Gzip compression/decompression in iOS

gistfile1.m

// from: http://deusty.blogspot.com/2007/07/gzip-compressiondecompression.html

- (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];
}