From 346d7d273c864411022f809945627866f6bc4cc6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tam=C3=A1s=20Gul=C3=A1csi?= <tgulacsi78@gmail.com>
Date: Fri, 25 Oct 2019 13:48:02 +0200
Subject: [PATCH] encoding/xml: fix reserved namespace check to be
 case-insensitive

Fixes the check for the reserved namespace prefix
"xml" to be case insensitive, so as to match all variants of:

    (('X'|'x')('M'|'m')('L'|'l'))

as mandated by Section 2.3 of https://www.w3.org/TR/REC-xml/

Fixes #35151.

Change-Id: Id5a98e5f9d69d3741dc16f567c4320f1ad0b3c70
Reviewed-on: https://go-review.googlesource.com/c/go/+/203417
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
---
 src/encoding/xml/marshal.go      |  7 +++++--
 src/encoding/xml/marshal_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/src/encoding/xml/marshal.go b/src/encoding/xml/marshal.go
index e325f31374..2440a51e20 100644
--- a/src/encoding/xml/marshal.go
+++ b/src/encoding/xml/marshal.go
@@ -345,8 +345,11 @@ func (p *printer) createAttrPrefix(url string) string {
 	if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
 		prefix = "_"
 	}
-	if strings.HasPrefix(prefix, "xml") {
-		// xmlanything is reserved.
+	// xmlanything is reserved and any variant of it regardless of
+	// case should be matched, so:
+	//    (('X'|'x') ('M'|'m') ('L'|'l'))
+	// See Section 2.3 of https://www.w3.org/TR/REC-xml/
+	if len(prefix) >= 3 && strings.EqualFold(prefix[:3], "xml") {
 		prefix = "_" + prefix
 	}
 	if p.attrNS[prefix] != "" {
diff --git a/src/encoding/xml/marshal_test.go b/src/encoding/xml/marshal_test.go
index 8473158bcd..6085ddbba2 100644
--- a/src/encoding/xml/marshal_test.go
+++ b/src/encoding/xml/marshal_test.go
@@ -2266,6 +2266,30 @@ var encodeTokenTests = []struct {
 		}},
 	},
 	want: `<foo xmlns="space"><bar xmlns="space" xmlns:space="space" space:attr="value">`,
+}, {
+	desc: "reserved namespace prefix -- all lower case",
+	toks: []Token{
+		StartElement{Name{"", "foo"}, []Attr{
+			{Name{"http://www.w3.org/2001/xmlSchema-instance", "nil"}, "true"},
+		}},
+	},
+	want: `<foo xmlns:_xmlSchema-instance="http://www.w3.org/2001/xmlSchema-instance" _xmlSchema-instance:nil="true">`,
+}, {
+	desc: "reserved namespace prefix -- all upper case",
+	toks: []Token{
+		StartElement{Name{"", "foo"}, []Attr{
+			{Name{"http://www.w3.org/2001/XMLSchema-instance", "nil"}, "true"},
+		}},
+	},
+	want: `<foo xmlns:_XMLSchema-instance="http://www.w3.org/2001/XMLSchema-instance" _XMLSchema-instance:nil="true">`,
+}, {
+	desc: "reserved namespace prefix -- all mixed case",
+	toks: []Token{
+		StartElement{Name{"", "foo"}, []Attr{
+			{Name{"http://www.w3.org/2001/XmLSchema-instance", "nil"}, "true"},
+		}},
+	},
+	want: `<foo xmlns:_XmLSchema-instance="http://www.w3.org/2001/XmLSchema-instance" _XmLSchema-instance:nil="true">`,
 }}
 
 func TestEncodeToken(t *testing.T) {