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Google Cloud Storage is object storage on Google Cloud. Zwiron can read files from GCS (as a source) or write files to GCS (as a destination). Supported formats include CSV, JSON, JSONL, Parquet, TSV, Excel, Avro, XML, and YAML. Setup is the same shape as Amazon S3: bucket + optional prefix + credentials.

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Supported sync modes

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Connection details

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IAM permissions

Grant the connecting principal:

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For source (read-only)

  • storage.objects.list
  • storage.objects.get
  • storage.buckets.get
Equivalent predefined role: roles/storage.objectViewer plus storage.buckets.get (or roles/storage.legacyBucketReader).

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For destination (read-write)

  • storage.objects.list
  • storage.objects.get
  • storage.objects.create
  • storage.objects.delete
  • storage.buckets.get
Equivalent predefined role: roles/storage.objectAdmin.

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Reading from GCS (source)

Zwiron lists objects in the configured bucket and prefix. Each recognized file becomes a stream. Format is auto-detected from the extension unless you set Format.

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Supported formats

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Writing to GCS (destination)

Zwiron writes one object per stream. Overwrite replaces the object for that stream; append writes an additional object. Files are named from the stream name and format.

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Troubleshooting

Confirm the service account (or ADC identity) has storage.objects.list and storage.buckets.get on the bucket. Object-level roles alone are not enough to list.
Check the path prefix — it must match exactly. GCS object names are case-sensitive. Also ensure the file extension matches the configured format filter.
Set Emulator host to host:port (no scheme), for example localhost:4443. Production connections should leave this blank.
Last modified on September 4, 2026