Gzip compression/decompression

A long time ago I grabbed some code from CocoaDev to allow zlib compression/decompression of NSData. But a couple months ago I went looking for similar code to allow gzip compression/decompression. At the time I didn't find any, and found myself wading through the zlib documentation and header files until I came up with a solution. I've recently noticed that someone else on CocoaDev has also mentioned the solution, but it looks like they didn't fully implement a deflate version of it. So, without further ado, here is an NSData category that adds support for gzip compression and decompression:

@interface NSData (DDData)

// gzip compression utilities
- (NSData *)gzipInflate;
- (NSData *)gzipDeflate;

@end

-----------------------------------------

#include 

@implementation NSData (DDData)

- (NSData *)gzipInflate
{
 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 (inflateInit2(&strm, (15+32)) != 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;
}

- (NSData *)gzipDeflate
{
 if ([self length] == 0) return self;
 
 z_stream strm;
 
 strm.zalloc = Z_NULL;
 strm.zfree = Z_NULL;
 strm.opaque = Z_NULL;
 strm.total_out = 0;
 strm.next_in=(Bytef *)[self bytes];
 strm.avail_in = [self length];
 
 // Compresssion Levels:
 //   Z_NO_COMPRESSION
 //   Z_BEST_SPEED
 //   Z_BEST_COMPRESSION
 //   Z_DEFAULT_COMPRESSION
 
 if (deflateInit2(&strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED, (15+16), 8, Z_DEFAULT_STRATEGY) != Z_OK) return nil;
 
 NSMutableData *compressed = [NSMutableData dataWithLength:16384];  // 16K chunks for expansion
 
 do {
  
  if (strm.total_out >= [compressed length])
   [compressed increaseLengthBy: 16384];
  
  strm.next_out = [compressed mutableBytes] + strm.total_out;
  strm.avail_out = [compressed length] - strm.total_out;
  
  deflate(&strm, Z_FINISH);  
  
 } while (strm.avail_out == 0);
 
 deflateEnd(&strm);
 
 [compressed setLength: strm.total_out];
 return [NSData dataWithData:compressed];
}

@end

I suppose I better go post this on CocoaDev as well now too.