extract method

@override Context extract(Context context, dynamic carrier, TextMapGetter getter)

Implementation

@override
api.Context extract(
  api.Context context,
  dynamic carrier,
  api.TextMapGetter getter,
) {
  final traceParentHeader = getter.get(carrier, _traceParentHeaderKey);
  if (traceParentHeader == null) {
    // Carrier did not contain a trace header.  Do nothing.
    return context;
  }

  final parentHeaderMatch = traceParentHeaderRegEx.firstMatch(
    traceParentHeader,
  );

  if (parentHeaderMatch == null) {
    // Encountered a malformed or unknown trace header.  Do nothing.
    return context;
  }

  final parentHeaderFields = Map<String, String>.fromIterable(
    parentHeaderMatch.groupNames,
    key: (element) => element.toString(),
    value: (element) => parentHeaderMatch.namedGroup(element)!,
  );

  final traceIdHeader = parentHeaderFields[_traceIdFieldKey];
  final traceId = (traceIdHeader != null)
      ? api.TraceId.fromString(traceIdHeader)
      : api.TraceId.invalid();
  final parentIdHeader = parentHeaderFields[_parentIdFieldKey];
  final parentId = (parentIdHeader != null)
      ? api.SpanId.fromString(parentIdHeader)
      : api.SpanId.invalid();
  final traceFlagsHeader = parentHeaderFields[_traceFlagsFieldKey];
  final traceFlags = (traceFlagsHeader != null)
      ? int.parse(traceFlagsHeader, radix: 16)
      : api.TraceFlags.none;
  final traceStateHeader = getter.get(carrier, _traceStateHeaderKey);
  final traceState = (traceStateHeader != null)
      ? api.TraceState.fromString(traceStateHeader)
      : api.TraceState.empty();

  return api.contextWithSpan(
    context,
    NonRecordingSpan(
      api.SpanContext.remote(traceId, parentId, traceFlags, traceState),
    ),
  );
}