Enforcing Strict JSON Schema Compliance in Genesys Cloud LLM Gateway Responses Using Go Middleware

What You Will Build

• A Go middleware that intercepts LLM Gateway API responses, validates them against Go struct tags, and automatically retries the generation when schema violations occur.
• This implementation uses the Genesys Cloud LLM Gateway REST API (/api/v2/ai/llm/conversations) and the official platform-client-sdk-go.
• The code is written in Go 1.21+ using standard HTTP patterns and the go-playground/validator library.

Prerequisites

• OAuth client credentials flow configured with ai:llm:read and ai:llm:write scopes
• Genesys Cloud API version v2
• Go runtime version 1.21 or later
• External dependencies: github.com/mypurecloud/platform-client-sdk-go, github.com/go-playground/validator/v10, github.com/google/uuid

Authentication Setup

Genesys Cloud uses OAuth 2.0 for API authentication. The following code implements a thread-safe token manager that handles initial token acquisition and automatic refresh before expiration. The manager caches the token and checks expiration with a thirty-second safety buffer to prevent mid-request authentication failures.

package main

import (
	"context"
	"crypto/tls"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"sync"
	"time"
)

type TokenManager struct {
	mu           sync.RWMutex
	token        string
	expiresAt    time.Time
	clientID     string
	clientSecret string
	baseURL      string
	httpClient   *http.Client
}

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

func NewTokenManager(clientID, clientSecret, baseURL string) *TokenManager {
	return &TokenManager{
		clientID:     clientID,
		clientSecret: clientSecret,
		baseURL:      baseURL,
		httpClient: &http.Client{
			Timeout: 10 * time.Second,
			Transport: &http.Transport{
				TLSClientConfig: &tls.Config{MinVersion: tls.VersionTLS12},
			},
		},
	}
}

func (tm *TokenManager) GetToken(ctx context.Context) (string, error) {
	tm.mu.RLock()
	if tm.token != "" && time.Now().Before(tm.expiresAt.Add(-30 * time.Second)) {
		token := tm.token
		tm.mu.RUnlock()
		return token, nil
	}
	tm.mu.RUnlock()

	tm.mu.Lock()
	defer tm.mu.Unlock()

	if tm.token != "" && time.Now().Before(tm.expiresAt.Add(-30 * time.Second)) {
		return tm.token, nil
	}

	payload := fmt.Sprintf("grant_type=client_credentials&client_id=%s&client_secret=%s&scope=ai:llm:read+ai:llm:write", tm.clientID, tm.clientSecret)
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, fmt.Sprintf("%s/oauth/token", tm.baseURL), strings.NewReader(payload))
	if err != nil {
		return "", fmt.Errorf("failed to create token request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	resp, err := tm.httpClient.Do(req)
	if err != nil {
		return "", fmt.Errorf("token request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("token request returned status %d", resp.StatusCode)
	}

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

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

Implementation

Step 1: Configure SDK Client with 429 Retry Logic

Genesys Cloud enforces strict rate limits across all API surfaces. The SDK client must wrap the underlying HTTP transport to handle 429 Too Many Requests responses with exponential backoff. This transport intercepts HTTP calls before the SDK processes them.

import (
	"fmt"
	"net/http"
	"time"

	platformclientv2 "github.com/mypurecloud/platform-client-sdk-go/platformclientv2"
)

func NewGenesysClient(baseURL, clientID, clientSecret string) (*platformclientv2.ApiClient, error) {
	config := platformclientv2.NewConfiguration()
	config.BasePath = baseURL
	config.Debug = false

	client := &http.Client{Timeout: 30 * time.Second}
	client.Transport = &RetryTransport{base: http.DefaultTransport}
	config.HTTPClient = client

	apiClient := platformclientv2.NewApiClient(config)
	authClient := apiClient.GetAuthClient()
	authClient.SetAuthMode("client_credentials")
	authClient.SetClientId(clientID)
	authClient.SetClientSecret(clientSecret)
	authClient.SetScopes([]string{"ai:llm:read", "ai:llm:write"})

