nw_connection_send packets data to Android

Question

I'm trying to send packet data from macOS to Android, I have the packet defined like int(dataType)|int(packet len)|data

Say dataType value 5 represents a string sent from the macOS side:

auto sendString = [](nw_connection_t connect, dispatch_queue_t q1, int dtType, std::string &data)
{
   int len = (int)data.length()
   int header[2] = {dtType, (int)(len * sizeof(char))}; //dtType=5
   auto dat_head = dispatch_data_create(&header[0], 2 * sizeof(int), q1, ^{});
   auto dat_str = dispatch_data_create(info.c_str(), sizeof(char) * len, q1, ^{});
   auto packet = dispatch_data_create_concat(dat_head, dat_str);
   nw_connection_send(connect, 
                      packet, 
                      NW_CONNECTION_DEFAULT_MESSAGE_CONTEXT, 
                      true, ^(nw_error_t  _Nullable error) 
        {
            if (error != NULL) {
                errno = nw_error_get_error_code(error);
                LOGEX(LOG_ERR, "error code:%d: [%s]", errno, strerror(errno));
            }
            else {
                LOGEX(LOG_INFO, "data sent out");
            }
        });
}

In the Android (Java) side, I use readInt to get the packet data type

int dataType = input.readInt();

what I got dataType is 16777216, not 5, I checked the byte order and it won't resolve the issue. How to format data in macOS side so that Android read the correct int?

Answer 1

I gave up sending the raw data, use NSString format the header into UTF8 string, parse the string at Android side and it works as expected

 NSString *dataHead = [NSString stringWithFormat:@"MTData type:%d,len:%d,\n", (int)dt, len];
 NSMutableData *data = [NSMutableData dataWithData:[dataHead dataUsingEncoding:NSUTF8StringEncoding]];
                    
[data appendBytes:info.c_str() length:info.length()];
auto dispatch_content = dispatchDataFromNSData(data);