Accept fallback defaults as a parameter in GetSpanLimitsFromEnv

Author: HrMathematiker

sdk/include/opentelemetry/sdk/trace/span_limits.h

@@ -71,13 +71,15 @@ namespace span_limits_env
  * OpenTelemetry specification
  * (https://opentelemetry.io/docs/specs/otel/configuration/sdk-environment-variables/#span-limits).
  *
- * A field whose environment variable is not set keeps its SpanLimits::NoLimits() value, so with
- * no variables set the result equals SpanLimits::NoLimits() and SDK behavior is unchanged. The
+ * A field whose environment variable is not set keeps its value from @p defaults, so with no
+ * variables set the result equals @p defaults. The default of SpanLimits::NoLimits() leaves SDK
+ * behavior unchanged; pass SpanLimits{} to fall back to the specification defaults instead. The
  * span-specific variables (OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT,
  * OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT) take precedence over the general ones
  * (OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT, OTEL_ATTRIBUTE_COUNT_LIMIT).
  */
-OPENTELEMETRY_EXPORT SpanLimits GetSpanLimitsFromEnv();
+OPENTELEMETRY_EXPORT SpanLimits
+GetSpanLimitsFromEnv(const SpanLimits &defaults = SpanLimits::NoLimits());
 
 }  // namespace span_limits_env
 

sdk/src/trace/span_limits.cc

@@ -51,9 +51,9 @@ void UpdateFromEnv(const char *env_var_name, std::size_t &limit)
 
 }  // namespace
 
-SpanLimits GetSpanLimitsFromEnv()
+SpanLimits GetSpanLimitsFromEnv(const SpanLimits &defaults)
 {
-  SpanLimits limits = SpanLimits::NoLimits();
+  SpanLimits limits = defaults;
 
   // General attribute limits first; the span-specific variables below take precedence.
   UpdateFromEnv(kAttributeValueLengthLimitEnv, limits.attribute_value_length_limit);

sdk/test/trace/tracer_provider_test.cc

@@ -628,6 +628,19 @@ TEST(TracerProvider, SpanLimitsFromEnvReadsVariables)
   UnsetSpanLimitsEnv();
 }
 
+TEST(TracerProvider, SpanLimitsFromEnvCustomFallbackDefaults)
+{
+  UnsetSpanLimitsEnv();
+  setenv("OTEL_SPAN_EVENT_COUNT_LIMIT", "42", 1);
+
+  const SpanLimits limits = span_limits_env::GetSpanLimitsFromEnv(SpanLimits{});
+  EXPECT_EQ(limits.event_count_limit, 42u);
+  EXPECT_EQ(limits.attribute_count_limit, SpanLimits::kDefaultAttributeCountLimit);
+  EXPECT_EQ(limits.link_count_limit, SpanLimits::kDefaultLinkCountLimit);
+
+  UnsetSpanLimitsEnv();
+}
+
 TEST(TracerProvider, SpanLimitsFromEnvGeneralAttributeVariablesApply)
 {
   UnsetSpanLimitsEnv();