From d4b835bf2b08a22e6a13cd9b33e62c88f9854677 Mon Sep 17 00:00:00 2001
From: Sam Whited <sam@samwhited.com>
Date: Tue, 24 Nov 2020 17:12:32 -0500
Subject: [PATCH] internal/marshal: prevent duplicate xmlns attr

Encoding the output of TokenReader can create multiple xmlns attributes
due to a bug in encoding/xml.
This patch uses RawToken in the decode stage to work around this and can
be reverted after the upstream issue is fixed and in all supported
versions of Go.

Upstream issue: https://golang.org/issue/42807 (golang/go#42807)
Upstream CL: https://golang.org/cl/272806 (golang/go#42808)

Fixes #74

Signed-off-by: Sam Whited <sam@samwhited.com>
---
 internal/marshal/encode.go      | 21 +++++++++++++++++----
 internal/marshal/encode_test.go | 21 +++++++++++++++++++++
 2 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/internal/marshal/encode.go b/internal/marshal/encode.go
index 2776012..d6ccb55 100644
--- a/internal/marshal/encode.go
+++ b/internal/marshal/encode.go
@@ -22,6 +22,10 @@ func TokenReader(v interface{}) (xml.TokenReader, error) {
 		return r, nil
 	}
 
+	return tokenDecoder(v)
+}
+
+func tokenDecoder(v interface{}) (*xml.Decoder, error) {
 	var b bytes.Buffer
 	err := xml.NewEncoder(&b).Encode(v)
 	if err != nil {
@@ -30,6 +34,15 @@ func TokenReader(v interface{}) (xml.TokenReader, error) {
 	return xml.NewDecoder(&b), nil
 }
 
+// rawTokenReader maps a decoders RawToken method onto its Token method.
+type rawTokenReader struct {
+	*xml.Decoder
+}
+
+func (r rawTokenReader) Token() (xml.Token, error) {
+	return r.RawToken()
+}
+
 // EncodeXML writes the XML encoding of v to the stream.
 //
 // See the documentation for xml.Marshal for details about the conversion of Go
@@ -38,11 +51,11 @@ func TokenReader(v interface{}) (xml.TokenReader, error) {
 // If the stream is an xmlstream.Flusher, EncodeXML calls Flush before
 // returning.
 func EncodeXML(w xmlstream.TokenWriter, v interface{}) error {
-	r, err := TokenReader(v)
+	d, err := tokenDecoder(v)
 	if err != nil {
 		return err
 	}
-	_, err = xmlstream.Copy(w, r)
+	_, err = xmlstream.Copy(w, rawTokenReader{Decoder: d})
 	if err != nil {
 		return err
 	}
@@ -62,11 +75,11 @@ func EncodeXML(w xmlstream.TokenWriter, v interface{}) error {
 // If the stream is an xmlstream.Flusher, EncodeXMLElement calls Flush before
 // returning.
 func EncodeXMLElement(w xmlstream.TokenWriter, v interface{}, start xml.StartElement) error {
-	r, err := TokenReader(v)
+	d, err := tokenDecoder(v)
 	if err != nil {
 		return err
 	}
-	_, err = xmlstream.Copy(w, xmlstream.Wrap(r, start))
+	_, err = xmlstream.Copy(w, rawTokenReader{Decoder: d})
 	if err != nil {
 		return err
 	}
diff --git a/internal/marshal/encode_test.go b/internal/marshal/encode_test.go
index cbe691a..117b707 100644
--- a/internal/marshal/encode_test.go
+++ b/internal/marshal/encode_test.go
@@ -122,3 +122,24 @@ func TestMarshalTokenReader(t *testing.T) {
 		t.Errorf("got different xml.TokenReader out: want=%v, got=%v", r, rr)
 	}
 }
+
+func TestTokenDecoder(t *testing.T) {
+	r := stanza.IQ{}
+	_, err := marshal.TokenReader(r)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+}
+
+func TestEncodeXMLNS(t *testing.T) {
+	var buf bytes.Buffer
+	e := xml.NewEncoder(&buf)
+	err := marshal.EncodeXML(e, simpleIn)
+	if err != nil {
+		t.Errorf("unexpected error encoding: %v", err)
+	}
+	const expected = `<local xmlns="space"></local>`
+	if s := buf.String(); s != expected {
+		t.Errorf("wrong output: want=%s, got=%s", expected, s)
+	}
+}
-- 
2.30.1