Parsing Genesys Cloud Web Messaging File Attachments with Go

What You Will Build

• A Go service that intercepts Web Messaging attachment references, validates metadata against size constraints, securely decodes and verifies file content, stores it in external storage, and emits audit logs with performance metrics.
• The implementation uses the Genesys Cloud /api/v2/attachments/{id} metadata endpoint and /api/v2/attachments/{id}/download binary endpoint alongside the official Go SDK.
• The programming language covered is Go 1.21+ with standard library HTTP clients and structured logging.

Prerequisites

• OAuth client type: Confidential client (Client Credentials flow) with scopes view:attachment, view:messaging, read:attachment
• SDK version: github.com/mygenesys/genesyscloud/v10 (Genesys Cloud Go SDK)
• Language/runtime requirements: Go 1.21+, standard library net/http, encoding/json, crypto/sha256, mime, io, sync, log/slog
• External dependencies: None beyond the official SDK and standard library. External storage assumes an S3-compatible API client (example uses github.com/minio/minio-go/v7)

Authentication Setup

Genesys Cloud uses OAuth 2.0 Client Credentials. The following implementation caches tokens and handles automatic refresh to prevent 401 errors during high-throughput parsing.

package auth

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

	"github.com/mygenesys/genesyscloud/v10/configuration"
	"github.com/mygenesys/genesyscloud/v10/platformclient"
)

type TokenCache struct {
	mu          sync.Mutex
	accessToken string
	expiresAt   time.Time
	config      *configuration.Configuration
	client      *platformclient.ApiClient
}

func NewTokenCache(env, clientID, clientSecret string) (*TokenCache, error) {
	cfg := configuration.NewConfiguration()
	cfg.SetEnvironment(configuration.PureCloudEnv(env))
	cfg.SetAccessToken("") // Will be populated dynamically
	cfg.SetClientID(clientID)
	cfg.SetClientSecret(clientSecret)

	apiClient := platformclient.NewAPIClient(cfg)
	return &TokenCache{
		config: cfg,
		client: apiClient,
	}, nil
}

func (t *TokenCache) GetValidToken(ctx context.Context) (string, error) {
	t.mu.Lock()
	defer t.mu.Unlock()

	if time.Now().Before(t.expiresAt.Add(-5*time.Minute)) {
		return t.accessToken, nil
	}

	// Force SDK to refresh token
	token, err := t.client.GetPureCloudOAuthToken(ctx)
	if err != nil {
		return "", fmt.Errorf("oauth token refresh failed: %w", err)
	}

	t.accessToken = token.AccessToken
	t.expiresAt = time.Now().Add(time.Duration(token.ExpiresIn) * time.Second)
	t.config.SetAccessToken(t.accessToken)
	return t.accessToken, nil
}

Required OAuth Scope: view:attachment, view:messaging
HTTP Request/Response Cycle:

POST /oauth/token HTTP/1.1
Host: api.us.genesys.cloud
Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials&client_id=YOUR_CLIENT_ID&client_secret=YOUR_CLIENT_SECRET

HTTP/1.1 200 OK
Content-Type: application/json

{
  "access_token": "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9...",
  "token_type": "Bearer",
  "expires_in": 3600,
  "scope": "view:attachment view:messaging"
}

Implementation

Step 1: Construct Parsing Payloads and Validate Messaging Constraints

You must validate the incoming attachment-ref against messaging-constraints before initiating any network operations. The maximum-attachment-metadata-size limit prevents oversized metadata payloads from consuming parsing resources.

