feat: add IsReference function to check if a DID is a reference

did.go

@@ -45,6 +45,12 @@ type parser struct {
 // a step in the parser state machine that returns the next step
 type parserStep func() parserStep
 
+// IsReference returns true if a DID has a Path or a Fragment
+// https://w3c-ccg.github.io/did-spec/#dfn-did-reference
+func (d *DID) IsReference() bool {
+	return (d.Path != "" || len(d.PathSegments) > 0 || d.Fragment != "")
+}
+
 // String encodes a DID struct into a valid DID string.
 func (d *DID) String() string {
 	var buf strings.Builder

did_test.go

@@ -4,6 +4,44 @@ import (
 	"testing"
 )
 
+func TestIsReference(t *testing.T) {
+
+	t.Run("returns false if no Path of Fragment", func(t *testing.T) {
+		d := &DID{Method: "example", ID: "123"}
+		if d.IsReference() {
+			t.Errorf("returned true")
+		}
+	})
+
+	t.Run("returns true if Path", func(t *testing.T) {
+		d := &DID{Method: "example", ID: "123", Path: "a/b"}
+		if !d.IsReference() {
+			t.Errorf("returned false")
+		}
+	})
+
+	t.Run("returns true if PathSegements", func(t *testing.T) {
+		d := &DID{Method: "example", ID: "123", PathSegments: []string{"a", "b"}}
+		if !d.IsReference() {
+			t.Errorf("returned false")
+		}
+	})
+
+	t.Run("returns true if Fragment", func(t *testing.T) {
+		d := &DID{Method: "example", ID: "123", Fragment: "00000"}
+		if !d.IsReference() {
+			t.Errorf("returned false")
+		}
+	})
+
+	t.Run("returns true if Path and Fragment", func(t *testing.T) {
+		d := &DID{Method: "example", ID: "123", Path: "a/b", Fragment: "00000"}
+		if !d.IsReference() {
+			t.Errorf("returned false")
+		}
+	})
+}
+
 // nolint
 func TestString(t *testing.T) {
 

example_test.go

@@ -55,3 +55,21 @@ func ExampleDID_String_withFragment() {
 	fmt.Println(d)
 	// Output: did:example:q7ckgxeq1lxmra0r#keys-1
 }
+
+func ExampleDID_IsReference_withPath() {
+	d := &did.DID{Method: "example", ID: "q7ckgxeq1lxmra0r", Path: "a/b"}
+	fmt.Println(d.IsReference())
+	// Output: true
+}
+
+func ExampleDID_IsReference_withFragment() {
+	d := &did.DID{Method: "example", ID: "q7ckgxeq1lxmra0r", Fragment: "keys-1"}
+	fmt.Println(d.IsReference())
+	// Output: true
+}
+
+func ExampleDID_IsReference_noPathOrFragment() {
+	d := &did.DID{Method: "example", ID: "q7ckgxeq1lxmra0r"}
+	fmt.Println(d.IsReference())
+	// Output: false
+}