	if err := authClient.Login(); err != nil {
		return nil, fmt.Errorf("failed to authenticate with Genesys Cloud: %w", err)
	}

	return apiClient, nil
}

type RetryTransport struct {
	base http.RoundTripper
}

func (rt *RetryTransport) RoundTrip(req *http.Request) (*http.Response, error) {
	var resp *http.Response
	var err error
	maxRetries := 3
	for attempt := 0; attempt <= maxRetries; attempt++ {
		resp, err = rt.base.RoundTrip(req)
		if err != nil {
			return nil, err
		}
		if resp.StatusCode == http.StatusTooManyRequests {
			retryAfter := 2 * time.Duration(attempt+1) * time.Second
			time.Sleep(retryAfter)
			continue
		}
		return resp, nil
	}
	return resp, fmt.Errorf("max retries exceeded for 429 response")
}

Step 2: Define Target Struct with Validation Tags

The middleware requires a Go struct that maps to the expected JSON response. The validator library uses struct tags to enforce schema compliance. This approach eliminates runtime JSON schema parsing overhead and leverages compile-time type safety.

import (
	"encoding/json"
	"fmt"

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

var validate = validator.New()

type LLMResponse struct {
	Intent     string  `json:"intent" validate:"required,oneof=booking cancellation inquiry"`
	Details    Detail  `json:"details" validate:"required,dive"`
	Confidence float64 `json:"confidence" validate:"required,min=0,max=1"`
}

type Detail struct {
	EntityID string `json:"entity_id" validate:"required,uuid"`
	Reason   string `json:"reason" validate:"required,min=3,max=100"`
}

func ValidateLLMResponse(rawJSON []byte) (*LLMResponse, error) {
	var result LLMResponse
	if err := json.Unmarshal(rawJSON, &result); err != nil {
		return nil, fmt.Errorf("JSON unmarshal failed: %w", err)
	}
	if err := validate.Struct(result); err != nil {
		return nil, fmt.Errorf("schema validation failed: %w", err)
	}
	return &result, nil
}

Step 3: Build the Interception Middleware and Re-generation Loop

This middleware wraps the LLM Gateway API call. It intercepts the raw JSON response, runs validation, and triggers a re-generation loop with a modified system prompt if validation fails. The endpoint /api/v2/ai/llm/conversations returns a single completion payload and does not support pagination. The middleware handles 401, 403, and 5xx responses explicitly before attempting validation.

import (
	"context"
	"fmt"
	"time"

	platformclientv2 "github.com/mypurecloud/platform-client-sdk-go/platformclientv2"
)

type LLMGatewayMiddleware struct {
	apiClient        *platformclientv2.ApiClient
	maxRetries       int
	baseSystemPrompt string
}

func NewLLMGatewayMiddleware(client *platformclientv2.ApiClient, maxRetries int, systemPrompt string) *LLMGatewayMiddleware {
	return &LLMGatewayMiddleware{
		apiClient:        client,
		maxRetries:       maxRetries,
		baseSystemPrompt: systemPrompt,
	}
}

func (m *LLMGatewayMiddleware) ExecuteWithValidation(ctx context.Context, userMessage string, model string) (*LLMResponse, error) {
	currentSystemPrompt := m.baseSystemPrompt
	for attempt := 0; attempt <= m.maxRetries; attempt++ {
		req := platformclientv2.Postaillmconversationsrequest{
			Model: platformclientv2.PtrString(model),
			Messages: []platformclientv2.Message{
				{Role: platformclientv2.PtrString("system"), Content: platformclientv2.PtrString(currentSystemPrompt)},
				{Role: platformclientv2.PtrString("user"), Content: platformclientv2.PtrString(userMessage)},
			},
		}

		api := platformclientv2.NewAiApi(m.apiClient)
		resp, httpResp, err := api.PostAiLlmConversations(ctx, req)
		if err != nil {
			return nil, fmt.Errorf("LLM Gateway API call failed: %w", err)
		}
		defer httpResp.Body.Close()

		if httpResp.StatusCode == http.StatusForbidden {
			return nil, fmt.Errorf("403 Forbidden: insufficient permissions for ai:llm:write")
		}
		if httpResp.StatusCode == http.StatusUnauthorized {
			return nil, fmt.Errorf("401 Unauthorized: token expired or invalid")
		}
		if httpResp.StatusCode >= 500 {
			return nil, fmt.Errorf("server error: status %d", httpResp.StatusCode)
		}

