This class wraps and Arduino Stream, and dumps all data to another Stream for debug purposes.

StreamDebugger.ino

/* This class wraps and Arduino Stream,
 * and dumps all data to another Stream for debug purposes.
 *
 * Usage:
 *   StreamDebugger StreamDbg(Serial1, Serial);
 */

#ifndef StreamDebugger_h
#define StreamDebugger_h

class StreamDebugger
  : public Stream
{
  public:
    StreamDebugger(Stream& data, Stream& dump)
      : _data(data), _dump(dump)
    {}

    virtual size_t write(uint8_t ch) {
      _dump.write(ch);
      return _data.write(ch);
    }
    virtual int read() {
      int ch = _data.read();
      if (ch != -1) { _dump.write(ch); }
      return ch;
    }
    virtual int available() { return _data.available(); }
    virtual int peek()      { return _data.peek();      }
    virtual void flush()    { _data.flush();            }

    void directAccess() {
      while(true) {
        if (_data.available()) {
          _dump.write(_data.read());
        }
        if (_dump.available()) {
          _data.write(_dump.read());
        }
        delay(0);
      }
    }
  private:
    Stream& _data;
    Stream& _dump;
};

#endif