Hi,

I'm using objective-c (iPhone) to read a sqlite table that contains blob data. The blob data is actually a gzipped string.

The blob data is read into memory as an NSData object I then use a method (gzipInflate) which I grabbed from here (http://www.cocoadev.com/index.pl?NSDataCategory) -- see method below.

However, the gzipInflate method is returning nil. If I step through the gzipInflate method, I can see that the status returned near the bottom of the method is -3, which I assume is some type of error (Z_STREAM_END = 1 and Z_OK = 0, but I don't know precisely what a status of -3 is).

Consequently, the function returns nil even though the input NSData is 841 bytes in length.

• Any thoughts on what I'm doing wrong?

• Is there something wrong with the method?

• Something wrong with how I'm using the method?

• Any thoughts on how to test this?

Thanks for any help!

- (NSData *)gzipInflate
{
 //   NSData *compressed_data = [self.description dataUsingEncoding: NSUTF16StringEncoding];
    NSData *compressed_data = self.description;

    if ([compressed_data length] == 0) return compressed_data;

    unsigned full_length = [compressed_data length];
    unsigned half_length = [compressed_data length] / 2;

    NSMutableData *decompressed = [NSMutableData dataWithLength: full_length + half_length];
    BOOL done = NO;
    int status;

    z_stream strm;
    strm.next_in = (Bytef *)[compressed_data bytes];
    strm.avail_in = [compressed_data 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);
        NSLog(@"zstreamend = %d", Z_STREAM_END);
        if (status == Z_STREAM_END) done = YES;
        else if (status != Z_OK) break; //status here actually is -3
    }
    if (inflateEnd (&strm) != Z_OK) return nil;

    // Set real length.
    if (done)
    {
        [decompressed setLength: strm.total_out];
        return [NSData dataWithData: decompressed];
    }
    else return nil;
}