		// Extract raw JSON from SDK response
		rawJSON, err := json.Marshal(resp.Choices[0].Message.Content)
		if err != nil {
			return nil, fmt.Errorf("failed to marshal response content: %w", err)
		}

		validated, err := ValidateLLMResponse(rawJSON)
		if err == nil {
			return validated, nil
		}

		// Schema violation detected. Trigger re-generation with stricter prompt.
		currentSystemPrompt = fmt.Sprintf("%s\n\nCRITICAL: Your previous response failed JSON schema validation. Errors: %v. You must output strictly valid JSON matching the required structure.", currentSystemPrompt, err)
		fmt.Printf("Attempt %d/%d: Validation failed. Retrying with corrected prompt.\n", attempt+1, m.maxRetries+1)
		time.Sleep(500 * time.Millisecond)
	}

	return nil, fmt.Errorf("max retries exceeded: LLM failed to produce valid JSON after %d attempts", m.maxRetries+1)
}

Complete Working Example

The following script combines all components into a runnable module. Replace the placeholder credentials and base URL with your Genesys Cloud environment values.

package main

import (
	"context"
	"crypto/tls"
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"strings"
	"sync"
	"time"

	platformclientv2 "github.com/mypurecloud/platform-client-sdk-go/platformclientv2"
	"github.com/go-playground/validator/v10"
)

// TokenManager handles OAuth client credentials flow
type TokenManager struct {
	mu           sync.RWMutex
	token        string
	expiresAt    time.Time
	clientID     string
	clientSecret string
	baseURL      string
	httpClient   *http.Client
}

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

func NewTokenManager(clientID, clientSecret, baseURL string) *TokenManager {
	return &TokenManager{
		clientID:     clientID,
		clientSecret: clientSecret,
		baseURL:      baseURL,
		httpClient: &http.Client{
			Timeout: 10 * time.Second,
			Transport: &http.Transport{
				TLSClientConfig: &tls.Config{MinVersion: tls.VersionTLS12},
			},
		},
	}
}

func (tm *TokenManager) GetToken(ctx context.Context) (string, error) {
	tm.mu.RLock()
	if tm.token != "" && time.Now().Before(tm.expiresAt.Add(-30 * time.Second)) {
		token := tm.token
		tm.mu.RUnlock()
		return token, nil
	}
	tm.mu.RUnlock()

	tm.mu.Lock()
	defer tm.mu.Unlock()

	if tm.token != "" && time.Now().Before(tm.expiresAt.Add(-30 * time.Second)) {
		return tm.token, nil
	}

	payload := fmt.Sprintf("grant_type=client_credentials&client_id=%s&client_secret=%s&scope=ai:llm:read+ai:llm:write", tm.clientID, tm.clientSecret)
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, fmt.Sprintf("%s/oauth/token", tm.baseURL), strings.NewReader(payload))
	if err != nil {
		return "", fmt.Errorf("failed to create token request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	resp, err := tm.httpClient.Do(req)
	if err != nil {
		return "", fmt.Errorf("token request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("token request returned status %d", resp.StatusCode)
	}

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

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

// RetryTransport handles 429 rate limits
type RetryTransport struct {
	base http.RoundTripper
}

func (rt *RetryTransport) RoundTrip(req *http.Request) (*http.Response, error) {
	var resp *http.Response
	var err error
	maxRetries := 3
	for attempt := 0; attempt <= maxRetries; attempt++ {
		resp, err = rt.base.RoundTrip(req)
		if err != nil {
			return nil, err
		}
		if resp.StatusCode == http.StatusTooManyRequests {
			retryAfter := 2 * time.Duration(attempt+1) * time.Second
			time.Sleep(retryAfter)
			continue
		}
		return resp, nil
	}
	return resp, fmt.Errorf("max retries exceeded for 429 response")
}

