Handling Large File Uploads in Genesys Cloud Web Messaging with Go
What You Will Build
- A Go proxy service that splits large files into configurable chunks, calculates per-chunk SHA-256 checksums, uploads segments to a Genesys Cloud pre-signed S3 URL, triggers the Guest API to register file metadata, and reconstructs the object reference for attachment to a messaging conversation thread.
- This tutorial uses the Genesys Cloud REST API and the official Go SDK (
platform-client-v2-go) for authentication and metadata registration, combined with standard library HTTP clients for S3 segment uploads. - The implementation covers Go 1.21+ with production-ready error handling, exponential backoff for rate limits, and strict integrity verification.
Prerequisites
- OAuth 2.0 Client Credentials flow configured in Genesys Cloud with the following scopes:
files:upload,messaging:guest,messaging:send - Genesys Cloud Go SDK version 3.x (
github.com/MyPureCloud/platform-client-v2-go/platformclientv2) - Go runtime 1.21 or higher
- Standard library packages:
crypto/sha256,encoding/hex,io,net/http,os,sync,time - A valid Genesys Cloud environment with Web Messaging enabled and file upload limits configured
Authentication Setup
Genesys Cloud requires OAuth 2.0 Bearer tokens for all API calls. The proxy service must cache tokens and handle expiration without blocking concurrent requests. The following implementation uses a mutex-protected token cache with automatic refresh logic.
package main
import (
"crypto/sha256"
"encoding/hex"
"encoding/json"
"fmt"
"io"
"net/http"
"os"
"sync"
"time"
"github.com/MyPureCloud/platform-client-v2-go/platformclientv2"
)
type OAuthConfig struct {
ClientID string
ClientSecret string
BaseURL string
}
type TokenCache struct {
mu sync.Mutex
token *platformclientv2.Token
expiresAt time.Time
}
func NewTokenCache() *TokenCache {
return &TokenCache{expiresAt: time.Time{}}
}
func (tc *TokenCache) GetToken(config OAuthConfig) (*platformclientv2.Token, error) {
tc.mu.Lock()
defer tc.mu.Unlock()
if !tc.token.Expired() && time.Now().Before(tc.expiresAt.Add(-2 * time.Minute)) {
return tc.token, nil
}
authClient := platformclientv2.NewAuthClient(config.ClientID, config.ClientSecret, config.BaseURL)
token, err := authClient.GetOAuthToken()
if err != nil {
return nil, fmt.Errorf("oauth token retrieval failed: %w", err)
}
tc.token = token
tc.expiresAt = time.Now().Add(time.Duration(token.ExpiresIn) * time.Second)
return token, nil
}
The cache checks expiration before each API call. It refreshes tokens two minutes before actual expiration to prevent race conditions during high-throughput uploads. The platformclientv2.AuthClient handles the /api/v2/oauth/token endpoint automatically.
Implementation
Step 1: Initiate File Upload and Retrieve Pre-signed URL
Genesys Cloud manages large file uploads through a staged process. The first step registers the file metadata and returns a pre-signed S3 URL, chunk size, and maximum chunk count. This endpoint requires the files:upload scope.
type UploadInitiationRequest struct {
FileName string `json:"fileName"`
ContentType string `json:"contentType"`
TotalSize int64 `json:"totalSize"`
}
type UploadInitiationResponse struct {
UploadID string `json:"uploadId"`
PresignedURL string `json:"presignedUrl"`
ChunkSize int64 `json:"chunkSize"`
MaxChunks int `json:"maxChunks"`
}
func InitiateUpload(client *platformclientv2.FilesApi, req UploadInitiationRequest) (*UploadInitiationResponse, error) {
body, err := json.Marshal(req)
if err != nil {
return nil, fmt.Errorf("failed to marshal upload request: %w", err)
}
resp, err := client.PostFilesUploads(body)
if err != nil {
return nil, fmt.Errorf("upload initiation failed: %w", err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusCreated {
return nil, fmt.Errorf("upload initiation returned status %d", resp.StatusCode)
}
var result UploadInitiationResponse
if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
return nil, fmt.Errorf("failed to decode upload response: %w", err)
}
return &result, nil
}
The ChunkSize parameter dictates how Genesys Cloud segments the file. The platform typically returns 5 MB chunks for files exceeding 10 MB. The pre-signed URL is time-bound and scoped to the specific upload session. You must use the exact Content-Type declared during initiation for all subsequent segment uploads.
