[FSSDK-11148] update: Implement CMAB Client (#453)

FarhanAnjum-opti · web-flow · commit 046d457efce0 · 2025-05-23T08:35:24.000+06:00
* Implement CMAB client with retry logic for fetching predictions

* Enhance CMAB client error handling and logging; add unit tests for fetch methods

* Refactor CMAB client: enhance docstrings for classes and methods, improve formatting, and clean up imports

* Add custom exceptions for CMAB client errors and enhance error handling in fetch methods

* Update fetch_decision method to set default timeout value to 10 seconds

* replace constant endpoint with formatted string in fetch_decision method

* chore: trigger CI

* refactor: streamline fetch_decision method and enhance test cases for improved clarity and functionality
diff --git a/optimizely/cmab/cmab_client.py b/optimizely/cmab/cmab_client.py
@@ -0,0 +1,193 @@
+# 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
+#
+# http://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.
+import json
+import time
+import requests
+import math
+from typing import Dict, Any, Optional
+from optimizely import logger as _logging
+from optimizely.helpers.enums import Errors
+from optimizely.exceptions import CmabFetchError, CmabInvalidResponseError
+
+# Default constants for CMAB requests
+DEFAULT_MAX_RETRIES = 3
+DEFAULT_INITIAL_BACKOFF = 0.1  # in seconds (100 ms)
+DEFAULT_MAX_BACKOFF = 10  # in seconds
+DEFAULT_BACKOFF_MULTIPLIER = 2.0
+MAX_WAIT_TIME = 10.0
+
+
+class CmabRetryConfig:
+    """Configuration for retrying CMAB requests.
+
+    Contains parameters for maximum retries, backoff intervals, and multipliers.
+    """
+    def __init__(
+        self,
+        max_retries: int = DEFAULT_MAX_RETRIES,
+        initial_backoff: float = DEFAULT_INITIAL_BACKOFF,
+        max_backoff: float = DEFAULT_MAX_BACKOFF,
+        backoff_multiplier: float = DEFAULT_BACKOFF_MULTIPLIER,
+    ):
+        self.max_retries = max_retries
+        self.initial_backoff = initial_backoff
+        self.max_backoff = max_backoff
+        self.backoff_multiplier = backoff_multiplier
+
+
+class DefaultCmabClient:
+    """Client for interacting with the CMAB service.
+
+    Provides methods to fetch decisions with optional retry logic.
+    """
+    def __init__(self, http_client: Optional[requests.Session] = None,
+                 retry_config: Optional[CmabRetryConfig] = None,
+                 logger: Optional[_logging.Logger] = None):
+        """Initialize the CMAB client.
+
+        Args:
+            http_client (Optional[requests.Session]): HTTP client for making requests.
+            retry_config (Optional[CmabRetryConfig]): Configuration for retry logic.
+            logger (Optional[_logging.Logger]): Logger for logging messages.
+        """
+        self.http_client = http_client or requests.Session()
+        self.retry_config = retry_config
+        self.logger = _logging.adapt_logger(logger or _logging.NoOpLogger())
+
+    def fetch_decision(
+        self,
+        rule_id: str,
+        user_id: str,
+        attributes: Dict[str, Any],
+        cmab_uuid: str,
+        timeout: float = MAX_WAIT_TIME
+    ) -> str:
+        """Fetch a decision from the CMAB prediction service.
+
+        Args:
+            rule_id (str): The rule ID for the experiment.
+            user_id (str): The user ID for the request.
+            attributes (Dict[str, Any]): User attributes for the request.
+            cmab_uuid (str): Unique identifier for the CMAB request.
+            timeout (float): Maximum wait time for request to respond in seconds. Defaults to 10 seconds.
+
+        Returns:
+            str: The variation ID.
+        """
+        url = f"https://prediction.cmab.optimizely.com/predict/{rule_id}"
+        cmab_attributes = [
+            {"id": key, "value": value, "type": "custom_attribute"}
+            for key, value in attributes.items()
+        ]
+
+        request_body = {
+            "instances": [{
+                "visitorId": user_id,
+                "experimentId": rule_id,
+                "attributes": cmab_attributes,
+                "cmabUUID": cmab_uuid,
+            }]
+        }
+        if self.retry_config:
+            variation_id = self._do_fetch_with_retry(url, request_body, self.retry_config, timeout)
+        else:
+            variation_id = self._do_fetch(url, request_body, timeout)
+        return variation_id
+
+    def _do_fetch(self, url: str, request_body: Dict[str, Any], timeout: float) -> str:
+        """Perform a single fetch request to the CMAB prediction service.
