access log: add DYNAMIC_METADATA_UNQUOTED formatter

docs/root/configuration/observability/access_log/usage.rst

@@ -415,6 +415,10 @@ The following command operators are supported:
     JSON struct or list is rendered. Structs and lists may be nested. In any event, the maximum
     length is ignored
 
+%DYNAMIC_METADATA_UNQUOTED(NAMESPACE:KEY*):Z%
+  Same as DYNAMIC_METADATA, but with quotes removed. Useful when you want to log a plain string or you want to
+  compose the JSON emitted by DYNAMIC_METADATA.
+
 .. _config_access_log_format_filter_state:
 
 %FILTER_STATE(KEY:F):Z%

docs/root/version_history/current.rst

@@ -63,6 +63,7 @@ Removed Config or Runtime
 New Features
 ------------
 * access log: added a :ref:`dynamic metadata filter<envoy_v3_api_msg_config.accesslog.v3.MetadataFilter>` for access logs, which filters whether to log based on matching dynamic metadata.
+* access log: added DYNAMIC_METADATA_UNQUOTED :ref:`access log formatter <config_access_log_format>`.
 * access log: added support for :ref:`%DOWNSTREAM_PEER_FINGERPRINT_1% <config_access_log_format_response_flags>` as a response flag.
 * access log: added support for nested objects in :ref:`JSON logging mode <config_access_log_format_dictionaries>`.
 * access log: added :ref:`omit_empty_values<envoy_v3_api_field_config.core.v3.SubstitutionFormatString.omit_empty_values>` option to omit unset value from formatted log.

source/common/formatter/substitution_formatter.cc

@@ -287,6 +287,7 @@ std::vector<FormatterProviderPtr> SubstitutionFormatParser::parse(const std::str
   std::string current_token;
   std::vector<FormatterProviderPtr> formatters;
   static constexpr absl::string_view DYNAMIC_META_TOKEN{"DYNAMIC_METADATA("};
+  static constexpr absl::string_view DYNAMIC_META_UNQUOTED_TOKEN{"DYNAMIC_METADATA_UNQUOTED("};
   static constexpr absl::string_view FILTER_STATE_TOKEN{"FILTER_STATE("};
   const std::regex command_w_args_regex(R"EOF(^%([A-Z]|_)+(\([^\)]*\))?(:[0-9]+)?(%))EOF");
 
@@ -348,6 +349,15 @@ std::vector<FormatterProviderPtr> SubstitutionFormatParser::parse(const std::str
         parseCommand(token, start, ":", filter_namespace, path, max_length);
         formatters.emplace_back(
             FormatterProviderPtr{new DynamicMetadataFormatter(filter_namespace, path, max_length)});
+      } else if (absl::StartsWith(token, DYNAMIC_META_UNQUOTED_TOKEN)) {
+        std::string filter_namespace;
+        absl::optional<size_t> max_length;
+        std::vector<std::string> path;
+        const size_t start = DYNAMIC_META_UNQUOTED_TOKEN.size();
+
+        parseCommand(token, start, ":", filter_namespace, path, max_length);
+        formatters.emplace_back(FormatterProviderPtr{
+            new DynamicMetadataFormatter(filter_namespace, path, max_length, true)});
       } else if (absl::StartsWith(token, FILTER_STATE_TOKEN)) {
         std::string key;
         absl::optional<size_t> max_length;
@@ -980,8 +990,9 @@ GrpcStatusFormatter::formatValue(const Http::RequestHeaderMap&,
 
 MetadataFormatter::MetadataFormatter(const std::string& filter_namespace,
                                      const std::vector<std::string>& path,
-                                     absl::optional<size_t> max_length)
-    : filter_namespace_(filter_namespace), path_(path), max_length_(max_length) {}
+                                     absl::optional<size_t> max_length, bool unquoted)
+    : filter_namespace_(filter_namespace), path_(path), max_length_(max_length),
+      unquoted_(unquoted) {}
 
 absl::optional<std::string>
 MetadataFormatter::formatMetadata(const envoy::config::core::v3::Metadata& metadata) const {
@@ -992,6 +1003,17 @@ MetadataFormatter::formatMetadata(const envoy::config::core::v3::Metadata& metad
 
   std::string json = MessageUtil::getJsonStringFromMessage(value, false, true);
   truncate(json, max_length_);
+
+  if (unquoted_) {
+    if (absl::StartsWith(json, "\"")) {
+      json.erase(0, 1);
+    }
+
+    if (absl::EndsWith(json, "\"")) {
+      json.pop_back();
+    }
+  }
+
   return json;
 }
 
@@ -1019,8 +1041,8 @@ MetadataFormatter::formatMetadataValue(const envoy::config::core::v3::Metadata&
 // See: https://github.com/envoyproxy/envoy/issues/3006
 DynamicMetadataFormatter::DynamicMetadataFormatter(const std::string& filter_namespace,
                                                    const std::vector<std::string>& path,
-                                                   absl::optional<size_t> max_length)
-    : MetadataFormatter(filter_namespace, path, max_length) {}
+                                                   absl::optional<size_t> max_length, bool unquoted)
+    : MetadataFormatter(filter_namespace, path, max_length, unquoted) {}
 
 absl::optional<std::string> DynamicMetadataFormatter::format(
     const Http::RequestHeaderMap&, const Http::ResponseHeaderMap&, const Http::ResponseTrailerMap&,

source/common/formatter/substitution_formatter.h

@@ -307,7 +307,7 @@ class StreamInfoFormatter : public FormatterProvider {
 class MetadataFormatter {
 public:
   MetadataFormatter(const std::string& filter_namespace, const std::vector<std::string>& path,
-                    absl::optional<size_t> max_length);
+                    absl::optional<size_t> max_length, bool unquoted = false);
 
 protected:
   absl::optional<std::string>
@@ -318,6 +318,7 @@ class MetadataFormatter {
   std::string filter_namespace_;
   std::vector<std::string> path_;
   absl::optional<size_t> max_length_;
+  const bool unquoted_;
 };
 
 /**
@@ -326,7 +327,8 @@ class MetadataFormatter {
 class DynamicMetadataFormatter : public FormatterProvider, MetadataFormatter {
 public:
   DynamicMetadataFormatter(const std::string& filter_namespace,
-                           const std::vector<std::string>& path, absl::optional<size_t> max_length);
+                           const std::vector<std::string>& path, absl::optional<size_t> max_length,
+                           bool unquoted = false);
 
   // FormatterProvider
   absl::optional<std::string> format(const Http::RequestHeaderMap&, const Http::ResponseHeaderMap&,

test/common/formatter/substitution_formatter_test.cc

@@ -1232,6 +1232,11 @@ TEST(SubstitutionFormatterTest, DynamicMetadataFormatter) {
                                       stream_info, body),
                 ProtoEq(ValueUtil::stringValue("test_value")));
   }
+  {
+    DynamicMetadataFormatter formatter("com.test", {"test_key"}, absl::optional<size_t>(), true);
+    EXPECT_EQ("test_value", formatter.format(request_headers, response_headers, response_trailers,
+                                             stream_info, body));
+  }
   {
     DynamicMetadataFormatter formatter("com.test", {"test_obj"}, absl::optional<size_t>());
     EXPECT_EQ(