Question

  final byte LOGIN_REQUEST = 1;
  long deviceId = 123456789;
  String nickname = "testid";

  Socket mSocket = new Socket("localhost", 12021);
  ByteBuffer bBuffer = ByteBuffer.allocate(1);
  bBuffer.order(ByteOrder.LITTLE_ENDIAN);

  //1
  bBuffer.put(LOGIN_REQUEST);

  //8
  bBuffer.putLong(deviceId);

  byte[] bString = nickname.getBytes();
  int sLength = bString.length;

  //4
  bBuffer.putInt(sLength);
  bBuffer.put(bString);

I am sending byte data like this and I want to parse it on my linux server using c++

In c++, I am reading

 char *pdata = new char[BUF_SIZE];
 int dataLength = read(m_events[i].data.fd, pdata, BUF_SIZE);

and push the pdata into the pthread’s queue. I think I have to read first byte to see the type of the packet and read the next 8byte to get the device id and so on..
Please give me some references or tutorial to do this in c++ code..

Thanks in advance..

Answer 1

The below code will effectively do the trick. I am assuming a java int is 32bit

#include <inttypes.h>

// Declare variables
unsigned char login_req;
int64_t       device_id;
uint32_t      name_len;
char*         name_str;

// Populate variables;
login_req = pdata[0];
memcpy( &device_id, pdata+1, 8 );
memcpy( &name_len, pdata+9, 4 );
name_str = (char*)malloc( name_len + 1 );
memcpy( name_str, pdata+13, name_len );
name_str[name_len] = '\0';

Note: I am glossing over some stuff, namely

• Does not handle when BUF_SIZE is to small
• Does not handle when the C program machine is not little ENDIAN. If it is big endian then you would need to switch the bytes after the memcpy for device_id and name_len
• Does not to type cast on memcpy calls to avoid possible compiler warnings

This solution is pure C, will work in C++ too