make it harder to forget to set smtputf8 on message.Composer

we should do better: first gather all headers, and only write it when we start
on the body, and then calculate smtputf8 ourselves.

dmarcdb/eval.go

@@ -875,7 +875,15 @@ Period: %s - %s UTC
 }
 
 func composeAggregateReport(ctx context.Context, log mlog.Log, mf *os.File, fromAddr smtp.Address, recipients []message.NameAddress, subject, text, filename string, reportXMLGzipFile *os.File) (msgPrefix string, has8bit, smtputf8 bool, messageID string, rerr error) {
-	xc := message.NewComposer(mf, 100*1024*1024)
+	// We only use smtputf8 if we have to, with a utf-8 localpart. For IDNA, we use ASCII domains.
+	smtputf8 = fromAddr.Localpart.IsInternational()
+	for _, r := range recipients {
+		if smtputf8 {
+			smtputf8 = r.Address.Localpart.IsInternational()
+			break
+		}
+	}
+	xc := message.NewComposer(mf, 100*1024*1024, smtputf8)
 	defer func() {
 		x := recover()
 		if x == nil {
@@ -888,14 +896,6 @@ func composeAggregateReport(ctx context.Context, log mlog.Log, mf *os.File, from
 		panic(x)
 	}()
 
-	// We only use smtputf8 if we have to, with a utf-8 localpart. For IDNA, we use ASCII domains.
-	for _, a := range recipients {
-		if a.Address.Localpart.IsInternational() {
-			xc.SMTPUTF8 = true
-			break
-		}
-	}
-
 	xc.HeaderAddrs("From", []message.NameAddress{{Address: fromAddr}})
 	xc.HeaderAddrs("To", recipients)
 	xc.Subject(subject)
@@ -1015,7 +1015,15 @@ Submitting-URI: %s
 }
 
 func composeErrorReport(ctx context.Context, log mlog.Log, mf *os.File, fromAddr smtp.Address, recipients []message.NameAddress, subject, text string) (msgPrefix string, has8bit, smtputf8 bool, messageID string, rerr error) {
-	xc := message.NewComposer(mf, 100*1024*1024)
+	// We only use smtputf8 if we have to, with a utf-8 localpart. For IDNA, we use ASCII domains.
+	smtputf8 = fromAddr.Localpart.IsInternational()
+	for _, r := range recipients {
+		if smtputf8 {
+			smtputf8 = r.Address.Localpart.IsInternational()
+			break
+		}
+	}
+	xc := message.NewComposer(mf, 100*1024*1024, smtputf8)
 	defer func() {
 		x := recover()
 		if x == nil {
@@ -1028,14 +1036,6 @@ func composeErrorReport(ctx context.Context, log mlog.Log, mf *os.File, fromAddr
 		panic(x)
 	}()
 
-	// We only use smtputf8 if we have to, with a utf-8 localpart. For IDNA, we use ASCII domains.
-	for _, a := range recipients {
-		if a.Address.Localpart.IsInternational() {
-			xc.SMTPUTF8 = true
-			break
-		}
-	}
-
 	xc.HeaderAddrs("From", []message.NameAddress{{Address: fromAddr}})
 	xc.HeaderAddrs("To", recipients)
 	xc.Header("Subject", subject)

message/compose.go

@@ -32,10 +32,14 @@ type Composer struct {
 
 // NewComposer initializes a new composer with a buffered writer around w, and
 // with a maximum message size if maxSize is greater than zero.
+//
+// smtputf8 must be set when the message must be delivered with smtputf8: if any
+// email address localpart has non-ascii (utf-8).
+//
 // Operations on a Composer do not return an error. Caller must use recover() to
 // catch ErrCompose and optionally ErrMessageSize errors.
-func NewComposer(w io.Writer, maxSize int64) *Composer {
-	return &Composer{bw: bufio.NewWriter(w), maxSize: maxSize}
+func NewComposer(w io.Writer, maxSize int64, smtputf8 bool) *Composer {
+	return &Composer{bw: bufio.NewWriter(w), maxSize: maxSize, SMTPUTF8: smtputf8, Has8bit: smtputf8}
 }
 
