demo: changing error hook api to contain object

This is a fast demo of open-feature/spec#326

As errors in the flag evaluation do not have to be exceptions,
this opens up improvements for flow control via error codes
from the EvaluationDetails.

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

Author: aepfli

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

@@ -0,0 +1,61 @@
+package dev.openfeature.sdk;
+
+import dev.openfeature.sdk.exceptions.OpenFeatureError;
+import lombok.Builder;
+import lombok.Value;
+
+/**
+ * Represents details about an error that occurred during a flag evaluation or other operations.
+ * This class captures the exception, evaluation details, error code, and an error message.
+ *
+ * @param <T> The type of the value being evaluated in the {@link FlagEvaluationDetails}.
+ */
+@Value
+@Builder
+public class ErrorDetails<T> {
+    Exception error;
+    FlagEvaluationDetails<T> details;
+    ErrorCode errorCode;
+    String errorMessage;
+
+    /**
+     * Creates an {@code ErrorDetails} instance from the given {@link FlagEvaluationDetails}.
+     * This method extracts the error message and error code from the provided details.
+     *
+     * @param details The {@link FlagEvaluationDetails} object containing flag evaluation information.
+     * @param <T>     The type of the value being evaluated in the {@link FlagEvaluationDetails}.
+     * @return An {@code ErrorDetails} object populated with the provided evaluation details.
+     */
+    public static <T> ErrorDetails<T> from(FlagEvaluationDetails<T> details) {
+        return ErrorDetails.<T>builder()
+                .details(details)
+                .errorMessage(details.getErrorMessage())
+                .errorCode(details.getErrorCode())
+                .build();
+    }
+
+    /**
+     * Creates an {@code ErrorDetails} instance from the given exception and {@link FlagEvaluationDetails}.
+     * If the exception is an instance of {@link OpenFeatureError}, its error code is extracted
+     * and set in the {@link FlagEvaluationDetails}. Otherwise, a general error code is used.
+     * The exception's message is also set as the error message.
+     *
+     * @param exception The exception that occurred during the operation.
+     * @param details   The {@link FlagEvaluationDetails} object containing flag evaluation information.
+     * @param <T>       The type of the value being evaluated in the {@link FlagEvaluationDetails}.
+     * @return An {@code ErrorDetails} object populated with the exception and evaluation details.
+     */
+    public static <T> ErrorDetails<T> from(Exception exception, FlagEvaluationDetails<T> details) {
+        if (exception instanceof OpenFeatureError) {
+            details.setErrorCode(((OpenFeatureError) exception).getErrorCode());
+        } else {
+            details.setErrorCode(ErrorCode.GENERAL);
+        }
+        details.setErrorMessage(exception.getMessage());
+        return ErrorDetails.<T>builder()
+                .error(exception)
+                .errorMessage(exception.getMessage())
+                .errorCode(details.getErrorCode())
+                .build();
+    }
+}

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

@@ -1,5 +1,6 @@
 package dev.openfeature.sdk;
 
+import dev.openfeature.sdk.exceptions.ExceptionUtils;
 import java.util.Map;
 import java.util.Optional;
 
@@ -35,9 +36,22 @@ default void after(HookContext<T> ctx, FlagEvaluationDetails<T> details, Map<Str
      * Run when evaluation encounters an error. This will always run. Errors thrown will be swallowed.
      *
      * @param ctx   Information about the particular flag evaluation
-     * @param error The exception that was thrown.
+     * @param error The error details might contain an exception that was thrown.
      * @param hints An immutable mapping of data for users to communicate to the hooks.
      */
+    default void error(HookContext<T> ctx, ErrorDetails<T> error, Map<String, Object> hints) {
+        error(ctx, ExceptionUtils.instantiateErrorByErrorCode(error.getErrorCode(), error.getErrorMessage()), hints);
+    }
+
+    /**
+     * Run when evaluation encounters an error. This will always run. Errors thrown will be swallowed.
+     *
+     * @param ctx   Information about the particular flag evaluation
+     * @param error The exception that was thrown or instantiated.
+     * @param hints An immutable mapping of data for users to communicate to the hooks.
+     * @deprecated Please use ErrorDetails instead of Exceptions.
+     */
+    @Deprecated
     default void error(HookContext<T> ctx, Exception error, Map<String, Object> hints) {}
 
     /**

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

@@ -40,7 +40,7 @@ public void afterAllHooks(
     public void errorHooks(
             FlagValueType flagValueType,
             HookContext hookCtx,
-            Exception e,
+            ErrorDetails e,
             List<Hook> hooks,
             Map<String, Object> hints) {
         executeHooks(flagValueType, hooks, "error", hook -> hook.error(hookCtx, e, hints));

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

@@ -1,9 +1,7 @@
 package dev.openfeature.sdk;
 
