refactor: bind in task constructor to ensure args are correct when validating

Author: alanshaw

validator/capability/capability.go

@@ -23,6 +23,7 @@ type Arguments interface {
 
 type Task[A Arguments] struct {
 	*invocation.Task
+	args A
 }
 
 func NewTask[A Arguments](
@@ -31,26 +32,26 @@ func NewTask[A Arguments](
 	arguments ipld.Map,
 	nonce ucan.Nonce,
 ) (*Task[A], error) {
-	task, err := invocation.NewTask(subject, command, arguments, nonce)
-	if err != nil {
-		return nil, err
-	}
-	return &Task[A]{Task: task}, nil
-}
-
-// BindArguments binds the arguments to the arguments type for this task.
-func (t *Task[A]) BindArguments() (A, error) {
 	var args A
 	// if args is a pointer type, then we need to create an instance of it because
 	// rebind requires a non-nil pointer.
 	typ := reflect.TypeOf(args)
 	if typ.Kind() == reflect.Ptr {
 		args = reflect.New(typ.Elem()).Interface().(A)
 	}
-	if err := datamodel.Rebind(datamodel.Map(t.Arguments()), args); err != nil {
-		return args, verrs.NewMalformedArgumentsError(t.Command(), err)
+	if err := datamodel.Rebind(datamodel.Map(arguments), args); err != nil {
+		return nil, verrs.NewMalformedArgumentsError(command, err)
 	}
-	return args, nil
+	task, err := invocation.NewTask(subject, command, arguments, nonce)
+	if err != nil {
+		return nil, err
+	}
+	return &Task[A]{Task: task, args: args}, nil
+}
+
+// BindArguments returns the arguments bound to the type for this task.
+func (t *Task[A]) BindArguments() A {
+	return t.args
 }
 
 var _ ucan.Task = (*Task[Arguments])(nil)
@@ -61,6 +62,8 @@ type Match[A Arguments] struct {
 	Proofs     map[cid.Cid]ucan.Delegation
 }
 
+// Capability is a capability that can be used to validate an invocation and its
+// proofs.
 type Capability[A Arguments] struct {
 	cmd ucan.Command
 	pol ucan.Policy

validator/validator_test.go

@@ -55,7 +55,7 @@ func TestFixtures(t *testing.T) {
 			authorization, err := validator.Access(t.Context(), vrf, cap, inv, opts...)
 			require.NoError(t, err, "validation should have passed for invocation with %s", vector.Description)
 
-			_, err = authorization.Task.BindArguments()
+			_ = authorization.Task.BindArguments()
 			require.NoError(t, err)
 		})
 	}