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