 // Write implements io.Writer, but calls panic (that is handled higher up) on

message/examples_test.go

@@ -91,7 +91,8 @@ func ExampleComposer() {
 	var b bytes.Buffer
 
 	// NewComposer. Keep in mind that operations on a Composer will panic on error.
-	xc := message.NewComposer(&b, 10*1024*1024)
+	const smtputf8 = false
+	xc := message.NewComposer(&b, 10*1024*1024, smtputf8)
 
 	// Catch and handle errors when composing.
 	defer func() {

tlsrptsend/send.go

@@ -620,7 +620,15 @@ Period: %s - %s UTC
 }
 
 func composeMessage(ctx context.Context, log mlog.Log, mf *os.File, policyDomain dns.Domain, confDKIM config.DKIM, fromAddr smtp.Address, recipients []message.NameAddress, subject, text, filename string, reportFile *os.File) (msgPrefix string, has8bit, smtputf8 bool, messageID string, rerr error) {
-	xc := message.NewComposer(mf, 100*1024*1024)
+	// We only use smtputf8 if we have to, with a utf-8 localpart. For IDNA, we use ASCII domains.
+	smtputf8 = fromAddr.Localpart.IsInternational()
+	for _, r := range recipients {
+		if smtputf8 {
+			smtputf8 = r.Address.Localpart.IsInternational()
+			break
+		}
+	}
+	xc := message.NewComposer(mf, 100*1024*1024, smtputf8)
 	defer func() {
 		x := recover()
 		if x == nil {
@@ -633,14 +641,6 @@ func composeMessage(ctx context.Context, log mlog.Log, mf *os.File, policyDomain
 		panic(x)
 	}()
 
-	// We only use smtputf8 if we have to, with a utf-8 localpart. For IDNA, we use ASCII domains.
-	for _, a := range recipients {
-		if a.Address.Localpart.IsInternational() {
-			xc.SMTPUTF8 = true
-			break
-		}
-	}
-
 	xc.HeaderAddrs("From", []message.NameAddress{{Address: fromAddr}})
 	xc.HeaderAddrs("To", recipients)
 	xc.Subject(subject)

webmail/api.go

@@ -366,8 +366,6 @@ func (w Webmail) MessageSubmit(ctx context.Context, m SubmitMessage) {
 		xcheckf(ctx, err, "checking send limit")
 	})
 
-	has8bit := false // We update this later on.
-
 	// We only use smtputf8 if we have to, with a utf-8 localpart. For IDNA, we use ASCII domains.
 	smtputf8 := false
 	for _, a := range recipients {
@@ -387,7 +385,7 @@ func (w Webmail) MessageSubmit(ctx context.Context, m SubmitMessage) {
 	defer store.CloseRemoveTempFile(log, dataFile, "message to submit")
 
 	// If writing to the message file fails, we abort immediately.
-	xc := message.NewComposer(dataFile, w.maxMessageSize)
+	xc := message.NewComposer(dataFile, w.maxMessageSize, smtputf8)
 	defer func() {
 		x := recover()
 		if x == nil {
@@ -643,7 +641,7 @@ func (w Webmail) MessageSubmit(ctx context.Context, m SubmitMessage) {
 			Localpart: rcpt.Localpart,
 			IPDomain:  dns.IPDomain{Domain: rcpt.Domain},
 		}
-		qm := queue.MakeMsg(fromPath, toPath, has8bit, smtputf8, msgSize, messageID, []byte(rcptMsgPrefix), m.RequireTLS, now)
+		qm := queue.MakeMsg(fromPath, toPath, xc.Has8bit, xc.SMTPUTF8, msgSize, messageID, []byte(rcptMsgPrefix), m.RequireTLS, now)
 		if m.FutureRelease != nil {
 			ival := time.Until(*m.FutureRelease)
 			if ival < 0 {