[FSSDK-11142] Add cmab client and tests

pkg/decision/cmab_client.go

@@ -0,0 +1,255 @@
+/****************************************************************************
+ * Copyright 2025, Optimizely, Inc. and contributors                        *
+ *                                                                          *
+ * 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.                                           *
+ ***************************************************************************/
+
+// Package decision provides CMAB client implementation
+package decision
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"math"
+	"net/http"
+	"time"
+
+	"github.com/optimizely/go-sdk/v2/pkg/logging"
+)
+
+// CMABPredictionEndpoint is the endpoint for CMAB predictions
+var CMABPredictionEndpoint = "https://prediction.cmab.optimizely.com/predict/%s"
+
+const (
+	// DefaultMaxRetries is the default number of retries for CMAB requests
+	DefaultMaxRetries = 3
+	// DefaultInitialBackoff is the default initial backoff duration
+	DefaultInitialBackoff = 100 * time.Millisecond
+	// DefaultMaxBackoff is the default maximum backoff duration
+	DefaultMaxBackoff = 10 * time.Second
+	// DefaultBackoffMultiplier is the default multiplier for exponential backoff
+	DefaultBackoffMultiplier = 2.0
+)
+
+// CMABAttribute represents an attribute in a CMAB request
+type CMABAttribute struct {
+	ID    string      `json:"id"`
+	Value interface{} `json:"value"`
+	Type  string      `json:"type"`
+}
+
+// CMABInstance represents an instance in a CMAB request
+type CMABInstance struct {
+	VisitorID    string          `json:"visitorId"`
+	ExperimentID string          `json:"experimentId"`
+	Attributes   []CMABAttribute `json:"attributes"`
+	CmabUUID     string          `json:"cmabUUID"`
+}
+
+// CMABRequest represents a request to the CMAB API
+type CMABRequest struct {
+	Instances []CMABInstance `json:"instances"`
+}
+
+// CMABPrediction represents a prediction in a CMAB response
+type CMABPrediction struct {
+	VariationID string `json:"variation_id"`
+}
+
+// CMABResponse represents a response from the CMAB API
+type CMABResponse struct {
+	Predictions []CMABPrediction `json:"predictions"`
+}
+
+// RetryConfig defines configuration for retry behavior
+type RetryConfig struct {
+	// MaxRetries is the maximum number of retry attempts
+	MaxRetries int
+	// InitialBackoff is the initial backoff duration
+	InitialBackoff time.Duration
+	// MaxBackoff is the maximum backoff duration
+	MaxBackoff time.Duration
+	// BackoffMultiplier is the multiplier for exponential backoff
+	BackoffMultiplier float64
+}
+
+// DefaultCmabClient implements the CmabClient interface
+type DefaultCmabClient struct {
+	httpClient  *http.Client
+	retryConfig *RetryConfig
+	logger      logging.OptimizelyLogProducer
+}
+
+// CmabClientOptions defines options for creating a CMAB client
+type CmabClientOptions struct {
+	HTTPClient  *http.Client
+	RetryConfig *RetryConfig
+	Logger      logging.OptimizelyLogProducer
+}
+
+// NewDefaultCmabClient creates a new instance of DefaultCmabClient
+func NewDefaultCmabClient(options CmabClientOptions) *DefaultCmabClient {
+	httpClient := options.HTTPClient
+	if httpClient == nil {
+		httpClient = &http.Client{
+			Timeout: 10 * time.Second,
+		}
+	}
+
+	// retry is optional:
+	// retryConfig can be nil - in that case, no retries will be performed
+	retryConfig := options.RetryConfig
+
+	logger := options.Logger
+	if logger == nil {
+		logger = logging.GetLogger("", "DefaultCmabClient")
+	}
+
+	return &DefaultCmabClient{
+		httpClient:  httpClient,
+		retryConfig: retryConfig,
+		logger:      logger,
+	}
+}
+
+// FetchDecision fetches a decision from the CMAB API
+func (c *DefaultCmabClient) FetchDecision(
