Selection Filter

A filter that evaluates a set of configurable predicates against each event in the pipeline to decide which records should be sent to the following stage.

Not every use-case requires each and every event to be processed. For example, a pipeline interested in creating a 'metadata' search engine might not care about transaction outputs. With a similar logic, a pipeline aggregating transaction amounts might not care about metadata. The selection filter provides a way to optimize the pipeline so that only relevant events are processed.

The filter works by evaluating a predicate against each event. If the predicate returns true, then the event will continue down the pipeline. If the predicate evalutes to false, the event will be dopped. We currently provide some common built-in predicate to facilitate common use-cases (eg: matching event type, matching policy id, matching a metadata key, etc.). We also provide some 'connecting' predicates like all_of, any_of, and not which can be used to create complex conditions by composing other predicates.

Configuration

Adding the following section to the daemon config file will enable the filter as part of the pipeline:

[[filters]]
type = "Selection"

[filters.check]
predicate = "<predicate kind>"
argument = <predicate argument>

Section: `filters`

type: the literal value Selection.

Section `filters.check`

predicate: the key of the predicate to use for the evaluation. See the list of available predicates for possible values.
argument: a polimorphic argument that specializes the behavior of the predicate in some way.

Available Predicates

variant_in (string[]): This predicate will yield true when the variant of the event matches any of the items in the argument array.
variant_not_in (string[]): This predicate will yield true when the variant of the event doesn't match any of the items in the argument array.
policy_equals (string): This predicate will yield true when the policy of a mint or output asset matches the value in the argument.
asset_equals (string): This predicate will yield true when the policy of a mint or output asset matches the value in the argument.
metadata_label_equals (string): This predicate will yield true when the root label of a metadata entry matches the value in the argument.
metadata_any_sub_label_equals (string): This predicate will yield true when at least one of the sub labels in a metadata entry matches the value in the argument.
not (predicate): This predicate will yield true when the predicate in the arguments yields false.
any_of (predicate[]): This predicate will yield true when any of the predicates in the argument yields true.
all_of (predicate[]): This predicate will yield true when all of the predicates in the argument yields true.

Examples

Allowing only block and transaction events to pass:

[[filters]]
type = "Selection"

[filters.check]
predicate = "variant_in"
argument = ["Block", "Transaction"]

Using the not predicate to allow all events except the variant Transaction:

[[filters]]
type = "Selection"

[filters.check]
predicate = "not"

[filters.check.argument]
predicate = "variant_in"
argument = ["Transaction"]

Using the any_of predicate to filter events presenting any of two different policies (Boolean "or"):

[filters.check]
predicate = "any_of"

[[filters.check.argument]]
predicate = "policy_equals"
argument = "4bf184e01e0f163296ab253edd60774e2d34367d0e7b6cbc689b567d"

[[filters.check.argument]]
predicate = "policy_equals"
argument = "a5bb0e5bb275a573d744a021f9b3bff73595468e002755b447e01559"

Using the all_of predicate to filter only "asset" events presenting a particular policy (Boolean "and") :

[filters.check]
predicate = "all_of"

[[filters.check.argument]]
predicate = "variant_in"
argument = ["OutputAsset"]

[[filters.check.argument]]
predicate = "policy_equals"
argument = "a5bb0e5bb275a573d744a021f9b3bff73595468e002755b447e01559"

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