perhaps not needed.
Bytestream - first 87 bytes of recvbuf.
recvbuf 0x0012f8a0 "T" char [256]
[0] 5 '' char
[1] 84 'T' char
[2] 0 char
[3] 83 'S' char
[4] 101 'e' char
[5] 114 'r' char
[6] 118 'v' char
[7] 101 'e' char
[8] 114 'r' char
[9] 78 'N' char
[10] 97 'a' char
[11] 109 'm' char
[12] 101 'e' char
[13] 59 ';' char
[14] 68 'D' char
[15] 69 'E' char
[16] 76 'L' char
[17] 76 'L' char
[18] 67 'C' char
[19] 53 '5' char
[20] 50 '2' char
[21] 49 '1' char
[22] 45 '-' char
[23] 48 '0' char
[24] 49 '1' char
[25] 59 ';' char
[26] 73 'I' char
[27] 110 'n' char
[28] 115 's' char
[29] 116 't' char
[30] 97 'a' char
[31] 110 'n' char
[32] 99 'c' char
[33] 101 'e' char
[34] 78 'N' char
[35] 97 'a' char
[36] 109 'm' char
[37] 101 'e' char
[38] 59 ';' char
[39] 83 'S' char
[40] 81 'Q' char
[41] 76 'L' char
[42] 69 'E' char
[43] 88 'X' char
[44] 80 'P' char
[45] 82 'R' char
[46] 69 'E' char
[47] 83 'S' char
[48] 83 'S' char
[49] 59 ';' char
[50] 73 'I' char
[51] 115 's' char
[52] 67 'C' char
[53] 108 'l' char
[54] 117 'u' char
[55] 115 's' char
[56] 116 't' char
[57] 101 'e' char
[58] 114 'r' char
[59] 101 'e' char
[60] 100 'd' char
[61] 59 ';' char
[62] 78 'N' char
[63] 111 'o' char
[64] 59 ';' char
[65] 86 'V' char
[66] 101 'e' char
[67] 114 'r' char
[68] 115 's' char
[69] 105 'i' char
[70] 111 'o' char
[71] 110 'n' char
[72] 59 ';' char
[73] 49 '1' char
[74] 48 '0' char
[75] 46 '.' char
[76] 53 '5' char
[77] 48 '0' char
[78] 46 '.' char
[79] 49 '1' char
[80] 54 '6' char
[81] 48 '0' char
[82] 48 '0' char
[83] 46 '.' char
[84] 49 '1' char
[85] 59 ';' char
[86] 59 ';' char
[87] 0 char
|
|
|
|
|
Does this code help point you in the right direction?
rcvBuffer is passed to the function processData
#include <iostream>
#include <vector>
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;
}
|
|
|
|
|
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);
Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman
|
|
|
|
|
|
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.
|
|
|
|
|
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"
|
|
|
|
|
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
|
|
|
|
|
So I still need to terminate the string with \0
Having trouble with the length, I did quick cheat with
int msgLength = bytesReceived - 3;
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
|
|
|
|
|
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 
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
|
|
|
|
|
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.
|
|
|
|
|
 great fun but we didnt solve the passing of byte arrays
|
|
|
|
|
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);
|
|
|
|
|
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
|
|
|
|
|
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;
}
|
|
|
|
|
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.
|
|
|
|
|
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
|
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
