dynatracesampler: refactor DynatraceTag code into own file (#41823)

Commit Message: Extracts DynatraceTag class into its own file in
preparation for upcoming features.
Additional Description:
Risk Level: Low
Testing: Unit tests
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional [API
Considerations](https://github.com/envoyproxy/envoy/blob/main/api/review_checklist.md):]

---------

Signed-off-by: Joao Grassi <[email protected]>
Co-authored-by: Copilot <[email protected]>

Author: joaopgrassi

source/extensions/tracers/opentelemetry/samplers/dynatrace/BUILD

@@ -31,6 +31,7 @@ envoy_cc_library(
     ],
     hdrs = [
         "dynatrace_sampler.h",
+        "dynatrace_tag.h",
         "sampler_config.h",
         "sampler_config_provider.h",
         "sampling_controller.h",

source/extensions/tracers/opentelemetry/samplers/dynatrace/dynatrace_sampler.cc

@@ -1,11 +1,10 @@
 #include "source/extensions/tracers/opentelemetry/samplers/dynatrace/dynatrace_sampler.h"
 
 #include <memory>
-#include <sstream>
 #include <string>
 
 #include "source/common/common/hash.h"
-#include "source/common/config/datasource.h"
+#include "source/extensions/tracers/opentelemetry/samplers/dynatrace/dynatrace_tag.h"
 #include "source/extensions/tracers/opentelemetry/samplers/dynatrace/tenant_id.h"
 #include "source/extensions/tracers/opentelemetry/samplers/sampler.h"
 #include "source/extensions/tracers/opentelemetry/span_context.h"
@@ -22,68 +21,6 @@ namespace {
 
 constexpr std::chrono::minutes SAMPLING_UPDATE_TIMER_DURATION{1};
 
-/**
- * @brief Helper for creating and reading the Dynatrace tag in the tracestate http header
- * This tag has at least 8 values delimited by semicolon:
- * - tag[0]: version (currently version 4)
- * - tag[1] - tag[4]: unused in the sampler (always 0)
- * - tag[5]: ignored field. 1 if a span is ignored (not sampled), 0 otherwise
- * - tag[6]: sampling exponent
- * - tag[7]: path info
- */
-class DynatraceTag {
-public:
-  static DynatraceTag createInvalid() { return {false, false, 0, 0}; }
-
-  // Creates a tag using the given values.
-  static DynatraceTag create(bool ignored, uint32_t sampling_exponent, uint32_t path_info) {
-    return {true, ignored, sampling_exponent, path_info};
-  }
-
-  // Creates a tag from a string.
-  static DynatraceTag create(const std::string& value) {
-    std::vector<absl::string_view> tracestate_components =
-        absl::StrSplit(value, ';', absl::AllowEmpty());
-    if (tracestate_components.size() < 8) {
-      return createInvalid();
-    }
-
-    if (tracestate_components[0] != "fw4") {
-      return createInvalid();
-    }
-    bool ignored = tracestate_components[5] == "1";
-    uint32_t sampling_exponent;
-    uint32_t path_info;
-    if (absl::SimpleAtoi(tracestate_components[6], &sampling_exponent) &&
-        absl::SimpleHexAtoi(tracestate_components[7], &path_info)) {
-      return {true, ignored, sampling_exponent, path_info};
-    }
-    return createInvalid();
-  }
-
-  // Returns a Dynatrace tag as string.
-  std::string asString() const {
-    std::string ret = absl::StrCat("fw4;0;0;0;0;", ignored_ ? "1" : "0", ";", sampling_exponent_,
-                                   ";", absl::Hex(path_info_));
-    return ret;
-  }
-
-  // Returns true if parsing was successful.
-  bool isValid() const { return valid_; };
-  bool isIgnored() const { return ignored_; };
-  uint32_t getSamplingExponent() const { return sampling_exponent_; };
-
-private:
-  DynatraceTag(bool valid, bool ignored, uint32_t sampling_exponent, uint32_t path_info)
-      : valid_(valid), ignored_(ignored), sampling_exponent_(sampling_exponent),
-        path_info_(path_info) {}
-
-  bool valid_;
-  bool ignored_;
-  uint32_t sampling_exponent_;
-  uint32_t path_info_;
-};
-
 // add Dynatrace specific span attributes
 void addSamplingAttributes(uint32_t sampling_exponent, OtelAttributes& attributes) {
 

