def extract(format, carrier)
      case format
      when OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY
        ::Instana.logger.debug 'Unsupported extract format'
      when OpenTracing::FORMAT_RACK
        ::Instana::SpanContext.new(::Instana::Util.header_to_id(carrier['HTTP_X_INSTANA_T']),
                                     ::Instana::Util.header_to_id(carrier['HTTP_X_INSTANA_S']))
      else
        ::Instana.logger.debug 'Unknown inject format'
        nil
      end
    end
def extract(format, carrier)
      case format
      when OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY
        ::Instana.logger.debug 'Unsupported extract format'
      when OpenTracing::FORMAT_RACK
        ::Instana::SpanContext.new(::Instana::Util.header_to_id(carrier['HTTP_X_INSTANA_T']),
                                     ::Instana::Util.header_to_id(carrier['HTTP_X_INSTANA_S']))
      else
        ::Instana.logger.debug 'Unknown inject format'
        nil
      end
    end
Extract a span from a carrier

 @param format [OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK]
 @param carrier [Carrier]

 @return [SpanContext]