func NewGenesysClient(baseURL, clientID, clientSecret string) (*platformclientv2.ApiClient, error) {
	config := platformclientv2.NewConfiguration()
	config.BasePath = baseURL
	config.Debug = false

	client := &http.Client{Timeout: 30 * time.Second}
	client.Transport = &RetryTransport{base: http.DefaultTransport}
	config.HTTPClient = client

	apiClient := platformclientv2.NewApiClient(config)
	authClient := apiClient.GetAuthClient()
	authClient.SetAuthMode("client_credentials")
	authClient.SetClientId(clientID)
	authClient.SetClientSecret(clientSecret)
	authClient.SetScopes([]string{"ai:llm:read", "ai:llm:write"})

	if err := authClient.Login(); err != nil {
		return nil, fmt.Errorf("failed to authenticate with Genesys Cloud: %w", err)
	}

	return apiClient, nil
}

var validate = validator.New()

type LLMResponse struct {
	Intent     string  `json:"intent" validate:"required,oneof=booking cancellation inquiry"`
	Details    Detail  `json:"details" validate:"required,dive"`
	Confidence float64 `json:"confidence" validate:"required,min=0,max=1"`
}

type Detail struct {
	EntityID string `json:"entity_id" validate:"required,uuid"`
	Reason   string `json:"reason" validate:"required,min=3,max=100"`
}

func ValidateLLMResponse(rawJSON []byte) (*LLMResponse, error) {
	var result LLMResponse
	if err := json.Unmarshal(rawJSON, &result); err != nil {
		return nil, fmt.Errorf("JSON unmarshal failed: %w", err)
	}
	if err := validate.Struct(result); err != nil {
		return nil, fmt.Errorf("schema validation failed: %w", err)
	}
	return &result, nil
}

type LLMGatewayMiddleware struct {
	apiClient        *platformclientv2.ApiClient
	maxRetries       int
	baseSystemPrompt string
}

func NewLLMGatewayMiddleware(client *platformclientv2.ApiClient, maxRetries int, systemPrompt string) *LLMGatewayMiddleware {
	return &LLMGatewayMiddleware{
		apiClient:        client,
		maxRetries:       maxRetries,
		baseSystemPrompt: systemPrompt,
	}
}

func (m *LLMGatewayMiddleware) ExecuteWithValidation(ctx context.Context, userMessage string, model string) (*LLMResponse, error) {
	currentSystemPrompt := m.baseSystemPrompt
	for attempt := 0; attempt <= m.maxRetries; attempt++ {
		req := platformclientv2.Postaillmconversationsrequest{
			Model: platformclientv2.PtrString(model),
			Messages: []platformclientv2.Message{
				{Role: platformclientv2.PtrString("system"), Content: platformclientv2.PtrString(currentSystemPrompt)},
				{Role: platformclientv2.PtrString("user"), Content: platformclientv2.PtrString(userMessage)},
			},
		}

		api := platformclientv2.NewAiApi(m.apiClient)
		resp, httpResp, err := api.PostAiLlmConversations(ctx, req)
		if err != nil {
			return nil, fmt.Errorf("LLM Gateway API call failed: %w", err)
		}
		defer httpResp.Body.Close()

		if httpResp.StatusCode == http.StatusForbidden {
			return nil, fmt.Errorf("403 Forbidden: insufficient permissions for ai:llm:write")
		}
		if httpResp.StatusCode == http.StatusUnauthorized {
			return nil, fmt.Errorf("401 Unauthorized: token expired or invalid")
		}
		if httpResp.StatusCode >= 500 {
			return nil, fmt.Errorf("server error: status %d", httpResp.StatusCode)
		}

		rawJSON, err := json.Marshal(resp.Choices[0].Message.Content)
		if err != nil {
			return nil, fmt.Errorf("failed to marshal response content: %w", err)
		}

		validated, err := ValidateLLMResponse(rawJSON)
		if err == nil {
			return validated, nil
		}