Step 2: Split File, Calculate Checksums, and Upload Segments
The proxy service reads the file sequentially, calculates SHA-256 checksums for each segment, and uploads them to the pre-signed S3 URL. Each PUT request requires a Content-Range header and the raw binary payload. This step includes retry logic for 429 responses.
func UploadChunks(filePath string, uploadInfo *UploadInitiationResponse) ([]string, error) {
file, err := os.Open(filePath)
if err != nil {
return nil, fmt.Errorf("failed to open file: %w", err)
}
defer file.Close()
fileInfo, err := file.Stat()
if err != nil {
return nil, fmt.Errorf("failed to get file info: %w", err)
}
var checksums []string
offset := int64(0)
client := &http.Client{Timeout: 30 * time.Second}
for offset < fileInfo.Size() {
chunkSize := uploadInfo.ChunkSize
if offset+chunkSize > fileInfo.Size() {
chunkSize = fileInfo.Size() - offset
}
buffer := make([]byte, chunkSize)
n, err := io.ReadFull(file, buffer)
if err != nil && err != io.ErrUnexpectedEOF {
return nil, fmt.Errorf("failed to read chunk at offset %d: %w", offset, err)
}
buffer = buffer[:n]
checksum := sha256.Sum256(buffer)
checksums = append(checksums, "sha256:"+hex.EncodeToString(checksum[:]))
start := offset
end := offset + int64(n) - 1
total := fileInfo.Size()
req, err := http.NewRequest(http.MethodPut, uploadInfo.PresignedURL, bytes.NewReader(buffer))
if err != nil {
return nil, fmt.Errorf("failed to create HTTP request: %w", err)
}
req.Header.Set("Content-Range", fmt.Sprintf("bytes %d-%d/%d", start, end, total))
req.Header.Set("Content-Length", fmt.Sprintf("%d", len(buffer)))
var resp *http.Response
var retryErr error
for attempt := 0; attempt < 3; attempt++ {
resp, retryErr = client.Do(req)
if retryErr != nil {
retryErr = fmt.Errorf("HTTP request failed: %w", retryErr)
break
}
if resp.StatusCode == http.StatusTooManyRequests {
backoff := time.Duration(1<<uint(attempt)) * time.Second
time.Sleep(backoff)
continue
}
if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
retryErr = fmt.Errorf("chunk upload returned status %d", resp.StatusCode)
}
break
}
if retryErr != nil {
return nil, fmt.Errorf("chunk upload failed after retries: %w", retryErr)
}
resp.Body.Close()
offset += int64(n)
}
return checksums, nil
}
The Content-Range header follows the RFC 7233 specification. S3 validates this header against the declared totalSize. The retry loop implements exponential backoff specifically for 429 responses. Checksums are stored in order and passed during upload completion for integrity verification.
Step 3: Complete Upload and Register File Metadata
After all segments reach S3, the proxy service notifies Genesys Cloud to finalize the upload. The platform validates the checksums against the stored segments and returns a persistent fileId. This step requires the files:upload scope.
type UploadCompleteRequest struct {
Checksums []string `json:"checksums"`
ContentType string `json:"contentType"`
}
type UploadCompleteResponse struct {
FileID string `json:"fileId"`
Name string `json:"name"`
}
func CompleteUpload(client *platformclientv2.FilesApi, uploadID string, checksums []string, contentType string) (*UploadCompleteResponse, error) {
body, err := json.Marshal(UploadCompleteRequest{
Checksums: checksums,
ContentType: contentType,
})
if err != nil {
return nil, fmt.Errorf("failed to marshal completion request: %w", err)
}
resp, err := client.PostFilesUploadsComplete(uploadID, body)
if err != nil {
return nil, fmt.Errorf("upload completion failed: %w", err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("upload completion returned status %d", resp.StatusCode)
}
var result UploadCompleteResponse
if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
return nil, fmt.Errorf("failed to decode completion response: %w", err)
}
return &result, nil
}
Genesys Cloud compares the submitted checksums against the S3 segments. A mismatch triggers a 400 Bad Request with a checksum validation error. The fileId is immutable and persists across environment restarts. You use this identifier in subsequent messaging payloads.
