code: public String readString() throws IOException {
      final int size = readRawVarint32();
      if (size <= (bufferSize - bufferPos) && size > 0) {
        // Fast path:  We already have the bytes in a contiguous buffer, so
        //   just copy directly from it.
        final String result = new String(buffer, bufferPos, size, "UTF-8");
        bufferPos += size;
        return result;
      } else {
        // Slow path:  Build a byte array first then copy it.
        return new String(readRawBytes(size), "UTF-8");
      }
    }
docs: Read a {@code string} field value from the stream.