> Part of the walkerOS documentation. Project overview and full index: <https://www.walkeros.io/llms.txt>

# Fingerprint to BigQuery

This server flow turns raw request signals into a privacy-friendly identifier before events reach BigQuery. The Express source extracts the client IP and user agent, the fingerprint transformer hashes them into `user.hash`, and the GCP destination writes the events to a table. The ingest keys (`ip`, `userAgent`) must match the fingerprint `fields` (`ingest.ip`, `ingest.userAgent`) exactly, or the hash is computed over empty strings.

```
{
  "version": 4,
  "flows": {
    "default": {
      "config": {
        "platform": "server",
        "bundle": {
          "packages": {
            "@walkeros/collector": {},
            "@walkeros/server-source-express": {},
            "@walkeros/server-transformer-fingerprint": {},
            "@walkeros/server-destination-gcp": {}
          }
        }
      },
      "sources": {
        "express": {
          "package": "@walkeros/server-source-express",
          "config": {
            "settings": { "port": 8080 },
            "ingest": {
              "map": {
                "ip": { "key": "ip" },
                "userAgent": { "key": "headers.user-agent" }
              }
            }
          }
        }
      },
      "transformers": {
        "fingerprint": {
          "package": "@walkeros/server-transformer-fingerprint",
          "config": {
            "settings": {
              "fields": ["ingest.ip", "ingest.userAgent"],
              "output": "user.hash",
              "length": 16
            }
          }
        }
      },
      "destinations": {
        "bigquery": {
          "package": "@walkeros/server-destination-gcp",
          "import": "destinationBigQuery",
          "config": {
            "settings": {
              "projectId": "my-analytics-project",
              "datasetId": "events",
              "tableId": "raw_events"
            }
          }
        }
      },
      "collector": { "run": true }
    }
  }
}
```

## Run it[​](#run-it "Direct link to Run it")

Save the config as `flow.json` and push an event through the built flow with the destination mocked. Nothing is written to BigQuery:

```
npx walkeros push flow.json -e '{"name":"page view"}' --simulate destination.bigquery
```

You should see:

```
success: true
  Duration: 42ms
```

## What you get[​](#what-you-get "Direct link to What you get")

In production every event lands as one row in your table, using the standard walkerOS schema (name, entity, action, timestamp, user, and more). The destination receives an `appendRows` call, and the `user` column carries the hash in place of a raw IP or user agent (from the package's examples):

```
['appendRows', [{
  "name": "page view",
  "entity": "page",
  "action": "view",
  "user": "{\"hash\":\"158f99cc06e33fd6\"}",
  ...
}]]
```

Add a daily rotation field to the fingerprint `fields` (see the transformer page) so the hash resets each day instead of persisting indefinitely.

## Next steps[​](#next-steps "Direct link to Next steps")

* [**Fingerprint transformer**](https://www.walkeros.io/docs/transformers/fingerprint.md): Rotation, IP anonymization, and hash fields
* [**GCP destination**](https://www.walkeros.io/docs/destinations/server/gcp.md): BigQuery table setup and mapping