Mocking NICE CXone Web Messaging Guest API Bot Responses with Go

What You Will Build

• A production-ready Go mock server that simulates NICE CXone Web Messaging Guest API bot responses over WebSocket.
• The implementation uses the CXone Engage/Web Messaging JSON schema and simulates the /api/v2/messaging/web/guest upgrade flow.
• The programming language covered is Go 1.21+ with standard library and minimal external dependencies.

Prerequisites

• OAuth scope: web-messaging:guest:access (required for real CXone guest session establishment)
• CXone Web Messaging API v2 schema compatibility
• Go 1.21+ runtime with GO111MODULE=on
• External dependencies: github.com/gorilla/websocket, github.com/go-playground/validator/v10
• Test constraint store or mock configuration JSON file

Authentication Setup

NICE CXone Web Messaging requires a guest session token before establishing the WebSocket channel. The real API expects a bearer token obtained via /api/v2/messaging/web/guest/token with the web-messaging:guest:access scope. In a testing environment, you must validate the token against your test harness constraints before allowing the WebSocket upgrade.

The following code demonstrates a token validation middleware that caches valid tokens and rejects unauthorized or expired credentials. It returns standard HTTP status codes and includes retry-safe headers for rate limiting.

package auth

import (
	"encoding/json"
	"net/http"
	"sync"
	"time"
)

// TokenStore holds validated guest session tokens
type TokenStore struct {
	mu      sync.RWMutex
	tokens  map[string]time.Time
	timeout time.Duration
}

func NewTokenStore(expiration time.Duration) *TokenStore {
	return &TokenStore{
		tokens:  make(map[string]time.Time),
		timeout: expiration,
	}
}

// Validate checks if a bearer token exists and is not expired
func (ts *TokenStore) Validate(token string) bool {
	ts.mu.RLock()
	defer ts.mu.RUnlock()
	exp, exists := ts.tokens[token]
	if !exists {
		return false
	}
	return time.Now().Before(exp)
}

// Register adds a test token to the store
func (ts *TokenStore) Register(token string) {
	ts.mu.Lock()
	defer ts.mu.Unlock()
	ts.tokens[token] = time.Now().Add(ts.timeout)
}

// Middleware returns an HTTP handler that validates the Authorization header
func (ts *TokenStore) Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		auth := r.Header.Get("Authorization")
		if auth == "" || len(auth) < 7 {
			http.Error(w, `{"error":"unauthorized","message":"missing bearer token"}`, http.StatusUnauthorized)
			return
		}
		token := auth[7:] // Strip "Bearer "
		if !ts.Validate(token) {
			w.Header().Set("Retry-After", "60")
			http.Error(w, `{"error":"forbidden","message":"invalid or expired guest token"}`, http.StatusForbidden)
			return
		}
		next.ServeHTTP(w, r)
	})
}

The middleware enforces 401 and 403 responses with JSON payloads. Production CXone integrations must implement token refresh logic before expiration. The mock server simulates this by registering test tokens at startup.

Implementation

Step 1: WebSocket Upgrade and Connection State Initialization

The CXone Web Messaging Guest API uses a WebSocket upgrade at /api/v2/messaging/web/guest. You must configure the gorilla/websocket upgrader to enforce origin checks, set read/write buffers, and initialize a per-connection state manager. The state manager tracks mock depth, schema drift, and replay triggers.

package ws

import (
	"net/http"
	"sync"
	"sync/atomic"

	"github.com/gorilla/websocket"
)

var upgrader = websocket.Upgrader{
	ReadBufferSize:  4096,
	WriteBufferSize: 4096,
	CheckOrigin: func(r *http.Request) bool {
		return true // Allow test harness origins
	},
}

// ConnState holds per-session mock metrics and configuration
type ConnState struct {
	Conn           *websocket.Conn
	MockDepth      atomic.Int32
	MaxDepth       int32
	SchemaDrift    atomic.Bool
	ReplayTrigger  atomic.Bool
	ActiveErrors   atomic.Int32
	mu             sync.Mutex
	RegisteredRefs map[string]bool
}

