Its y first time trying to use NSData and Gamekit. So was wondering am i packing the data properly?
- (void)sendNetworkPacket:(GKSession *)session packetID:(int)packetID
reliable:(BOOL)howtosend
{
// the packet we'll send is resued
static unsigned char networkPacket[kMaxTankPacketSize];
const unsigned int packetHeaderSize = 2 * sizeof(int); // we have two "ints" for our
header
int *pIntData = (int *)&networkPacket[0];
// header info
pIntData[0] = gamePacketNumber++;
pIntData[1] = packetID;
int theLength = 2 * sizeof(int);
for (int i=0; i<([theHands.player1Hand count]); i++)
{
pIntData[2+i] = [[theHands.player1Hand objectAtIndex:i] intValue];
theLenght += sizeof(int);
}
NSData *packet = [NSData dataWithBytes: networkPacket length: theLength];
[session sendData:packet toPeers:[NSArray arrayWithObject:gamePeerId]
withDataMode:GKSendDataReliable error:nil];
}
Will the data I put into NSData *packet be valid?
Many Thanks,
-Code
You create the NSData correctly, and it will contain what you expect. But this is rather more complicated than necessary. The following will do too:
enum { kHeaderLength = 2 };
NSMutableData *packet = [NSMutableData dataWithLength: (kHeaderLength + [theHands.player1Hand count]) * sizeof( int )];
int *pIntData = (int *)[packet mutableBytes];
*pIntData++ = gamePacketNumber++;
*pIntData++ = packetID;
for (id thing in theHands.player1Hand) {
*pIntData++ = [thing intValue];
}
[session sendData: packet toPeers: [NSArray arrayWithObject: gamePeerId] withDataMode: GKSendDataReliable error: NULL];
This will have some advantages:
The packet data will not be copied to the NSData object, it will be created directly in there.
You don’t have to depend on a maximum packet size. You used a constant, which is good since you could change that in one place if bigger packets are required some time. But this is not really needed.
Your version is not thread safe since it depends on the static buffer. This might be fine, since not every method has to be thread-safe. But this is something one has to look out for.
Using fast enumeration also helps keeping the overhead down and is more readable.
Related
I have to use Blowfish algorithm in my code for encryption and decryption. After calling the decryption method, blowfishDecrypt, I am getting the value in NSData but it give me always null when I convert it to NSString.
I am using the following code :
-(void)methodCalled
{
syncTime=#"c7c937169084b20c3ff882dcda193a59";
NSData* data = [syncTime dataUsingEncoding:NSUTF8StringEncoding];
NSData* data2 = [#"R=U!LH$O2B#" dataUsingEncoding:NSUTF8StringEncoding];
NSData* dycryptData=[self blowfishDecrypt:data usingKey:data2];
// prints <0eec37b6 2b76c2df cdf72356 0f033ed8 d6bd37dd 5223bf66 5c318ebe 07f3cf71>
NSLog(#"%#",dycryptData);
NSString *dSync=[[NSString alloc] initWithBytes:[dycryptData bytes]
length:[dycryptData length]
encoding:NSUTF8StringEncoding];
// prints (null)
NSLog(#"Sync timeis %#",dSync);
}
-(NSData *)blowfishDecrypt:(NSData *)messageData
usingKey:(NSData *)secretKeyData {
NSMutableData *decryptedData = [messageData mutableCopy];
BLOWFISH_CTX ctx;
Blowfish_Init (&ctx, (unsigned char*)[secretKeyData bytes], [secretKeyData length]);
NSRange aLeftRange, aRightRange;
NSData *aLeftBox, *aRightBox;
unsigned long dl = 0, dr = 0;
for (int i = 0; i< [decryptedData length]; i += 8) { // Divide data into octets...
// …and then into quartets
aLeftRange = NSMakeRange(i, 4);
aRightRange = NSMakeRange(i + 4, 4);
aLeftBox = [decryptedData subdataWithRange:aLeftRange];
aRightBox = [decryptedData subdataWithRange:aRightRange];
// Convert bytes into unsigned long
[aLeftBox getBytes:&dl length:sizeof(unsigned long)];
[aRightBox getBytes:&dr length:sizeof(unsigned long)];
// Decipher
Blowfish_Decrypt(&ctx, &dl, &dr);
// Put bytes back
[decryptedData replaceBytesInRange:aLeftRange withBytes:&dl];
[decryptedData replaceBytesInRange:aRightRange withBytes:&dr];
}
return decryptedData;
}
Blowfish library code can be found eg. here
HINT#1 //general answer
NSString provides an initializer for this purpose. You can see more info using the docs here.