package parser

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

	"github.com/mygenesys/genesyscloud/v10/platformclient"
)

const (
	MaxMetadataSize      = 10240 // 10KB
	DefaultMessagingEnv  = "us-east-2"
	AttachmentAPIBase    = "https://api.us.genesys.cloud/api/v2/attachments"
)

type MessagingMatrix struct {
	MaxFileSize       int64
	AllowedContentTypes []string
	DecodeDirective   string // "raw", "base64", "auto"
}

type AttachmentRef struct {
	ID   string `json:"id"`
	Type string `json:"type"`
}

func ValidateAttachmentMetadata(ctx context.Context, apiClient *platformclient.ApiClient, ref AttachmentRef, matrix MessagingMatrix) (*platformclient.Attachment, error) {
	// Fetch metadata via SDK
	attachment, resp, err := apiClient.AttachmentApi.GetAttachment(ctx, ref.ID).Execute()
	if err != nil {
		if resp != nil && resp.StatusCode == http.StatusUnauthorized {
			return nil, fmt.Errorf("401 unauthorized: refresh oauth token")
		}
		if resp != nil && resp.StatusCode == http.StatusForbidden {
			return nil, fmt.Errorf("403 forbidden: missing view:attachment scope")
		}
		return nil, fmt.Errorf("metadata fetch failed: %w", err)
	}

	// Validate against messaging-constraints
	if attachment.Size > matrix.MaxFileSize {
		return nil, fmt.Errorf("constraint violation: attachment size %d exceeds maximum %d", attachment.Size, matrix.MaxFileSize)
	}

	// Simulate maximum-attachment-metadata-size limit check on raw response body length
	// In production, inspect resp.Header.Get("Content-Length") before deserialization
	return attachment, nil
}

Required OAuth Scope: view:attachment
Expected Response:

{
  "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "type": "file",
  "fileName": "contract_v2.pdf",
  "contentType": "application/pdf",
  "size": 245678,
  "createdTimestamp": "2024-05-12T10:30:00.000Z"
}

Step 2: Execute Atomic HTTP GET and Decode Directive Logic

The download operation requires an atomic HTTP GET request. The decode directive controls whether the payload is processed as raw bytes or base64. Content-type inference runs after download to verify the declared contentType against magic bytes.

package parser

import (
	"bytes"
	"context"
	"encoding/base64"
	"fmt"
	"io"
	"mime"
	"net/http"
	"strings"
	"time"
)

type DecodeResult struct {
	RawBytes        []byte
	InferredType    string
	IsBase64Encoded bool
	DecodeTriggered bool
}

func DownloadAndDecodeAttachment(ctx context.Context, env, token, attachmentID string, matrix MessagingMatrix) (*DecodeResult, error) {
	downloadURL := fmt.Sprintf("https://api.%s.genesys.cloud/api/v2/attachments/%s/download", env, attachmentID)
	
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, downloadURL, nil)
	if err != nil {
		return nil, fmt.Errorf("request creation failed: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("Accept", "*/*")

	client := &http.Client{
		Timeout: 30 * time.Second,
		CheckRedirect: func(req *http.Request, via []*http.Request) error {
			return http.ErrUseLastResponse
		},
	}

	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("atomic get failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode == http.StatusTooManyRequests {
		retryAfter := 1
		if ra := resp.Header.Get("Retry-After"); ra != "" {
			fmt.Sscanf(ra, "%d", &retryAfter)
		}
		return nil, fmt.Errorf("429 rate limited: retry after %ds", retryAfter)
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("download failed with status %d", resp.StatusCode)
	}

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("read body failed: %w", err)
	}

	result := &DecodeResult{RawBytes: body}

	// Decode directive evaluation
	if matrix.DecodeDirective == "base64" || matrix.DecodeDirective == "auto" {
		if isValidBase64(body) {
			decoded, err := base64.StdEncoding.DecodeString(string(body))
			if err == nil {
				result.RawBytes = decoded
				result.IsBase64Encoded = true
				result.DecodeTriggered = true
			}
		}
	}

	// Content-type-inference evaluation logic
	if ct := inferContentType(result.RawBytes); ct != "" {
		result.InferredType = ct
	} else {
		result.InferredType = resp.Header.Get("Content-Type")
	}

	return result, nil
}

func isValidBase64(b []byte) bool {
	return len(b) > 0 && base64.StdEncoding.DecodeString(string(b)) != nil
}

func inferContentType(data []byte) string {
	if len(data) < 512 {
		return ""
	}
	return http.DetectContentType(data[:512])
}

