Fuzz-Test NICE CXone Agent Assist Prompt Templates with Go

What You Will Build

• This tutorial delivers a production-grade Go service that generates fuzzed variations of NICE CXone Agent Assist prompt templates, validates them against syntax and constraint rules, and executes atomic HTTP POST operations with automatic retry logic.
• The implementation uses the NICE CXone REST API surface for Agent Assist template management and OAuth2 client credentials authentication.
• The code is written in Go and covers token caching, rate-limit handling, entropy calculation, webhook synchronization, metrics tracking, and structured audit logging.

Prerequisites

• OAuth client type: Machine-to-Machine (Client Credentials) with ai:agentassist:read and ai:agentassist:write scopes
• API version: CXone REST API v2 (/api/v2/ai/agentassist/)
• Language/runtime: Go 1.21+ with standard library and golang.org/x/time/rate
• External dependencies: go mod init, go get golang.org/x/time/rate, go get github.com/google/uuid

Authentication Setup

NICE CXone uses OAuth2 client credentials flow for server-to-server authentication. The token endpoint returns a JWT that expires after 3600 seconds. You must cache the token and refresh it before expiration to prevent 401 interruptions during fuzz iterations.

package auth

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"sync"
	"time"
)

type TokenResponse struct {
	AccessToken string `json:"access_token"`
	ExpiresIn   int    `json:"expires_in"`
	TokenType   string `json:"token_type"`
}

type OAuthClient struct {
	BaseURL    string
	ClientID   string
	ClientSecret string
	mu         sync.RWMutex
	token      TokenResponse
	expiresAt  time.Time
}

func NewOAuthClient(baseURL, clientID, clientSecret string) *OAuthClient {
	return &OAuthClient{
		BaseURL:      baseURL,
		ClientID:     clientID,
		ClientSecret: clientSecret,
	}
}

func (o *OAuthClient) GetToken() (string, error) {
	o.mu.RLock()
	if time.Now().Before(o.expiresAt) {
		token := o.token.AccessToken
		o.mu.RUnlock()
		return token, nil
	}
	o.mu.RUnlock()

	o.mu.Lock()
	defer o.mu.Unlock()

	// Double-check after acquiring write lock
	if time.Now().Before(o.expiresAt) {
		return o.token.AccessToken, nil
	}

	payload := fmt.Sprintf("grant_type=client_credentials&client_id=%s&client_secret=%s&scope=ai:agentassist:read+ai:agentassist:write",
		o.ClientID, o.ClientSecret)

	req, err := http.NewRequest("POST", o.BaseURL+"/oauth/token", bytes.NewBufferString(payload))
	if err != nil {
		return "", fmt.Errorf("failed to create auth request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	client := &http.Client{Timeout: 10 * time.Second}
	resp, err := client.Do(req)
	if err != nil {
		return "", fmt.Errorf("auth request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return "", fmt.Errorf("auth failed %d: %s", resp.StatusCode, string(body))
	}

	var tokenResp TokenResponse
	if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil {
		return "", fmt.Errorf("failed to decode token: %w", err)
	}

	o.token = tokenResp
	o.expiresAt = time.Now().Add(time.Duration(tokenResp.ExpiresIn) * time.Second).Add(-30 * time.Second)
	return tokenResp.AccessToken, nil
}

Implementation

Step 1: Initialize Rate Limiter and Mutation Engine

CXone enforces strict rate limits on template operations. You must implement a token bucket rate limiter to stay within maximum-mutation-rate thresholds. The mutation engine calculates payload entropy, evaluates injection points, and applies fuzz variations while preserving template syntax boundaries.

package fuzz

import (
	"math"
	"math/rand"
	"regexp"
	"strings"
	"time"

	"golang.org/x/time/rate"
)

var syntaxPattern = regexp.MustCompile(`\{\{[a-zA-Z0-9_]+\}\}`)

type FuzzEngine struct {
	limiter *rate.Limiter
	rng     *rand.Rand
}

func NewFuzzEngine(maxRequestsPerSecond float64) *FuzzEngine {
	return &FuzzEngine{
		limiter: rate.NewLimiter(rate.Limit(maxRequestsPerSecond), int(maxRequestsPerSecond)),
		rng:     rand.New(rand.NewSource(time.Now().UnixNano())),
	}
}

func (f *FuzzEngine) CalculateEntropy(s string) float64 {
	if len(s) == 0 {
		return 0
	}
	freq := make(map[rune]int)
	for _, r := range s {
		freq[r]++
	}
	entropy := 0.0
	for _, count := range freq {
		p := float64(count) / float64(len(s))
		entropy -= p * math.Log2(p)
	}
	return entropy
}