NSString * dSync = [[NSString alloc] initWithData: dycryptData
encoding:NSUTF8StringEncoding];
Assuming you use ARC.
HINT#2 // the answer for this particular question
I tried your code and confirm the above NSString conversion returns null. So why it is not working? dycryptData is stream of bytes represented as hex, so I tried the following and received the desired result:
int dycryptData_len = [dycryptData length];
NSMutableString *dSync_hex = [NSMutableString stringWithCapacity:dycryptData_len*2];
const unsigned char *dycryptData_bytes = [dycryptData bytes];
for (int i = 0; i < dycryptData_len; ++i) {
[dSync_hex appendFormat:#"%02x", dycryptData_bytes[i]];
}
NSLog(#"dSync_hex=%#",dSync_hex);
I can see this result in log output:
dSync_hex=0eec37b62b76c2dfcdf723560f033ed8d6bd37dd5223bf665c318ebe07f3cf71
Can anyone suggest a method to read bytes from NSData (like read function in #interface NSInputStream : NSStream)
How to read binary bytes in NSData? may help you:
NSString *path = #"…put the path to your file here…";
NSData * fileData = [NSData dataWithContentsOfFile: path];
const char* fileBytes = (const char*)[fileData bytes];
NSUInteger length = [fileData length];
NSUInteger index;
for (index = 0; index<length; index++) {
char aByte = fileBytes[index];
//Do something with each byte
}
You can also create an NSInputStream from an NSData object, if you need the read interface:
NSData *data = ...;
NSInputStream *readData = [[NSInputStream alloc] initWithData:data];
[readData open];
However, you should be aware that initWithData copies the contents of data.
One of the simplest ways is to use NSData getBytes:range:.
NSData *data = ...;
char buffer[numberOfBytes];
[data getBytes:buffer range:NSMakeRange(position, numberOfBytes)];
where position and length is the position you want to read from in NSData and the length is how many bytes you want to read. No need to copy.
Alex already mentioned NSData getBytes:range: but there is also NSData getBytes:length: which starts from the first byte.
NSData *data = ...;
char buffer[numberOfBytes];
[data getBytes:buffer length:numberOfBytes];
May way of doing that..
do not forget to free byte array after usage.
NSData* dat = //your code
NSLog(#"Receive from Peripheral: %#",dat);
NSUInteger len = [dat length];
Byte *bytedata = (Byte*)malloc(len);
[dat getBytes:bytedata length:len];
int p = 0;
while(p < len)
{
printf("%02x",bytedata[p]);
if(p!=len-1)
{
printf("-");
}//printf("%c",bytedata[p]);
p++;
}
printf("\n");
// byte array manipulation
free(bytedata);
Please any one guide me how to create bytes array from nsdata here is my code for createing nsdata
NSData* data = UIImagePNGRepresentation(img);
If you only want to read them, there's a really easy method :
unsigned char *bytes = [data bytes];
If you want to edit the data, there's a method on NSData that does this.
// Make your array to hold the bytes
NSUInteger length = [data length];
unsigned char *bytes = malloc( length * sizeof(unsigned char) );
// Get the data
[data getBytes:bytes length:length];
NB Don't forget - if you're copying the data, you also have to call free(bytes) at some point ;)
Here is fastest way (but pretty danger) to get array:
unsigned char *bytesArray = data.bytes;
NSUInteger lengthOfBytesArray = data.length;
before trying to get byte#100 you should check lengthOfBytesArray like:
if (lengthOfBytesArray > 100 + 1)
{
unsigned char byteWithOffset100 = bytesArray[100];
}
And another safe and more objc-like way:
- (NSArray*) arrayOfBytesFromData:(NSData*) data
{
if (data.length > 0)
{
NSMutableArray *array = [NSMutableArray arrayWithCapacity:data.length];
NSUInteger i = 0;
for (i = 0; i < data.length; i++)
{
unsigned char byteFromArray = data.bytes[i];
[array addObject:[NSValue valueWithBytes:&byteFromArray
objCType:#encode(unsigned char)]];
}
return [NSArray arrayWithArray:array];
}
return nil;
}
Hi I am writing a iphone application where I need to store binary data i.e.; image in the Ultralite database.
I am using following code for this purpose.
