NSData find sequence of bytes - ios

Question

I need to find the sequence of bytes in my image data. I have next code on java, but I need make the same in obj-c.
Java:
private static int searchInBuffer(byte[] pBuf, int iBufferLen) {
for(int i = 0; i<iBufferLen - 7; i++) {
if (pBuf[i] == 'l' && pBuf[i + 1] == 'i' && pBuf[i + 2] == 'n' && pBuf[i + 3] == 'k')
return (int)pBuf[i + 4];
}
return -1;
}
public static int checkFlagInJpeg(String pFullFileName) {
int iRes = -1;
try {
File f = new File(pFullFileName);
FileInputStream is = new FileInputStream(f);
int iBufferSize = 6 * 1024, iCount = 15;
byte buf[] = new byte[iBufferSize];
while((is.available() > 0) && (iCount >= 0)) {
int iRead = is.read(buf),
iFlag = searchInBuffer(buf, iRead);
if (iFlag > 0) {
iRes = iFlag;
break;
}
iCount--;
}
is.close();
}
}
Obj-C (my version):
UIImage *image = [UIImage imageWithCGImage:[[[self.assets objectAtIndex:indexPath.row] defaultRepresentation] fullScreenImage]];
NSData *imageData = UIImageJPEGRepresentation(image, 1.0f);
NSUInteger length = MIN(6*1024, [imageData length]);
Byte *buffer = (Byte *)malloc(length);
memcpy(buffer, [imageData bytes], length);
for (int i=0; i < length - 1; i++) {
if (buffer[i] == 'l' && buffer[i + 1] == 'i' && buffer[i + 2] == 'n' && buffer[i + 3] == 'k')
NSLog(#"%c", buffer[i + 4]);
}
free(buffer);
I'm still not sure, that I understand all aspects of work with bytes, so I need a help.
UPDATE:
The problem was in getting image data. With help of Martin R. I combine to solutions in one and get next working code:
ALAssetRepresentation *repr = [[self.assets objectAtIndex:indexPath.row] defaultRepresentation];
NSUInteger size = (NSUInteger) repr.size;
NSMutableData *data = [NSMutableData dataWithLength:size];
NSError *error;
[repr getBytes:data.mutableBytes fromOffset:0 length:size error:&error];
NSData *pattern = [#"link" dataUsingEncoding:NSUTF8StringEncoding];
NSRange range = [data rangeOfData:pattern options:0 range:NSMakeRange(0, data.length)];
int iRes = -1;
if (range.location != NSNotFound) {
uint8_t flag;
[data getBytes:&flag range:NSMakeRange(range.location + range.length, 1)];
iRes = flag;
}
NSLog(#"%i", iRes);
It's working perfect! Thank you again!

Answer 1

NSData has a method rangeOfData:... which you can use to find the pattern:
NSData *pattern = [#"link" dataUsingEncoding:NSUTF8StringEncoding];
NSRange range = [imageData rangeOfData:pattern options:0 range:NSMakeRange(0, imageData.length)];
If the pattern was found, get the next byte:
int iRes = -1;
if (range.location != NSNotFound && range.location + range.length < imageData.length) {
uint8_t flag;
[imageData getBytes:&flag range:NSMakeRange(range.location + range.length, 1)];
iRes = flag;
}