source/extensions/tracers/opentelemetry/samplers/dynatrace/dynatrace_tag.h

@@ -0,0 +1,85 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "absl/strings/numbers.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_split.h"
+#include "absl/strings/string_view.h"
+
+namespace Envoy {
+namespace Extensions {
+namespace Tracers {
+namespace OpenTelemetry {
+
+/**
+ * @brief Helper for creating and reading the Dynatrace tag in the tracestate http header
+ * This tag has at least 8 values delimited by semicolon:
+ * - tag[0]: version (currently version 4)
+ * - tag[1] - tag[4]: unused in the sampler (always 0)
+ * - tag[5]: ignored field. 1 if a span is ignored (not sampled), 0 otherwise
+ * - tag[6]: sampling exponent
+ * - tag[7]: path info
+ */
+class DynatraceTag {
+public:
+  static DynatraceTag createInvalid() { return {false, false, 0, 0}; }
+
+  // Creates a tag using the given values.
+  static DynatraceTag create(bool ignored, uint32_t sampling_exponent, uint32_t path_info) {
+    return {true, ignored, sampling_exponent, path_info};
+  }
+
+  // Creates a DynatraceTag from the value in the tracestate
+  static DynatraceTag create(const std::string& value) {
+    std::vector<absl::string_view> tracestate_components =
+        absl::StrSplit(value, ';', absl::AllowEmpty());
+    if (tracestate_components.size() < 8) {
+      return createInvalid();
+    }
+
+    if (tracestate_components[0] != "fw4") {
+      return createInvalid();
+    }
+    bool ignored = tracestate_components[5] == "1";
+    uint32_t sampling_exponent;
+    uint32_t path_info;
+    if (absl::SimpleAtoi(tracestate_components[6], &sampling_exponent) &&
+        absl::SimpleHexAtoi(tracestate_components[7], &path_info)) {
+      return {true, ignored, sampling_exponent, path_info};
+    }
+    return createInvalid();
+  }
+
+  // Returns a DynatraceTag as string.
+  std::string asString() const {
+    std::string ret = absl::StrCat("fw4;0;0;0;0;", ignored_ ? "1" : "0", ";", sampling_exponent_,
+                                   ";", absl::Hex(path_info_));
+    return ret;
+  }
+
+  // Returns true if parsing was successful.
+  bool isValid() const { return valid_; };
+
+  // Returns true if the ignored flag is set.
+  bool isIgnored() const { return ignored_; };
+
+  // Returns the sampling exponent.
+  uint32_t getSamplingExponent() const { return sampling_exponent_; };
+
+private:
+  DynatraceTag(bool valid, bool ignored, uint32_t sampling_exponent, uint32_t path_info)
+      : valid_(valid), ignored_(ignored), sampling_exponent_(sampling_exponent),
+        path_info_(path_info) {}
+
+  const bool valid_;
+  const bool ignored_;
+  const uint32_t sampling_exponent_;
+  const uint32_t path_info_;
+};
+
+} // namespace OpenTelemetry
+} // namespace Tracers
+} // namespace Extensions
+} // namespace Envoy

test/extensions/tracers/opentelemetry/samplers/dynatrace/BUILD

@@ -29,6 +29,7 @@ envoy_extension_cc_test(
     name = "dynatrace_sampler_test",
     srcs = [
         "dynatrace_sampler_test.cc",
+        "dynatrace_tag_test.cc",
         "sampler_config_provider_test.cc",
         "sampler_config_test.cc",
         "sampling_controller_test.cc",

test/extensions/tracers/opentelemetry/samplers/dynatrace/dynatrace_tag_test.cc

@@ -0,0 +1,53 @@
+#include "source/extensions/tracers/opentelemetry/samplers/dynatrace/dynatrace_tag.h"
+
+#include "gtest/gtest.h"
+
+namespace Envoy {
+namespace Extensions {
+namespace Tracers {
+namespace OpenTelemetry {
+
+class DynatraceTagTest : public ::testing::Test {};
+
+TEST(DynatraceTagTest, ValidTag) {
+  DynatraceTag new_tag = DynatraceTag::create("fw4;0;0;0;0;0;10;7b");
+
+  EXPECT_EQ(new_tag.isValid(), true);
+  EXPECT_EQ(new_tag.isIgnored(), false);
+  EXPECT_EQ(new_tag.getSamplingExponent(), 10);
+  EXPECT_EQ(new_tag.asString(), "fw4;0;0;0;0;0;10;7b");
+}
+
+TEST(DynatraceTagTest, IgnoredFieldSet) {
+  DynatraceTag new_tag = DynatraceTag::create("fw4;0;0;0;0;1;10;7b");
+
+  EXPECT_EQ(new_tag.isValid(), true);
+  EXPECT_EQ(new_tag.isIgnored(), true);
+  EXPECT_EQ(new_tag.getSamplingExponent(), 10);
+  EXPECT_EQ(new_tag.asString(), "fw4;0;0;0;0;1;10;7b");
+}
+
+class DynatraceTagInvalidTest : public ::testing::TestWithParam<std::string> {};
+
+// Verify parsing of an invalid tags
+TEST_P(DynatraceTagInvalidTest, InvalidTag) {
+  DynatraceTag new_tag = DynatraceTag::create(GetParam());
+  EXPECT_EQ(new_tag.isValid(), false);
+  EXPECT_EQ(new_tag.asString(), "fw4;0;0;0;0;0;0;0");
+}
+
+INSTANTIATE_TEST_SUITE_P(
+    InvalidTagsCase, DynatraceTagInvalidTest,
+    ::testing::Values("fw4;0;0;0;0;0;10",    // missing path info
+                      "fw4;0;0;0;0;0",       // missing sampling exponent and path info
+                      "fw4;0;0;0;0",         // missing ignored, sampling exponent and path info
+                      "fw3;0;0;0;0;0;10;7b", // invalid version
+                      "",                    // empty string
+                      "invalid_tag",         // completely invalid string
+                      "fw400;0;0;0;10;7b"    // missing delimiter between fields
+                      ));
+
+} // namespace OpenTelemetry
+} // namespace Tracers
+} // namespace Extensions
+} // namespace Envoy