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Google Cloud Storage (GCS)

The Amazon S3 integration also works with files on Google Cloud Storage through its interoperability. ODCS defines no gcs server type, so a GCS contract uses type: s3 with https://storage.googleapis.com as the endpoint URL and the s3:// scheme for the location — datacontract import gcs writes exactly that.

1. Install​

uv tool install --python python3.11 --upgrade 'datacontract-cli[gcs]'

See Installation for pip, pipx, and Docker.

2. Authenticate​

Create an HMAC key for your user or service account, then create a .env file in your working directory (or export the variables):

# .env
DATACONTRACT_S3_ACCESS_KEY_ID=GOOG1EZZZXXXXXXXXXXXXX
DATACONTRACT_S3_SECRET_ACCESS_KEY=PDWWpbXXXXXXXXXXXXX

3. Create a contract from your files​

Import the schema straight from the bucket. This also generates a ready-to-test servers block:

datacontract import gcs \
  --source s3://my-bucket/orders/*.json \
  --output datacontract.yaml

duckdb reads Google Cloud Storage through its S3-compatible endpoint, so the location uses the s3:// scheme rather than gs://; a gs:// source is rewritten for you. The format is taken from the file suffix; pass --format for Delta tables, which have none.

4. Test the actual data​

datacontract test datacontract.yaml
Testing datacontract.yaml
Server: production (type=s3, format=json, location=s3://my-bucket/orders/*.json)
╭────────┬─────────────────────────────────────────────────┬─────────────────┬─────────╮
│ Result │ Check                                           │ Field           │ Details │
├────────┼─────────────────────────────────────────────────┼─────────────────┼─────────┤
│ passed │ Check that field 'order_id' is present          │ orders.order_id │         │
│ passed │ Check that field order_id has no missing values │ orders.order_id │         │
│  ...   │                                                 │                 │         │
╰────────┴─────────────────────────────────────────────────┴─────────────────┴─────────╯
🟢 data contract is valid. Run 24 checks. Took 3.1 seconds.

5. Let it catch a violation​

The contract becomes valuable when it detects drift. Tighten an expectation — for example, mark a field as required: true that occasionally arrives empty, or add a quality rule:

schema:
  - name: orders
    # ...
    quality:
      - type: sql
        description: No order has a negative total
        query: SELECT COUNT(*) FROM orders WHERE order_total < 0
        mustBe: 0

Run datacontract test datacontract.yaml again: every violation is listed as an error, and the command exits with code 1 — ready for CI/CD and scheduled runs so you catch drift before your consumers do.

Reference​

All authentication options and the data type handling per file format: GCS Reference.

Troubleshooting​

  • 403 Forbidden — the HMAC key's principal lacks storage.objects.get/storage.objects.list on the bucket, or the key was deactivated.
  • No files found that match the pattern — the location must use the s3:// scheme (not gs://), and endpointUrl must be https://storage.googleapis.com.