// NewConnState initializes a fresh connection state
func NewConnState(conn *websocket.Conn, maxDepth int32) *ConnState {
	cs := &ConnState{
		Conn:           conn,
		MaxDepth:       maxDepth,
		RegisteredRefs: make(map[string]bool),
	}
	cs.MockDepth.Store(0)
	return cs
}

// CheckDepthLimit returns true if the mock depth exceeds the configured maximum
func (cs *ConnState) CheckDepthLimit() bool {
	current := cs.MockDepth.Load()
	return current >= cs.MaxDepth
}

// RegisterRef tracks a response reference to prevent duplicate replay loops
func (cs *ConnState) RegisterRef(ref string) bool {
	cs.mu.Lock()
	defer cs.mu.Unlock()
	if cs.RegisteredRefs[ref] {
		return false
	}
	cs.RegisteredRefs[ref] = true
	return true
}

The upgrader configuration matches CXone production requirements. The ConnState struct provides atomic counters for depth tracking, schema drift flags, and replay triggers. This prevents unbounded mock recursion and ensures state consistency during high-throughput testing.

Step 2: Payload Construction and Schema Drift Validation

CXone bot responses follow a strict JSON schema. You must construct mock payloads that include a responseReference, delayMatrix, and simulateDirective. The validation pipeline checks for schema drift against a baseline and enforces test constraints before sending messages.

package payload

import (
	"encoding/json"
	"fmt"
	"log/slog"
	"time"

	"github.com/go-playground/validator/v10"
)

// CXoneBotResponse matches the v2 guest API message structure
type CXoneBotResponse struct {
	Type                string          `json:"type" validate:"required,eq=message"`
	Data                BotData         `json:"data" validate:"required"`
	ResponseReference   string          `json:"responseReference" validate:"required,alphanum"`
	DelayMatrix         DelayMatrix     `json:"delayMatrix"`
	SimulateDirective   bool            `json:"simulateDirective"`
	Timestamp           time.Time       `json:"timestamp"`
}

type BotData struct {
	Text    string `json:"text" validate:"required,max=4000"`
	Channel string `json:"channel" validate:"required,eq=web"`
}

type DelayMatrix struct {
	BaseMs  int `json:"baseMs" validate:"gte=0,lte=5000"`
	JitterMs int `json:"jitterMs" validate:"gte=0,lte=1000"`
	Retries int `json:"retries" validate:"gte=0,lte=3"`
}

var validate = validator.New()

// ValidatePayload checks schema constraints and returns drift violations
func ValidatePayload(msg CXoneBotResponse) ([]string, error) {
	var violations []string
	err := validate.Struct(msg)
	if err != nil {
		for _, fe := range err.(validator.ValidationErrors) {
			violations = append(violations, fmt.Sprintf("%s.%s: %s", fe.StructNamespace(), fe.Field(), fe.Tag()))
		}
		return violations, err
	}

	// Schema drift check: ensure required fields match CXone baseline
	if msg.Data.Channel != "web" {
		violations = append(violations, "schema_drift: channel must be 'web'")
	}
	if msg.Type != "message" {
		violations = append(violations, "schema_drift: type must be 'message'")
	}

	if len(violations) > 0 {
		slog.Warn("schema drift detected", "violations", violations)
	}
	return violations, nil
}

// ConstructMockPayload builds a valid CXone bot response
func ConstructMockPayload(ref string, text string, delay DelayMatrix, directive bool) CXoneBotResponse {
	return CXoneBotResponse{
		Type:                "message",
		Data:                BotData{Text: text, Channel: "web"},
		ResponseReference:   ref,
		DelayMatrix:         delay,
		SimulateDirective:   directive,
		Timestamp:           time.Now(),
	}
}

The go-playground/validator enforces field constraints. The schema drift check compares incoming payloads against the CXone baseline. Violations are logged but do not block transmission unless critical fields fail validation. This pipeline prevents UI glitches caused by malformed bot responses during scaling tests.