-import dev.openfeature.sdk.exceptions.ExceptionUtils;
 import dev.openfeature.sdk.exceptions.FatalError;
 import dev.openfeature.sdk.exceptions.GeneralError;
-import dev.openfeature.sdk.exceptions.OpenFeatureError;
 import dev.openfeature.sdk.exceptions.ProviderNotReadyError;
 import dev.openfeature.sdk.internal.ObjectUtils;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
@@ -204,9 +202,8 @@ private <T> FlagEvaluationDetails<T> evaluateFlag(
 
             details = FlagEvaluationDetails.from(providerEval, key);
             if (details.getErrorCode() != null) {
-                var error =
-                        ExceptionUtils.instantiateErrorByErrorCode(details.getErrorCode(), details.getErrorMessage());
                 enrichDetailsWithErrorDefaults(defaultValue, details);
+                ErrorDetails error = ErrorDetails.from(details);
                 hookSupport.errorHooks(type, afterHookContext, error, mergedHooks, hints);
             } else {
                 hookSupport.afterHooks(type, afterHookContext, details, mergedHooks, hints);
@@ -215,14 +212,9 @@ private <T> FlagEvaluationDetails<T> evaluateFlag(
             if (details == null) {
                 details = FlagEvaluationDetails.<T>builder().flagKey(key).build();
             }
-            if (e instanceof OpenFeatureError) {
-                details.setErrorCode(((OpenFeatureError) e).getErrorCode());
-            } else {
-                details.setErrorCode(ErrorCode.GENERAL);
-            }
-            details.setErrorMessage(e.getMessage());
             enrichDetailsWithErrorDefaults(defaultValue, details);
-            hookSupport.errorHooks(type, afterHookContext, e, mergedHooks, hints);
+            ErrorDetails error = ErrorDetails.from(e, details);
+            hookSupport.errorHooks(type, afterHookContext, error, mergedHooks, hints);
         } finally {
             hookSupport.afterAllHooks(type, afterHookContext, details, mergedHooks, hints);
         }

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

@@ -4,7 +4,6 @@
 import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.assertj.core.api.Assertions.fail;
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
@@ -16,7 +15,6 @@
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
-import dev.openfeature.sdk.exceptions.FlagNotFoundError;
 import dev.openfeature.sdk.fixtures.HookFixtures;
 import dev.openfeature.sdk.testutils.TestEventsProvider;
 import java.util.ArrayList;
@@ -200,7 +198,7 @@ void error_hook_run_during_non_finally_stage() {
         Hook h = mockBooleanHook();
         doThrow(RuntimeException.class).when(h).finallyAfter(any(), any(), any());
 
-        verify(h, times(0)).error(any(), any(), any());
+        verify(h, times(0)).error(any(), any(Exception.class), any());
     }
 
     @Test
@@ -225,16 +223,16 @@ void error_hook_must_run_if_resolution_details_returns_an_error_code() {
                 invocationCtx,
                 FlagEvaluationOptions.builder().hook(hook).build());
 
-        ArgumentCaptor<Exception> captor = ArgumentCaptor.forClass(Exception.class);
+        ArgumentCaptor<ErrorDetails> captor = ArgumentCaptor.forClass(ErrorDetails.class);
 
         verify(hook, times(1)).before(any(), any());
         verify(hook, times(1)).error(any(), captor.capture(), any());
         verify(hook, times(1)).finallyAfter(any(), any(), any());
         verify(hook, never()).after(any(), any(), any());
 
-        Exception exception = captor.getValue();
-        assertEquals(errorMessage, exception.getMessage());
-        assertInstanceOf(FlagNotFoundError.class, exception);
+        ErrorDetails errorDetails = captor.getValue();
+        assertEquals(errorMessage, errorDetails.getErrorMessage());
+        assertEquals(ErrorCode.FLAG_NOT_FOUND, errorDetails.getErrorCode());
     }
 
     @Specification(
@@ -279,7 +277,8 @@ public void after(
                     }
 
                     @Override
-                    public void error(HookContext<Boolean> ctx, Exception error, Map<String, Object> hints) {
+                    public void error(
+                            HookContext<Boolean> ctx, ErrorDetails<Boolean> error, Map<String, Object> hints) {
                         evalOrder.add("provider error");
                     }
 
@@ -308,7 +307,7 @@ public void after(
             }
 
             @Override
-            public void error(HookContext<Boolean> ctx, Exception error, Map<String, Object> hints) {
+            public void error(HookContext<Boolean> ctx, ErrorDetails<Boolean> error, Map<String, Object> hints) {
                 evalOrder.add("api error");
             }
 
@@ -334,7 +333,7 @@ public void after(
             }
 
             @Override
-            public void error(HookContext<Boolean> ctx, Exception error, Map<String, Object> hints) {
+            public void error(HookContext<Boolean> ctx, ErrorDetails<Boolean> error, Map<String, Object> hints) {
                 evalOrder.add("client error");
             }
 
