refactor: update DefaultCmabClient to use synchronous fetchDecision method with improved error handling and retry logic

Author: FarhanAnjum-opti

core-api/src/main/java/com/optimizely/ab/cmab/CmabClient.java renamed to core-api/src/main/java/com/optimizely/ab/cmab/client/CmabClient.java

@@ -13,10 +13,9 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package com.optimizely.ab.cmab;
+package com.optimizely.ab.cmab.client;
 
 import java.util.Map;
-import java.util.concurrent.CompletableFuture;
 
 public interface CmabClient {
     /**
@@ -25,8 +24,8 @@ public interface CmabClient {
      * @param ruleId     The rule/experiment ID
      * @param userId     The user ID
      * @param attributes User attributes
-     * @param cmabUuid   The CMAB UUID
+     * @param cmabUUID   The CMAB UUID
      * @return CompletableFuture containing the variation ID as a String
      */
-    CompletableFuture<String> fetchDecision(String ruleId, String userId, Map<String, Object> attributes, String cmabUuid);
+    String fetchDecision(String ruleId, String userId, Map<String, Object> attributes, String cmabUUID);
 }

core-api/src/main/java/com/optimizely/ab/cmab/CmabClientConfig.java renamed to core-api/src/main/java/com/optimizely/ab/cmab/client/CmabClientConfig.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package com.optimizely.ab.cmab;
+package com.optimizely.ab.cmab.client;
 
 import javax.annotation.Nullable;
 

core-api/src/main/java/com/optimizely/ab/cmab/client/CmabFetchException.java

@@ -0,0 +1,28 @@
+/**
+ * Copyright 2025, Optimizely
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.optimizely.ab.cmab.client;
+
+import com.optimizely.ab.OptimizelyRuntimeException;
+
+public class CmabFetchException extends OptimizelyRuntimeException {
+    public CmabFetchException(String message) {
+        super(message);
+    }
+
+    public CmabFetchException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

core-api/src/main/java/com/optimizely/ab/cmab/client/CmabInvalidResponseException.java

@@ -0,0 +1,27 @@
+/**
+ * Copyright 2025, Optimizely
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.optimizely.ab.cmab.client;
+
+import com.optimizely.ab.OptimizelyRuntimeException;
+
+public class CmabInvalidResponseException extends OptimizelyRuntimeException{
+    public CmabInvalidResponseException(String message) {
+        super(message);
+    }
+    public CmabInvalidResponseException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

core-api/src/main/java/com/optimizely/ab/cmab/RetryConfig.java renamed to core-api/src/main/java/com/optimizely/ab/cmab/client/RetryConfig.java

@@ -13,23 +13,25 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package com.optimizely.ab.cmab;
+package com.optimizely.ab.cmab.client;
 /**
  * Configuration for retry behavior in CMAB client operations.
  */
 public class RetryConfig {
     private final int maxRetries;
     private final long backoffBaseMs;
     private final double backoffMultiplier;
-
+    private final int maxTimeoutMs;
+    
     /**
      * Creates a RetryConfig with custom retry and backoff settings.
      *
      * @param maxRetries         Maximum number of retry attempts
      * @param backoffBaseMs      Base delay in milliseconds for the first retry
      * @param backoffMultiplier  Multiplier for exponential backoff (e.g., 2.0 for doubling)
+     * @param maxTimeoutMs       Maximum total timeout in milliseconds for all retry attempts
      */
-    public RetryConfig(int maxRetries, long backoffBaseMs, double backoffMultiplier) {
+    public RetryConfig(int maxRetries, long backoffBaseMs, double backoffMultiplier, int maxTimeoutMs) {
         if (maxRetries < 0) {
             throw new IllegalArgumentException("maxRetries cannot be negative");
         }
@@ -39,19 +41,23 @@ public RetryConfig(int maxRetries, long backoffBaseMs, double backoffMultiplier)
         if (backoffMultiplier < 1.0) {
             throw new IllegalArgumentException("backoffMultiplier must be >= 1.0");
         }
+        if (maxTimeoutMs < 0) {
+            throw new IllegalArgumentException("maxTimeoutMs cannot be negative");
+        }
 
         this.maxRetries = maxRetries;
         this.backoffBaseMs = backoffBaseMs;
         this.backoffMultiplier = backoffMultiplier;
+        this.maxTimeoutMs = maxTimeoutMs;
     }
 
     /**
-     * Creates a RetryConfig with default backoff settings (1 second base, 2x multiplier).
+     * Creates a RetryConfig with default backoff settings and timeout (1 second base, 2x multiplier, 10 second timeout).
      *
      * @param maxRetries Maximum number of retry attempts
      */
     public RetryConfig(int maxRetries) {
-        this(maxRetries, 1000, 2.0); // Default: 1 second base, exponential backoff
+        this(maxRetries, 1000, 2.0, 10000); // Default: 1 second base, exponential backoff, 10 second timeout
     }
 
     /**
@@ -65,7 +71,7 @@ public static RetryConfig defaultConfig() {
      * Creates a RetryConfig with no retries (single attempt only).
      */
     public static RetryConfig noRetry() {
-        return new RetryConfig(0);
+        return new RetryConfig(0, 0, 1.0, 0);
     }
 
     public int getMaxRetries() {
@@ -80,6 +86,10 @@ public double getBackoffMultiplier() {
         return backoffMultiplier;
     }
 
+    public int getMaxTimeoutMs() {
+        return maxTimeoutMs;
+    }
+
     /**
      * Calculates the delay for a specific retry attempt.
      *
@@ -95,8 +105,8 @@ public long calculateDelay(int attemptNumber) {
 
     @Override
     public String toString() {
-        return String.format("RetryConfig{maxRetries=%d, backoffBaseMs=%d, backoffMultiplier=%.1f}",
-            maxRetries, backoffBaseMs, backoffMultiplier);
+        return String.format("RetryConfig{maxRetries=%d, backoffBaseMs=%d, backoffMultiplier=%.1f, maxTimeoutMs=%d}",
+            maxRetries, backoffBaseMs, backoffMultiplier, maxTimeoutMs);
     }
 
     @Override
@@ -107,6 +117,7 @@ public boolean equals(Object obj) {
         RetryConfig that = (RetryConfig) obj;
         return maxRetries == that.maxRetries &&
             backoffBaseMs == that.backoffBaseMs &&
+            maxTimeoutMs == that.maxTimeoutMs &&
             Double.compare(that.backoffMultiplier, backoffMultiplier) == 0;
     }
 
@@ -115,6 +126,7 @@ public int hashCode() {
         int result = maxRetries;
         result = 31 * result + Long.hashCode(backoffBaseMs);
         result = 31 * result + Double.hashCode(backoffMultiplier);
+        result = 31 * result + Integer.hashCode(maxTimeoutMs);
         return result;
     }
 }