Add ability to give HTTP Filters names, and nameWithFallback utility to resolve it

Signed-off-by: Nick Shipilov <nick.shipilov.n@gmail.com>

Author: nshipilov

envoy/http/filter.h

@@ -888,6 +888,11 @@ class StreamFilterBase {
 public:
   virtual ~StreamFilterBase() = default;
 
+  /**
+   * A name for the filter. Used for monitoring and disagnostics.
+   */
+  virtual absl::string_view name() { return {}; }
+
   /**
    * This routine is called before the access log handlers' final log() is called. Filters can use
    * this callback to enrich the data passed in to the log handlers.

source/common/http/utility.cc

@@ -1641,6 +1641,14 @@ std::string Utility::newUri(::Envoy::OptRef<const Utility::RedirectConfig> redir
   return fmt::format("{}://{}{}{}", final_scheme, final_host, final_port, final_path);
 }
 
+absl::string_view Utility::nameWithFallback(StreamFilterBase& stream_filter) {
+  absl::string_view name = stream_filter.name();
+  if (!name.empty()) {
+    return name;
+  }
+  return typeid(stream_filter).name();
+}
+
 bool Utility::isValidRefererValue(absl::string_view value) {
 
   // First, we try to parse it as an absolute URL and

source/common/http/utility.h

@@ -728,6 +728,11 @@ bool schemeIsHttps(const absl::string_view scheme);
 std::string newUri(::Envoy::OptRef<const RedirectConfig> redirect_config,
                    const Http::RequestHeaderMap& headers);
 
+/*
+ * Returns the filter's name, if empty, resolves it using RTTI.
+ */
+absl::string_view nameWithFallback(StreamFilterBase& stream_filter);
+
 } // namespace Utility
 } // namespace Http
 } // namespace Envoy

test/common/http/utility_test.cc

@@ -2055,5 +2055,29 @@ TEST(HeaderIsValidTest, SchemeIsHttps) {
   EXPECT_FALSE(Utility::schemeIsHttps("http"));
 }
 
+class ExampleFilterWithName : public PassThroughDecoderFilter {
+public:
+  virtual ~ExampleFilterWithName() = default;
+
+  static constexpr absl::string_view filter_name{"example_filter"};
+  absl::string_view name() override { return ExampleFilterWithName::filter_name; }
+};
+
+class ExampleFilterWithoutName : public PassThroughDecoderFilter {
+public:
+  virtual ~ExampleFilterWithoutName() = default;
+};
+
+TEST(TestNameWithFallback, ProvidesName) {
+  ExampleFilterWithName filter_with_name;
+  EXPECT_EQ(Utility::nameWithFallback(filter_with_name), "example_filter");
+
+  // Check that there is *some* name returned,  for the fallback case.
+  // Different compilers handle this differently --
+  // some return mangled names directly, others return human readable names.
+  ExampleFilterWithoutName filter_without_name;
+  EXPECT_FALSE(Utility::nameWithFallback(filter_without_name).empty());
+}
+
 } // namespace Http
 } // namespace Envoy