fix: support Signature element on the root level

Issue: #46
Issue: #47

envelopedsignature.go

@@ -2,6 +2,7 @@ package signedxml
 
 import (
 	"errors"
+	"strings"
 
 	"github.com/beevik/etree"
 )
@@ -57,15 +58,23 @@ func (e EnvelopedSignature) Process(inputXML string, transformXML string) (outpu
 }
 
 func (e EnvelopedSignature) processElement(inputXML *etree.Element, transformXML string) (outputXML *etree.Element, err error) {
-	sig := inputXML.FindElement(".//Signature")
+	sig := inputXML.FindElement("//Signature")
+	if sig == nil {
+		// TODO(adam): Why can't ./Signature (or /Signature, or //Signature) find the root Signature element?
+		if strings.EqualFold(inputXML.Tag, "Signature") {
+			sig = inputXML
+		}
+	}
 	if sig == nil {
 		return nil, errors.New("signedxml: unable to find Signature node")
 	}
 
 	sigParent := sig.Parent()
-	elem := sigParent.RemoveChild(sig)
-	if elem == nil {
-		return nil, errors.New("signedxml: unable to remove Signature element")
+	if sigParent != nil {
+		elem := sigParent.RemoveChild(sig)
+		if elem == nil {
+			return nil, errors.New("signedxml: unable to remove Signature element")
+		}
 	}
 
 	return inputXML, nil

signedxml.go

@@ -112,7 +112,7 @@ func (s *signatureData) SetSignature(sig string) error {
 }
 
 func (s *signatureData) parseEnvelopedSignature() error {
-	sig := s.xml.FindElement(".//Signature")
+	sig := s.xml.FindElement("//Signature")
 	if sig != nil {
 		s.signature = sig
 	} else {

signedxml_test.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/beevik/etree"
@@ -98,6 +99,26 @@ func TestSign(t *testing.T) {
 
 	})
 
+	Convey("Signature at the Root level, surrounding the Object", t, func() {
+		xml, _ := os.ReadFile(filepath.Join("testdata", "root-level-signature.xml"))
+
+		doc := etree.NewDocument()
+		doc.ReadFromBytes(xml)
+		signature := doc.FindElement("//Signature")
+		t.Logf("signature: %#v", signature)
+
+		signer, _ := NewSigner(string(xml))
+		signer.SetReferenceIDAttribute("Id")
+		xmlStr, err := signer.Sign(key)
+		So(err, ShouldBeNil)
+
+		validator, _ := NewValidator(xmlStr)
+		validator.SetReferenceIDAttribute("Id")
+		validator.Certificates = append(validator.Certificates, *cert)
+		refs, err := validator.ValidateReferences()
+		So(err, ShouldBeNil)
+		So(len(refs), ShouldEqual, 1)
+	})
 }
 
 func TestValidate(t *testing.T) {
@@ -223,18 +244,6 @@ func TestEnvelopedSignatureProcess(t *testing.T) {
 			})
 		})
 	})
-
-	Convey("Given an unparented signature element", t, func() {
-		doc := "<Signature></Signature>"
-		Convey("When ProcessDocument is called", func() {
-			envSig := EnvelopedSignature{}
-			_, err := envSig.Process(doc, "")
-			Convey("Then an error occurs", func() {
-				So(err, ShouldNotBeNil)
-				So(err.Error(), ShouldContainSubstring, "signedxml:")
-			})
-		})
-	})
 }
 
 func TestSignatureDataParsing(t *testing.T) {

testdata/root-level-signature.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
+    <SignedInfo>
+        <CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"></CanonicalizationMethod>
+        <SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"></SignatureMethod>
+        <Reference URI="#test">
+            <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"></DigestMethod>
+            <Transforms>
+                <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"></Transform>
+            </Transforms>
+            <DigestValue></DigestValue>
+        </Reference>
+    </SignedInfo>
+    <SignatureValue></SignatureValue>
+    <KeyInfo>
+        <X509Data>
+            <X509Certificate>testtest</X509Certificate>
+        </X509Data>
+    </KeyInfo>
+    <Object xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Id="test">
+      <Foo>name</Foo>
+    </Object>
+</Signature>