encoding/xml: error when closing tag does not match opening tag

Comparing opening and closing tag is done using the prefix when available.
Documentation states that Token returns URI in the Space part of the Name.
Translation has been moved for the End tag before the namespace is removed
from the stack.

After closing a tag using a namespace, the valid namespace must be taken
from the opening tag. Tests added.

Fixes golang#20685

Change-Id: I4d90b19f7e21a76663f0ea1c1db6c6bf9fd2a389
Reviewed-on: https://go-review.googlesource.com/c/go/+/107255
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

src/encoding/xml/xml.go

@@ -314,15 +314,14 @@ func (d *Decoder) Token() (Token, error) {
 			}
 		}
 
+		d.pushElement(t1.Name)
 		d.translate(&t1.Name, true)
 		for i := range t1.Attr {
 			d.translate(&t1.Attr[i].Name, false)
 		}
-		d.pushElement(t1.Name)
 		t = t1
 
 	case EndElement:
-		d.translate(&t1.Name, true)
 		if !d.popElement(&t1) {
 			return nil, d.err
 		}
@@ -495,6 +494,8 @@ func (d *Decoder) popElement(t *EndElement) bool {
 		return false
 	}
 
+	d.translate(&t.Name, true)
+
 	// Pop stack until a Start or EOF is on the top, undoing the
 	// translations that were associated with the element we just closed.
 	for d.stk != nil && d.stk.kind != stkStart && d.stk.kind != stkEOF {

src/encoding/xml/xml_test.go

@@ -1059,6 +1059,41 @@ func TestIssue12417(t *testing.T) {
 	}
 }
 
+func TestIssue20685(t *testing.T) {
+	testCases := []struct {
+		s  string
+		ok bool
+	}{
+		{`<x:book xmlns:x="abcd" xmlns:y="abcd"><unclosetag>one</x:book>`, false},
+		{`<x:book xmlns:x="abcd" xmlns:y="abcd">one</x:book>`, true},
+		{`<x:book xmlns:x="abcd" xmlns:y="abcd">one</y:book>`, false},
+		{`<x:book xmlns:y="abcd" xmlns:x="abcd">one</y:book>`, false},
+		{`<x:book xmlns:x="abcd">one</y:book>`, false},
+		{`<x:book>one</y:book>`, false},
+		{`<xbook>one</ybook>`, false},
+	}
+	for _, tc := range testCases {
+		d := NewDecoder(strings.NewReader(tc.s))
+		var err error
+		for {
+			_, err = d.Token()
+			if err != nil {
+				if err == io.EOF {
+					err = nil
+				}
+				break
+			}
+		}
+		if err != nil && tc.ok {
+			t.Errorf("%q: Closing tag with namespace : expected no error, got %s", tc.s, err)
+			continue
+		}
+		if err == nil && !tc.ok {
+			t.Errorf("%q: Closing tag with namespace : expected error, got nil", tc.s)
+		}
+	}
+}
+
 func tokenMap(mapping func(t Token) Token) func(TokenReader) TokenReader {
 	return func(src TokenReader) TokenReader {
 		return mapper{