+
+        Args:
+            url (str): The endpoint URL.
+            request_body (Dict[str, Any]): The request payload.
+            timeout (float): Maximum wait time for request to respond in seconds.
+        Returns:
+            str: The variation ID
+        """
+        headers = {'Content-Type': 'application/json'}
+        try:
+            response = self.http_client.post(url, data=json.dumps(request_body), headers=headers, timeout=timeout)
+        except requests.exceptions.RequestException as e:
+            error_message = Errors.CMAB_FETCH_FAILED.format(str(e))
+            self.logger.error(error_message)
+            raise CmabFetchError(error_message)
+
+        if not 200 <= response.status_code < 300:
+            error_message = Errors.CMAB_FETCH_FAILED.format(str(response.status_code))
+            self.logger.error(error_message)
+            raise CmabFetchError(error_message)
+
+        try:
+            body = response.json()
+        except json.JSONDecodeError:
+            error_message = Errors.INVALID_CMAB_FETCH_RESPONSE
+            self.logger.error(error_message)
+            raise CmabInvalidResponseError(error_message)
+
+        if not self.validate_response(body):
+            error_message = Errors.INVALID_CMAB_FETCH_RESPONSE
+            self.logger.error(error_message)
+            raise CmabInvalidResponseError(error_message)
+
+        return str(body['predictions'][0]['variation_id'])
+
+    def validate_response(self, body: Dict[str, Any]) -> bool:
+        """Validate the response structure from the CMAB service.
+
+        Args:
+            body (Dict[str, Any]): The response body to validate.
+
+        Returns:
+            bool: True if the response is valid, False otherwise.
+        """
+        return (
+            isinstance(body, dict) and
+            'predictions' in body and
+            isinstance(body['predictions'], list) and
+            len(body['predictions']) > 0 and
+            isinstance(body['predictions'][0], dict) and
+            "variation_id" in body["predictions"][0]
+        )
+
+    def _do_fetch_with_retry(
+        self,
+        url: str,
+        request_body: Dict[str, Any],
+        retry_config: CmabRetryConfig,
+        timeout: float
+    ) -> str:
+        """Perform a fetch request with retry logic.
+
+        Args:
+            url (str): The endpoint URL.
+            request_body (Dict[str, Any]): The request payload.
+            retry_config (CmabRetryConfig): Configuration for retry logic.
+            timeout (float): Maximum wait time for request to respond in seconds.
+        Returns:
+            str: The variation ID
+        """
+        backoff = retry_config.initial_backoff
+        for attempt in range(retry_config.max_retries + 1):
+            try:
+                variation_id = self._do_fetch(url, request_body, timeout)
+                return variation_id
+            except:
+                if attempt < retry_config.max_retries:
+                    self.logger.info(f"Retrying CMAB request (attempt: {attempt + 1}) after {backoff} seconds...")
+                    time.sleep(backoff)
+                    backoff = min(backoff * math.pow(retry_config.backoff_multiplier, attempt + 1),
+                                  retry_config.max_backoff)
+
+        error_message = Errors.CMAB_FETCH_FAILED.format('Exhausted all retries for CMAB request.')
+        self.logger.error(error_message)
+        raise CmabFetchError(error_message)
diff --git a/optimizely/exceptions.py b/optimizely/exceptions.py
@@ -82,3 +82,21 @@ class OdpInvalidData(Exception):
     """ Raised when passing invalid ODP data. """
 
     pass
+
+
+class CmabError(Exception):
+    """Base exception for CMAB client errors."""
+
+    pass
+
+
+class CmabFetchError(CmabError):
+    """Exception raised when CMAB fetch fails."""
+
+    pass
+
+
+class CmabInvalidResponseError(CmabError):
+    """Exception raised when CMAB response is invalid."""
+
+    pass
diff --git a/optimizely/helpers/enums.py b/optimizely/helpers/enums.py
@@ -127,6 +127,8 @@ class Errors:
     ODP_INVALID_DATA: Final = 'ODP data is not valid.'
     ODP_INVALID_ACTION: Final = 'ODP action is not valid (cannot be empty).'
     MISSING_SDK_KEY: Final = 'SDK key not provided/cannot be found in the datafile.'
+    CMAB_FETCH_FAILED: Final = 'CMAB decision fetch failed with status: {}'
+    INVALID_CMAB_FETCH_RESPONSE = 'Invalid CMAB fetch response'
 
 
 class ForcedDecisionLogs:
diff --git a/tests/test_cmab_client.py b/tests/test_cmab_client.py
