I have a fairly large NSData (or NSMutableData if necessary) object which I want to take a small chunk out of and leave the rest. Since I'm working with large amounts of NSData bytes, I don't want to make a big copy, but instead just truncate the existing bytes. Basically:

• NSData *source: < a few bytes I want to discard > + < big chunk of bytes I want to keep >
• NSData *destination: < big chunk of bytes I want to keep >

There are truncation methods in NSMutableData, but they only truncate the end of it, whereas I want to truncate the beginning. My thoughts are to do this with the methods:

- getBytes:range:

and

- initWithBytesNoCopy:length:freeWhenDone:

However, I'm trying to figure out how to manage memory with these. I'm guessing the process will be like this (I've placed ????s where I don't know what to do):

void *buffer

// Get range of bytes
[source getBytes:buffer range:NSMakeRange(myStart, myLength)];

// Somehow (m)alloc the memory which will be freed up in the following step
?????

// Release the source, now that I've allocated the bytes
[source release];

// Create a new data, recycling the bytes so they don't have to be copied
NSData destination = [[NSData alloc]
                      initWithBytesNoCopy:buffer
                      length:myLength
                      freeWhenDone:YES];

Thanks for the help!