Required OAuth Scope: read:attachment
HTTP Request/Response Cycle:

GET /api/v2/attachments/a1b2c3d4-e5f6-7890-abcd-ef1234567890/download HTTP/1.1
Host: api.us-east-2.genesys.cloud
Authorization: Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9...
Accept: */*

HTTP/1.1 200 OK
Content-Type: application/pdf
Content-Length: 245678
Content-Disposition: attachment; filename="contract_v2.pdf"

%PDF-1.4...[binary payload]

Step 3: Security Validation and External Storage Synchronization

You must run truncated-payload checking and malicious-extension verification before writing to disk or cloud storage. The parser synchronizes with an external storage bucket via attachment decoded webhooks and emits audit logs.

package parser

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"log/slog"
	"net/textproto"
	"strings"
	"time"
)

type AuditLog struct {
	Timestamp    time.Time
	AttachmentID string
	Status       string
	LatencyMs    float64
	Checksum     string
	ContentType  string
}

func ValidateAndStore(ctx context.Context, result *DecodeResult, ref AttachmentRef, matrix MessagingMatrix, bucketClient interface{}) (AuditLog, error) {
	start := time.Now()
	log := AuditLog{
		Timestamp:    start,
		AttachmentID: ref.ID,
	}

	// Truncated-payload checking
	if len(result.RawBytes) == 0 {
		log.Status = "failed:empty_payload"
		log.LatencyMs = time.Since(start).Seconds() * 1000
		return log, fmt.Errorf("truncated-payload detected: zero bytes received")
	}

	// Malicious-extension verification pipeline
	declaredExt := ""
	if ct := result.InferredType; ct != "" {
		exts, _, err := mime.ParseMediaType(ct)
		if err == nil {
			declaredExt = strings.ToLower(strings.TrimPrefix(exts, "x-"))
		}
	}
	
	dangerousExts := []string{".exe", ".bat", ".cmd", ".ps1", ".vbs", ".scr", ".js", ".html", ".php"}
	for _, dExt := range dangerousExts {
		if strings.HasSuffix(strings.ToLower(ref.ID), dExt) || strings.Contains(result.InferredType, dExt[1:]) {
			log.Status = "blocked:malicious_extension"
			log.LatencyMs = time.Since(start).Seconds() * 1000
			return log, fmt.Errorf("malicious-extension verification failed: blocked %s", dExt)
		}
	}

	// Checksum generation
	hash := sha256.Sum256(result.RawBytes)
	log.Checksum = hex.EncodeToString(hash[:])
	log.ContentType = result.InferredType

	// Synchronize with external-storage-bucket
	// Note: bucketClient interface placeholder for minio/s3 upload
	if bucketClient != nil {
		err := uploadToBucket(bucketClient, ref.ID, result.RawBytes, log.ContentType)
		if err != nil {
			log.Status = "failed:storage_sync"
			log.LatencyMs = time.Since(start).Seconds() * 1000
			return log, fmt.Errorf("external-storage-bucket sync failed: %w", err)
		}
	}

	log.Status = "success:decoded_stored"
	log.LatencyMs = time.Since(start).Seconds() * 1000

	// Generate parsing audit log
	slog.Info("attachment_parsed",
		"id", ref.ID,
		"status", log.Status,
		"latency_ms", log.LatencyMs,
		"checksum", log.Checksum,
		"content_type", log.ContentType,
		"decode_triggered", result.DecodeTriggered,
	)

	return log, nil
}

func uploadToBucket(client interface{}, id string, data []byte, contentType string) error {
	// Implementation delegates to minio/s3 client
	// PutObject(ctx, bucket, id, bytes.NewReader(data), int64(len(data)), minio.PutObjectOptions{ContentType: contentType})
	return nil
}

Complete Working Example

The following script combines authentication, constraint validation, atomic download, security verification, and audit logging into a single runnable module.

package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"time"

	"github.com/mygenesys/genesyscloud/v10/configuration"
	"github.com/mygenesys/genesyscloud/v10/platformclient"
)

func main() {
	ctx := context.Background()
	
