Output and status

output: names what the route answers with: an Output type, an object made to be sent to clients. It must be exactly what the action returns, so the route shows its contract without anyone opening the action.

A route that succeeds answers 200, unless status: says otherwise:

POST / {    input: CreateTodo    output: TodoView    status: SuccessStatus.created    run: create_todo(input, current_principal.user)}

Only the output's declared fields are sent. IssuedToken and IssuedKey, the built-in types for an issued sign-in token and a service's key (Identity), are sent as the objects they are: an id, started_at and ends_at.

A route never writes a failure's status. It comes from the kind of each failure the action can produce (Failures).

Map layers

A route may also answer with a map layer: a FeatureCollection<G, P>, a collection of shapes of geometry G, each with properties of type P (Geospatial). It is sent bare, as the whole response, in plain RFC 7946 GeoJSON, so a mapping library fetches it as its source. A GET gets one from a query (Reads and writes, "A query giving a map layer"); a route with another method gets one from an action that builds it.

• Only a collection, only bare. A List or Page of layers, or a lone Feature<G, P>, is route.output_not_output. A mapping library takes a collection as its source, and nothing asks for the others.
• What P may not hold is what an Output's fields may not: a caller, a password's hash or a secret value, however deep. P is an Object, which could hold any of them, so the route checks it: a layer whose properties hold one is route.output_not_output at output:, naming what and where. The same search looks inside a feature's properties wherever a layer appears, so an Output with a layer field whose properties hold a password's hash is refused at that field.
• Field policy. A layer an action returns is shown to its caller, just as an Output the action builds is. So every return of a FeatureCollection in an action carries only fields every caller of the action may read. Otherwise it is policy.output_field_unproved at the value returned (Field restrictions), whichever route or action calls it.
• Sent as GeoJSON. The response's body is the collection as json.write writes it, {"type":"FeatureCollection","features":[...]}. A route test reads it back through the same codec, so response.output is the layer the action returned.