		currentSystemPrompt = fmt.Sprintf("%s\n\nCRITICAL: Your previous response failed JSON schema validation. Errors: %v. You must output strictly valid JSON matching the required structure.", currentSystemPrompt, err)
		fmt.Printf("Attempt %d/%d: Validation failed. Retrying with corrected prompt.\n", attempt+1, m.maxRetries+1)
		time.Sleep(500 * time.Millisecond)
	}

	return nil, fmt.Errorf("max retries exceeded: LLM failed to produce valid JSON after %d attempts", m.maxRetries+1)
}

func main() {
	ctx := context.Background()
	baseURL := os.Getenv("GENESYS_BASE_URL")
	clientID := os.Getenv("GENESYS_CLIENT_ID")
	clientSecret := os.Getenv("GENESYS_CLIENT_SECRET")

	if baseURL == "" || clientID == "" || clientSecret == "" {
		fmt.Println("Set GENESYS_BASE_URL, GENESYS_CLIENT_ID, and GENESYS_CLIENT_SECRET environment variables")
		os.Exit(1)
	}

	apiClient, err := NewGenesysClient(baseURL, clientID, clientSecret)
	if err != nil {
		fmt.Printf("Failed to initialize client: %v\n", err)
		os.Exit(1)
	}

	systemPrompt := "You are a customer service classifier. Respond only with valid JSON matching this schema: {\"intent\": \"booking|cancellation|inquiry\", \"details\": {\"entity_id\": \"uuid\", \"reason\": \"string\"}, \"confidence\": 0.0-1.0}"
	middleware := NewLLMGatewayMiddleware(apiClient, 3, systemPrompt)

	result, err := middleware.ExecuteWithValidation(ctx, "I need to change my flight to next Tuesday.", "gpt-4")
	if err != nil {
		fmt.Printf("Middleware execution failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("Validated response: %+v\n", result)
}

Common Errors & Debugging

Error: 401 Unauthorized

• Cause: The OAuth token expired during a long-running validation loop, or the client credentials lack the ai:llm:read and ai:llm:write scopes.
• Fix: Ensure the token manager refreshes tokens before expiration. Verify the OAuth application in the Genesys Cloud admin console has the correct scopes assigned to the client credentials grant type.
• Code showing the fix: The TokenManager.GetToken method includes a thirty-second safety buffer. If the SDK fails with 401, call authClient.Login() again to force a fresh token exchange.

Error: 403 Forbidden

• Cause: The OAuth token is valid, but the associated user or application lacks the ai:llm:manage or ai:llm:write permission sets in Genesys Cloud.
• Fix: Navigate to the Genesys Cloud admin interface, locate the application, and assign the AI and Machine Learning permission set with Manage capabilities.
• Code showing the fix: The middleware explicitly checks httpResp.StatusCode == http.StatusForbidden and returns a descriptive error. Add permission verification logic before initialization if automated provisioning is required.

Error: 429 Too Many Requests

• Cause: The re-generation loop or concurrent API calls exceeded the Genesys Cloud rate limit threshold for the organization.
• Fix: The RetryTransport implements exponential backoff. Increase the base delay or implement a token bucket algorithm if running in high-throughput environments.
• Code showing the fix: The RetryTransport.RoundTrip method sleeps for 2 * time.Duration(attempt+1) * time.Second before retrying. Adjust the multiplier based on your organization rate limit tier.

Error: Schema Validation Failed After Max Retries

• Cause: The LLM model cannot produce the required structure despite prompt adjustments, often due to conflicting system instructions or unsupported JSON features in the model version.
• Fix: Simplify the target struct, reduce validation constraints, or switch to a model with stronger JSON mode support. Add response_format: { type: "json_object" } to the API request if the model supports it.
• Code showing the fix: Modify the currentSystemPrompt concatenation logic to inject explicit JSON formatting instructions and strip markdown code blocks before validation.

Official References

• Genesys Cloud LLM Gateway API Documentation
• Genesys Cloud Go SDK Reference
• OAuth 2.0 Client Credentials Flow
• go-playground/validator Documentation