3 files changed, 68 insertions(+), 13 deletions(-)

M CHANGELOG.md
M session.go
M session_test.go

@@ 57,6 57,8 @@ All notable changes to this project will be documented in this file.
   now done concurrently to make the initial connection faster
 - dial: the fallback for dialing an XMPP connection when no SRV records exist is
   now more robust
+- xmpp: stanzas sent over S2S connections now always have the "from" attribute
+  set
 
 
 ### Fixed

@@ 185,7 185,11 @@ func NegotiateSession(ctx context.Context, location, origin jid.JID, rw io.ReadW
 	}
 
 	s.in.d = intstream.Reader(s.in.d)
-	s.out.e = &stanzaEncoder{TokenWriteFlusher: s.out.e}
+	se := &stanzaEncoder{TokenWriteFlusher: s.out.e}
+	if s.state&S2S == S2S {
+		se.from = s.LocalAddr()
+	}
+	s.out.e = se
 
 	return s, nil
 }


@@ 946,27 950,48 @@ func (s *Session) closeInputStream() {
 type stanzaEncoder struct {
 	xmlstream.TokenWriteFlusher
 	depth int
+	from  jid.JID
 }
 
 func (se *stanzaEncoder) EncodeToken(t xml.Token) error {
-tokswitch:
 	switch tok := t.(type) {
 	case xml.StartElement:
 		se.depth++
-		// RFC6120 §8.1.3
-		// For <message/> and <presence/> stanzas, it is RECOMMENDED for the
-		// originating entity to include an 'id' attribute; for <iq/> stanzas, it is
-		// REQUIRED.
+		// Add required attributes if missing:
 		if se.depth == 1 && isStanzaEmptySpace(tok.Name) {
+			var foundID, foundFrom bool
 			for _, attr := range tok.Attr {
-				if attr.Name.Local == "id" {
-					break tokswitch
+				switch attr.Name.Local {
+				case "id":
+					// RFC6120 § 8.1.3
+					// For <message/> and <presence/> stanzas, it is RECOMMENDED for the
+					// originating entity to include an 'id' attribute; for <iq/> stanzas,
+					// it is REQUIRED.
+					foundID = true
+				case "from":
+					// RFC6120 § 4.7.1
+					// the 'to' and 'from' attributes are OPTIONAL on stanzas sent over
+					// XML streams qualified by the 'jabber:client' namespace, whereas
+					// they are REQUIRED on stanzas sent over XML streams qualified by the
+					// 'jabber: server' namespace
+					foundFrom = true
+				}
+				if foundID && foundFrom {
+					break
 				}
 			}
-			tok.Attr = append(tok.Attr, xml.Attr{
-				Name:  xml.Name{Local: "id"},
-				Value: attr.RandomID(),
-			})
+			if f := se.from.String(); f != "" && !foundFrom {
+				tok.Attr = append(tok.Attr, xml.Attr{
+					Name:  xml.Name{Local: "from"},
+					Value: se.from.String(),
+				})
+			}
+			if !foundID {
+				tok.Attr = append(tok.Attr, xml.Attr{
+					Name:  xml.Name{Local: "id"},
+					Value: attr.RandomID(),
+				})
+			}
 			t = tok
 		}
 	case xml.EndElement:

@@ 172,6 172,7 @@ var serveTests = [...]struct {
 	in           string
 	err          error
 	errStringCmp bool
+	state        xmpp.SessionState
 }{
 	0: {
 		in:  `<test></test>`,


@@ 324,6 325,33 @@ var serveTests = [...]struct {
 		in:  `<a>test</a><b></b>`,
 		out: `<a xmlns="jabber:client">test</a></stream:stream>`,
 	},
+	15: {
+		// S2S stanzas always have "from" set if not already set.
+		handler: xmpp.HandlerFunc(func(rw xmlstream.TokenReadEncoder, start *xml.StartElement) error {
+			_, err := xmlstream.Copy(rw, stanza.IQ{
+				ID:   "1234",
+				Type: stanza.ResultIQ,
+			}.Wrap(nil))
+			return err
+		}),
+		in:    `<iq type="get" id="1234"><unknownpayload xmlns="unknown"/></iq>`,
+		out:   `<iq type="result" id="1234" from="test@example.net"></iq></stream:stream>`,
+		state: xmpp.S2S,
+	},
+	16: {
+		// S2S stanzas always have "from" set, unless it was already set.
+		handler: xmpp.HandlerFunc(func(rw xmlstream.TokenReadEncoder, start *xml.StartElement) error {
+			_, err := xmlstream.Copy(rw, stanza.IQ{
+				ID:   "1234",
+				From: jid.MustParse("from@example.net"),
+				Type: stanza.ResultIQ,
+			}.Wrap(nil))
+			return err
+		}),
+		in:    `<iq type="get" id="1234"><unknownpayload xmlns="unknown"/></iq>`,
+		out:   `<iq type="result" from="from@example.net" id="1234"></iq></stream:stream>`,
+		state: xmpp.S2S,
+	},
 }
 
 func TestServe(t *testing.T) {


@@ 331,7 359,7 @@ func TestServe(t *testing.T) {
 		t.Run(strconv.Itoa(i), func(t *testing.T) {
 			out := &bytes.Buffer{}
 			in := strings.NewReader(tc.in)
-			s := xmpptest.NewSession(0, struct {
+			s := xmpptest.NewSession(tc.state, struct {
 				io.Reader
 				io.Writer
 			}{