Implementing secure file attachments in Web Messaging guest sessions using the Guest API and S3 presigned URLs with a Node.js backend

What You Will Build

• A Node.js backend service that creates a Web Messaging guest session, retrieves an Amazon S3 presigned URL, uploads a file directly to storage, and attaches the file to an outbound conversation message.
• This implementation uses the Genesys Cloud CX Web Messaging Guest API and Conversation API.
• The tutorial covers Node.js 18+ with the official genesys-cloud-platform-client-node SDK and native fetch for S3 operations.

Prerequisites

• OAuth client type: Service account configured with the Client Credentials grant type
• Required OAuth scopes: webchat:guest, webchat:guest:write, webchat:conversation, webchat:conversation:write
• SDK: genesys-cloud-platform-client-node version 2.0.0 or higher
• Runtime: Node.js 18.x or 20.x LTS
• External dependencies: dotenv, genesys-cloud-platform-client-node
• Environment variables: GENESYS_ENVIRONMENT, GENESYS_CLIENT_ID, GENESYS_CLIENT_SECRET, GENESYS_QUEUE_ID

Authentication Setup

The Genesys Cloud Node SDK handles OAuth2 token acquisition, caching, and automatic refresh when initialized with client credentials. You must configure the environment hostname and inject the client identifier and secret before making any API calls.

import { PureCloudPlatformClientV2 } from 'genesys-cloud-platform-client-node';
import dotenv from 'dotenv';

dotenv.config();

const client = new PureCloudPlatformClientV2();
client.setEnvironment(process.env.GENESYS_ENVIRONMENT);

await client.loginClientCredentials(
  process.env.GENESYS_CLIENT_ID,
  process.env.GENESYS_CLIENT_SECRET
);

// The SDK now manages the access token lifecycle. 
// Subsequent API calls will automatically refresh the token if it expires.

The SDK caches the token in memory. If your process runs for extended periods, the SDK intercepts 401 Unauthorized responses on API calls and triggers a silent refresh. You do not need to implement manual token rotation logic.

Implementation

Step 1: Create the Guest Session

You must establish a guest session before requesting any attachment presigned URLs. The session requires the attachments capability flag enabled in the request body. Without this flag, the platform rejects subsequent upload URL requests with a 400 Bad Request.

API Endpoint: POST /api/v2/webchat/guest
OAuth Scope: webchat:guest:write

const webchatApi = client.WebchatApi;

const guestRequestBody = {
  capabilities: {
    attachments: true,
    typing: true
  },
  routing: {
    queueId: process.env.GENESYS_QUEUE_ID,
    skills: [
      { id: 'support-document-review', level: 1 }
    ]
  },
  metadata: {
    source: 'backend-integration',
    version: '1.0.0'
  }
};

let guestResponse;
try {
  guestResponse = await webchatApi.createWebchatGuest(guestRequestBody);
  console.log('Guest created:', guestResponse.body.guestId);
} catch (error) {
  if (error.status === 400) {
    throw new Error('Guest creation failed: capabilities or routing configuration is invalid.');
  }
  if (error.status === 401 || error.status === 403) {
    throw new Error('Authentication or authorization failed. Verify OAuth scopes.');
  }
  throw error;
}

const guestId = guestResponse.body.guestId;

Expected Response Body:

{
  "guestId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "conversationId": null,
  "capabilities": {
    "attachments": true,
    "typing": true
  },
  "routing": {
    "queueId": "q-12345",
    "skills": []
  },
  "createdTimestamp": "2024-01-15T10:30:00.000Z",
  "modifiedTimestamp": "2024-01-15T10:30:00.000Z"
}

The conversationId returns null because no message has been sent yet. The conversation initializes automatically when you submit the first message payload.

Step 2: Request and Validate the S3 Presigned URL

You must request a presigned URL before uploading any file. The platform generates a time-limited Amazon S3 PUT URL scoped to the guest session. You must specify the exact file size and MIME type. Mismatched values cause S3 to reject the upload with a 403 Forbidden.

API Endpoint: POST /api/v2/webchat/guest/{guestId}/attachments/upload
OAuth Scope: webchat:guest:write

const fileBuffer = await fs.promises.readFile('/path/to/document.pdf');
const fileName = 'quarterly-report.pdf';
const contentType = 'application/pdf';
const fileSize = fileBuffer.length;

const uploadUrlRequestBody = {
  fileName: fileName,
  contentType: contentType,
  fileSize: fileSize
};

let uploadUrlResponse;
try {
  uploadUrlResponse = await webchatApi.getWebchatGuestUploadUrl(guestId, uploadUrlRequestBody);
} catch (error) {
  if (error.status === 400) {
    throw new Error('Upload URL request failed: file size exceeds 10MB limit or invalid content type.');
  }
  throw error;
}

const { uploadUrl, uploadMethod, attachmentId } = uploadUrlResponse.body;
console.log('Presigned URL generated. Attachment ID:', attachmentId);

Expected Response Body:

{
  "uploadUrl": "https://genesys-webchat-uploads.s3.amazonaws.com/a1b2c3d4-e5f6-7890-abcd-ef1234567890/quarterly-report.pdf?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAIOSFODNN7EXAMPLE%2F20240115%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20240115T103000Z&X-Amz-Expires=300&X-Amz-SignedHeaders=content-type&X-Amz-Signature=abcdef1234567890",
  "uploadMethod": "PUT",
  "attachmentId": "att-98765-4321",
  "contentType": "application/pdf",
  "expiresIn": 300
}

The expiresIn field returns seconds until the URL becomes invalid. You must complete the S3 upload within this window. The platform typically provides a five-minute window.

