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;
  }
  if (!traceParentHeaderRegEx.hasMatch(traceParentHeader)) {
    // Encountered a malformed or unknown trace header.  Do nothing.
    return context;
  }

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

  final traceId =
      api.TraceId.fromString(parentHeaderFields[_traceIdFieldKey]!);
  final parentId =
      api.SpanId.fromString(parentHeaderFields[_parentIdFieldKey]!);
  final traceFlags =
      int.parse(parentHeaderFields[_traceFlagsFieldKey]!, radix: 16);

  final traceStateHeader = getter.get(carrier, _traceStateHeaderKey);
  final traceState = (traceStateHeader != null)
      ? sdk.TraceState.fromString(traceStateHeader)
      : sdk.TraceState.empty();

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