code: protected final int readBytes()
          throws IOException
      {
          mBytePtr = 0;
          mByteBufferEnd = 0;
          if (mIn != null) {
              int count = mIn.read(mByteBuffer, 0, mByteBuffer.length);
              if (count > 0) {
                  mByteBufferEnd = count;
              }
              return count;
          }
          return -1;
      }
docs: Method for reading as many bytes from the underlying stream as possible
  (that fit in the buffer), to the beginning of the buffer.