Step 3: Upload the File and Attach to a Conversation

The presigned URL points directly to Amazon S3. You bypass the Genesys Cloud API gateway for the actual file transfer. You must send the raw file buffer with the exact Content-Type returned in the presigned URL response. You must not add multipart/form-data boundaries or JSON wrappers to the S3 request.

After a successful upload, you submit the attachmentId to the Conversation API. The platform validates that the S3 object exists and matches the declared hash before linking it to the message.

API Endpoint: PUT {uploadUrl} (S3 Direct)
API Endpoint: POST /api/v2/webchat/conversations
OAuth Scope: webchat:conversation:write

// Step 3a: Upload directly to S3
let s3UploadSuccess = false;
try {
  const s3Response = await fetch(uploadUrl, {
    method: 'PUT',
    headers: {
      'Content-Type': contentType,
      'x-amz-meta-genesys-attachment-id': attachmentId
    },
    body: fileBuffer
  });

  if (!s3Response.ok) {
    const errorText = await s3Response.text();
    throw new Error(`S3 upload failed with status ${s3Response.status}: ${errorText}`);
  }
  s3UploadSuccess = true;
  console.log('File uploaded successfully to S3.');
} catch (error) {
  throw new Error(`Attachment upload failed: ${error.message}`);
}

// Step 3b: Send conversation message with attachment
const conversationRequestBody = {
  guestId: guestId,
  messages: [
    {
      type: 'text',
      text: 'Please review the attached quarterly report and confirm receipt.'
    }
  ],
  attachments: [
    {
      id: attachmentId,
      fileName: fileName,
      contentType: contentType,
      fileSize: fileSize
    }
  ]
};

let conversationResponse;
try {
  conversationResponse = await webchatApi.createWebchatConversation(conversationRequestBody);
  console.log('Conversation created with attachment. ID:', conversationResponse.body.conversationId);
} catch (error) {
  if (error.status === 400) {
    throw new Error('Conversation creation failed: attachment ID is invalid or upload did not complete.');
  }
  if (error.status === 429) {
    throw new Error('Rate limit exceeded. Implement exponential backoff and retry.');
  }
  throw error;
}

Expected Response Body:

{
  "conversationId": "conv-12345-67890",
  "guestId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "messages": [
    {
      "id": "msg-001",
      "type": "text",
      "text": "Please review the attached quarterly report and confirm receipt.",
      "from": {
        "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
        "name": "Guest"
      },
      "timestamp": "2024-01-15T10:31:00.000Z"
    }
  ],
  "attachments": [
    {
      "id": "att-98765-4321",
      "fileName": "quarterly-report.pdf",
      "contentType": "application/pdf",
      "fileSize": 245890,
      "downloadUrl": "https://genesys-webchat-downloads.s3.amazonaws.com/secure/att-98765-4321?token=xyz"
    }
  ],
  "status": "active",
  "createdTimestamp": "2024-01-15T10:31:00.000Z"
}

The platform returns a downloadUrl that the agent UI uses to retrieve the file. The URL includes a short-lived authentication token. You do not need to manage download permissions manually.

Complete Working Example

The following script combines authentication, guest creation, presigned URL generation, S3 upload, and conversation initialization into a single executable module. Replace the environment variables and file path before execution.

import { PureCloudPlatformClientV2 } from 'genesys-cloud-platform-client-node';
import dotenv from 'dotenv';
import fs from 'fs/promises';

dotenv.config();

async function runWebchatAttachmentFlow() {
  const client = new PureCloudPlatformClientV2();
  client.setEnvironment(process.env.GENESYS_ENVIRONMENT);

  try {
    await client.loginClientCredentials(
      process.env.GENESYS_CLIENT_ID,
      process.env.GENESYS_CLIENT_SECRET
    );
  } catch (error) {
    console.error('OAuth initialization failed:', error.message);
    process.exit(1);
  }

  const webchatApi = client.WebchatApi;

  // 1. Create Guest Session
  const guestRequestBody = {
    capabilities: { attachments: true, typing: true },
    routing: { queueId: process.env.GENESYS_QUEUE_ID }
  };

  let guestResponse;
  try {
    guestResponse = await webchatApi.createWebchatGuest(guestRequestBody);
  } catch (error) {
    console.error('Guest creation failed:', error.message);
    process.exit(1);
  }
  const guestId = guestResponse.body.guestId;