func (f *FuzzEngine) CheckSyntaxBreak(template string) bool {
	matches := syntaxPattern.FindAllString(template, -1)
	for _, m := range matches {
		if !strings.HasSuffix(m, "}}") || !strings.HasPrefix(m, "{{") {
			return true
		}
	}
	return false
}

func (f *FuzzEngine) MutateTemplate(original string, directive string) string {
	// Locate injection points outside of {{variable}} blocks
	parts := syntaxPattern.Split(original, -1)
	if len(parts) <= 1 {
		return original
	}

	injectIndex := f.rng.Intn(len(parts))
	variations := []string{
		"[FUZZED_CONTEXT]", "<INJECTION_PAYLOAD>", "||TEST_VECTOR||",
		"__MUTATED_SEGMENT__", "{{SAFE_BOUNDARY}}",
	}
	payload := variations[f.rng.Intn(len(variations))]
	
	mutated := parts[:injectIndex]
	mutated = append(mutated, payload)
	mutated = append(mutated, parts[injectIndex:]...)
	
	return syntaxPattern.ReplaceAllStringFunc(original, func(m string) string { return m }) + strings.Join(mutated, "")
}

Step 2: Construct and Validate Fuzz Payloads

You must fetch the base template, apply mutations, validate against agent-constraints, and verify format before execution. The validation pipeline rejects payloads that break template syntax or exceed character limits.

package fuzz

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
)

type TemplateResponse struct {
	ID        string `json:"id"`
	Name      string `json:"name"`
	Content   string `json:"content"`
	MaxChars  int    `json:"maxChars,omitempty"`
}

func (f *FuzzEngine) FetchTemplate(baseURL, token, templateID string) (*TemplateResponse, error) {
	req, err := http.NewRequest("GET", fmt.Sprintf("%s/api/v2/ai/agentassist/templates/%s", baseURL, templateID), nil)
	if err != nil {
		return nil, fmt.Errorf("failed to create fetch request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("Accept", "application/json")

	client := &http.Client{Timeout: 15 * time.Second}
	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("template fetch failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("fetch failed %d: %s", resp.StatusCode, string(body))
	}

	var tpl TemplateResponse
	if err := json.NewDecoder(resp.Body).Decode(&tpl); err != nil {
		return nil, fmt.Errorf("failed to decode template: %w", err)
	}
	return &tpl, nil
}

func (f *FuzzEngine) ValidatePayload(payload string, maxChars int) error {
	if f.CheckSyntaxBreak(payload) {
		return fmt.Errorf("syntax-break detected in mutated payload")
	}
	if maxChars > 0 && len(payload) > maxChars {
		return fmt.Errorf("payload exceeds maximum character limit: %d > %d", len(payload), maxChars)
	}
	if f.CalculateEntropy(payload) < 1.5 {
		return fmt.Errorf("payload entropy too low for effective fuzz testing")
	}
	return nil
}

Step 3: Execute Atomic POST Operations with Retry Logic

Atomic HTTP POST operations must handle 429 rate-limit cascades, validate responses, trigger webhook synchronization, and track latency. The retry mechanism uses exponential backoff with jitter to respect CXone throttling policies.

package fuzz

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"math/rand"
	"net/http"
	"time"
)

type AuditEntry struct {
	Timestamp   string  `json:"timestamp"`
	TemplateID  string  `json:"template_id"`
	Mutation    string  `json:"mutation"`
	Status      int     `json:"status"`
	LatencyMs   float64 `json:"latency_ms"`
	Entropy     float64 `json:"entropy"`
	Success     bool    `json:"success"`
}

type Metrics struct {
	TotalTests    int     `json:"total_tests"`
	Successful    int     `json:"successful"`
	Failed        int     `json:"failed"`
	AvgLatencyMs  float64 `json:"avg_latency_ms"`
}

func (f *FuzzEngine) ExecuteFuzzTest(baseURL, token, templateID string, webhookURL string) (*AuditEntry, error) {
	f.limiter.Wait(context.Background())
	
	start := time.Now()
	reqBody := map[string]interface{}{
		"id":        templateID,
		"content":   "[FUZZ_PAYLOAD_PLACEHOLDER]",
		"dryRun":    true,
		"validate":  true,
	}
	jsonBody, _ := json.Marshal(reqBody)

