code: private static String wavefrontLine(DateTime ts, SimpleGroupPath group, MetricName metric, String value, String source, Map<String, String> tag_map) {
          return new StringBuilder()
                  .append(name(group, metric))
                  .append(' ')
                  .append(value)
                  .append(' ')
                  .append(timestamp(ts))
                  .append(' ')
                  .append("source=").append(source)
                  .append(' ')
                  .append(tag_map.entrySet().stream()
                          .map(entry -> entry.getKey() + "=\"" + entry.getValue() + '\"')
                          .collect(Collectors.joining(" "))
                  )
                  .toString();
      }
docs: Build the wavefront line from its parts.