NSDataCompression.m

//
//  NSDataCompression.m
//  ObjGit
//
//  thankfully borrowed from the Etoile framework
//

#import "NSDataCompression.h"
#include <zlib.h>

@implementation NSData (Compression)
- (NSData *) compressedData
{
	unsigned int srcLength = [self length];
	if (srcLength > 0)
	{
		uLong buffLength = srcLength * 1.001 + 12;
		NSMutableData *compData = [[NSMutableData alloc] initWithCapacity:buffLength];
		[compData increaseLengthBy:buffLength];
		int error = compress( [compData mutableBytes], &buffLength,
							 [self bytes], srcLength );
		switch( error ) {
			case Z_OK:
				[compData setLength: buffLength];
				return [NSData dataWithBytes:[compData bytes] length:buffLength];
				break;
			default:
				NSAssert( YES, @"Error compressing: Memory Error!" );
				break;
		}
		//[compData release];
    }
    return nil;
}

- (NSData *) decompressedData
{
	if ([self length] == 0) return self;
	
	unsigned full_length = [self length];
	unsigned half_length = [self length] / 2;
	
	NSMutableData *decompressed = [NSMutableData dataWithLength: full_length + half_length];
	BOOL done = NO;
	int status;
	
	z_stream strm;
	strm.next_in = (Bytef *)[self bytes];
	strm.avail_in = [self length];
	strm.total_out = 0;
	strm.zalloc = Z_NULL;
	strm.zfree = Z_NULL;
	
	if (inflateInit (&strm) != Z_OK) return nil;
	while (!done)
	{
		// Make sure we have enough room and reset the lengths.
		if (strm.total_out >= [decompressed length])
			[decompressed increaseLengthBy: half_length];
		strm.next_out = [decompressed mutableBytes] + strm.total_out;
		strm.avail_out = [decompressed length] - strm.total_out;
		
		// Inflate another chunk.
		status = inflate (&strm, Z_SYNC_FLUSH);
		if (status == Z_STREAM_END) done = YES;
		else if (status != Z_OK) break;
	}
	if (inflateEnd (&strm) != Z_OK) return nil;
	
	// Set real length.
	if (done)
	{
		[decompressed setLength: strm.total_out];
		return [NSData dataWithData: decompressed];
	}
	else 
		return nil;
	
}
@end