stats: strip inner custom namespaces in prometheus names

The Prometheus formatter only stripped a registered custom stat
namespace when it was the leading segment of the tag-extracted name.
This worked for listener/root-scoped Wasm custom stats but not for
upstream Wasm stats scoped under a cluster, where after tag extraction
the namespace ends up in the middle (e.g. `cluster.wasmcustom.foo`),
producing names like `envoy_cluster_wasmcustom_foo`.

Add `CustomStatNamespaces::stripRegisteredInnerNamespace()` and call it
from the Prometheus formatter to strip a registered namespace appearing
as a non-leading, non-trailing segment, without hard-coding `wasmcustom`
or a specific scope depth. Gated by
`envoy.reloadable_features.strip_scoped_custom_stat_namespace`
(default true).

Signed-off-by: Yueshang zuo <zuoyueshang.zys@alibaba-inc.com>

Author: yueshangzuo

changelogs/current.yaml

@@ -34,6 +34,17 @@ minor_behavior_changes:
     Optimized prometheus stats endpoint. Users should see a roughly 30-40% latency improvement in calls to the endpoint
     for cases where the scrape results in lots of cluster stats.
     There should be no visible changes to users, or incompatibilities.
+- area: stats
+  change: |
+    The prometheus formatter now strips a registered custom stat namespace (e.g. ``wasmcustom``) when
+    it appears as a non-leading, non-trailing segment of a tag-extracted stat name, so that custom
+    metrics created on a non-root scope render with the standard ``envoy_`` prefix and without the
+    internal namespace. For example an upstream Wasm counter that previously rendered as
+    ``envoy_cluster_wasmcustom_upstream_rq_2xx`` now renders as ``envoy_cluster_upstream_rq_2xx``,
+    matching listener Wasm and native cluster metrics. The cluster_name (and other extracted) labels
+    are preserved. This primarily fixes upstream HTTP filter Wasm metrics emitted under cluster
+    scope. This behavioral change can be temporarily reverted by setting runtime guard
+    ``envoy.reloadable_features.strip_scoped_custom_stat_namespace`` to ``false``.
 - area: tls
   change: |
     ``SslSocket`` now reports ``ECONNRESET`` as ``ConnectionReset`` by reading the system error

envoy/stats/custom_stat_namespaces.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <string>
+
 #include "envoy/common/pure.h"
 
 #include "absl/strings/string_view.h"
@@ -46,6 +48,15 @@ class CustomStatNamespaces {
    */
   virtual absl::optional<absl::string_view>
   stripRegisteredPrefix(const absl::string_view stat_name) const PURE;
+
+  /**
+   * Like stripRegisteredPrefix, but for a registered namespace appearing as a non-leading,
+   * non-trailing segment of the dotted stat name (e.g. "cluster.wasmcustom.<m>"). Returns
+   * std::string rather than string_view because the result spans both sides of the removed
+   * segment.
+   */
+  virtual absl::optional<std::string>
+  stripRegisteredInnerNamespace(absl::string_view stat_name) const PURE;
 };
 
 } // namespace Stats

source/common/runtime/runtime_features.cc

@@ -102,6 +102,7 @@ RUNTIME_GUARD(envoy_reloadable_features_skip_dns_lookup_for_proxied_requests);
 RUNTIME_GUARD(envoy_reloadable_features_skip_pending_overflow_count_on_active_rq);
 RUNTIME_GUARD(envoy_reloadable_features_ssl_socket_report_connection_reset);
 RUNTIME_GUARD(envoy_reloadable_features_strict_stats_matcher_unpacked);
+RUNTIME_GUARD(envoy_reloadable_features_strip_scoped_custom_stat_namespace);
 RUNTIME_GUARD(envoy_reloadable_features_tcp_proxy_odcds_over_ads_fix);
 RUNTIME_GUARD(envoy_reloadable_features_test_feature_true);
 RUNTIME_GUARD(envoy_reloadable_features_tls_certificate_compression_brotli);

source/common/stats/custom_stat_namespaces_impl.cc

@@ -3,6 +3,8 @@
 #include "source/common/common/assert.h"
 #include "source/common/common/thread.h"
 
