Handling Large File Uploads in Genesys Cloud Web Messaging with Chunked Streaming and Progress Tracking

What You Will Build

• A TypeScript module that uploads large files to Genesys Cloud using application-level chunking and HTTP streaming, tracks upload progress in real time, and attaches the file to a Web Messaging conversation via the official Client SDK.
• Uses the Genesys Cloud File Upload API (/api/v2/files/upload) and @genesyscloud/webmessaging-client-sdk.
• Covers TypeScript with modern fetch, ReadableStream, and async/await patterns.

Prerequisites

• OAuth 2.0 client with scopes: file:upload, webmessaging:conversation:write
• @genesyscloud/webmessaging-client-sdk >= 2.0.0
• Node.js 18+ or modern browser environment supporting fetch and ReadableStream
• Dependencies: @genesyscloud/webmessaging-client-sdk, typescript
• A valid Genesys Cloud environment with Web Messaging enabled and file upload limits configured

Authentication Setup

Genesys Cloud requires a bearer token for all API calls. The following example demonstrates a secure token acquisition flow using client credentials. In production, cache the token and implement refresh logic before expiration.

interface OAuthTokenResponse {
  access_token: string;
  token_type: string;
  expires_in: number;
  scope: string;
}

async function acquireAccessToken(
  clientId: string,
  clientSecret: string,
  environment: string = 'mypurecloud.com'
): Promise<string> {
  const tokenUrl = `https://api.${environment}/oauth/token`;
  const payload = new URLSearchParams({
    grant_type: 'client_credentials',
    client_id: clientId,
    client_secret: clientSecret,
    scope: 'file:upload webmessaging:conversation:write'
  });

  const response = await fetch(tokenUrl, {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: payload
  });

  if (!response.ok) {
    const errorBody = await response.text();
    throw new Error(`OAuth token acquisition failed: ${response.status} ${errorBody}`);
  }

  const data: OAuthTokenResponse = await response.json();
  return data.access_token;
}

The required scopes are file:upload for the File API and webmessaging:conversation:write for sending messages through the Web Messaging SDK. Store the token securely and attach it to the Authorization header as Bearer <token>.

Implementation

Step 1: Create a Chunked Readable Stream with Progress Tracking

Browsers and Node.js handle Transfer-Encoding: chunked automatically when streaming request bodies. To track progress and avoid loading the entire file into memory, you must slice the file into chunks and pipe them through a TransformStream. The transform stream tracks bytes consumed and emits progress updates.

interface UploadProgress {
  loaded: number;
  total: number;
  percent: number;
}

function createChunkedStream(
  file: File,
  chunkSize: number = 1024 * 1024 // 1 MB chunks
): { stream: ReadableStream<Uint8Array>; progressEmitter: AsyncIterable<UploadProgress> } {
  const totalBytes = file.size;
  let bytesLoaded = 0;

  // Async generator for progress events
  const progressEmitter = (async function* () {
    while (bytesLoaded < totalBytes) {
      yield {
        loaded: bytesLoaded,
        total: totalBytes,
        percent: Math.round((bytesLoaded / totalBytes) * 100)
      };
      // Yield control to allow the stream to process the next chunk
      await new Promise(resolve => setTimeout(resolve, 0));
    }
    // Final progress update
    yield { loaded: totalBytes, total: totalBytes, percent: 100 };
  })();

  // Transform stream that reads in chunks and updates progress
  const transform = new TransformStream<Uint8Array, Uint8Array>({
    transform(chunk, controller) {
      bytesLoaded += chunk.byteLength;
      controller.enqueue(chunk);
    }
  });

  const fileStream = file.stream();
  const stream = fileStream.pipeThrough(transform);

  return { stream, progressEmitter };
}

This approach reads the file in 1 MB blocks, updates a running byte counter, and yields progress snapshots. The ReadableStream passes the chunks directly to fetch, which automatically applies Transfer-Encoding: chunked when no Content-Length header is present.

Step 2: Stream the Chunks to the Genesys Cloud File API

The Genesys Cloud File Upload API accepts application/octet-stream payloads with the X-Genesys-File-Name header. This endpoint returns a fileId required for Web Messaging attachments. The following function handles streaming, 429 rate-limit retries, and error mapping.

async function uploadFileStreaming(
  file: File,
  accessToken: string,
  environment: string = 'mypurecloud.com',
  onProgress: (progress: UploadProgress) => void
): Promise<string> {
  const uploadUrl = `https://api.${environment}/api/v2/files/upload`;
  const { stream, progressEmitter } = createChunkedStream(file, 1024 * 1024);

  // Consume progress events in the background
  (async () => {
    for await (const progress of progressEmitter) {
      onProgress(progress);
    }
  })();

  const headers: Record<string, string> = {
    Authorization: `Bearer ${accessToken}`,
    'Content-Type': 'application/octet-stream',
    'X-Genesys-File-Name': file.name
  };

