feat: add enum for official media types

Signed-off-by: nscuro <nscuro@protonmail.com>

cyclonedx.go

@@ -19,10 +19,11 @@ package cyclonedx
 
 import (
 	"encoding/xml"
+	"fmt"
 	"regexp"
 )
 
-//go:generate stringer -linecomment -output cyclonedx_string.go -type SpecVersion
+//go:generate stringer -linecomment -output cyclonedx_string.go -type MediaType,SpecVersion
 
 const (
 	BOMFormat = "CycloneDX"
@@ -319,6 +320,24 @@ type LicenseChoice struct {
 	Expression string   `json:"expression,omitempty" xml:"-"`
 }
 
+// MediaType defines the official media types for CycloneDX BOMs.
+// See https://cyclonedx.org/specification/overview/#registered-media-types
+type MediaType int
+
+const (
+	MediaTypeJSON     MediaType = iota + 1 // application/vnd.cyclonedx+json
+	MediaTypeXML                           // application/vnd.cyclonedx+xml
+	MediaTypeProtobuf                      // application/x.vnd.cyclonedx+protobuf
+)
+
+func (mt MediaType) WithVersion(specVersion SpecVersion) (string, error) {
+	if mt == MediaTypeJSON && specVersion < SpecVersion1_2 {
+		return "", fmt.Errorf("json format is not supported for specification versions lower than %s", SpecVersion1_2)
+	}
+
+	return fmt.Sprintf("%s; version=%s", mt, specVersion), nil
+}
+
 type Metadata struct {
 	Timestamp   string                   `json:"timestamp,omitempty" xml:"timestamp,omitempty"`
 	Tools       *[]Tool                  `json:"tools,omitempty" xml:"tools>tool,omitempty"`

cyclonedx_test.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/bradleyjkemp/cupaloy/v2"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 var snapShooter = cupaloy.NewDefaultConfig().
@@ -35,6 +36,19 @@ func TestBool(t *testing.T) {
 	assert.Equal(t, false, *Bool(false))
 }
 
+func TestMediaType_WithVersion(t *testing.T) {
+	t.Run("ShouldReturnVersionedMediaType", func(t *testing.T) {
+		res, err := MediaTypeJSON.WithVersion(SpecVersion1_2)
+		require.NoError(t, err)
+		require.Equal(t, "application/vnd.cyclonedx+json; version=1.2", res)
+	})
+
+	t.Run("ShouldReturnErrorForSpecLowerThan1.2AndJSON", func(t *testing.T) {
+		_, err := MediaTypeJSON.WithVersion(SpecVersion1_1)
+		require.Error(t, err)
+	})
+}
+
 func TestVulnerability_Properties(t *testing.T) {
 	// GIVEN
 	properties := []Property{}

encode.go

@@ -52,7 +52,7 @@ type jsonBOMEncoder struct {
 // Encode implements the BOMEncoder interface.
 func (j jsonBOMEncoder) Encode(bom *BOM) error {
 	if bom.SpecVersion < SpecVersion1_2 {
-		return fmt.Errorf("json format is not supported for specification versions lower than 1.2")
+		return fmt.Errorf("json format is not supported for specification versions lower than %s", SpecVersion1_2)
 	}
 
 	encoder := json.NewEncoder(j.writer)