+#include "absl/strings/str_cat.h"
+
 namespace Envoy {
 namespace Stats {
 
@@ -29,5 +31,32 @@ CustomStatNamespacesImpl::stripRegisteredPrefix(const absl::string_view stat_nam
   return absl::nullopt;
 };
 
+absl::optional<std::string>
+CustomStatNamespacesImpl::stripRegisteredInnerNamespace(absl::string_view stat_name) const {
+  ASSERT_IS_MAIN_OR_TEST_THREAD();
+  if (namespaces_.empty()) {
+    return absl::nullopt;
+  }
+
+  // Skip the leading scope segment, scan inner segments left-to-right, stop before the leaf.
+  size_t segment_start = stat_name.find('.');
+  if (segment_start == absl::string_view::npos) {
+    return absl::nullopt;
+  }
+  ++segment_start;
+
+  while (segment_start < stat_name.size()) {
+    const size_t segment_end = stat_name.find('.', segment_start);
+    if (segment_end == absl::string_view::npos) {
+      return absl::nullopt;
+    }
+    if (registered(stat_name.substr(segment_start, segment_end - segment_start))) {
+      return absl::StrCat(stat_name.substr(0, segment_start), stat_name.substr(segment_end + 1));
+    }
+    segment_start = segment_end + 1;
+  }
+  return absl::nullopt;
+}
+
 } // namespace Stats
 } // namespace Envoy

source/common/stats/custom_stat_namespaces_impl.h

@@ -16,6 +16,8 @@ class CustomStatNamespacesImpl : public CustomStatNamespaces {
   void registerStatNamespace(const absl::string_view name) override;
   absl::optional<absl::string_view>
   stripRegisteredPrefix(const absl::string_view stat_name) const override;
+  absl::optional<std::string>
+  stripRegisteredInnerNamespace(absl::string_view stat_name) const override;
 
 private:
   absl::flat_hash_set<std::string> namespaces_;

source/server/admin/BUILD

@@ -224,6 +224,7 @@ envoy_cc_library(
         ":utils_lib",
         "//envoy/stats:custom_stat_namespaces_interface",
         "//source/common/buffer:buffer_lib",
+        "//source/common/runtime:runtime_lib",
         "//source/common/stats:histogram_lib",
         "//source/common/upstream:host_utility_lib",
         "@prometheus_metrics_model//:client_model_cc_proto",

source/server/admin/prometheus_stats.cc

@@ -8,6 +8,7 @@
 #include "source/common/common/macros.h"
 #include "source/common/common/regex.h"
 #include "source/common/protobuf/protobuf.h"
+#include "source/common/runtime/runtime_features.h"
 #include "source/common/stats/histogram_impl.h"
 #include "source/common/upstream/host_utility.h"
 
@@ -956,6 +957,17 @@ PrometheusStatsFormatter::metricName(std::string&& extracted_name,
     return sanitized_name;
   }
 
+  // Inner-segment custom namespace (e.g. upstream Wasm under a cluster scope).
+  if (Runtime::runtimeFeatureEnabled(
+          "envoy.reloadable_features.strip_scoped_custom_stat_namespace")) {
+    absl::optional<std::string> inner_namespace_stripped =
+        custom_namespaces.stripRegisteredInnerNamespace(extracted_name);
+    if (inner_namespace_stripped.has_value()) {
+      sanitizeNameInPlace(inner_namespace_stripped.value());
+      return absl::StrCat("envoy_", inner_namespace_stripped.value());
+    }
+  }
+
   // If it does not have a custom namespace, add namespacing prefix to avoid conflicts, as per best
   // practice: https://prometheus.io/docs/practices/naming/#metric-names Also, naming conventions on
   // https://prometheus.io/docs/concepts/data_model/

source/server/admin/prometheus_stats.h

@@ -126,10 +126,12 @@ class PrometheusStatsFormatter {
                                      const Http::RequestHeaderMap& headers);
 