  // 2. Prepare File Metadata
  const filePath = process.env.FILE_PATH || './sample-document.pdf';
  const fileBuffer = await fs.readFile(filePath);
  const fileName = 'sample-document.pdf';
  const contentType = 'application/pdf';
  const fileSize = fileBuffer.length;

  // 3. Request Presigned Upload URL
  const uploadUrlRequestBody = { fileName, contentType, fileSize };
  let uploadUrlResponse;
  try {
    uploadUrlResponse = await webchatApi.getWebchatGuestUploadUrl(guestId, uploadUrlRequestBody);
  } catch (error) {
    console.error('Presigned URL request failed:', error.message);
    process.exit(1);
  }

  const { uploadUrl, uploadMethod, attachmentId } = uploadUrlResponse.body;

  // 4. Upload File to S3
  let s3Response;
  try {
    s3Response = await fetch(uploadUrl, {
      method: 'PUT',
      headers: {
        'Content-Type': contentType,
        'x-amz-meta-genesys-attachment-id': attachmentId
      },
      body: fileBuffer
    });
  } catch (error) {
    console.error('Network error during S3 upload:', error.message);
    process.exit(1);
  }

  if (!s3Response.ok) {
    const errorBody = await s3Response.text();
    console.error(`S3 upload rejected (${s3Response.status}): ${errorBody}`);
    process.exit(1);
  }
  console.log('S3 upload completed successfully.');

  // 5. Send Message with Attachment
  const conversationRequestBody = {
    guestId,
    messages: [
      { type: 'text', text: 'Document attached for review. Please acknowledge.' }
    ],
    attachments: [
      { id: attachmentId, fileName, contentType, fileSize }
    ]
  };

  try {
    const conversationResponse = await webchatApi.createWebchatConversation(conversationRequestBody);
    console.log('Conversation initialized. ID:', conversationResponse.body.conversationId);
    console.log('Attachment linked. ID:', attachmentId);
  } catch (error) {
    if (error.status === 429) {
      console.warn('Rate limit hit. Back off and retry manually.');
    } else {
      console.error('Conversation creation failed:', error.message);
    }
    process.exit(1);
  }
}

runWebchatAttachmentFlow().catch((err) => {
  console.error('Unhandled fatal error:', err);
  process.exit(1);
});

Execute the script with node attachment-flow.mjs. The script exits with code zero on success and exits with code one on any validation or network failure.

Common Errors & Debugging

Error: 400 Bad Request on Guest Creation

• Cause: The capabilities.attachments flag is missing or set to false. The platform disables the attachment pipeline for that session.
• Fix: Ensure the request body contains "capabilities": { "attachments": true }. Verify that the queue ID exists and supports web messaging routing.

Error: 403 Forbidden on S3 PUT Request

• Cause: The Content-Type header in the fetch request does not match the contentType returned in the presigned URL response. S3 enforces strict header matching for signed requests.
• Fix: Extract contentType directly from uploadUrlResponse.body.contentType and reuse it verbatim in the S3 upload headers. Do not infer MIME types from file extensions.

Error: 400 Bad Request on Conversation Creation

• Cause: The attachmentId was submitted before the S3 upload completed, or the upload failed silently. The platform validates object existence before linking.
• Fix: Implement strict sequential execution. Do not parallelize the S3 upload and the conversation creation call. Verify s3Response.ok before proceeding.

Error: 429 Too Many Requests

• Cause: Exceeding the Web Messaging API rate limits (typically 100 requests per second per client credential). Presigned URL generation and guest creation share the same quota pool.
• Fix: Implement exponential backoff with jitter. The following retry utility handles 429 responses automatically:

async function fetchWithRetry(url, options, maxRetries = 3) {
  let attempt = 0;
  while (attempt < maxRetries) {
    const response = await fetch(url, options);
    if (response.status !== 429) return response;
    
    const retryAfter = response.headers.get('Retry-After');
    const delay = retryAfter ? parseInt(retryAfter, 10) * 1000 : Math.pow(2, attempt) * 1000 + Math.random() * 1000;
    console.warn(`Rate limited. Retrying in ${delay}ms...`);
    await new Promise(resolve => setTimeout(resolve, delay));
    attempt++;
  }
  throw new Error('Max retries exceeded for 429 response.');
}

Error: 413 Payload Too Large

• Cause: File size exceeds the platform attachment limit (10MB for standard web messaging, 25MB for enhanced configurations).
• Fix: Validate fileSize against 10485760 bytes before requesting the presigned URL. Compress or split files that exceed the threshold.

Official References

• Web Messaging Guest API Documentation
• Web Messaging Conversation API Documentation
• Node.js SDK Reference
• OAuth2 Client Credentials Flow Guide
• S3 Presigned Upload Security Model