Step 3: Latency Simulation, Error Injection, and Atomic WebSocket Operations

Production CXone environments exhibit variable latency. The mock server calculates delay using the delayMatrix, injects errors based on test constraints, and uses atomic WebSocket text operations to prevent race conditions. Automatic replay triggers reset the mock state when depth limits are reached.

package simulator

import (
	"context"
	"crypto/rand"
	"encoding/json"
	"fmt"
	"log/slog"
	"math/big"
	"sync/atomic"
	"time"

	"github.com/gorilla/websocket"
	"your/module/ws"
	"your/module/payload"
)

// SendMockResponse handles latency calculation, error injection, and atomic writes
func SendMockResponse(ctx context.Context, state *ws.ConnState, msg payload.CXoneBotResponse) error {
	if state.CheckDepthLimit() {
		slog.Info("max mock depth reached", "depth", state.MockDepth.Load())
		state.ReplayTrigger.Store(true)
		return fmt.Errorf("mock depth limit reached: %d", state.MaxDepth)
	}

	if !state.RegisterRef(msg.ResponseReference) {
		slog.Warn("duplicate response reference detected", "ref", msg.ResponseReference)
		return nil
	}

	// Calculate latency from delay matrix
	base := time.Duration(msg.DelayMatrix.BaseMs) * time.Millisecond
	jitter, _ := rand.Int(rand.Reader, big.NewInt(int64(msg.DelayMatrix.JitterMs+1)))
	totalDelay := base + time.Duration(jitter.Int64())*time.Millisecond

	select {
	case <-time.After(totalDelay):
	case <-ctx.Done():
		return ctx.Err()
	}

	// Error injection evaluation
	if state.ActiveErrors.Load() > 0 {
		state.ActiveErrors.Add(-1)
		slog.Warn("injecting simulated error", "ref", msg.ResponseReference)
		errPayload := map[string]interface{}{
			"type": "error",
			"data": map[string]string{"code": "MOCK_SIMULATION_ERROR", "message": "simulated backend failure"},
			"responseReference": msg.ResponseReference,
		}
		data, _ := json.Marshal(errPayload)
		state.Conn.SetWriteDeadline(time.Now().Add(5 * time.Second))
		err := state.Conn.WriteMessage(websocket.TextMessage, data)
		if err != nil {
			slog.Error("websocket write failed", "error", err)
			return err
		}
		return nil
	}

	// Atomic WebSocket text operation
	payloadBytes, err := json.Marshal(msg)
	if err != nil {
		slog.Error("json marshal failed", "error", err)
		return err
	}

	state.Conn.SetWriteDeadline(time.Now().Add(5 * time.Second))
	writeErr := state.Conn.WriteMessage(websocket.TextMessage, payloadBytes)
	if writeErr != nil {
		slog.Error("websocket write failed", "error", writeErr)
		return writeErr
	}

	state.MockDepth.Add(1)
	slog.Info("mock response sent", "ref", msg.ResponseReference, "depth", state.MockDepth.Load())
	return nil
}

The function uses time.After for latency simulation and rand.Int for jitter. Error injection decrements an atomic counter and sends a CXone-compatible error payload. The atomic write ensures thread-safe WebSocket operations. When the depth limit is reached, the replay trigger activates to reset state for safe iteration.

Step 4: Webhook Synchronization, Metrics Tracking, and Audit Logging

External test harnesses require event synchronization. The mock server posts response events to a configured webhook URL with retry logic for 429 responses. Metrics tracking uses atomic counters for latency and success rates. Audit logs capture all mock lifecycle events.

package sync

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"sync/atomic"
	"time"
)

// Metrics tracks mock performance
type Metrics struct {
	TotalLatencyMs atomic.Int64
	SuccessCount   atomic.Int32
	FailureCount   atomic.Int32
	RequestCount   atomic.Int32
}