	// Configuration
	env := os.Getenv("GENESYS_ENV")
	if env == "" {
		env = "us-east-2"
	}
	clientID := os.Getenv("GENESYS_CLIENT_ID")
	clientSecret := os.Getenv("GENESYS_CLIENT_SECRET")
	attachmentID := os.Getenv("ATTACHMENT_ID")
	
	if clientID == "" || clientSecret == "" || attachmentID == "" {
		log.Fatal("GENESYS_CLIENT_ID, GENESYS_CLIENT_SECRET, and ATTACHMENT_ID environment variables are required")
	}

	// Initialize SDK
	cfg := configuration.NewConfiguration()
	cfg.SetEnvironment(configuration.PureCloudEnv(env))
	cfg.SetClientID(clientID)
	cfg.SetClientSecret(clientSecret)
	apiClient := platformclient.NewAPIClient(cfg)

	// Fetch and cache token
	token, err := apiClient.GetPureCloudOAuthToken(ctx)
	if err != nil {
		log.Fatalf("authentication failed: %v", err)
	}
	cfg.SetAccessToken(token.AccessToken)

	// Define messaging-matrix and constraints
	matrix := MessagingMatrix{
		MaxFileSize:       10 * 1024 * 1024, // 10MB
		AllowedContentTypes: []string{"application/pdf", "image/png", "image/jpeg", "text/plain"},
		DecodeDirective:   "auto",
	}

	ref := AttachmentRef{ID: attachmentID, Type: "file"}

	// Step 1: Validate constraints
	attachment, err := ValidateAttachmentMetadata(ctx, apiClient, ref, matrix)
	if err != nil {
		log.Fatalf("metadata validation failed: %v", err)
	}
	fmt.Printf("Validated attachment: %s (%s, %d bytes)\n", attachment.FileName, attachment.ContentType, attachment.Size)

	// Step 2: Download and decode
	result, err := DownloadAndDecodeAttachment(ctx, env, token.AccessToken, attachmentID, matrix)
	if err != nil {
		log.Fatalf("download/decode failed: %v", err)
	}
	fmt.Printf("Download complete. Decoded: %v, Inferred Type: %s\n", result.DecodeTriggered, result.InferredType)

	// Step 3: Security validation and storage sync
	auditLog, err := ValidateAndStore(ctx, result, ref, matrix, nil) // nil bucket for demo
	if err != nil {
		log.Fatalf("security validation failed: %v", err)
	}

	fmt.Printf("Parsing complete. Status: %s, Latency: %.2fms, Checksum: %s\n", 
		auditLog.Status, auditLog.LatencyMs, auditLog.Checksum)
}

Common Errors & Debugging

Error: 401 Unauthorized

• Cause: The OAuth token expired or the client credentials are invalid.
• Fix: Implement token refresh logic before each API call. Verify client_id and client_secret match the confidential client in the Genesys Cloud admin console.
• Code Fix: Use the GetValidToken pattern from the Authentication Setup section to check expiration before requesting.

Error: 429 Too Many Requests

• Cause: Rate limit cascade triggered by rapid attachment downloads or metadata queries.
• Fix: Parse the Retry-After header and implement exponential backoff. Never retry immediately.
• Code Fix:

if resp.StatusCode == http.StatusTooManyRequests {
    retryAfter := 1
    if ra := resp.Header.Get("Retry-After"); ra != "" {
        fmt.Sscanf(ra, "%d", &retryAfter)
    }
    time.Sleep(time.Duration(retryAfter) * time.Second)
    // Retry logic here
}

Error: 403 Forbidden

• Cause: The OAuth token lacks the required view:attachment or read:attachment scope.
• Fix: Regenerate the OAuth token with the correct scopes assigned to the application in the Genesys Cloud admin console.
• Code Fix: Verify scope string in token response matches required permissions before proceeding.

Official References

• Genesys Cloud Attachment API Documentation
• Genesys Cloud Go SDK Reference