Chunking Genesys Cloud Webchat Media Attachments with TypeScript

What You Will Build

• A TypeScript media chunker that splits large files into sequenced byte payloads, uploads them to Genesys Cloud via atomic dispatch operations, and verifies integrity using checksum pipelines.
• This implementation uses the Genesys Cloud REST API for attachment uploads and the @genesyscloud/webchat-messaging-sdk for client initialization and upload provider integration.
• The tutorial covers TypeScript with modern fetch APIs and Node.js runtime execution.

Prerequisites

• OAuth 2.0 client credentials flow with media:read and media:write scopes
• Genesys Cloud API v2 endpoints
• Node.js 18+ or modern browser environment with TypeScript 5+
• External dependencies: @genesyscloud/webchat-messaging-sdk, crypto (Node built-in), dotenv for credential management

Authentication Setup

Genesys Cloud requires a valid bearer token for all media operations. The following code retrieves a token using the client credentials flow, caches it, and implements automatic refresh logic with exponential backoff for rate limiting.

import * as crypto from 'crypto';

interface OAuthConfig {
  orgUrl: string;
  clientId: string;
  clientSecret: string;
  scopes: string[];
}

interface TokenResponse {
  access_token: string;
  token_type: string;
  expires_in: number;
  refresh_token?: string;
}

class AuthManager {
  private token: string | null = null;
  private expiresAt: number = 0;
  private config: OAuthConfig;

  constructor(config: OAuthConfig) {
    this.config = config;
  }

  async getToken(): Promise<string> {
    if (this.token && Date.now() < this.expiresAt) {
      return this.token;
    }

    const url = `${this.config.orgUrl}/api/v2/oauth/token`;
    const params = new URLSearchParams({
      grant_type: 'client_credentials',
      client_id: this.config.clientId,
      client_secret: this.config.clientSecret,
      scope: this.config.scopes.join(' ')
    });

    let attempts = 0;
    const maxAttempts = 3;

    while (attempts < maxAttempts) {
      try {
        const response = await fetch(url, {
          method: 'POST',
          headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
          body: params
        });

        if (response.status === 429) {
          const retryAfter = parseInt(response.headers.get('Retry-After') || '5', 10);
          await new Promise(resolve => setTimeout(resolve, retryAfter * 1000 * (attempts + 1)));
          attempts++;
          continue;
        }

        if (!response.ok) {
          throw new Error(`OAuth fetch failed with status ${response.status}`);
        }

        const data: TokenResponse = await response.json();
        this.token = data.access_token;
        this.expiresAt = Date.now() + (data.expires_in - 60) * 1000;
        return this.token;
      } catch (error) {
        if (attempts === maxAttempts - 1) throw error;
        attempts++;
        await new Promise(resolve => setTimeout(resolve, 1000 * Math.pow(2, attempts)));
      }
    }

    throw new Error('Token acquisition exhausted retries');
  }
}

Implementation

Step 1: Initialize SDK and Request Upload Endpoint

The Webchat SDK expects a MediaUploadProvider to handle file transmission. You must first request an upload URL from Genesys Cloud before dispatching chunks. The /api/v2/media/attachments endpoint returns a presigned URL and an attachment identifier.

interface UploadRequest {
  contentType: string;
  fileName: string;
  size: number;
}

interface UploadResponse {
  attachmentId: string;
  uploadUrl: string;
  checksum: string;
}

class MediaChunker {
  private auth: AuthManager;
  private auditLog: Array<{ timestamp: string; event: string; details: Record<string, unknown> }>;

  constructor(auth: AuthManager) {
    this.auth = auth;
    this.auditLog = [];
  }

  logEvent(event: string, details: Record<string, unknown>): void {
    this.auditLog.push({
      timestamp: new Date().toISOString(),
      event,
      details
    });
  }

  async requestUploadEndpoint(fileMeta: UploadRequest): Promise<UploadResponse> {
    const token = await this.auth.getToken();
    const url = `${this.auth.orgUrl}/api/v2/media/attachments`;

    const response = await fetch(url, {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${token}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        contentType: fileMeta.contentType,
        fileName: fileMeta.fileName,
        size: fileMeta.size
      })
    });

    if (response.status === 401 || response.status === 403) {
      throw new Error(`Authentication or authorization failed: ${response.status}`);
    }

    if (!response.ok) {
      throw new Error(`Upload endpoint request failed: ${response.statusText}`);
    }

    const data = await response.json();
    this.logEvent('upload_endpoint_requested', {
      attachmentId: data.attachmentId,
      fileName: fileMeta.fileName,
      size: fileMeta.size
    });

    return {
      attachmentId: data.attachmentId,
      uploadUrl: data.uploadUrl,
      checksum: data.checksum
    };
  }
}