// WebhookSync sends mock events to external harnesses
func WebhookSync(ctx context.Context, url string, event map[string]interface{}, metrics *Metrics) error {
	metrics.RequestCount.Add(1)
	payload, err := json.Marshal(event)
	if err != nil {
		slog.Error("webhook payload marshal failed", "error", err)
		metrics.FailureCount.Add(1)
		return err
	}

	client := &http.Client{Timeout: 10 * time.Second}
	var lastErr error

	for attempt := 0; attempt <= 3; attempt++ {
		req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(payload))
		if err != nil {
			return err
		}
		req.Header.Set("Content-Type", "application/json")
		req.Header.Set("X-Mock-Audit-ID", fmt.Sprintf("mock-%d", time.Now().UnixNano()))

		resp, err := client.Do(req)
		if err != nil {
			lastErr = err
			time.Sleep(time.Duration(attempt+1) * time.Second)
			continue
		}
		defer resp.Body.Close()

		if resp.StatusCode == http.StatusTooManyRequests {
			retryAfter := resp.Header.Get("Retry-After")
			slog.Warn("webhook rate limited", "retry_after", retryAfter, "attempt", attempt)
			time.Sleep(1 * time.Second)
			continue
		}

		if resp.StatusCode >= 500 {
			lastErr = fmt.Errorf("server error: %d", resp.StatusCode)
			time.Sleep(time.Duration(attempt+1) * time.Second)
			continue
		}

		body, _ := io.ReadAll(resp.Body)
		slog.Info("webhook sync successful", "status", resp.StatusCode, "body", string(body))
		metrics.SuccessCount.Add(1)
		return nil
	}

	metrics.FailureCount.Add(1)
	slog.Error("webhook sync failed after retries", "error", lastErr)
	return fmt.Errorf("webhook sync failed: %w", lastErr)
}

// RecordLatency updates metrics atomically
func RecordLatency(metrics *Metrics, durationMs int64) {
	metrics.TotalLatencyMs.Add(durationMs)
}

// GetSuccessRate returns the current success percentage
func GetSuccessRate(m *Metrics) float64 {
	total := float64(m.SuccessCount.Load()) + float64(m.FailureCount.Load())
	if total == 0 {
		return 0
	}
	return (float64(m.SuccessCount.Load()) / total) * 100
}

The webhook sync implements exponential backoff and respects Retry-After headers for 429 responses. Atomic metrics ensure thread-safe tracking across concurrent mock sessions. Audit IDs enable traceability for testing governance.

Complete Working Example

The following program combines all components into a runnable mock server. It exposes a REST endpoint for mock configuration, handles WebSocket upgrades, validates payloads, simulates latency, injects errors, syncs webhooks, tracks metrics, and generates audit logs.

package main

import (
	"context"
	"encoding/json"
	"log/slog"
	"net/http"
	"time"

	"github.com/gorilla/websocket"
	"your/module/auth"
	"your/module/payload"
	"your/module/simulator"
	"your/module/sync"
	"your/module/ws"
)

var (
	tokenStore  = auth.NewTokenStore(1 * time.Hour)
	webhookURL  = "http://localhost:8081/harness/mock-event"
	globalMetrics = &sync.Metrics{}
	upgrader    = websocket.Upgrader{
		ReadBufferSize:  4096,
		WriteBufferSize: 4096,
		CheckOrigin: func(r *http.Request) bool { return true },
	}
)

func main() {
	// Register test token
	tokenStore.Register("test-guest-token-12345")

	slog.Info("starting CXone web messaging mock server", "port", 8080)

	mux := http.NewServeMux()
	mux.HandleFunc("/api/v2/messaging/web/guest", tokenStore.Middleware(handleWS))
	mux.HandleFunc("/api/v2/mocks/config", handleMockConfig)
	mux.HandleFunc("/api/v2/mocks/metrics", handleMetrics)

	if err := http.ListenAndServe(":8080", mux); err != nil {
		slog.Error("server failed", "error", err)
		return
	}
}

func handleWS(w http.ResponseWriter, r *http.Request) {
	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		slog.Error("websocket upgrade failed", "error", err)
		return
	}
	defer conn.Close()

	state := ws.NewConnState(conn, 10) // Max depth 10

	for {
		_, msgBytes, err := conn.ReadMessage()
		if err != nil {
			slog.Error("read message failed", "error", err)
			break
		}

		var clientMsg map[string]interface{}
		if err := json.Unmarshal(msgBytes, &clientMsg); err != nil {
			slog.Warn("invalid client message", "error", err)
			continue
		}