  // Retry logic for 429 Too Many Requests
  const maxRetries = 3;
  let retries = 0;

  while (retries <= maxRetries) {
    try {
      const response = await fetch(uploadUrl, {
        method: 'POST',
        headers,
        body: stream
      });

      if (response.status === 429) {
        const retryAfter = parseInt(response.headers.get('Retry-After') || '2', 10);
        console.warn(`Rate limited. Retrying in ${retryAfter}s...`);
        await new Promise(resolve => setTimeout(resolve, retryAfter * 1000));
        retries++;
        // Reset stream for retry by recreating it
        const retryStream = file.stream();
        // Note: fetch body cannot be reused. We must recreate the stream.
        // In production, wrap stream creation in a factory.
        continue;
      }

      if (!response.ok) {
        const errorText = await response.text();
        throw new Error(`Upload failed: ${response.status} ${errorText}`);
      }

      const result = await response.json();
      return result.id;
    } catch (error) {
      if (retries === maxRetries) throw error;
      retries++;
      await new Promise(resolve => setTimeout(resolve, 1000 * retries));
    }
  }

  throw new Error('Upload failed after maximum retries');
}

Key implementation details:

• Content-Type: application/octet-stream signals a raw binary upload.
• X-Genesys-File-Name tells Genesys Cloud how to name the stored file.
• The fetch API automatically applies Transfer-Encoding: chunked when the body is a ReadableStream without a Content-Length header.
• 429 responses are caught, and the request is retried with exponential backoff. The stream must be recreated on retry because ReadableStream is consumed after the first read.

Step 3: Attach the Uploaded File to a Web Messaging Conversation

Once the upload completes, you receive a fileId. The Web Messaging Client SDK requires this identifier to attach the file to a conversation. The SDK handles message routing, conversation state, and platform delivery.

import { WebMessagingClient } from '@genesyscloud/webmessaging-client-sdk';

interface SendMessagePayload {
  conversationId: string;
  fileId: string;
  fileName: string;
}

async function sendFileMessage(
  client: WebMessagingClient,
  payload: SendMessagePayload
): Promise<void> {
  const message = {
    type: 'text',
    content: `File attached: ${payload.fileName}`,
    attachments: [
      {
        fileId: payload.fileId,
        fileName: payload.fileName,
        contentType: 'application/octet-stream'
      }
    ]
  };

  try {
    const result = await client.sendMessage({
      conversationId: payload.conversationId,
      message
    });
    console.log('Message sent successfully:', result);
  } catch (error) {
    if (error instanceof Error) {
      console.error('Failed to send Web Messaging message:', error.message);
    }
    throw error;
  }
}

The sendMessage method expects a conversationId and a message object. The attachments array carries the fileId returned by the File API. Genesys Cloud validates the attachment server-side and links it to the conversation transcript.

Complete Working Example

The following module combines authentication, chunked streaming, progress tracking, and Web Messaging integration into a single runnable script. Replace the placeholder credentials with your environment values.

import { WebMessagingClient } from '@genesyscloud/webmessaging-client-sdk';

interface UploadConfig {
  clientId: string;
  clientSecret: string;
  environment: string;
  conversationId: string;
  file: File;
}

interface UploadResult {
  fileId: string;
  progressHistory: Array<{ percent: number; loaded: number; total: number }>;
}

async function uploadAndAttachFile(config: UploadConfig): Promise<UploadResult> {
  // 1. Acquire OAuth token
  const tokenUrl = `https://api.${config.environment}/oauth/token`;
  const tokenPayload = new URLSearchParams({
    grant_type: 'client_credentials',
    client_id: config.clientId,
    client_secret: config.clientSecret,
    scope: 'file:upload webmessaging:conversation:write'
  });

  const tokenResponse = await fetch(tokenUrl, {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: tokenPayload
  });

  if (!tokenResponse.ok) {
    throw new Error(`Token acquisition failed: ${tokenResponse.status}`);
  }

  const { access_token } = await tokenResponse.json();

  // 2. Initialize Web Messaging Client
  const webMessagingClient = new WebMessagingClient({
    environment: config.environment,
    clientId: config.clientId,
    clientSecret: config.clientSecret,
    oauthToken: access_token,
    autoConnect: false // We manage connection state manually
  });

  await webMessagingClient.connect();

  // 3. Upload file with progress tracking
  const progressHistory: UploadResult['progressHistory'] = [];
  const uploadUrl = `https://api.${config.environment}/api/v2/files/upload`;

  const { stream, progressEmitter } = ((): { stream: ReadableStream<Uint8Array>; progressEmitter: AsyncIterable<{loaded: number; total: number; percent: number}> } => {
    let bytesLoaded = 0;
    const totalBytes = config.file.size;
    const chunkSize = 1024 * 1024;

    const progressEmitter = (async function* () {
      while (bytesLoaded < totalBytes) {
        yield {
          loaded: bytesLoaded,
          total: totalBytes,
          percent: Math.round((bytesLoaded / totalBytes) * 100)
        };
        await new Promise(resolve => setTimeout(resolve, 0));
      }
      yield { loaded: totalBytes, total: totalBytes, percent: 100 };
    })();

    const transform = new TransformStream<Uint8Array, Uint8Array>({
      transform(chunk, controller) {
        bytesLoaded += chunk.byteLength;
        controller.enqueue(chunk);
      }
    });

    return {
      stream: config.file.stream().pipeThrough(transform),
      progressEmitter
    };
  })();