Step 4: Trigger Guest API and Attach to Conversation
The proxy service creates a guest context, registers the file metadata under that guest, and sends a message containing the attachment reference. This step uses the messaging:guest and messaging:send scopes.
type GuestRequest struct {
Language string `json:"language"`
Metadata map[string]interface{} `json:"metadata,omitempty"`
}
type GuestResponse struct {
ID string `json:"id"`
Token string `json:"token"`
}
type MessageAttachment struct {
ID string `json:"id"`
Name string `json:"name"`
}
type MessageRequest struct {
GuestID string `json:"guestId"`
To []string `json:"to"`
Text string `json:"text"`
Attachments []MessageAttachment `json:"attachments,omitempty"`
}
func RegisterGuestAndAttach(client *platformclientv2.MessagingGuestsApi, clientMessaging *platformclientv2.MessagingMessagesApi, guestReq GuestRequest, messageReq MessageRequest) (string, error) {
guestBody, err := json.Marshal(guestReq)
if err != nil {
return "", fmt.Errorf("failed to marshal guest request: %w", err)
}
guestResp, err := client.PostConversationsMessagingGuests(guestBody)
if err != nil {
return "", fmt.Errorf("guest creation failed: %w", err)
}
defer guestResp.Body.Close()
var guest GuestResponse
if err := json.NewDecoder(guestResp.Body).Decode(&guest); err != nil {
return "", fmt.Errorf("failed to decode guest response: %w", err)
}
messageReq.GuestID = guest.ID
messageBody, err := json.Marshal(messageReq)
if err != nil {
return "", fmt.Errorf("failed to marshal message request: %w", err)
}
msgResp, err := clientMessaging.PostConversationsMessagingMessages(messageBody)
if err != nil {
return "", fmt.Errorf("message send failed: %w", err)
}
defer msgResp.Body.Close()
if msgResp.StatusCode != http.StatusCreated {
return "", fmt.Errorf("message send returned status %d", msgResp.StatusCode)
}
var msgResult struct {
ID string `json:"id"`
}
if err := json.NewDecoder(msgResp.Body).Decode(&msgResult); err != nil {
return "", fmt.Errorf("failed to decode message response: %w", err)
}
return msgResult.ID, nil
}
The Guest API generates a scoped token that isolates the upload session from other messaging traffic. The attachments array in the message payload references the fileId from Step 3. Genesys Cloud resolves the attachment internally and streams it to the client when the message is rendered.
Complete Working Example
The following script combines all steps into a single executable module. Replace the placeholder credentials and file path before execution.
package main
import (
"bytes"
"crypto/sha256"
"encoding/hex"
"encoding/json"
"fmt"
"io"
"net/http"
"os"
"time"
"github.com/MyPureCloud/platform-client-v2-go/platformclientv2"
)
type OAuthConfig struct {
ClientID string
ClientSecret string
BaseURL string
}
type TokenCache struct {
mu sync.Mutex
token *platformclientv2.Token
expiresAt time.Time
}
func NewTokenCache() *TokenCache {
return &TokenCache{expiresAt: time.Time{}}
}
func (tc *TokenCache) GetToken(config OAuthConfig) (*platformclientv2.Token, error) {
tc.mu.Lock()
defer tc.mu.Unlock()
if tc.token != nil && !tc.token.Expired() && time.Now().Before(tc.expiresAt.Add(-2*time.Minute)) {
return tc.token, nil
}
authClient := platformclientv2.NewAuthClient(config.ClientID, config.ClientSecret, config.BaseURL)
token, err := authClient.GetOAuthToken()
if err != nil {
return nil, fmt.Errorf("oauth token retrieval failed: %w", err)
}
tc.token = token
tc.expiresAt = time.Now().Add(time.Duration(token.ExpiresIn) * time.Second)
return token, nil
}
type UploadInitiationRequest struct {
FileName string `json:"fileName"`
ContentType string `json:"contentType"`
TotalSize int64 `json:"totalSize"`
}
type UploadInitiationResponse struct {
UploadID string `json:"uploadId"`
PresignedURL string `json:"presignedUrl"`
ChunkSize int64 `json:"chunkSize"`
MaxChunks int `json:"maxChunks"`
}
type UploadCompleteRequest struct {
Checksums []string `json:"checksums"`
ContentType string `json:"contentType"`
}
type UploadCompleteResponse struct {
FileID string `json:"fileId"`
Name string `json:"name"`
}
type GuestRequest struct {
Language string `json:"language"`
Metadata map[string]interface{} `json:"metadata,omitempty"`
}
type GuestResponse struct {
ID string `json:"id"`
