fix: Circuit breaker exception handling (#971)

Author: Jonas-Isr

cloudplatform/resilience4j/src/main/java/com/sap/cloud/sdk/cloudplatform/resilience4j/DefaultCircuitBreakerProvider.java

@@ -66,7 +66,6 @@ public CircuitBreaker getCircuitBreaker( @Nonnull final ResilienceConfiguration
         return circuitBreaker;
     }
 
-    @SuppressWarnings( "PMD.PreserveStackTrace" ) // The circuit breaker stack-trace doesn't contain any info
     @Nonnull
     @Override
     public <T> Callable<T> decorateCallable(
@@ -83,9 +82,19 @@ public <T> Callable<T> decorateCallable(
                 return CircuitBreaker.decorateCallable(circuitBreaker, callable).call();
             }
             catch( CallNotPermittedException e ) {
-                log.debug("Circuit breaker '{}' is open, call not permitted.", circuitBreaker.getName());
+                val message =
+                    "CircuitBreaker '" + circuitBreaker.getName() + "' is OPEN and does not permit further calls";
+                log.debug(message);
                 val lastException = lastExceptions.get(circuitBreaker.getName());
-                throw new ResilienceRuntimeException(lastException != null ? lastException : e);
+                if( lastException == null ) {
+                    throw new ResilienceRuntimeException(message, e);
+                }
+                val resilienceRuntimeException =
+                    new ResilienceRuntimeException(
+                        message + ". Triggered by " + lastException.getMessage(),
+                        lastException);
+                resilienceRuntimeException.addSuppressed(e);
+                throw resilienceRuntimeException;
             }
         };
     }

cloudplatform/resilience4j/src/test/java/com/sap/cloud/sdk/cloudplatform/resilience4j/CircuitBreakerTest.java

@@ -2,6 +2,7 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.Assertions.catchThrowable;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
@@ -21,6 +22,7 @@
 import com.sap.cloud.sdk.cloudplatform.resilience.ResilienceRuntimeException;
 import com.sap.cloud.sdk.cloudplatform.thread.exception.ThreadContextExecutionException;
 
+import io.github.resilience4j.circuitbreaker.CallNotPermittedException;
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 
@@ -76,12 +78,22 @@ void testCircuitBreakerOpens()
         assertThat(callResults).hasSize(attemptedInvocations);
         assertThat(callResults).startsWith(attempts.toArray(new Boolean[0]));
 
-        assertThatThrownBy(wrappedCallable::call)
+        Throwable thrown = catchThrowable(wrappedCallable::call);
+
+        assertThat(thrown)
             .isExactlyInstanceOf(ResilienceRuntimeException.class)
             .hasCauseExactlyInstanceOf(ThreadContextExecutionException.class)
             .hasRootCauseExactlyInstanceOf(Exception.class)
             .hasMessage(
-                "com.sap.cloud.sdk.cloudplatform.thread.exception.ThreadContextExecutionException: java.lang.Exception: Simulated failure, attempt nr: 3");
+                "CircuitBreaker 'circuitbreaker.test.2' is OPEN and does not permit further calls. Triggered by java.lang.Exception: Simulated failure, attempt nr: 3");
+
+        assertThat(thrown.getCause()).hasMessage("java.lang.Exception: Simulated failure, attempt nr: 3");
+
+        assertThat(thrown.getSuppressed().length).isEqualTo(1);
+        Throwable suppressed = thrown.getSuppressed()[0];
+        assertThat(suppressed)
+            .isExactlyInstanceOf(CallNotPermittedException.class)
+            .hasMessage("CircuitBreaker 'circuitbreaker.test.2' is OPEN and does not permit further calls");
 
         verify(callable, times(circuitBreakerConfiguration.closedBufferSize())).call();
     }

release_notes.md

@@ -16,7 +16,7 @@
 
 ### 📈 Improvements
 
-- 
+- When the circuit breaker opens, the resulting `ResilienceRuntimeException` will have the original `CallNotPermittedException` from the circuit breaker stored as a suppressed exception. 
 
 ### 🐛 Fixed Issues