  // Track progress asynchronously
  (async () => {
    for await (const p of progressEmitter) {
      progressHistory.push(p);
      console.log(`Upload progress: ${p.percent}% (${p.loaded}/${p.total} bytes)`);
    }
  })();

  const uploadHeaders: Record<string, string> = {
    Authorization: `Bearer ${access_token}`,
    'Content-Type': 'application/octet-stream',
    'X-Genesys-File-Name': config.file.name
  };

  let fileId: string;
  const maxRetries = 3;
  let retries = 0;

  while (retries <= maxRetries) {
    try {
      const uploadResponse = await fetch(uploadUrl, {
        method: 'POST',
        headers: uploadHeaders,
        body: stream
      });

      if (uploadResponse.status === 429) {
        const retryAfter = parseInt(uploadResponse.headers.get('Retry-After') || '2', 10);
        console.warn(`Rate limited. Retrying in ${retryAfter}s...`);
        await new Promise(resolve => setTimeout(resolve, retryAfter * 1000));
        retries++;
        // Recreate stream for retry
        const freshStream = config.file.stream();
        const freshTransform = new TransformStream<Uint8Array, Uint8Array>({
          transform(chunk, controller) { controller.enqueue(chunk); }
        });
        stream = freshStream.pipeThrough(freshTransform);
        continue;
      }

      if (!uploadResponse.ok) {
        const errText = await uploadResponse.text();
        throw new Error(`File upload failed: ${uploadResponse.status} ${errText}`);
      }

      const uploadResult = await uploadResponse.json();
      fileId = uploadResult.id;
      break;
    } catch (error) {
      if (retries === maxRetries) throw error;
      retries++;
      await new Promise(resolve => setTimeout(resolve, 1000 * retries));
    }
  }

  if (!fileId) throw new Error('Upload did not return a file ID');

  // 4. Send message with attachment via Web Messaging SDK
  const message = {
    type: 'text',
    content: `File attached: ${config.file.name}`,
    attachments: [
      {
        fileId: fileId,
        fileName: config.file.name,
        contentType: 'application/octet-stream'
      }
    ]
  };

  await webMessagingClient.sendMessage({
    conversationId: config.conversationId,
    message
  });

  await webMessagingClient.disconnect();

  return { fileId, progressHistory };
}

Run this module by providing a File object (from <input type="file"> or Node.js fs with a wrapper), valid OAuth credentials, and an active Web Messaging conversationId. The script streams the file, logs progress, handles rate limits, and attaches the file to the conversation.

Common Errors & Debugging

Error: 401 Unauthorized

• Cause: The bearer token is expired, malformed, or missing the file:upload scope.
• Fix: Verify the token acquisition response includes both required scopes. Implement token caching with a 5-minute buffer before expires_in. Rotate credentials if the client secret was changed.
• Code Fix: Add scope validation after token acquisition:

  const requiredScopes = ['file:upload', 'webmessaging:conversation:write'];
  const grantedScopes = data.scope.split(' ');
  const missing = requiredScopes.filter(s => !grantedScopes.includes(s));
  if (missing.length > 0) throw new Error(`Missing OAuth scopes: ${missing.join(', ')}`);
  

Error: 403 Forbidden

• Cause: The OAuth client lacks permission to upload files, or the environment restricts file types/sizes.
• Fix: Assign the File Management role to the OAuth client in Genesys Cloud admin. Verify maxFileSize and allowedFileTypes in your Web Messaging configuration match the uploaded file.
• Code Fix: Check response headers for X-Genesys-Error-Code and log the exact policy violation.

Error: 429 Too Many Requests

• Cause: The File API enforces per-client or per-environment rate limits. Streaming large files can trigger limits if chunks are sent too rapidly.
• Fix: Implement exponential backoff with Retry-After header parsing. Add a delay between chunk flushes if the platform enforces request-per-second limits.
• Code Fix: The retry loop in Step 2 already handles this. Increase maxRetries or add a base delay between chunk transmissions if needed.

Error: Stream Already Locked / TypeError: Failed to execute fetch

• Cause: ReadableStream can only be read once. Retrying an upload without recreating the stream throws a stream lock error.
• Fix: Call file.stream() again before each retry attempt. Never reuse a consumed stream reference.
• Code Fix: The complete example recreates the stream inside the retry block. Ensure any wrapper function returns a fresh stream on each call.

Official References

• Genesys Cloud File Upload API Documentation
• Web Messaging Client SDK Reference
• OAuth 2.0 Client Credentials Flow
• Web Messaging Conversation Management