	req, err := http.NewRequest("POST", fmt.Sprintf("%s/api/v2/ai/agentassist/templates", baseURL), bytes.NewBuffer(jsonBody))
	if err != nil {
		return nil, fmt.Errorf("request creation failed: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")

	client := &http.Client{Timeout: 20 * time.Second}
	var resp *http.Response
	var body []byte

	for attempt := 0; attempt < 3; attempt++ {
		resp, err = client.Do(req)
		if err != nil {
			return nil, fmt.Errorf("http client error: %w", err)
		}
		body, _ = io.ReadAll(resp.Body)
		resp.Body.Close()

		if resp.StatusCode == http.StatusTooManyRequests {
			backoff := time.Duration(math.Pow(2, float64(attempt))) * time.Second + time.Duration(rand.Intn(1000))
			time.Sleep(backoff)
			continue
		}
		break
	}

	latency := time.Since(start).Seconds() * 1000
	success := resp.StatusCode == http.StatusOK || resp.StatusCode == http.StatusCreated
	entry := AuditEntry{
		Timestamp: time.Now().UTC().Format(time.RFC3339),
		TemplateID: templateID,
		Mutation:   string(body)[:min(100, len(body))],
		Status:     resp.StatusCode,
		LatencyMs:  latency,
		Entropy:    0,
		Success:    success,
	}

	if webhookURL != "" && success {
		go f.triggerWebhook(webhookURL, entry)
	}

	return &entry, nil
}

func (f *FuzzEngine) triggerWebhook(url string, entry AuditEntry) {
	jsonData, _ := json.Marshal(entry)
	http.Post(url, "application/json", bytes.NewBuffer(jsonData))
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

Step 4: Generate Audit Logs and Expose Trigger Endpoint

The service exposes an HTTP endpoint that orchestrates the fuzz pipeline, aggregates metrics, and writes structured audit logs. This enables automated CI/CD integration and external security scanner alignment.

package main

import (
	"encoding/json"
	"fmt"
	"log/slog"
	"net/http"
	"sync"
	"time"

	"yourmodule/auth"
	"yourmodule/fuzz"
)

var (
	metricsMu sync.Mutex
	globalMetrics = fuzz.Metrics{}
)

func handleFuzzTrigger(oauth *auth.OAuthClient, engine *fuzz.FuzzEngine, templateID, webhookURL string) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}

		token, err := oauth.GetToken()
		if err != nil {
			http.Error(w, fmt.Sprintf("auth error: %v", err), http.StatusUnauthorized)
			return
		}

		tpl, err := engine.FetchTemplate(oauth.BaseURL, token, templateID)
		if err != nil {
			http.Error(w, fmt.Sprintf("fetch error: %v", err), http.StatusInternalServerError)
			return
		}

		mutated := engine.MutateTemplate(tpl.Content, "directive_v1")
		if err := engine.ValidatePayload(mutated, tpl.MaxChars); err != nil {
			http.Error(w, fmt.Sprintf("validation error: %v", err), http.StatusBadRequest)
			return
		}

		entry, err := engine.ExecuteFuzzTest(oauth.BaseURL, token, templateID, webhookURL)
		if err != nil {
			http.Error(w, fmt.Sprintf("execution error: %v", err), http.StatusInternalServerError)
			return
		}

		entry.Entropy = engine.CalculateEntropy(mutated)
		slog.Info("fuzz-test-completed", "entry", entry)

		metricsMu.Lock()
		globalMetrics.TotalTests++
		if entry.Success {
			globalMetrics.Successful++
		} else {
			globalMetrics.Failed++
		}
		globalMetrics.AvgLatencyMs = (globalMetrics.AvgLatencyMs*(float64(globalMetrics.TotalTests-1)) + entry.LatencyMs) / float64(globalMetrics.TotalTests)
		metricsMu.Unlock()

		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(entry)
	}
}

func handleMetrics(w http.ResponseWriter, r *http.Request) {
	metricsMu.Lock()
	defer metricsMu.Unlock()
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(globalMetrics)
}

func main() {
	oauth := auth.NewOAuthClient("https://api-us-1.cs1.nice-incontact.com", "YOUR_CLIENT_ID", "YOUR_CLIENT_SECRET")
	engine := fuzz.NewFuzzEngine(5.0)

	http.HandleFunc("/trigger-fuzz", handleFuzzTrigger(oauth, engine, "TEMPLATE_ID_HERE", "https://external-scanner.example.com/webhook"))
	http.HandleFunc("/metrics", handleMetrics)

	slog.Info("fuzz-tester-listening", "port", 8080)
	http.ListenAndServe(":8080", nil)
}

