obsuild2: support additional layers in oci-archive

The org.osbuild.oci-archive stage now supports an arbitrary number of
layers on top of the Base layer.  The keys for these layers follow the
pattern "layer.N" (N = 1, 2, 3, ...).

We use a custom marshaller and unmarshaller for the
OCIArchiveStageInputs to handle this.  The unmarshaller also validates
the layer keys to match the pattern in the schema.

internal/osbuild2/oci_archive_stage.go

@@ -1,5 +1,13 @@
 package osbuild2
 
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"regexp"
+	"sort"
+)
+
 type OCIArchiveStageOptions struct {
 	// The CPU architecture of the image
 	Architecture string `json:"architecture"`
@@ -25,7 +33,10 @@ type OCIArchiveConfig struct {
 func (OCIArchiveStageOptions) isStageOptions() {}
 
 type OCIArchiveStageInputs struct {
+	// Base layer for the container
 	Base *OCIArchiveStageInput `json:"base"`
+	// Additional layers in ascending order
+	Layers []OCIArchiveStageInput `json:",omitempty"`
 }
 
 func (OCIArchiveStageInputs) isStageInputs() {}
@@ -49,3 +60,80 @@ func NewOCIArchiveStage(options *OCIArchiveStageOptions, inputs *OCIArchiveStage
 		Inputs:  inputs,
 	}
 }
+
+// Custom marshaller for OCIArchiveStageInputs, needed to generate keys of the
+// form "layer.N", (where N = 1, 2, ...) for the Layers property
+func (inputs *OCIArchiveStageInputs) MarshalJSON() ([]byte, error) {
+	if inputs == nil {
+		return json.Marshal(inputs)
+	}
+
+	layers := inputs.Layers
+	inputsMap := make(map[string]OCIArchiveStageInput, len(layers)+1)
+	if inputs.Base != nil {
+		inputsMap["base"] = *inputs.Base
+	}
+
+	for idx, input := range layers {
+		key := fmt.Sprintf("layer.%d", idx+1)
+		inputsMap[key] = input
+	}
+
+	return json.Marshal(inputsMap)
+}
+
+// Get the sorted keys that match the pattern "layer.N" (for N > 0)
+func layerKeys(layers map[string]OCIArchiveStageInput) ([]string, error) {
+	keys := make([]string, 0, len(layers))
+	for key := range layers {
+		re := regexp.MustCompile(`layer\.[1-9]\d*`)
+		if key == "base" {
+			continue
+		}
+		if !re.MatchString(key) {
+			return nil, fmt.Errorf("invalid key: %q", key)
+		}
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	return keys, nil
+}
+
+// Custom unmarshaller for OCIArchiveStageInputs, needed to handle keys of the
+// form "layer.N", (where N = 1, 2, ...) for the Layers property
+func (inputs *OCIArchiveStageInputs) UnmarshalJSON(data []byte) error {
+	if len(data) == 0 {
+		return nil
+	}
+
+	if inputs == nil {
+		inputs = new(OCIArchiveStageInputs)
+	}
+
+	inputsMap := make(map[string]OCIArchiveStageInput)
+
+	dec := json.NewDecoder(bytes.NewReader(data))
+	dec.DisallowUnknownFields()
+
+	if err := dec.Decode(&inputsMap); err != nil {
+		return err
+	}
+
+	// "base" layer is required
+	base, ok := inputsMap["base"]
+	if !ok {
+		return fmt.Errorf("missing required key \"base\"")
+	}
+
+	inputs.Base = &base
+	keys, err := layerKeys(inputsMap)
+	if err != nil {
+		return err
+	}
+	inputs.Layers = make([]OCIArchiveStageInput, len(inputsMap)-1)
+	for idx, key := range keys {
+		inputs.Layers[idx] = inputsMap[key]
+	}
+
+	return nil
+}

internal/osbuild2/oci_archive_stage_test.go

@@ -0,0 +1,105 @@
+package osbuild2
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestOCIArchiveStage(t *testing.T) {
+	expectedStage := &Stage{
+		Type:    "org.osbuild.oci-archive",
+		Options: &OCIArchiveStageOptions{},
+		Inputs:  &OCIArchiveStageInputs{},
+	}
+	actualStage := NewOCIArchiveStage(&OCIArchiveStageOptions{}, &OCIArchiveStageInputs{})
+	assert.Equal(t, expectedStage, actualStage)
+}
+
+func TestOCIArchiveInputs(t *testing.T) {
+	exp := `{
+		"base": {
+			"type": "org.osbuild.oci-archive",
+			"origin":"org.osbuild.pipeline",
+			"references": ["name:container-tree"]
+		},
+		"layer.1": {
+			"type": "org.osbuild.tree",
+			"origin": "org.osbuild.pipeline",
+			"references": ["name:container-ostree"]
+		},
+		"layer.2": {
+			"type": "org.osbuild.tree",
+			"origin": "org.osbuild.pipeline",
+			"references": ["name:container-ostree2"]
+		}
+	}`
+	inputs := new(OCIArchiveStageInputs)
+	base := &OCIArchiveStageInput{
+		References: []string{
+			"name:container-tree",
+		},
+	}
+	base.Type = "org.osbuild.oci-archive"
+	base.Origin = "org.osbuild.pipeline"
+
+	layer1 := OCIArchiveStageInput{
+		References: []string{
+			"name:container-ostree",
+		},
+	}
+	layer1.Type = "org.osbuild.tree"
+	layer1.Origin = "org.osbuild.pipeline"
+	layer2 := OCIArchiveStageInput{
+		References: []string{
+			"name:container-ostree2",
+		},
+	}
+	layer2.Type = "org.osbuild.tree"
+	layer2.Origin = "org.osbuild.pipeline"
+
+	inputs.Base = base
+	inputs.Layers = []OCIArchiveStageInput{layer1, layer2}
+
+	data, err := json.Marshal(inputs)
+	assert.NoError(t, err)
+	assert.JSONEq(t, exp, string(data))
+
+	inputsRead := new(OCIArchiveStageInputs)
+	err = json.Unmarshal([]byte(exp), inputsRead)
+	assert.NoError(t, err)
+	assert.Equal(t, inputs, inputsRead)
+}
+
+func TestOCIArchiveInputsErrors(t *testing.T) {
+	noBase := `{
+		"layer.10": {
+			"type": "org.osbuild.tree",
+			"origin": "org.osbuild.pipeline",
+			"references": ["name:container-ostree"]
+		},
+		"layer.2": {
+			"type": "org.osbuild.tree",
+			"origin": "org.osbuild.pipeline",
+			"references": ["name:container-ostree2"]
+		}
+	}`
+
+	inputsRead := new(OCIArchiveStageInputs)
+	assert.Error(t, json.Unmarshal([]byte(noBase), inputsRead))
+
+	invalidKey := `{
+		"base": {
+			"type": "org.osbuild.oci-archive",
+			"origin":"org.osbuild.pipeline",
+			"references": ["name:container-tree"]
+		},
+		"not-a-layer": {
+			"type": "org.osbuild.tree",
+			"origin": "org.osbuild.pipeline",
+			"references": ["name:container-ostree2"]
+		}
+	}`
+	assert.Error(t, json.Unmarshal([]byte(invalidKey), inputsRead))
+}