Resuming Genesys Cloud Web Messaging File Upload Chunks with Python

What You Will Build

A Python chunk resumer that reconstructs interrupted Web Messaging file uploads by tracking missing fragments, validating sequence integrity, and synchronizing completion events via external webhooks. This tutorial uses the Genesys Cloud Web Messaging File Upload API with direct httpx calls to manage atomic POST operations, hash verification, and retry matrices. The implementation covers Python 3.9+ with type hints, exponential backoff, and audit logging.

Prerequisites

• Genesys Cloud OAuth 2.0 Client Credentials grant configuration
• Required scopes: webmessaging:fileupload:write, webmessaging:fileupload:read
• Python 3.9 or higher
• Dependencies: httpx>=0.24.0, python-dotenv>=1.0.0, hashlib, time, logging, base64, json
• Environment variables: GENESYS_CLIENT_ID, GENESYS_CLIENT_SECRET, GENESYS_REGION (e.g., mypurecloud.com)

Authentication Setup

Genesys Cloud uses the standard OAuth 2.0 client credentials flow. You must cache the access token and handle expiration before issuing chunk requests. The following code retrieves and caches a token, then returns it for subsequent API calls.

import httpx
import time
import os
from dataclasses import dataclass
from typing import Optional

@dataclass
class OAuthToken:
    access_token: str
    expires_at: float

class GenesysAuthManager:
    def __init__(self, client_id: str, client_secret: str, region: str):
        self.client_id = client_id
        self.client_secret = client_secret
        self.region = region
        self.token_endpoint = f"https://api.{region}/api/v2/oauth/token"
        self._cached_token: Optional[OAuthToken] = None

    def get_access_token(self) -> str:
        if self._cached_token and time.time() < self._cached_token.expires_at:
            return self._cached_token.access_token

        payload = {
            "grant_type": "client_credentials",
            "client_id": self.client_id,
            "client_secret": self.client_secret,
            "scope": "webmessaging:fileupload:write webmessaging:fileupload:read"
        }

        response = httpx.post(self.token_endpoint, data=payload, timeout=15.0)
        response.raise_for_status()

        data = response.json()
        self._cached_token = OAuthToken(
            access_token=data["access_token"],
            expires_at=time.time() + data["expires_in"] - 30
        )
        return self._cached_token.access_token

Implementation

Step 1: Initialize the Chunk Matrix and Upload Session

You must initiate a multipart upload session before sending fragments. The server returns an uploadId, recommended chunkSize, and maxChunks. You will construct a chunk index matrix to track upload status, local hashes, and retry counts.

import hashlib
import base64
import logging
from typing import Dict, List, Tuple

logging.basicConfig(level=logging.INFO, format="%(asctime)s [%(levelname)s] %(message)s")
logger = logging.getLogger("WebMessagingResumer")

class ChunkMatrix:
    def __init__(self, max_chunks: int):
        self.max_chunks = max_chunks
        self.status: Dict[int, str] = {}
        self.local_hashes: Dict[int, str] = {}
        self.retry_counts: Dict[int, int] = {}

    def mark_uploaded(self, index: int, chunk_hash: str) -> None:
        self.status[index] = "success"
        self.local_hashes[index] = chunk_hash
        self.retry_counts[index] = 0

    def mark_failed(self, index: int) -> None:
        self.status[index] = "failed"
        self.retry_counts[index] = self.retry_counts.get(index, 0) + 1

    def get_pending_indices(self) -> List[int]:
        return [i for i in range(self.max_chunks) if self.status.get(i) != "success"]

    def verify_sequence_gaps(self) -> List[int]:
        uploaded = [i for i, s in self.status.items() if s == "success"]
        expected = list(range(self.max_chunks))
        return [i for i in expected if i not in uploaded]

Initiate the upload session using the uploadId returned by Genesys Cloud.

class GenesysFileUploader:
    def __init__(self, auth: GenesysAuthManager, region: str):
        self.auth = auth
        self.base_url = f"https://api.{region}"
        self.client = httpx.Client(timeout=httpx.Timeout(30.0, connect=10.0))

    def initiate_upload(self, file_name: str, content_type: str, file_size: int) -> Dict:
        url = f"{self.base_url}/api/v2/webmessaging/fileupload/initiate"
        headers = {
            "Authorization": f"Bearer {self.auth.get_access_token()}",
            "Content-Type": "application/json"
        }
        payload = {
            "fileName": file_name,
            "contentType": content_type,
            "fileSize": file_size
        }

        response = self.client.post(url, json=payload, headers=headers)
        response.raise_for_status()
        return response.json()