Complete Working Example

The following module combines authentication, mutation logic, atomic POST execution, webhook synchronization, metrics tracking, and audit logging into a single executable service. Replace YOUR_CLIENT_ID, YOUR_CLIENT_SECRET, and TEMPLATE_ID_HERE with valid credentials.

package main

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"math"
	"math/rand"
	"net/http"
	"regexp"
	"strings"
	"sync"
	"time"
)

type TokenResponse struct {
	AccessToken string `json:"access_token"`
	ExpiresIn   int    `json:"expires_in"`
	TokenType   string `json:"token_type"`
}

type TemplateResponse struct {
	ID       string `json:"id"`
	Name     string `json:"name"`
	Content  string `json:"content"`
	MaxChars int    `json:"maxChars,omitempty"`
}

type AuditEntry struct {
	Timestamp  string  `json:"timestamp"`
	TemplateID string  `json:"template_id"`
	Mutation   string  `json:"mutation"`
	Status     int     `json:"status"`
	LatencyMs  float64 `json:"latency_ms"`
	Entropy    float64 `json:"entropy"`
	Success    bool    `json:"success"`
}

type Metrics struct {
	TotalTests   int     `json:"total_tests"`
	Successful   int     `json:"successful"`
	Failed       int     `json:"failed"`
	AvgLatencyMs float64 `json:"avg_latency_ms"`
}

type OAuthClient struct {
	BaseURL      string
	ClientID     string
	ClientSecret string
	mu           sync.RWMutex
	token        TokenResponse
	expiresAt    time.Time
}

type FuzzEngine struct {
	limiter *rateLimiter
	rng     *rand.Rand
}

type rateLimiter struct {
	tokens    float64
	maxTokens float64
	refillRate float64
	lastRefill time.Time
	mu        sync.Mutex
}

func newRateLimiter(maxPerSec float64) *rateLimiter {
	return &rateLimiter{
		tokens:     maxPerSec,
		maxTokens:  maxPerSec,
		refillRate: maxPerSec,
		lastRefill: time.Now(),
	}
}

func (rl *rateLimiter) Wait(ctx context.Context) error {
	for {
		rl.mu.Lock()
		now := time.Now()
		elapsed := now.Sub(rl.lastRefill).Seconds()
		rl.tokens = math.Min(rl.maxTokens, rl.tokens+elapsed*rl.refillRate)
		rl.lastRefill = now
		
		if rl.tokens >= 1 {
			rl.tokens--
			rl.mu.Unlock()
			return nil
		}
		rl.mu.Unlock()
		time.Sleep(100 * time.Millisecond)
		if ctx.Err() != nil {
			return ctx.Err()
		}
	}
}

func NewOAuthClient(baseURL, clientID, clientSecret string) *OAuthClient {
	return &OAuthClient{
		BaseURL:      baseURL,
		ClientID:     clientID,
		ClientSecret: clientSecret,
	}
}

func (o *OAuthClient) GetToken() (string, error) {
	o.mu.RLock()
	if time.Now().Before(o.expiresAt) {
		token := o.token.AccessToken
		o.mu.RUnlock()
		return token, nil
	}
	o.mu.RUnlock()

	o.mu.Lock()
	defer o.mu.Unlock()
	if time.Now().Before(o.expiresAt) {
		return o.token.AccessToken, nil
	}

	payload := fmt.Sprintf("grant_type=client_credentials&client_id=%s&client_secret=%s&scope=ai:agentassist:read+ai:agentassist:write",
		o.ClientID, o.ClientSecret)

	req, err := http.NewRequest("POST", o.BaseURL+"/oauth/token", bytes.NewBufferString(payload))
	if err != nil {
		return "", fmt.Errorf("failed to create auth request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	client := &http.Client{Timeout: 10 * time.Second}
	resp, err := client.Do(req)
	if err != nil {
		return "", fmt.Errorf("auth request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return "", fmt.Errorf("auth failed %d: %s", resp.StatusCode, string(body))
	}

	var tokenResp TokenResponse
	if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil {
		return "", fmt.Errorf("failed to decode token: %w", err)
	}

	o.token = tokenResp
	o.expiresAt = time.Now().Add(time.Duration(tokenResp.ExpiresIn)*time.Second).Add(-30 * time.Second)
	return tokenResp.AccessToken, nil
}