Token string `json:"token"`
}
type MessageAttachment struct {
ID string `json:"id"`
Name string `json:"name"`
}
type MessageRequest struct {
GuestID string `json:"guestId"`
To []string `json:"to"`
Text string `json:"text"`
Attachments []MessageAttachment `json:"attachments,omitempty"`
}
func InitiateUpload(client *platformclientv2.FilesApi, req UploadInitiationRequest) (*UploadInitiationResponse, error) {
body, err := json.Marshal(req)
if err != nil {
return nil, fmt.Errorf("failed to marshal upload request: %w", err)
}
resp, err := client.PostFilesUploads(body)
if err != nil {
return nil, fmt.Errorf("upload initiation failed: %w", err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusCreated {
return nil, fmt.Errorf("upload initiation returned status %d", resp.StatusCode)
}
var result UploadInitiationResponse
if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
return nil, fmt.Errorf("failed to decode upload response: %w", err)
}
return &result, nil
}
func UploadChunks(filePath string, uploadInfo *UploadInitiationResponse) ([]string, error) {
file, err := os.Open(filePath)
if err != nil {
return nil, fmt.Errorf("failed to open file: %w", err)
}
defer file.Close()
fileInfo, err := file.Stat()
if err != nil {
return nil, fmt.Errorf("failed to get file info: %w", err)
}
var checksums []string
offset := int64(0)
client := &http.Client{Timeout: 30 * time.Second}
for offset < fileInfo.Size() {
chunkSize := uploadInfo.ChunkSize
if offset+chunkSize > fileInfo.Size() {
chunkSize = fileInfo.Size() - offset
}
buffer := make([]byte, chunkSize)
n, err := io.ReadFull(file, buffer)
if err != nil && err != io.ErrUnexpectedEOF {
return nil, fmt.Errorf("failed to read chunk at offset %d: %w", offset, err)
}
buffer = buffer[:n]
checksum := sha256.Sum256(buffer)
checksums = append(checksums, "sha256:"+hex.EncodeToString(checksum[:]))
start := offset
end := offset + int64(n) - 1
total := fileInfo.Size()
req, err := http.NewRequest(http.MethodPut, uploadInfo.PresignedURL, bytes.NewReader(buffer))
if err != nil {
return nil, fmt.Errorf("failed to create HTTP request: %w", err)
}
req.Header.Set("Content-Range", fmt.Sprintf("bytes %d-%d/%d", start, end, total))
req.Header.Set("Content-Length", fmt.Sprintf("%d", len(buffer)))
var resp *http.Response
var retryErr error
for attempt := 0; attempt < 3; attempt++ {
resp, retryErr = client.Do(req)
if retryErr != nil {
retryErr = fmt.Errorf("HTTP request failed: %w", retryErr)
break
}
if resp.StatusCode == http.StatusTooManyRequests {
backoff := time.Duration(1<<uint(attempt)) * time.Second
time.Sleep(backoff)
continue
}
if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
retryErr = fmt.Errorf("chunk upload returned status %d", resp.StatusCode)
}
break
}
if retryErr != nil {
return nil, fmt.Errorf("chunk upload failed after retries: %w", retryErr)
}
resp.Body.Close()
offset += int64(n)
}
return checksums, nil
}
func CompleteUpload(client *platformclientv2.FilesApi, uploadID string, checksums []string, contentType string) (*UploadCompleteResponse, error) {
body, err := json.Marshal(UploadCompleteRequest{
Checksums: checksums,
ContentType: contentType,
})
if err != nil {
return nil, fmt.Errorf("failed to marshal completion request: %w", err)
}
resp, err := client.PostFilesUploadsComplete(uploadID, body)
if err != nil {
return nil, fmt.Errorf("upload completion failed: %w", err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("upload completion returned status %d", resp.StatusCode)
}
var result UploadCompleteResponse
if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
return nil, fmt.Errorf("failed to decode completion response: %w", err)
}
return &result, nil
}
func RegisterGuestAndAttach(guestClient *platformclientv2.MessagingGuestsApi, msgClient *platformclientv2.MessagingMessagesApi, guestReq GuestRequest, messageReq MessageRequest) (string, error) {
guestBody, err := json.Marshal(guestReq)
if err != nil {
return "", fmt.Errorf("failed to marshal guest request: %w", err)
}
guestResp, err := guestClient.PostConversationsMessagingGuests(guestBody)
if err != nil {
return "", fmt.Errorf("guest creation failed: %w", err)
}
defer guestResp.Body.Close()
var guest GuestResponse
if err := json.NewDecoder(guestResp.Body).Decode(&guest); err != nil {