Step 2: Execute Atomic Chunk Uploads with Retry and Resume Logic

Each chunk upload is an independent POST operation. You will implement exponential backoff for 429 rate limits, enforce maximum fragment retry limits, and use a continuation directive to resume from the last successful index. Hash mismatch detection occurs by comparing the server-returned receipt hash against the local computed hash.

import time
import json
from typing import Optional

class WebMessagingChunkResumer:
    def __init__(self, auth: GenesysAuthManager, region: str, max_retries_per_chunk: int = 3):
        self.uploader = GenesysFileUploader(auth, region)
        self.max_retries = max_retries_per_chunk
        self.upload_id: Optional[str] = None
        self.chunk_matrix: Optional[ChunkMatrix] = None
        self.audit_log: List[Dict] = []
        self.recovery_metrics = {"total_chunks": 0, "successful": 0, "failed": 0, "latency_ms": []}

    def _compute_chunk_hash(self, chunk_bytes: bytes) -> str:
        return hashlib.sha256(chunk_bytes).hexdigest()

    def _upload_chunk(self, chunk_index: int, chunk_data: bytes, chunk_hash: str) -> bool:
        url = f"{self.uploader.base_url}/api/v2/webmessaging/fileupload/chunks/{self.upload_id}"
        headers = {
            "Authorization": f"Bearer {self.uploader.auth.get_access_token()}",
            "Content-Type": "application/json",
            "Idempotency-Key": f"{self.upload_id}-chunk-{chunk_index}"
        }
        payload = {
            "chunkIndex": chunk_index,
            "chunkData": base64.b64encode(chunk_data).decode("utf-8"),
            "chunkHash": chunk_hash
        }

        retries = 0
        start_time = time.time()

        while retries <= self.max_retries:
            try:
                response = self.uploader.client.post(url, json=payload, headers=headers)
                latency = (time.time() - start_time) * 1000
                self.recovery_metrics["latency_ms"].append(latency)

                if response.status_code == 200:
                    receipt = response.json()
                    server_hash = receipt.get("chunkHash")
                    if server_hash != chunk_hash:
                        logger.warning(f"Hash mismatch detected for chunk {chunk_index}. Local: {chunk_hash}, Server: {server_hash}")
                        self._log_audit("hash_mismatch", chunk_index, latency)
                        return False
                    self.chunk_matrix.mark_uploaded(chunk_index, chunk_hash)
                    self.recovery_metrics["successful"] += 1
                    logger.info(f"Chunk {chunk_index} uploaded successfully in {latency:.2f}ms")
                    return True

                elif response.status_code == 429:
                    retry_after = int(response.headers.get("Retry-After", 2 ** retries))
                    logger.warning(f"Rate limited on chunk {chunk_index}. Retrying in {retry_after}s")
                    time.sleep(retry_after)
                    retries += 1
                    continue

                elif response.status_code in (401, 403):
                    logger.error(f"Authentication/Authorization failed for chunk {chunk_index}")
                    raise PermissionError("OAuth token invalid or missing scopes")

                else:
                    logger.error(f"Chunk {chunk_index} failed with status {response.status_code}: {response.text}")
                    self.chunk_matrix.mark_failed(chunk_index)
                    return False

            except httpx.HTTPError as e:
                logger.error(f"Network error on chunk {chunk_index}: {e}")
                time.sleep(2 ** retries)
                retries += 1
                continue

        logger.error(f"Chunk {chunk_index} exceeded max retries ({self.max_retries})")
        self.recovery_metrics["failed"] += 1
        return False

    def resume_upload(self, file_path: str, chunk_size: int) -> bool:
        if not self.chunk_matrix:
            raise RuntimeError("Upload session not initiated. Call initiate() first.")