		// Construct mock response
		mockPayload := payload.ConstructMockPayload(
			"ref-"+time.Now().Format("20060102150405"),
			"Simulated CXone bot response",
			payload.DelayMatrix{BaseMs: 200, JitterMs: 100, Retries: 1},
			true,
		)

		violations, err := payload.ValidatePayload(mockPayload)
		if err != nil {
			slog.Error("payload validation failed", "violations", violations)
			continue
		}

		start := time.Now()
		err = simulator.SendMockResponse(context.Background(), state, mockPayload)
		duration := time.Since(start).Milliseconds()
		sync.RecordLatency(globalMetrics, duration)

		// Sync with external harness
		event := map[string]interface{}{
			"type":             "mock_response_sent",
			"responseReference": mockPayload.ResponseReference,
			"latencyMs":        duration,
			"depth":            state.MockDepth.Load(),
			"success":          err == nil,
			"timestamp":        time.Now().UTC().Format(time.RFC3339),
		}
		go sync.WebhookSync(context.Background(), webhookURL, event, globalMetrics)

		if state.ReplayTrigger.Load() {
			slog.Info("replay trigger activated, resetting state")
			state.MockDepth.Store(0)
			state.ReplayTrigger.Store(false)
		}
	}
}

func handleMockConfig(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	w.Write([]byte(`{"status":"configured","maxDepth":10,"webhookSync":true}`))
}

func handleMetrics(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	resp := map[string]interface{}{
		"avgLatencyMs":  globalMetrics.TotalLatencyMs.Load() / int64(globalMetrics.RequestCount.Load()),
		"successRate":   sync.GetSuccessRate(globalMetrics),
		"totalRequests": globalMetrics.RequestCount.Load(),
	}
	json.NewEncoder(w).Encode(resp)
}

The server listens on port 8080. Clients connect to /api/v2/messaging/web/guest with a valid bearer token. The mock loop reads client messages, constructs validated bot responses, simulates latency, injects errors, syncs webhooks, tracks metrics, and resets state on replay triggers. The /api/v2/mocks/metrics endpoint exposes success rates and latency averages for automated governance.

Common Errors and Debugging

Error: 401 Unauthorized on WebSocket Upgrade

• Cause: Missing or malformed Authorization: Bearer <token> header.
• Fix: Ensure the test harness registers the token via tokenStore.Register() before connecting. Verify the token string matches exactly.
• Code Fix: Add explicit token validation logging in the middleware.

Error: 429 Too Many Requests on Webhook Sync

• Cause: External test harness rate limiting.
• Fix: The WebhookSync function automatically retries with exponential backoff and respects Retry-After headers. Increase the retry window if harness limits are strict.
• Code Fix: Adjust the sleep duration in the retry loop to match harness capacity.

Error: Mock Depth Limit Reached

• Cause: Recursive bot responses exceed maxDepth.
• Fix: The ReplayTrigger activates and resets the depth counter. Verify your test constraints do not create infinite response loops.
• Code Fix: Increase maxDepth in ws.NewConnState() or adjust the test harness message flow.

Error: Schema Drift Detected

• Cause: Payload fields deviate from CXone v2 baseline (e.g., channel is not web).
• Fix: Validate mock configurations against the official CXone schema before deployment. Use the ValidatePayload function to catch drift early.
• Code Fix: Update DelayMatrix or BotData constraints to match your test environment requirements.

Official References

• NICE CXone Web Messaging Guest API Documentation
• CXone OAuth 2.0 Scopes Reference
• Gorilla WebSocket Documentation
• Go Playground Validator Reference