+	ruleID string,
+	userID string,
+	attributes map[string]interface{},
+	cmabUUID string,
+) (string, error) {
+	// Create the URL
+	url := fmt.Sprintf(CMABPredictionEndpoint, ruleID)
+
+	// Convert attributes to CMAB format
+	cmabAttributes := make([]CMABAttribute, 0, len(attributes))
+	for key, value := range attributes {
+		cmabAttributes = append(cmabAttributes, CMABAttribute{
+			ID:    key,
+			Value: value,
+			Type:  "custom_attribute",
+		})
+	}
+
+	// Create the request body
+	requestBody := CMABRequest{
+		Instances: []CMABInstance{
+			{
+				VisitorID:    userID,
+				ExperimentID: ruleID,
+				Attributes:   cmabAttributes,
+				CmabUUID:     cmabUUID,
+			},
+		},
+	}
+
+	// Serialize the request body
+	bodyBytes, err := json.Marshal(requestBody)
+	if err != nil {
+		return "", fmt.Errorf("failed to marshal CMAB request: %w", err)
+	}
+
+	// Create context for cancellation
+	ctx := context.Background()
+
+	// If no retry config, just do a single fetch
+	if c.retryConfig == nil {
+		return c.doFetch(ctx, url, bodyBytes)
+	}
+
+	// Retry sending request with exponential backoff
+	for i := 0; i <= c.retryConfig.MaxRetries; i++ {
+		// Make the request
+		result, err := c.doFetch(ctx, url, bodyBytes)
+		if err == nil {
+			return result, nil
+		}
+
+		// If this is the last retry, return the error
+		if i == c.retryConfig.MaxRetries {
+			return "", fmt.Errorf("failed to fetch CMAB decision after %d attempts: %w",
+				c.retryConfig.MaxRetries, err)
+		}
+
+		// Calculate backoff duration
+		backoffDuration := c.retryConfig.InitialBackoff * time.Duration(math.Pow(c.retryConfig.BackoffMultiplier, float64(i)))
+		if backoffDuration > c.retryConfig.MaxBackoff {
+			backoffDuration = c.retryConfig.MaxBackoff
+		}
+
+		c.logger.Debug(fmt.Sprintf("CMAB request retry %d/%d, backing off for %v",
+			i+1, c.retryConfig.MaxRetries, backoffDuration))
+
+		// Wait for backoff duration
+		time.Sleep(backoffDuration)
+
+		c.logger.Warning(fmt.Sprintf("CMAB API request failed (attempt %d/%d): %v",
+			i+1, c.retryConfig.MaxRetries, err))
+	}
+
+	// This should never be reached due to the return in the loop above
+	return "", fmt.Errorf("unexpected error in retry loop")
+}
+
+// doFetch performs a single fetch operation to the CMAB API
+func (c *DefaultCmabClient) doFetch(ctx context.Context, url string, bodyBytes []byte) (string, error) {
+	// Create the request
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(bodyBytes))
+	if err != nil {
+		return "", fmt.Errorf("failed to create CMAB request: %w", err)
+	}
+
+	// Set headers
+	req.Header.Set("Content-Type", "application/json")
+
+	// Execute the request
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("CMAB request failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	// Check status code
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return "", fmt.Errorf("CMAB API returned non-success status code: %d", resp.StatusCode)
+	}
+
+	// Read response body
+	respBody, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", fmt.Errorf("failed to read CMAB response body: %w", err)
+	}
+
+	// Parse response
+	var cmabResponse CMABResponse
+	if err := json.Unmarshal(respBody, &cmabResponse); err != nil {
+		return "", fmt.Errorf("failed to unmarshal CMAB response: %w", err)
+	}
+
+	// Validate response
+	if !c.validateResponse(cmabResponse) {
+		return "", fmt.Errorf("invalid CMAB response: missing predictions or variation_id")
+	}
+
+	// Return the variation ID
+	return cmabResponse.Predictions[0].VariationID, nil
+}
+
+// validateResponse validates the CMAB response
+func (c *DefaultCmabClient) validateResponse(response CMABResponse) bool {
+	return len(response.Predictions) > 0 && response.Predictions[0].VariationID != ""
+}