        with open(file_path, "rb") as f:
            file_data = f.read()

        total_chunks = (len(file_data) + chunk_size - 1) // chunk_size
        self.recovery_metrics["total_chunks"] = total_chunks

        pending = self.chunk_matrix.get_pending_indices()
        if not pending:
            logger.info("All chunks already uploaded. Proceeding to completion.")
            return True

        logger.info(f"Resuming upload. Pending indices: {pending}")
        self._log_audit("resume_start", 0, 0)

        all_success = True
        for index in pending:
            start = index * chunk_size
            end = min(start + chunk_size, len(file_data))
            chunk_bytes = file_data[start:end]
            chunk_hash = self._compute_chunk_hash(chunk_bytes)

            success = self._upload_chunk(index, chunk_bytes, chunk_hash)
            if not success:
                all_success = False

        return all_success

Step 3: Validate Sequence Gaps and Hash Integrity Before Completion

Before finalizing the upload, you must verify that no sequence gaps remain and that all local hashes match the expected file integrity. You will then trigger the completion endpoint and synchronize with an external media processor via a webhook callback.

import hashlib

class WebMessagingChunkResumer:
    # ... (previous methods remain identical)

    def validate_and_complete(self, file_path: str) -> Dict:
        gaps = self.chunk_matrix.verify_sequence_gaps()
        if gaps:
            raise ValueError(f"Sequence gap detected. Missing chunks: {gaps}")

        expected_file_hash = hashlib.sha256(open(file_path, "rb").read()).hexdigest()
        local_hashes = sorted(self.chunk_matrix.local_hashes.items())
        
        if len(local_hashes) != self.chunk_matrix.max_chunks:
            raise ValueError("Chunk count mismatch between matrix and server limits.")

        url = f"{self.uploader.base_url}/api/v2/webmessaging/fileupload/complete/{self.upload_id}"
        headers = {
            "Authorization": f"Bearer {self.uploader.auth.get_access_token()}",
            "Content-Type": "application/json"
        }
        payload = {
            "fileHash": expected_file_hash,
            "chunkCount": self.chunk_matrix.max_chunks
        }

        response = self.uploader.client.post(url, json=payload, headers=headers)
        response.raise_for_status()
        completion_data = response.json()

        self._log_audit("upload_complete", 0, 0)
        self._trigger_external_webhook(completion_data)
        
        avg_latency = sum(self.recovery_metrics["latency_ms"]) / len(self.recovery_metrics["latency_ms"]) if self.recovery_metrics["latency_ms"] else 0
        self.recovery_metrics["avg_latency_ms"] = avg_latency
        self.recovery_metrics["success_rate"] = self.recovery_metrics["successful"] / self.recovery_metrics["total_chunks"] if self.recovery_metrics["total_chunks"] > 0 else 0

        logger.info(f"Upload complete. Avg latency: {avg_latency:.2f}ms. Success rate: {self.recovery_metrics['success_rate']:.2%}")
        return completion_data

    def _trigger_external_webhook(self, completion_data: Dict) -> None:
        webhook_url = os.getenv("MEDIA_PROCESSOR_WEBHOOK_URL", "https://example.com/webhook/genesys-upload")
        if not webhook_url:
            logger.warning("No webhook URL configured. Skipping external synchronization.")
            return

        try:
            httpx.post(
                webhook_url,
                json={
                    "event": "webmessaging.fileupload.complete",
                    "uploadId": self.upload_id,
                    "fileHash": completion_data.get("fileHash"),
                    "timestamp": time.time()
                },
                timeout=10.0
            )
            logger.info("External media processor webhook triggered successfully.")
        except httpx.HTTPError as e:
            logger.error(f"Webhook delivery failed: {e}")

    def _log_audit(self, event_type: str, chunk_index: int, latency_ms: float) -> None:
        self.audit_log.append({
            "timestamp": time.time(),
            "upload_id": self.upload_id,
            "event": event_type,
            "chunk_index": chunk_index,
            "latency_ms": latency_ms
        })
        logger.info(f"Audit: {event_type} | Chunk: {chunk_index} | Latency: {latency_ms:.2f}ms")

    def get_audit_log(self) -> List[Dict]:
        return self.audit_log

    def get_recovery_metrics(self) -> Dict:
        return self.recovery_metrics

Complete Working Example

The following script combines authentication, session initiation, chunk resumption, validation, and completion into a single executable module. Replace the environment variables with your Genesys Cloud credentials.

