// [0] - protocol type
// [1...4] - packet number
// [5...512] - email(254 symbols in UTF-8)
// [513...514] - email length
// [515...578] - password(32 symbols in UTF-8)
// [579] - password length

...

const std::wstring email = L"player@gmail.com";
const std::wstring password = L"difficult_password";

std::unique_ptr<Protocol::LoginPacket> packetToServer = std::make_unique<Protocol::LoginPacket>();
packetToServer->setPacketNumber(mPacketNumber++);
packetToServer->setEmailSize((std::int16_t) email.size());
packetToServer->setPasswordSize((std::int8_t) password.size());
packetToServer->setEmail(email.data());
packetToServer->setPassword(password.data());
mConnection.sendBuffer(packetToServer->toBuffer(), sizeof(Protocol::LoginPacket));

...

...

private final static byte POSITION_EMAIL = 5; // index
private final static short SIZE_EMAIL = 254 * Primitives.CHAR_SIZE; // bytes
private final static short POSITION_OF_SIZE_EMAIL = 513; // index
private final static byte SIZE_OF_EMAIL_SIZE = Primitives.SHORT_SIZE; // bytes

...

public String getEmail(){
    return new String(buffer, POSITION_EMAIL, ByteBuffer.wrap(buffer, POSITION_OF_SIZE_EMAIL, SIZE_OF_EMAIL_SIZE).getShort() * Primitives.CHAR_SIZE);
}

...

if ("player@gmail.com".equals(protocol.getPassword())) {
   ...
}