LibCurl.Curl.internal_OnReadCallback C# (CSharp) Method

        int internal_OnReadCallback(IntPtr ptrBuffer, int sz, int nmemb, IntPtr ptrUserdata)
        {
            if (_OnReadCallback != null)
            {
                object userdata = GetObject(ptrUserdata);
                byte[] buffer;
                int size = _OnReadCallback(out buffer, sz * nmemb, userdata);
                if (size == 0 || buffer == null)
                    return 0;
                Marshal.Copy(buffer, 0, ptrBuffer, size);
                return buffer.Length;
            }
            return 0;
        }