formatter: support %TRACE_ID% substitution formatter in custom response policy local response body (#43851)

Author: lboynton

changelogs/current.yaml

@@ -913,6 +913,10 @@ new_features:
     destroyed. This could cause use-after-free conditions when filter callbacks were invoked on filters that
     had already received ``onDestroy()``. The fix ensures that ``decodeHeaders()``, ``decodeData()``,
     ``decodeTrailers()``, and ``decodeMetadata()`` are blocked after a downstream reset.
+- area: formatter
+  change: |
+    Added support for ``%TRACE_ID%`` in the custom response policy filter's local response policy to allow
+    trace ID to be substituted into the response body.
 - area: redis
   change: |
     Added support for ``BITFIELD_RO`` in ``redis_proxy``.

source/extensions/http/custom_response/local_response_policy/BUILD

@@ -24,8 +24,10 @@ envoy_cc_extension(
         "//envoy/http:header_map_interface",
         "//envoy/server:filter_config_interface",
         "//envoy/stream_info:stream_info_interface",
+        "//envoy/tracing:trace_driver_interface",
         "//source/common/common:enum_to_int",
         "//source/common/config:datasource_lib",
+        "//source/common/formatter:formatter_extension_lib",
         "//source/common/formatter:substitution_format_string_lib",
         "//source/common/formatter:substitution_formatter_lib",
         "//source/common/http:header_map_lib",

source/extensions/http/custom_response/local_response_policy/local_response_policy.cc

@@ -50,13 +50,15 @@ LocalResponsePolicy::LocalResponsePolicy(
 void LocalResponsePolicy::formatBody(const Envoy::Http::RequestHeaderMap& request_headers,
                                      const Envoy::Http::ResponseHeaderMap& response_headers,
                                      const StreamInfo::StreamInfo& stream_info,
-                                     std::string& body) const {
+                                     const Tracing::Span& active_span, std::string& body) const {
   if (local_body_.has_value()) {
     body = local_body_.value();
   }
 
   if (formatter_) {
-    body = formatter_->format({&request_headers, &response_headers, nullptr, body}, stream_info);
+    body = formatter_->format({&request_headers, &response_headers, nullptr, body,
+                               AccessLog::AccessLogType::NotSet, &active_span},
+                              stream_info);
   }
 }
 
@@ -73,7 +75,7 @@ Envoy::Http::FilterHeadersStatus LocalResponsePolicy::encodeHeaders(
   formatBody(encoder_callbacks->streamInfo().getRequestHeaders() == nullptr
                  ? *Envoy::Http::StaticEmptyHeaders::get().request_headers
                  : *encoder_callbacks->streamInfo().getRequestHeaders(),
-             headers, encoder_callbacks->streamInfo(), body);
+             headers, encoder_callbacks->streamInfo(), encoder_callbacks->activeSpan(), body);
 
   const auto mutate_headers = [this, encoder_callbacks](Envoy::Http::ResponseHeaderMap& headers) {
     header_parser_->evaluateHeaders(headers, encoder_callbacks->streamInfo());

source/extensions/http/custom_response/local_response_policy/local_response_policy.h

@@ -2,6 +2,7 @@
 
 #include "envoy/extensions/http/custom_response/local_response_policy/v3/local_response_policy.pb.h"
 #include "envoy/extensions/http/custom_response/local_response_policy/v3/local_response_policy.pb.validate.h"
+#include "envoy/tracing/trace_driver.h"
 
 #include "source/common/router/header_parser.h"
 #include "source/extensions/filters/http/custom_response/policy.h"
@@ -36,7 +37,8 @@ class LocalResponsePolicy : public Extensions::HttpFilters::CustomResponse::Poli
   // Rewrite the response body for locally specified bodies.
   void formatBody(const Envoy::Http::RequestHeaderMap& request_headers,
                   const Envoy::Http::ResponseHeaderMap& response_headers,
-                  const StreamInfo::StreamInfo& stream_info, std::string& body) const;
+                  const StreamInfo::StreamInfo& stream_info, const Tracing::Span& active_span,
+                  std::string& body) const;
 
   // Body read from local data source.
   const absl::optional<std::string> local_body_;

test/extensions/filters/http/custom_response/BUILD

@@ -70,6 +70,7 @@ envoy_extension_cc_test(
         "//test/mocks/event:event_mocks",
         "//test/mocks/server:factory_context_mocks",
         "//test/mocks/server:server_mocks",
+        "//test/mocks/tracing:tracing_mocks",
         "//test/test_common:test_runtime_lib",
         "//test/test_common:utility_lib",
         "@envoy_api//envoy/extensions/filters/http/custom_response/v3:pkg_cc_proto",

test/extensions/filters/http/custom_response/custom_response_filter_test.cc

@@ -10,6 +10,7 @@
 #include "test/mocks/init/mocks.h"
 #include "test/mocks/server/factory_context.h"
 #include "test/mocks/server/mocks.h"
+#include "test/mocks/tracing/mocks.h"
 #include "test/test_common/utility.h"
 
 #include "gmock/gmock.h"
@@ -145,6 +146,36 @@ TEST_F(CustomResponseFilterTest, DontChangeStatusCode) {
   EXPECT_EQ("200", response_headers.getStatusValue());
 }
 
+TEST_F(CustomResponseFilterTest, TraceIdInBodyFormat) {
+  createConfig(R"EOF(
+  custom_response_matcher:
+    on_no_match:
+      action:
+        name: action
+        typed_config:
+          "@type": type.googleapis.com/envoy.extensions.http.custom_response.local_response_policy.v3.LocalResponsePolicy
+          status_code: 503
+          body_format:
+            text_format_source:
+              inline_string: "trace=%TRACE_ID%"
+)EOF");
+  setupFilterAndCallback();
+
+  const std::string trace_id = "abc123trace";
+  ON_CALL(encoder_callbacks_.active_span_, getTraceId()).WillByDefault(Return(trace_id));
+
+  ::Envoy::Http::TestRequestHeaderMapImpl request_headers{};
+  ::Envoy::Http::TestResponseHeaderMapImpl response_headers{{":status", "503"}};
+  EXPECT_EQ(filter_->decodeHeaders(request_headers, false),
+            ::Envoy::Http::FilterHeadersStatus::Continue);
+  EXPECT_CALL(encoder_callbacks_,
+              sendLocalReply(static_cast<::Envoy::Http::Code>(503), "trace=abc123trace", _, _, _));
+  ON_CALL(encoder_callbacks_.stream_info_, getRequestHeaders())
+      .WillByDefault(Return(&request_headers));
+  EXPECT_EQ(filter_->encodeHeaders(response_headers, true),
+            ::Envoy::Http::FilterHeadersStatus::StopIteration);
+}
+
 TEST_F(CustomResponseFilterTest, InvalidHostRedirect) {
   // Create config with invalid host_redirect field
   createConfig(R"EOF(