docs: private String guessMimeTypeFromContents(final ChannelBuffer buf) {
      if (!buf.readable()) {
        logWarn("Sending an empty result?! buf=" + buf);
        return "text/plain";
      }
      final int firstbyte = buf.getUnsignedByte(buf.readerIndex());
      switch (firstbyte) {
        case '<':  // <html or <!DOCTYPE
          return HTML_CONTENT_TYPE;
        case '{':  // JSON object
        case '[':  // JSON array
          return "application/json";  // RFC 4627 section 6 mandates this.
        case 0x89:  // magic number in PNG files.
          return "image/png";
      }
      return "text/plain";  // Default.
    }