Allowing flowcontrol with out exceptions

So far we used exception to handle our flowcontrol, but
Exceptions are costly. In the end we enriched our
evaluation Details with errorCode and errorMessage.
This can be also handled by the providers if desired,
to reduce the execution footprint in errornous cases,
which do not have to be exceptions.

Eg FlagNotFound - it might be the case, but in performance
critical environments, an exception rather than a normal
return, can cause overhead and can be already too costly.

Signed-off-by: Simon Schrottner <simon.schrottner@dynatrace.com>

Author: aepfli

src/main/java/dev/openfeature/sdk/OpenFeatureClient.java

@@ -21,7 +21,7 @@
  * You should not instantiate this or reference this class.
  * Use the dev.openfeature.sdk.Client interface instead.
  * @see Client
- * 
+ *
  * @deprecated // TODO: eventually we will make this non-public. See issue #872
  */
 @Slf4j
@@ -132,7 +132,11 @@ private <T> FlagEvaluationDetails<T> evaluateFlag(FlagValueType type, String key
 
             details = FlagEvaluationDetails.from(providerEval, key);
             if (details.getErrorCode() != null) {
-                throw ExceptionUtils.instantiateErrorByErrorCode(details.getErrorCode(), details.getErrorMessage());
+                OpenFeatureError error = ExceptionUtils.instantiateErrorByErrorCode(
+                        details.getErrorCode(),
+                        details.getErrorMessage());
+                details.setValue(defaultValue);
+                hookSupport.errorHooks(type, afterHookContext, error, mergedHooks, hints);
             } else {
                 hookSupport.afterHooks(type, afterHookContext, details, mergedHooks, hints);
             }

src/test/java/dev/openfeature/sdk/AlwaysBrokenWithDetailsProvider.java

@@ -0,0 +1,53 @@
+package dev.openfeature.sdk;
+
+import dev.openfeature.sdk.exceptions.FlagNotFoundError;
+
+public class AlwaysBrokenWithDetailsProvider implements FeatureProvider {
+
+    @Override
+    public Metadata getMetadata() {
+        return () -> {
+            throw new FlagNotFoundError(TestConstants.BROKEN_MESSAGE);
+        };
+    }
+
+    @Override
+    public ProviderEvaluation<Boolean> getBooleanEvaluation(String key, Boolean defaultValue, EvaluationContext ctx) {
+        return ProviderEvaluation.<Boolean>builder()
+                .errorMessage(TestConstants.BROKEN_MESSAGE)
+                .errorCode(ErrorCode.FLAG_NOT_FOUND)
+                .build();
+    }
+
+    @Override
+    public ProviderEvaluation<String> getStringEvaluation(String key, String defaultValue, EvaluationContext ctx) {
+        return ProviderEvaluation.<String>builder()
+                .errorMessage(TestConstants.BROKEN_MESSAGE)
+                .errorCode(ErrorCode.FLAG_NOT_FOUND)
+                .build();
+    }
+
+    @Override
+    public ProviderEvaluation<Integer> getIntegerEvaluation(String key, Integer defaultValue, EvaluationContext ctx) {
+        return ProviderEvaluation.<Integer>builder()
+                .errorMessage(TestConstants.BROKEN_MESSAGE)
+                .errorCode(ErrorCode.FLAG_NOT_FOUND)
+                .build();
+    }
+
+    @Override
+    public ProviderEvaluation<Double> getDoubleEvaluation(String key, Double defaultValue, EvaluationContext ctx) {
+        return ProviderEvaluation.<Double>builder()
+                .errorMessage(TestConstants.BROKEN_MESSAGE)
+                .errorCode(ErrorCode.FLAG_NOT_FOUND)
+                .build();
+    }
+
+    @Override
+    public ProviderEvaluation<Value> getObjectEvaluation(String key, Value defaultValue, EvaluationContext invocationContext) {
+        return ProviderEvaluation.<Value>builder()
+                .errorMessage(TestConstants.BROKEN_MESSAGE)
+                .errorCode(ErrorCode.FLAG_NOT_FOUND)
+                .build();
+    }
+}

src/test/java/dev/openfeature/sdk/FlagEvaluationSpecTest.java

@@ -259,10 +259,27 @@ public void initialize(EvaluationContext evaluationContext) throws Exception {
     @Test void broken_provider() {
         FeatureProviderTestUtils.setFeatureProvider(new AlwaysBrokenProvider());
         Client c = api.getClient();
-        assertFalse(c.getBooleanValue("key", false));
-        FlagEvaluationDetails<Boolean> details = c.getBooleanDetails("key", false);
+        boolean defaultValue = false;
+        assertFalse(c.getBooleanValue("key", defaultValue));
+        FlagEvaluationDetails<Boolean> details = c.getBooleanDetails("key", defaultValue);
         assertEquals(ErrorCode.FLAG_NOT_FOUND, details.getErrorCode());
         assertEquals(TestConstants.BROKEN_MESSAGE, details.getErrorMessage());
+        assertEquals(defaultValue, details.getValue());
+    }
+
+    @Specification(number="1.4.8", text="In cases of abnormal execution, the `evaluation details` structure's `error code` field **MUST** contain an `error code`.")
+    @Specification(number="1.4.9", text="In cases of abnormal execution (network failure, unhandled error, etc) the `reason` field in the `evaluation details` SHOULD indicate an error.")
+    @Specification(number="1.4.10", text="Methods, functions, or operations on the client MUST NOT throw exceptions, or otherwise abnormally terminate. Flag evaluation calls must always return the `default value` in the event of abnormal execution. Exceptions include functions or methods for the purposes for configuration or setup.")
+    @Specification(number="1.4.13", text="In cases of abnormal execution, the `evaluation details` structure's `error message` field **MAY** contain a string containing additional details about the nature of the error.")
+    @Test void broken_provider_withDetails() {
+        FeatureProviderTestUtils.setFeatureProvider(new AlwaysBrokenWithDetailsProvider());
+        Client c = api.getClient();
+        boolean defaultValue = false;
+        assertFalse(c.getBooleanValue("key", defaultValue));
+        FlagEvaluationDetails<Boolean> details = c.getBooleanDetails("key", defaultValue);
+        assertEquals(ErrorCode.FLAG_NOT_FOUND, details.getErrorCode());
+        assertEquals(TestConstants.BROKEN_MESSAGE, details.getErrorMessage());
+        assertEquals(defaultValue, details.getValue());
     }
 
     @Specification(number="1.4.11", text="Methods, functions, or operations on the client SHOULD NOT write log messages.")