Receive and parse an EDI 856 ASN in Python

Inbound ASN flow

When a partner sends an 856, SignalEDI validates structure against the partner profile and emits a webhook with normalized JSON. Your Python handler verifies the signature, idempotently processes the payload, and updates inventory or fulfillment state.

• document.received for new ASNs
• document.partner_ack when retailers return 997 status on your outbound traffic
• HL hierarchy already flattened to lines and carton context where applicable

Webhook verification in Python

Always verify X-SignalEDI-Signature and X-SignalEDI-Delivery-ID before side effects. Replay protection belongs in your handler, not in ad-hoc scripts.

import os
import hmac
import hashlib

def verify_signaledi_webhook(raw_body: str, signature: str, timestamp: str, secret: str) -> bool:
    provided = signature.removeprefix("sha256=").lower()
    expected = hmac.new(
        secret.encode(),
        f"{timestamp}.{raw_body}".encode(),
        hashlib.sha256,
    ).hexdigest()
    return hmac.compare_digest(provided, expected)

# Example document.received payload (abbreviated)
# {
#   "event": "document.received",
#   "documentTypeCode": "856",
#   "payload": {
#     "shipmentId": "SHIP-4421",
#     "shipDate": "2025-06-09",
#     "lines": [{"sku": "SKU-100", "quantityShipped": 24}]
#   }
# }

Retailer timing matters more than syntax

Major retailers score ASN latency and hierarchy accuracy — read retailer requirement guides alongside this tutorial. A valid 856 sent after the carrier window still triggers chargebacks.

• BSN ship date and shipment ID anchor retailer reconciliation
• SSCC and HL nesting must match physical cartons
• See /blog/walmart-edi-requirements and /blog/target-edi-requirements