Schemas, constraints, defaults

The compiler reads Go library source to derive input schemas, output fields, constraints, and defaults.

Struct fields

Input structs become UB object fields. Field names use kebab case by default, and ub tags can set the UB name:

type File struct {
    Path          string
    CreateParents bool `ub:"create-parents"`
    Tags          map[string]string
}

Pointer fields are optional. Output structs use the same field naming rules. An output field can be marked sensitive:

type SecretOutput struct {
    Label string
    Value string `ub:",sensitive"`
}

Defaults

A type can declare defaults with a Defaults method:

func (f File) Defaults() []defaults.Default {
    return []defaults.Default{
        defaults.Value(f.CreateParents, true),
        defaults.Optional(f.Tags),
    }
}

defaults.Value fills a value before the type's runtime method runs. defaults.Optional says the field may be omitted and the zero value is acceptable.

Constraints

A type can declare cross-field constraints:

func (f File) Constraints() []constraint.Constraint {
    return []constraint.Constraint{
        constraint.Must(constraint.NotEmpty(f.Path)).Message("path is required"),
        constraint.Must(constraint.AtLeast(f.Mode, 0)).Message("mode must be non-negative"),
    }
}

Set constraints include ExactlyOneOf, AtLeastOneOf, AtMostOneOf, RequiredTogether, RequiredWith, and ForbiddenWith. Predicate constraints use Must or When(...).Require(...).

Check timing

Deep schema and constraint checks happen at compile time when the source and selected libraries are known. The compiled factory trusts those checks and decodes runtime values into the registered Go types.

For checks that need live configuration or external state, a resource can also implement runtime.InputValidator; see Resources.