   /**
-   * Format the given metric name, and prefixed with "envoy_" if it does not have a custom
-   * stat namespace. If it has a custom stat namespace AND the name without the custom namespace
-   * has a valid prometheus namespace, the trimmed name is returned.
-   * Otherwise, return nullopt.
+   * Format a tag-extracted name for Prometheus output:
+   *   - leading registered custom namespace -> stripped, no "envoy_" prefix.
+   *   - inner registered custom namespace   -> stripped, "envoy_" prefix kept.
+   *     Gated by "envoy.reloadable_features.strip_scoped_custom_stat_namespace".
+   *   - otherwise                           -> "envoy_" prefix added.
+   * Returns nullopt if the result would not be a valid Prometheus name.
    */
   static absl::optional<std::string>
   metricName(std::string&& extracted_name,

test/common/stats/custom_stat_namespaces_impl_test.cc

@@ -32,5 +32,53 @@ TEST(CustomStatNamespacesImpl, StripRegisteredPrefix) {
   EXPECT_EQ(actual.value(), "my.extension.metric");
 }
 
+TEST(CustomStatNamespacesImpl, StripRegisteredInnerNamespace) {
+  CustomStatNamespacesImpl namespaces;
+
+  // Empty registry.
+  EXPECT_FALSE(namespaces.stripRegisteredInnerNamespace("cluster.foo.metric").has_value());
+
+  namespaces.registerStatNamespace("wasmcustom");
+
+  // Depth 1.
+  {
+    const absl::optional<std::string> actual =
+        namespaces.stripRegisteredInnerNamespace("cluster.wasmcustom.upstream_rq_2xx");
+    EXPECT_TRUE(actual.has_value());
+    EXPECT_EQ(actual.value(), "cluster.upstream_rq_2xx");
+  }
+
+  // Depth 2.
+  {
+    const absl::optional<std::string> actual =
+        namespaces.stripRegisteredInnerNamespace("scope.subscope.wasmcustom.metric");
+    EXPECT_TRUE(actual.has_value());
+    EXPECT_EQ(actual.value(), "scope.subscope.metric");
+  }
+
+  // Multi-token leaf.
+  {
+    const absl::optional<std::string> actual =
+        namespaces.stripRegisteredInnerNamespace("cluster.wasmcustom.foo.bar.baz");
+    EXPECT_TRUE(actual.has_value());
+    EXPECT_EQ(actual.value(), "cluster.foo.bar.baz");
+  }
+
+  // Leading match: caller should use stripRegisteredPrefix instead.
+  EXPECT_FALSE(namespaces.stripRegisteredInnerNamespace("wasmcustom.metric").has_value());
+
+  // Trailing match: that's the metric leaf, not a namespace boundary.
+  EXPECT_FALSE(namespaces.stripRegisteredInnerNamespace("cluster.foo.wasmcustom").has_value());
+
+  // No registered segment in the middle.
+  EXPECT_FALSE(namespaces.stripRegisteredInnerNamespace("cluster.foo.bar.metric").has_value());
+
+  // Substring within a segment doesn't count.
+  EXPECT_FALSE(namespaces.stripRegisteredInnerNamespace("cluster.wasmcustomx.metric").has_value());
+
+  // No dot at all.
+  EXPECT_FALSE(namespaces.stripRegisteredInnerNamespace("wasmcustom").has_value());
+}
+
 } // namespace Stats
 } // namespace Envoy

test/server/admin/BUILD

@@ -207,6 +207,7 @@ envoy_cc_test(
         "//test/mocks/thread_local:thread_local_mocks",
         "//test/mocks/upstream:cluster_manager_mocks",
         "//test/test_common:stats_utility_lib",
+        "//test/test_common:test_runtime_lib",
         "//test/test_common:utility_lib",
     ],
 )