@@ -367,7 +366,8 @@ public void after(
                             }
 
                             @Override
-                            public void error(HookContext<Boolean> ctx, Exception error, Map<String, Object> hints) {
+                            public void error(
+                                    HookContext<Boolean> ctx, ErrorDetails<Boolean> error, Map<String, Object> hints) {
                                 evalOrder.add("invocation error");
                             }
 
@@ -546,7 +546,7 @@ void error_hooks__before() {
                 new ImmutableContext(),
                 FlagEvaluationOptions.builder().hook(hook).build());
         verify(hook, times(1)).before(any(), any());
-        verify(hook, times(1)).error(any(), any(), any());
+        verify(hook, times(1)).error(any(), any(ErrorDetails.class), any());
         assertEquals(false, value, "Falls through to the default.");
     }
 
@@ -564,7 +564,7 @@ void error_hooks__after() {
                 new ImmutableContext(),
                 FlagEvaluationOptions.builder().hook(hook).build());
         verify(hook, times(1)).after(any(), any(), any());
-        verify(hook, times(1)).error(any(), any(), any());
+        verify(hook, times(1)).error(any(), any(ErrorDetails.class), any());
     }
 
     @Test
@@ -609,7 +609,7 @@ void shortCircuit_flagResolution_runsHooksWithAllFields() {
                 FlagEvaluationOptions.builder().hook(hook).build());
 
         verify(hook).before(any(), any());
-        verify(hook).error(any(HookContext.class), any(Exception.class), any(Map.class));
+        verify(hook).error(any(HookContext.class), any(ErrorDetails.class), any(Map.class));
         verify(hook).finallyAfter(any(HookContext.class), any(FlagEvaluationDetails.class), any(Map.class));
     }
 
@@ -655,8 +655,8 @@ void multi_hooks_early_out__before() {
         verify(hook, times(1)).before(any(), any());
         verify(hook2, times(0)).before(any(), any());
 
-        verify(hook, times(1)).error(any(), any(), any());
-        verify(hook2, times(1)).error(any(), any(), any());
+        verify(hook, times(1)).error(any(), any(ErrorDetails.class), any());
+        verify(hook2, times(1)).error(any(), any(ErrorDetails.class), any());
     }
 
     @Specification(number = "4.1.4", text = "The evaluation context MUST be mutable only within the before hook.")
@@ -760,7 +760,7 @@ void first_finally_broken() {
     void first_error_broken() {
         Hook hook = mockBooleanHook();
         doThrow(RuntimeException.class).when(hook).before(any(), any());
-        doThrow(RuntimeException.class).when(hook).error(any(), any(), any());
+        doThrow(RuntimeException.class).when(hook).error(any(), any(Exception.class), any());
         Hook hook2 = mockBooleanHook();
         InOrder order = inOrder(hook, hook2);
 
@@ -772,8 +772,8 @@ void first_error_broken() {
                 FlagEvaluationOptions.builder().hook(hook2).hook(hook).build());
 
         order.verify(hook).before(any(), any());
-        order.verify(hook2).error(any(), any(), any());
-        order.verify(hook).error(any(), any(), any());
+        order.verify(hook2).error(any(), any(ErrorDetails.class), any());
+        order.verify(hook).error(any(), any(ErrorDetails.class), any());
     }
 
     private Client getClient(FeatureProvider provider) {

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

@@ -55,31 +55,22 @@ void shouldAlwaysCallGenericHook(FlagValueType flagValueType) {
                 () -> "client",
                 () -> "provider");
 
+        FlagEvaluationDetails<Object> details = FlagEvaluationDetails.builder().build();
+        ErrorDetails<Object> error = ErrorDetails.from(expectedException, details);
+
         hookSupport.beforeHooks(
                 flagValueType, hookContext, Collections.singletonList(genericHook), Collections.emptyMap());
         hookSupport.afterHooks(
-                flagValueType,
-                hookContext,
-                FlagEvaluationDetails.builder().build(),
-                Collections.singletonList(genericHook),
-                Collections.emptyMap());
+                flagValueType, hookContext, details, Collections.singletonList(genericHook), Collections.emptyMap());
         hookSupport.afterAllHooks(
-                flagValueType,
-                hookContext,
-                FlagEvaluationDetails.builder().build(),
-                Collections.singletonList(genericHook),
-                Collections.emptyMap());
+                flagValueType, hookContext, details, Collections.singletonList(genericHook), Collections.emptyMap());
         hookSupport.errorHooks(
-                flagValueType,
-                hookContext,
-                expectedException,
-                Collections.singletonList(genericHook),
-                Collections.emptyMap());
+                flagValueType, hookContext, error, Collections.singletonList(genericHook), Collections.emptyMap());
 
         verify(genericHook).before(any(), any());
         verify(genericHook).after(any(), any(), any());
         verify(genericHook).finallyAfter(any(), any(), any());
-        verify(genericHook).error(any(), any(), any());
+        verify(genericHook).error(any(), any(ErrorDetails.class), any());
     }
 
     private Object createDefaultValue(FlagValueType flagValueType) {