Always on sampler (#122)

sdk/include/opentelemetry/sdk/trace/sampler.h

@@ -17,7 +17,7 @@ namespace trace
 namespace trace_api = opentelemetry::trace;
 
 /**
- * A sampling Decision for a Span to be created.  
+ * A sampling Decision for a Span to be created.
  */
 enum class Decision
 {
@@ -31,7 +31,7 @@ enum class Decision
 };
 
 /**
- * The output of ShouldSample. 
+ * The output of ShouldSample.
  * It contains a sampling Decision and a set of Span Attributes.
  */
 struct SamplingResult

sdk/include/opentelemetry/sdk/trace/samplers/always_on.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include "opentelemetry/sdk/trace/sampler.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace sdk
+{
+namespace trace
+{
+namespace trace_api = opentelemetry::trace;
+/**
+ * The always on sampler is a default sampler which always return Decision::RECORD_AND_SAMPLE
+ */
+class AlwaysOnSampler : public Sampler
+{
+public:
+  /**
+   * @return Always return Decision RECORD_AND_SAMPLE
+   */
+  inline SamplingResult ShouldSample(const SpanContext * /*parent_context*/,
+                              trace_api::TraceId /*trace_id*/,
+                              nostd::string_view /*name*/,
+                              trace_api::SpanKind /*span_kind*/,
+                              const trace_api::KeyValueIterable & /*attributes*/) noexcept override
+  {
+    return {Decision::RECORD_AND_SAMPLE, nullptr};
+  }
+
+  /**
+   * @return Description MUST be AlwaysOnSampler
+   */
+  inline std::string GetDescription() const noexcept override { return "AlwaysOnSampler"; }
+};
+}  // namespace trace
+}  // namespace sdk
+OPENTELEMETRY_END_NAMESPACE

sdk/test/trace/BUILD

@@ -43,12 +43,25 @@ cc_test(
 )
 
 cc_test(
-    name = "always_off_sampler_test",
+    name = "always_on_sampler_test",
     srcs = [
-        "always_off_sampler_test.cc"
+        "always_on_sampler_test.cc",
     ],
     deps = [
         "//sdk/src/trace",
         "@com_google_googletest//:gtest_main",
-    ]
+    ],
 )
+
+
+
+cc_test(
+    name = "always_off_sampler_test",
+    srcs = [
+        "always_off_sampler_test.cc",
+    ],
+    deps = [
+        "//sdk/src/trace",
+        "@com_google_googletest//:gtest_main",
+    ],
+)

sdk/test/trace/CMakeLists.txt

@@ -1,5 +1,5 @@
 foreach(testname tracer_provider_test span_data_test simple_processor_test
-                 tracer_test always_off_sampler_test)
+                 tracer_test always_off_sampler_test always_on_sampler_test)
   add_executable(${testname} "${testname}.cc")
   target_link_libraries(${testname} ${GTEST_BOTH_LIBRARIES}
                         ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace)

sdk/test/trace/always_on_sampler_test.cc

@@ -0,0 +1,43 @@
+#include "opentelemetry/nostd/span.h"
+#include "opentelemetry/sdk/trace/samplers/always_on.h"
+
+#include <gtest/gtest.h>
+#include <map>
+
+using namespace opentelemetry::sdk::trace;
+using namespace opentelemetry::nostd;
+
+TEST(AlwaysOnSampler, ShouldSample)
+{
+  AlwaysOnSampler sampler;
+
+  // A buffer of trace_id with no specific meaning
+  constexpr uint8_t buf[] = {0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7};
+
+  trace_api::TraceId trace_id_invalid;
+  trace_api::TraceId trace_id_valid(buf);
+  std::map<std::string, int> key_value_container = {{"key", 0}};
+
+  // Test with invalid (empty) trace id and empty parent context
+  auto sampling_result = sampler.ShouldSample(
+      nullptr, trace_id_invalid, "invalid trace id test", trace_api::SpanKind::kServer,
+      trace_api::KeyValueIterableView<std::map<std::string, int>>(key_value_container));
+
+  ASSERT_EQ(Decision::RECORD_AND_SAMPLE, sampling_result.decision);
+  ASSERT_EQ(nullptr, sampling_result.attributes);
+
+  // Test with a valid trace id and empty parent context
+  sampling_result = sampler.ShouldSample(
+      nullptr, trace_id_valid, "valid trace id test", trace_api::SpanKind::kServer,
+      trace_api::KeyValueIterableView<std::map<std::string, int>>(key_value_container));
+
+  ASSERT_EQ(Decision::RECORD_AND_SAMPLE, sampling_result.decision);
+  ASSERT_EQ(nullptr, sampling_result.attributes);
+}
+
+TEST(AlwaysOnSampler, GetDescription)
+{
+  AlwaysOnSampler sampler;
+
+  ASSERT_EQ("AlwaysOnSampler", sampler.GetDescription());
+}