Objective-C Zlib method with potential leak

Question

I have just analyzed my code and found a analysis error.

Potential leak of memory pointed to by 'decompressedBytes'

I have never had such an error, I have done some hunting around but cannot figure out how to fix this "potential leak".

This is what my code looks like

- (NSData*) dataByDecompressingData:(NSData*)data{
    Byte* bytes = (Byte*)[data bytes];
    NSInteger len = [data length];
    NSMutableData *decompressedData = [[NSMutableData alloc] initWithCapacity:COMPRESSION_BLOCK];
    Byte* decompressedBytes = (Byte*) malloc(COMPRESSION_BLOCK);
    
    z_stream stream;
    int err;
    stream.zalloc = (alloc_func)0;
    stream.zfree = (free_func)0;
    stream.opaque = (voidpf)0;
    
    stream.next_in = bytes;
    err = inflateInit(&stream);
    CHECK_ERR(err, @"inflateInit");
    
    while (true) {
        stream.avail_in = len - stream.total_in;
        stream.next_out = decompressedBytes;
        stream.avail_out = COMPRESSION_BLOCK;
        err = inflate(&stream, Z_NO_FLUSH);
        [decompressedData appendBytes:decompressedBytes length:(stream.total_out-[decompressedData length])];
        if(err == Z_STREAM_END)
            break;
        CHECK_ERR(err, @"inflate");
    }
    
    err = inflateEnd(&stream);
    CHECK_ERR(err, @"inflateEnd");
    
    free(decompressedBytes);
    return decompressedData;
}

Answer 1

if your CHECK_ERR happen to be something like if (err) return nil then the warning means your function have early return and may not always free memory you malloc ed

you should avoid malloc if possible.

try this

NSMutableData *decompressedBytesData = [[NSMutableData alloc] initWithCapacity:COMPRESSION_BLOCK]; // autorelease if not ARC
Byte* decompressedBytes = (Byte*)[decompressedBytesData mutableBytes];

// you don't need free(decompressedBytes);