public Set<AsciiString> requestHeaders() {
        if (reqHeaders == null) {
            return ImmutableSet.of();
        }
        return Arrays.stream(reqHeaders).map(e -> e.key).collect(toImmutableSet());
    }
Returns all HTTP request header names in the export list.
core/src/main/java/com/linecorp/armeria/common/logging/RequestContextExporter.java