// We use big-endian as DataOutputStream does
sclass ByteHead /*is DataOutput*/ {
  settable bool readMode;
  settable bool writeMode;
  settable InputStream inputStream;
  settable OutputStream outputStream;
  
  *() {}
  *(InputStream *inputStream) { readMode(true); }
  *(OutputStream *outputStream) { writeMode(true); }
  
  void writeShort(int i) {
    write(i >> 8);
    write(i);
  }
  
  void writeByte aka write(int i) ctex {
    ensureWriteMode();
    outputStream?.write(i);
  }
  
  short readShort() {
    int i = read() << 8;
    ret (short) (i | read());
  }
  
  // -1 for EOF
  int readByte aka read() ctex {
    ensureReadMode();
    ret inputStream.read();
  }
  
  void ensureReadMode {
    if (!readMode) fail("Not in read mode");
  }
  
  void ensureWriteMode {
    if (!writeMode) fail("Not in write mode");
  }
  
  // exchange = read or write depending on mode
  
  void exchangeShort(IF0<Short> getter, IVF1<Short> setter) {
    if (writeMode()) {
      writeShort(getter!);
    }
    
    if (readMode()) {
      setter.get(readShort());
    }
  }
  
  void exchange(ByteIO writable) {
    writable.readWrite(this);
  }
}