NSString *filePath = [[NSBundle mainBundle] pathForResource:#"file_name" ofType:#"png"];
NSData *data = [NSData dataWithContentsOfFile:filePath];
NSUInteger len = [data length];
ul_binary *byteData = (ul_binary*)malloc(len);
memcpy(byteData, [data bytes], len);
ULTable *table = connection->OpenTable("NAMES");
if(table->InsertBegin()){
table->SetInt(1, (maxId+1));
table->SetString(2, [name UTF8String]);
table->SetBinary(3, byteData);
table->Insert();
table->Close();
connection->Commit();
}
This code is giving error 'EXC_BAD_ERROR' on line::
table->SetBinary(3, byteData);
This code works fine if i comment this line.
Any help would be appreciated!
Thanks
The definition of ul_binary is this:
typedef struct ul_binary {
/// The number of bytes in the value.
ul_length len;
/// The actual data to be set (for insert) or that was fetched (for select).
ul_byte data[ MAX_UL_BINARY ];
} ul_binary, * p_ul_binary;
So it's a struct. By simply doing the memcpy as you do, you also overwrite the len field and everythings messed up. So here's how you should do it (as far as I can see):
ul_binary *byteData = (ul_binary *)malloc(sizeof(ul_binary));
memcpy(&byteData->data, [data bytes], len);
byteData->len = len;
You also need to check that len <= MAX_UL_BINARY before you try to allocate the memory. And don't forget to free(byteData);.
Ok Here is the problem. I am trying to send through a structure or anything through the apple bluetooth send network packet code. The code to send is below
-(void)sendMessagePacket:(GKSession *)session packetID:(int)packetID withData:(void *)data ofLength:(int)length reliable:(BOOL)howtosend {
static unsigned char networkPacket[maxPacketSize];
const unsigned int packetHeaderSize = 2 * sizeof(int); // we have two "ints" for our header
if(length < (maxPacketSize - packetHeaderSize)) { // our networkPacket buffer size minus the size of the header info
int *pIntData = (int *)&networkPacket[0];
// header info
pIntData[0] = 10;
pIntData[1] = packetID;
// copy data in after the header
memcpy( &networkPacket[packetHeaderSize], data, length );
NSData *packet = [NSData dataWithBytes: networkPacket length: (length+8)];
if(howtosend == YES) {
[session sendDataToAllPeers:packet withDataMode:GKSendDataReliable error:nil];
} else {
[session sendDataToAllPeers:packet withDataMode:GKSendDataUnreliable error:nil];
}
}
}
If anyone could go through this with a comb and explain what is going on that would be greatly appreciated. Next, the receive code.
- (void)receiveData:(NSData *)data fromPeer:(NSString *)peer inSession: (GKSession *)session context:(void *)context {
// Caller whenever data is received from the session
unsigned char *incomingPacket = (unsigned char *)[data bytes];
//EXPECTS THAT WHAT IS IN INCOMING PACKET [0] TO BE OF DATA TYPE INTEGER
int *pIntData = (int *)&incomingPacket[0];
int packetTime = pIntData[0];
int packetID = pIntData[1];
static int lastPacketTime = -1;
switch (packetID) {
case NETWORK_COINTOSS:
//DO SOMETHING
break;
case NETWORK_TEXT_EVENT:
NSString *fewMore = (NSString *)&incomingPacket[8];
fewThings *bitMore = &fewMore[peer];
//NSLog(#"Trace Bit More: %#",fewMore);
break;
default:
break;
}
NSInteger lengthBytes = [data length];
NSLog(#"Length of data : %i", lengthBytes);
}
What i am struggling to understnad being a newcome to objective c is how all this works, how do i access the string that i have send as all efforts to log it cause the program to crash.
Below is the code used to start the send:
NSString *bigWord = #"BigWordBigWord";
NSInteger len = [bigWord length];
[self sendMessagePacket:gameSession packetID:NETWORK_TEXT_EVENT withData:bigWord ofLength:(len) reliable:YES];
Any help would be so appreciated. Thank You.
You really need to change the NSString object into either a UTF8 representation to send, or to archive it as an NSData object you send with the full length - you can't just cast an NSString as a C string (either for sending or receiving!!!).
You can get a C string version of NSString using:
const char *sendString = [bigWord cStringUsingEncoding:NSUTF8StringEncoding]
And then get it out of your incoming NSData object with
NSString *result = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
This guy is sending and receiving the string over network just fine. But, I'm also still getting error on the receiving end.
http://discussions.apple.com/thread.jspa?messageID=10215848
At last got it. GKTank is transferring the data using struct, so I placed my string inside the struct and rest is the history.
typedef struct {
NSString *strInfo;
} myInfo;