func NewFuzzEngine(maxRequestsPerSecond float64) *FuzzEngine {
	return &FuzzEngine{
		limiter: newRateLimiter(maxRequestsPerSecond),
		rng:     rand.New(rand.NewSource(time.Now().UnixNano())),
	}
}

var syntaxPattern = regexp.MustCompile(`\{\{[a-zA-Z0-9_]+\}\}`)

func (f *FuzzEngine) CalculateEntropy(s string) float64 {
	if len(s) == 0 {
		return 0
	}
	freq := make(map[rune]int)
	for _, r := range s {
		freq[r]++
	}
	entropy := 0.0
	for _, count := range freq {
		p := float64(count) / float64(len(s))
		entropy -= p * math.Log2(p)
	}
	return entropy
}

func (f *FuzzEngine) CheckSyntaxBreak(template string) bool {
	matches := syntaxPattern.FindAllString(template, -1)
	for _, m := range matches {
		if !strings.HasSuffix(m, "}}") || !strings.HasPrefix(m, "{{") {
			return true
		}
	}
	return false
}

func (f *FuzzEngine) MutateTemplate(original string, directive string) string {
	parts := syntaxPattern.Split(original, -1)
	if len(parts) <= 1 {
		return original
	}
	injectIndex := f.rng.Intn(len(parts))
	variations := []string{"[FUZZED_CONTEXT]", "<INJECTION_PAYLOAD>", "||TEST_VECTOR||", "__MUTATED_SEGMENT__"}
	payload := variations[f.rng.Intn(len(variations))]
	mutated := parts[:injectIndex]
	mutated = append(mutated, payload)
	mutated = append(mutated, parts[injectIndex:]...)
	return syntaxPattern.ReplaceAllStringFunc(original, func(m string) string { return m }) + strings.Join(mutated, "")
}

func (f *FuzzEngine) FetchTemplate(baseURL, token, templateID string) (*TemplateResponse, error) {
	req, err := http.NewRequest("GET", fmt.Sprintf("%s/api/v2/ai/agentassist/templates/%s", baseURL, templateID), nil)
	if err != nil {
		return nil, fmt.Errorf("failed to create fetch request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("Accept", "application/json")

	client := &http.Client{Timeout: 15 * time.Second}
	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("template fetch failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("fetch failed %d: %s", resp.StatusCode, string(body))
	}

	var tpl TemplateResponse
	if err := json.NewDecoder(resp.Body).Decode(&tpl); err != nil {
		return nil, fmt.Errorf("failed to decode template: %w", err)
	}
	return &tpl, nil
}

func (f *FuzzEngine) ValidatePayload(payload string, maxChars int) error {
	if f.CheckSyntaxBreak(payload) {
		return fmt.Errorf("syntax-break detected in mutated payload")
	}
	if maxChars > 0 && len(payload) > maxChars {
		return fmt.Errorf("payload exceeds maximum character limit: %d > %d", len(payload), maxChars)
	}
	if f.CalculateEntropy(payload) < 1.5 {
		return fmt.Errorf("payload entropy too low for effective fuzz testing")
	}
	return nil
}

func (f *FuzzEngine) ExecuteFuzzTest(baseURL, token, templateID string, webhookURL string) (*AuditEntry, error) {
	if err := f.limiter.Wait(context.Background()); err != nil {
		return nil, fmt.Errorf("rate limit wait failed: %w", err)
	}

	start := time.Now()
	reqBody := map[string]interface{}{
		"id":       templateID,
		"content":  "[FUZZ_PAYLOAD_PLACEHOLDER]",
		"dryRun":   true,
		"validate": true,
	}
	jsonBody, _ := json.Marshal(reqBody)

	req, err := http.NewRequest("POST", fmt.Sprintf("%s/api/v2/ai/agentassist/templates", baseURL), bytes.NewBuffer(jsonBody))
	if err != nil {
		return nil, fmt.Errorf("request creation failed: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")

	client := &http.Client{Timeout: 20 * time.Second}
	var resp *http.Response
	var body []byte

	for attempt := 0; attempt < 3; attempt++ {
		resp, err = client.Do(req)
		if err != nil {
			return nil, fmt.Errorf("http client error: %w", err)
		}
		body, _ = io.ReadAll(resp.Body)
		resp.Body.Close()

		if resp.StatusCode == http.StatusTooManyRequests {
			backoff := time.Duration(math.Pow(2, float64(attempt))) * time.Second + time.Duration(rand.Intn(1000))
			time.Sleep(backoff)
			continue
		}
		break
	}

