Writing a script
Custom tranformation scripts may be defined in Javascript or Lua, and provided to Snowbridge.
The scripting interface
The script - whether Lua or Javascript - must define a main function with a single argument. Snowbridge will pass the engineProtocol data structure as the argument:
type engineProtocol struct {
FilterOut bool
PartitionKey string
Data interface{}
}
This data structure will serve as both the input and the output of the script - for Javascript it will be an object, and for Lua a table.
Scripts must define a main function with a single input argument:
function main(input) {
return input
}
function main(input)
return input
end
Accessing data
Scripts can access the message Data at input.Data, and can return modified data by returning it in the Data field of the output. Likewise for the partition key to be used for the destination - input.PartitionKey and the PartitionKey field of the output.
By default, the Data field will be a string. For Snowplow enriched TSV data, the Javascript transformation has a snowplow_mode option, which transforms the data to an object first.
The output of the script must be an object (Javascript) or a table (Lua) which maps to engineProtocol.
Transforming Data
To modify the message data, return an object which conforms to EngineProtocol, with the Data field set to the modified data. The Data field may be returned as either a string, or an object (Javascript) / table (Lua).
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Filtering
If the FilterOut field of the output is returned as true, the message will be acked immediately and won't be sent to the target. This will be the behavior regardelss of what is returned to the other fields in the protocol.
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Setting the Partition Key
To set the Partition Key in the message, you can simply set the input's PartitionKey field, and return it:
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Or, if modifying the data as well, return the modified data and PartitionKey field:
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Configuration
Once your script is ready, you can configure it in the app by following the Javascript or Lua configuration pages.
You can also find some complete example use cases in the examples section.