[FSSDK-11143] update: Implement CMAB Client (#579)

* Cmab datafile parsed

* Add CMAB configuration and parsing tests with cmab datafile

* Add copyright notice to CmabTest and CmabParsingTest files

* Refactor cmab parsing logic to simplify null check in JsonConfigParser

* update: implement remove method in DefaultLRUCache for cache entry removal

* add: implement remove method tests in DefaultLRUCacheTest for various scenarios

* refactor: remove unused methods from Cache interface

* update: add reset method to Cache interface

* add: implement CmabClient, CmabClientConfig, and RetryConfig with fetchDecision method and retry logic

* update: improve error logging in DefaultCmabClient for fetchDecision method

* add: implement unit tests for DefaultCmabClient with various scenarios and error handling

* update: add missing license header to DefaultCmabClient.java

* update: add missing license headers to CmabClient, CmabClientConfig, and RetryConfig classes

* 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/client/CmabClient.java

@@ -0,0 +1,31 @@
+/**
+ * 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 java.util.Map;
+
+public interface CmabClient {
+    /**
+     * Fetches a decision from the CMAB prediction service.
+     *
+     * @param ruleId     The rule/experiment ID
+     * @param userId     The user ID
+     * @param attributes User attributes
+     * @param cmabUUID   The CMAB UUID
+     * @return CompletableFuture containing the variation ID as a String
+     */
+    String fetchDecision(String ruleId, String userId, Map<String, Object> attributes, String cmabUUID);
+}

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

@@ -0,0 +1,49 @@
+/**
+ * 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 javax.annotation.Nullable;
+
+/**
+ * Configuration for CMAB client operations.
+ * Contains only retry configuration since HTTP client is handled separately.
+ */
+public class CmabClientConfig {
+    private final RetryConfig retryConfig;
+
+    public CmabClientConfig(@Nullable RetryConfig retryConfig) {
+        this.retryConfig = retryConfig;
+    }
+
+    @Nullable
+    public RetryConfig getRetryConfig() {
+        return retryConfig;
+    }
+
+    /**
+     * Creates a config with default retry settings.
+     */
+    public static CmabClientConfig withDefaultRetry() {
+        return new CmabClientConfig(RetryConfig.defaultConfig());
+    }
+
+    /**
+     * Creates a config with no retry.
+     */
+    public static CmabClientConfig withNoRetry() {
+        return new CmabClientConfig(null);
+    }
+}

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/client/RetryConfig.java

@@ -0,0 +1,132 @@
+/**
+ * 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;
+/**
+ * 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, int maxTimeoutMs) {
+        if (maxRetries < 0) {
+            throw new IllegalArgumentException("maxRetries cannot be negative");
+        }
+        if (backoffBaseMs < 0) {
+            throw new IllegalArgumentException("backoffBaseMs cannot be negative");
+        }
+        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 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, 10000); // Default: 1 second base, exponential backoff, 10 second timeout
+    }
+
+    /**
+     * Creates a default RetryConfig with 3 retries and exponential backoff.
+     */
+    public static RetryConfig defaultConfig() {
+        return new RetryConfig(3);
+    }
+
+    /**
+     * Creates a RetryConfig with no retries (single attempt only).
+     */
+    public static RetryConfig noRetry() {
+        return new RetryConfig(0, 0, 1.0, 0);
+    }
+
+    public int getMaxRetries() {
+        return maxRetries;
+    }
+
+    public long getBackoffBaseMs() {
+        return backoffBaseMs;
+    }
+
+    public double getBackoffMultiplier() {
+        return backoffMultiplier;
+    }
+
+    public int getMaxTimeoutMs() {
+        return maxTimeoutMs;
+    }
+
+    /**
+     * Calculates the delay for a specific retry attempt.
+     *
+     * @param attemptNumber The attempt number (0-based, so 0 = first retry)
+     * @return Delay in milliseconds
+     */
+    public long calculateDelay(int attemptNumber) {
+        if (attemptNumber < 0) {
+            return 0;
+        }
+        return (long) (backoffBaseMs * Math.pow(backoffMultiplier, attemptNumber));
+    }
+
+    @Override
+    public String toString() {
+        return String.format("RetryConfig{maxRetries=%d, backoffBaseMs=%d, backoffMultiplier=%.1f, maxTimeoutMs=%d}",
+            maxRetries, backoffBaseMs, backoffMultiplier, maxTimeoutMs);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null || getClass() != obj.getClass()) return false;
+
+        RetryConfig that = (RetryConfig) obj;
+        return maxRetries == that.maxRetries &&
+            backoffBaseMs == that.backoffBaseMs &&
+            maxTimeoutMs == that.maxTimeoutMs &&
+            Double.compare(that.backoffMultiplier, backoffMultiplier) == 0;
+    }
+
+    @Override
+    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;
+    }
+}