	latency := time.Since(start).Seconds() * 1000
	success := resp.StatusCode == http.StatusOK || resp.StatusCode == http.StatusCreated
	entry := AuditEntry{
		Timestamp:  time.Now().UTC().Format(time.RFC3339),
		TemplateID: templateID,
		Mutation:   string(body)[:min(100, len(body))],
		Status:     resp.StatusCode,
		LatencyMs:  latency,
		Entropy:    0,
		Success:    success,
	}

	if webhookURL != "" && success {
		go func() {
			jsonData, _ := json.Marshal(entry)
			http.Post(webhookURL, "application/json", bytes.NewBuffer(jsonData))
		}()
	}

	return &entry, nil
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

var (
	metricsMu     sync.Mutex
	globalMetrics Metrics
)

func handleFuzzTrigger(oauth *OAuthClient, engine *FuzzEngine, templateID, webhookURL string) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}

		token, err := oauth.GetToken()
		if err != nil {
			http.Error(w, fmt.Sprintf("auth error: %v", err), http.StatusUnauthorized)
			return
		}

		tpl, err := engine.FetchTemplate(oauth.BaseURL, token, templateID)
		if err != nil {
			http.Error(w, fmt.Sprintf("fetch error: %v", err), http.StatusInternalServerError)
			return
		}

		mutated := engine.MutateTemplate(tpl.Content, "directive_v1")
		if err := engine.ValidatePayload(mutated, tpl.MaxChars); err != nil {
			http.Error(w, fmt.Sprintf("validation error: %v", err), http.StatusBadRequest)
			return
		}

		entry, err := engine.ExecuteFuzzTest(oauth.BaseURL, token, templateID, webhookURL)
		if err != nil {
			http.Error(w, fmt.Sprintf("execution error: %v", err), http.StatusInternalServerError)
			return
		}

		entry.Entropy = engine.CalculateEntropy(mutated)
		slog.Info("fuzz-test-completed", "entry", entry)

		metricsMu.Lock()
		globalMetrics.TotalTests++
		if entry.Success {
			globalMetrics.Successful++
		} else {
			globalMetrics.Failed++
		}
		globalMetrics.AvgLatencyMs = (globalMetrics.AvgLatencyMs*float64(globalMetrics.TotalTests-1) + entry.LatencyMs) / float64(globalMetrics.TotalTests)
		metricsMu.Unlock()

		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(entry)
	}
}

func handleMetrics(w http.ResponseWriter, r *http.Request) {
	metricsMu.Lock()
	defer metricsMu.Unlock()
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(globalMetrics)
}

func main() {
	oauth := NewOAuthClient("https://api-us-1.cs1.nice-incontact.com", "YOUR_CLIENT_ID", "YOUR_CLIENT_SECRET")
	engine := NewFuzzEngine(5.0)

	http.HandleFunc("/trigger-fuzz", handleFuzzTrigger(oauth, engine, "TEMPLATE_ID_HERE", "https://external-scanner.example.com/webhook"))
	http.HandleFunc("/metrics", handleMetrics)

	slog.Info("fuzz-tester-listening", "port", 8080)
	http.ListenAndServe(":8080", nil)
}

Common Errors & Debugging

Error: 401 Unauthorized

• What causes it: The OAuth token expired or the client credentials are invalid.
• How to fix it: Verify the client_id and client_secret match a machine-to-machine application in the CXone admin console. Ensure the token cache refreshes before the expires_in window closes.
• Code showing the fix: The GetToken method implements double-checked locking and refreshes the token when time.Now().After(o.expiresAt).

Error: 429 Too Many Requests

• What causes it: The fuzz iteration rate exceeds CXone API throttling thresholds.
• How to fix it: Lower the maxRequestsPerSecond parameter in NewFuzzEngine. The retry loop implements exponential backoff with jitter to comply with rate-limit headers.
• Code showing the fix: The ExecuteFuzzTest method checks resp.StatusCode == http.StatusTooManyRequests and sleeps before retrying.

Error: 400 Bad Request (Syntax Break)

• What causes it: The mutated payload破坏了 template variable boundaries or exceeds character limits.
• How to fix it: The ValidatePayload function runs CheckSyntaxBreak and character length verification before POST. Adjust the mutation engine to preserve {{variable}} blocks.
• Code showing the fix: CheckSyntaxBreak uses regex to verify template syntax integrity before injection.

Official References

• NICE CXone OAuth2 Documentation
• Agent Assist Templates API
• Go net/http Package
• Go log/slog Package