import os
import sys
from dotenv import load_dotenv

load_dotenv()

def main():
    client_id = os.getenv("GENESYS_CLIENT_ID")
    client_secret = os.getenv("GENESYS_CLIENT_SECRET")
    region = os.getenv("GENESYS_REGION", "mypurecloud.com")
    file_path = os.getenv("FILE_PATH", "sample_document.pdf")

    if not client_id or not client_secret:
        logger.error("GENESYS_CLIENT_ID and GENESYS_CLIENT_SECRET must be set.")
        sys.exit(1)

    auth = GenesysAuthManager(client_id, client_secret, region)
    resumer = WebMessagingChunkResumer(auth, region, max_retries_per_chunk=3)

    file_size = os.path.getsize(file_path)
    file_name = os.path.basename(file_path)
    content_type = "application/pdf"
    chunk_size = 5 * 1024 * 1024

    logger.info("Initiating upload session...")
    session = resumer.uploader.initiate_upload(file_name, content_type, file_size)
    resumer.upload_id = session["uploadId"]
    resumer.chunk_matrix = ChunkMatrix(session["maxChunks"])

    logger.info(f"Session initiated. Upload ID: {resumer.upload_id}, Max Chunks: {session['maxChunks']}")

    try:
        success = resumer.resume_upload(file_path, chunk_size)
        if not success:
            logger.error("Resume failed due to unrecoverable chunk errors.")
            sys.exit(1)

        completion = resumer.validate_and_complete(file_path)
        logger.info("Upload finalized successfully.")
        logger.info(f"Completion payload: {completion}")
        logger.info(f"Audit log entries: {len(resumer.get_audit_log())}")
        logger.info(f"Recovery metrics: {resumer.get_recovery_metrics()}")

    except Exception as e:
        logger.error(f"Upload pipeline failed: {e}")
        sys.exit(1)
    finally:
        resumer.uploader.client.close()

if __name__ == "__main__":
    main()

Common Errors & Debugging

Error: 429 Too Many Requests

• Cause: Genesys Cloud enforces strict rate limits on the /api/v2/webmessaging/fileupload/chunks/{uploadId} endpoint. Concurrent chunk uploads or rapid retries trigger this response.
• Fix: Implement exponential backoff using the Retry-After header. The provided code reads Retry-After and falls back to 2 ** retries seconds. Never retry synchronously without delay.
• Code Fix: The _upload_chunk method already handles this by sleeping for retry_after and incrementing the retry counter.

Error: 400 Bad Request (Invalid Chunk Index or Hash Mismatch)

• Cause: The chunkIndex exceeds maxChunks, or the chunkHash does not match the server-computed hash of the payload.
• Fix: Verify that your chunk slicing matches the server-recommended chunkSize. Ensure you compute SHA-256 on the exact raw bytes before base64 encoding. The resume_upload method recalculates hashes on every attempt to guarantee alignment.
• Code Fix: The _upload_chunk method compares server_hash against chunk_hash and returns False on mismatch, triggering the matrix failure tracking.

Error: 401 Unauthorized

• Cause: The OAuth token expired during a long-running upload session, or the client lacks webmessaging:fileupload:write.
• Fix: Refresh the token before each chunk upload. The GenesysAuthManager caches tokens and checks expiration. If the region is incorrect, the token endpoint returns 401.
• Code Fix: Call self.uploader.auth.get_access_token() immediately before constructing the Authorization header. The code does this automatically.

Error: Sequence Gap Verification Failure

• Cause: Network interruptions or silent failures leave chunks in a pending state. The validate_and_complete method blocks completion if gaps exist.
• Fix: Review the chunk_matrix.status dictionary. The resume_upload method iterates only over pending indices. If a chunk consistently fails, increase max_retries_per_chunk or inspect firewall/proxy interference.
• Code Fix: The verify_sequence_gaps method returns missing indices. The script raises a ValueError to prevent corrupted media attachments from reaching the storage engine.

Official References

• Genesys Cloud Web Messaging File Upload API Documentation
• OAuth 2.0 Client Credentials Flow
• Python httpx Documentation
• Genesys Cloud Python SDK (PureCloudPlatformClientV2)