feat: add unit result type

core/result/ok/datamodel/unit.go

@@ -0,0 +1,31 @@
+package datamodel
+
+import (
+	// to use go:embed
+	_ "embed"
+	"fmt"
+
+	"github.com/ipld/go-ipld-prime"
+	"github.com/ipld/go-ipld-prime/schema"
+)
+
+//go:embed unit.ipldsch
+var unitSchema []byte
+
+var unitType schema.Type
+
+func init() {
+	ts, err := ipld.LoadSchemaBytes(unitSchema)
+	if err != nil {
+		panic(fmt.Errorf("loading unit schema: %w", err))
+	}
+	unitType = ts.TypeByName("Unit")
+}
+
+func UnitType() schema.Type {
+	return unitType
+}
+
+func Schema() []byte {
+	return unitSchema
+}

core/result/ok/datamodel/unit.ipldsch

@@ -0,0 +1 @@
+type Unit struct {}

core/result/ok/unit.go

@@ -0,0 +1,21 @@
+package ok
+
+import (
+	"github.com/ipld/go-ipld-prime/datamodel"
+	"github.com/ipld/go-ipld-prime/node/basicnode"
+)
+
+// Unit is a success type that can be used when there is no data to return from
+// a capability handler.
+type Unit struct{}
+
+func (u Unit) ToIPLD() (datamodel.Node, error) {
+	np := basicnode.Prototype.Any
+	nb := np.NewBuilder()
+	ma, err := nb.BeginMap(0)
+	if err != nil {
+		return nil, err
+	}
+	ma.Finish()
+	return nb.Build(), nil
+}

core/result/ok/unit_test.go

@@ -0,0 +1,32 @@
+package ok
+
+import (
+	"testing"
+
+	"github.com/ipld/go-ipld-prime/datamodel"
+	"github.com/storacha/go-ucanto/core/ipld/codec/cbor"
+	udm "github.com/storacha/go-ucanto/core/result/ok/datamodel"
+	"github.com/stretchr/testify/require"
+)
+
+func TestUnit(t *testing.T) {
+	u := Unit{}
+	nd, err := u.ToIPLD()
+	require.NoError(t, err)
+
+	// should be represented as a map
+	require.Equal(t, nd.Kind(), datamodel.Kind_Map)
+
+	// should contain no items
+	it := nd.MapIterator()
+	require.True(t, it.Done())
+
+	bytes, err := cbor.Encode(&u, udm.UnitType())
+	require.NoError(t, err)
+
+	u2 := Unit{}
+	err = cbor.Decode(bytes, &u2, udm.UnitType())
+	require.NoError(t, err)
+
+	require.Equal(t, u, u2)
+}