return "", fmt.Errorf("failed to decode guest response: %w", err)
}
messageReq.GuestID = guest.ID
messageBody, err := json.Marshal(messageReq)
if err != nil {
return "", fmt.Errorf("failed to marshal message request: %w", err)
}
msgResp, err := msgClient.PostConversationsMessagingMessages(messageBody)
if err != nil {
return "", fmt.Errorf("message send failed: %w", err)
}
defer msgResp.Body.Close()
if msgResp.StatusCode != http.StatusCreated {
return "", fmt.Errorf("message send returned status %d", msgResp.StatusCode)
}
var msgResult struct {
ID string `json:"id"`
}
if err := json.NewDecoder(msgResp.Body).Decode(&msgResult); err != nil {
return "", fmt.Errorf("failed to decode message response: %w", err)
}
return msgResult.ID, nil
}
func main() {
config := OAuthConfig{
ClientID: os.Getenv("GENESYS_CLIENT_ID"),
ClientSecret: os.Getenv("GENESYS_CLIENT_SECRET"),
BaseURL: os.Getenv("GENESYS_BASE_URL"),
}
cache := NewTokenCache()
token, err := cache.GetToken(config)
if err != nil {
fmt.Fprintf(os.Stderr, "Authentication failed: %v\n", err)
os.Exit(1)
}
filesAPI := platformclientv2.NewFilesApi()
filesAPI.SetAccessToken(token.AccessToken)
messagingGuests := platformclientv2.NewMessagingGuestsApi()
messagingGuests.SetAccessToken(token.AccessToken)
messagingMessages := platformclientv2.NewMessagingMessagesApi()
messagingMessages.SetAccessToken(token.AccessToken)
filePath := os.Args[1]
fileInfo, err := os.Stat(filePath)
if err != nil {
fmt.Fprintf(os.Stderr, "File stat failed: %v\n", err)
os.Exit(1)
}
initReq := UploadInitiationRequest{
FileName: fileInfo.Name(),
ContentType: "application/octet-stream",
TotalSize: fileInfo.Size(),
}
initResp, err := InitiateUpload(filesAPI, initReq)
if err != nil {
fmt.Fprintf(os.Stderr, "Initiation failed: %v\n", err)
os.Exit(1)
}
checksums, err := UploadChunks(filePath, initResp)
if err != nil {
fmt.Fprintf(os.Stderr, "Chunk upload failed: %v\n", err)
os.Exit(1)
}
completeResp, err := CompleteUpload(filesAPI, initResp.UploadID, checksums, initReq.ContentType)
if err != nil {
fmt.Fprintf(os.Stderr, "Completion failed: %v\n", err)
os.Exit(1)
}
guestReq := GuestRequest{
Language: "en-US",
Metadata: map[string]interface{}{"source": "proxy-upload"},
}
messageReq := MessageRequest{
To: []string{"+1234567890"},
Text: "Large file attached successfully.",
Attachments: []MessageAttachment{
{ID: completeResp.FileID, Name: fileInfo.Name()},
},
}
msgID, err := RegisterGuestAndAttach(messagingGuests, messagingMessages, guestReq, messageReq)
if err != nil {
fmt.Fprintf(os.Stderr, "Message send failed: %v\n", err)
os.Exit(1)
}
fmt.Printf("Upload complete. Message ID: %s\n", msgID)
}
Common Errors & Debugging
Error: 401 Unauthorized
- Cause: OAuth token expired or missing
files:uploadscope. - Fix: Verify the token cache refresh logic. Ensure the client credentials are registered in Genesys Cloud with the correct scopes. Check the
ExpiresInfield and adjust the cache refresh threshold if concurrent requests exceed token lifetime.
Error: 403 Forbidden
- Cause: Client lacks
messaging:guestormessaging:sendscopes. The environment may have file upload limits disabled. - Fix: Update the OAuth client configuration in the Genesys Cloud admin console. Verify that Web Messaging file uploads are enabled for the organization.
Error: 429 Too Many Requests
- Cause: Rate limit exceeded during chunk uploads or guest creation. S3 pre-signed URLs enforce independent rate limits.
- Fix: The retry loop implements exponential backoff. Increase the initial backoff duration if concurrent upload workers exceed 10 requests per second. Throttle chunk uploads to one per file rather than parallelizing across multiple files.
Error: 400 Bad Request (Checksum Mismatch)
- Cause: File modified during read, network corruption during PUT, or incorrect
Content-Rangeboundaries. - Fix: Validate file integrity before initiation. Ensure
Content-Rangeend values use inclusive indexing. Log checksums before and after upload to isolate corruption points.
Error: 413 Payload Too Large
- Cause: Single chunk exceeds the platform limit or
TotalSizemismatch. - Fix: Use the
ChunkSizereturned by the initiation response. Never override it. Verify thatTotalSizematches the actual file bytes.