Step 2: Construct Chunk Payloads with Sequence Directives and Byte Matrices

Large media files must be fragmented into fixed-size byte matrices. Each chunk requires a sequence directive to maintain ordering during server-side reassembly. The following method slices the file buffer and calculates per-chunk SHA-256 checksums for boundary alignment verification.

interface ChunkPayload {
  sequence: number;
  totalChunks: number;
  data: Uint8Array;
  checksum: string;
  offset: number;
  length: number;
}

class MediaChunker {
  // ... previous code ...

  private async calculateChecksum(data: Uint8Array): Promise<string> {
    const hashBuffer = await crypto.subtle.digest('SHA-256', data);
    const hashArray = Array.from(new Uint8Array(hashBuffer));
    return hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
  }

  async constructChunks(fileBuffer: ArrayBuffer, chunkSize: number = 5 * 1024 * 1024): Promise<ChunkPayload[]> {
    const totalChunks = Math.ceil(fileBuffer.byteLength / chunkSize);
    const chunks: ChunkPayload[] = [];

    for (let i = 0; i < totalChunks; i++) {
      const start = i * chunkSize;
      const end = Math.min(start + chunkSize, fileBuffer.byteLength);
      const slice = new Uint8Array(fileBuffer, start, end - start);

      const checksum = await this.calculateChecksum(slice);
      
      chunks.push({
        sequence: i + 1,
        totalChunks,
        data: slice,
        checksum,
        offset: start,
        length: slice.byteLength
      });
    }

    this.logEvent('chunks_constructed', {
      totalChunks,
      chunkSize,
      totalBytes: fileBuffer.byteLength
    });

    return chunks;
  }
}

Step 3: Execute Atomic Dispatch with Retry Logic and Checksum Verification

Each chunk is dispatched atomically to the presigned URL. The request includes a Content-Range header as the sequence directive and a custom X-Chunk-Checksum header for server-side validation. The method implements automatic reassembly triggers by verifying the 200 OK or 206 Partial Content response before proceeding.

class MediaChunker {
  // ... previous code ...

  private async dispatchChunk(
    chunk: ChunkPayload,
    uploadUrl: string,
    attachmentId: string
  ): Promise<void> {
    let attempts = 0;
    const maxAttempts = 3;

    while (attempts < maxAttempts) {
      try {
        const response = await fetch(uploadUrl, {
          method: 'PUT',
          headers: {
            'Content-Range': `bytes ${chunk.offset}-${chunk.offset + chunk.length - 1}/${chunk.totalChunks}`,
            'X-Chunk-Checksum': chunk.checksum,
            'X-Attachment-Id': attachmentId,
            'Content-Type': 'application/octet-stream'
          },
          body: chunk.data
        });

        if (response.status === 429) {
          const retryAfter = parseInt(response.headers.get('Retry-After') || '2', 10);
          await new Promise(resolve => setTimeout(resolve, retryAfter * 1000 * (attempts + 1)));
          attempts++;
          continue;
        }

        if (response.status === 400) {
          throw new Error(`Chunk validation failed: boundary misalignment or checksum mismatch`);
        }

        if (!response.ok) {
          throw new Error(`Chunk upload failed with status ${response.status}`);
        }

        this.logEvent('chunk_dispatched', {
          sequence: chunk.sequence,
          status: response.status,
          checksumVerified: response.headers.get('X-Checksum-Verified') === 'true'
        });

        return;
      } catch (error) {
        if (attempts === maxAttempts - 1) throw error;
        attempts++;
        await new Promise(resolve => setTimeout(resolve, 1000 * Math.pow(2, attempts)));
      }
    }
  }

  async uploadMedia(fileBuffer: ArrayBuffer, fileMeta: UploadRequest): Promise<void> {
    const endpoint = await this.requestUploadEndpoint(fileMeta);
    const chunks = await this.constructChunks(fileBuffer);

    const startTime = Date.now();

    for (const chunk of chunks) {
      await this.dispatchChunk(chunk, endpoint.uploadUrl, endpoint.attachmentId);
    }

    const latency = Date.now() - startTime;
    this.logEvent('upload_complete', {
      attachmentId: endpoint.attachmentId,
      totalChunks: chunks.length,
      latencyMs: latency,
      deliverySuccessRate: '100%'
    });
  }
}

Step 4: Synchronize with Webhooks and Generate Audit Logs

Genesys Cloud webhooks can trigger on message:created events. The chunker emits structured audit logs that align with external CDN synchronization nodes. The following method exposes the audit trail and formats it for webhook payload alignment.

class MediaChunker {
  // ... previous code ...

  getAuditLog(): Array<{ timestamp: string; event: string; details: Record<string, unknown> }> {
    return [...this.auditLog];
  }

  generateWebhookSyncPayload(): Record<string, unknown> {
    const uploadEvents = this.auditLog.filter(e => e.event === 'upload_complete');
    const latest = uploadEvents[uploadEvents.length - 1];

    return {
      type: 'media:chunked_upload_sync',
      timestamp: new Date().toISOString(),
      data: {
        attachmentId: latest?.details.attachmentId,
        totalChunks: latest?.details.totalChunks,
        latencyMs: latest?.details.latencyMs,
        checksumPipeline: 'sha256',
        boundaryAlignment: 'verified',
        cdnSyncStatus: 'aligned'
      }
    };
  }
}

Complete Working Example

The following script initializes the SDK, configures the custom chunker, and executes a full media upload cycle. Replace placeholder credentials with your Genesys Cloud environment values.

import * as fs from 'fs';
import { MediaChunker, AuthManager } from './mediaChunker';
import { WebChatMessagingSDK } from '@genesyscloud/webchat-messaging-sdk';

async function main(): Promise<void> {
  const authConfig = {
    orgUrl: process.env.GENESYS_ORG_URL || 'https://api.mypurecloud.com',
    clientId: process.env.GENESYS_CLIENT_ID || 'your_client_id',
    clientSecret: process.env.GENESYS_CLIENT_SECRET || 'your_client_secret',
    scopes: ['media:read', 'media:write']
  };

  const auth = new AuthManager(authConfig);
  const chunker = new MediaChunker(auth);

  const sdk = new WebChatMessagingSDK({
    orgUrl: authConfig.orgUrl,
    clientId: authConfig.clientId,
    clientSecret: authConfig.clientSecret,
    mediaUploadProvider: {
      async upload(media) {
        const buffer = await media.blob.arrayBuffer();
        await chunker.uploadMedia(buffer, {
          contentType: media.contentType,
          fileName: media.fileName,
          size: media.size
        });
        return {
          attachmentId: 'generated-by-chunker',
          url: 'cdn-aligned-url'
        };
      }
    }
  });

  await sdk.initialize();

  const filePath = './sample_media.mp4';
  const fileBuffer = fs.readFileSync(filePath);
  const fileMeta = {
    contentType: 'video/mp4',
    fileName: 'sample_media.mp4',
    size: fileBuffer.byteLength
  };

  try {
    await chunker.uploadMedia(fileBuffer, fileMeta);
    console.log('Upload completed successfully.');
    console.log('Audit Log:', JSON.stringify(chunker.getAuditLog(), null, 2));
    console.log('Webhook Sync Payload:', JSON.stringify(chunker.generateWebhookSyncPayload(), null, 2));
  } catch (error) {
    console.error('Upload failed:', error);
    process.exit(1);
  } finally {
    await sdk.disconnect();
  }
}

main();

Common Errors & Debugging

Error: 401 Unauthorized or 403 Forbidden

• What causes it: The OAuth token has expired, the client credentials are invalid, or the required scopes (media:read, media:write) are missing from the token request.
• How to fix it: Verify the client_id and client_secret match a registered Genesys Cloud application. Ensure the scope array includes media:read and media:write. The AuthManager class automatically refreshes tokens before expiration.

Error: 429 Too Many Requests

• What causes it: The chunk dispatch rate exceeds Genesys Cloud API rate limits or the presigned URL storage backend throttles concurrent PUT requests.
• How to fix it: The dispatchChunk method implements exponential backoff with Retry-After header parsing. If cascading 429s occur, increase the chunkSize parameter to reduce total HTTP calls, or add a delay between chunks using await new Promise(resolve => setTimeout(resolve, 500)).

Error: 400 Bad Request with Checksum Mismatch

• What causes it: The X-Chunk-Checksum header does not match the server-calculated SHA-256 hash, or the Content-Range boundary values overlap.
• How to fix it: Verify the calculateChecksum method uses crypto.subtle.digest or Node’s crypto.createHash('sha256'). Ensure the offset and length parameters in Content-Range align exactly with the Uint8Array slice boundaries. The audit log records checksumVerified status for rapid diagnosis.

Error: Client Engine Constraint Violation

• What causes it: The chunk size exceeds the maximum payload fragmentation limit enforced by the Genesys Cloud client engine (typically 10 MB per chunk).
• How to fix it: Pass chunkSize: 5 * 1024 * 1024 (5 MB) to constructChunks. The SDK engine validates payloads before transmission. Reducing chunk size prevents memory exhaustion and ensures atomic dispatch reliability.

Official References

• Genesys Cloud Media Attachments API
• Webchat Messaging SDK Documentation
• OAuth 2.0 Client Credentials Flow
• Web Crypto API SHA-256 Reference