Replaced Message.Export by Message.WriteTo

Message now implement io.WriterTo. It allows streaming
the message directly to the SMTP server without buffering it
first into memory.

export.go

@@ -1,18 +1,29 @@
 package gomail
 
 import (
-	"bytes"
 	"encoding/base64"
+	"errors"
 	"io"
 	"mime/multipart"
 	"mime/quotedprintable"
-	"net/mail"
 	"time"
 )
 
-// Export converts the message into a net/mail.Message.
+// WriteTo implements io.WriterTo.
-func (msg *Message) Export() *mail.Message {
+func (msg *Message) WriteTo(w io.Writer) (int64, error) {
-	w := newMessageWriter(msg)
+	mw := &messageWriter{w: w}
+	mw.writeMessage(msg)
+	return mw.n, mw.err
+}
+
+func (w *messageWriter) writeMessage(msg *Message) {
+	if _, ok := msg.header["Mime-Version"]; !ok {
+		w.writeString("Mime-Version: 1.0\r\n")
+	}
+	if _, ok := msg.header["Date"]; !ok {
+		w.writeHeader("Date", msg.FormatDate(now()))
+	}
+	w.writeHeaders(msg.header)
 
 	if msg.hasMixedPart() {
 		w.openMultipart("mixed")
@@ -26,11 +37,12 @@ func (msg *Message) Export() *mail.Message {
 		w.openMultipart("alternative")
 	}
 	for _, part := range msg.parts {
-		h := make(map[string][]string)
+		contentType := part.contentType + "; charset=" + msg.charset
-		h["Content-Type"] = []string{part.contentType + "; charset=" + msg.charset}
+		w.writeHeaders(map[string][]string{
-		h["Content-Transfer-Encoding"] = []string{string(msg.encoding)}
+			"Content-Type":              []string{contentType},
-
+			"Content-Transfer-Encoding": []string{string(msg.encoding)},
-		w.write(h, part.body.Bytes(), msg.encoding)
+		})
+		w.writeBody(part.body.Bytes(), msg.encoding)
 	}
 	if msg.hasAlternativePart() {
 		w.closeMultipart()
@@ -45,8 +57,6 @@ func (msg *Message) Export() *mail.Message {
 	if msg.hasMixedPart() {
 		w.closeMultipart()
 	}
-
-	return w.export()
 }
 
 func (msg *Message) hasMixedPart() bool {
@@ -61,52 +71,33 @@ func (msg *Message) hasAlternativePart() bool {
 	return len(msg.parts) > 1
 }
 
-// messageWriter helps converting the message into a net/mail.Message
 type messageWriter struct {
-	header     map[string][]string
+	w          io.Writer
-	buf        *bytes.Buffer
+	n          int64
 	writers    [3]*multipart.Writer
 	partWriter io.Writer
 	depth      uint8
+	err        error
 }
 
-func newMessageWriter(msg *Message) *messageWriter {
-	// We copy the header so Export does not modify the message
-	header := make(map[string][]string, len(msg.header)+2)
-	for k, v := range msg.header {
-		header[k] = v
-	}
-
-	if _, ok := header["Mime-Version"]; !ok {
-		header["Mime-Version"] = []string{"1.0"}
-	}
-	if _, ok := header["Date"]; !ok {
-		header["Date"] = []string{msg.FormatDate(now())}
-	}
-
-	return &messageWriter{header: header, buf: new(bytes.Buffer)}
-}
-
-// Stubbed out for testing.
-var now = time.Now
-
 func (w *messageWriter) openMultipart(mimeType string) {
-	w.writers[w.depth] = multipart.NewWriter(w.buf)
+	mw := multipart.NewWriter(w)
-	contentType := "multipart/" + mimeType + "; boundary=" + w.writers[w.depth].Boundary()
+	contentType := "multipart/" + mimeType + "; boundary=" + mw.Boundary()
+	w.writers[w.depth] = mw
 
 	if w.depth == 0 {
-		w.header["Content-Type"] = []string{contentType}
+		w.writeHeader("Content-Type", contentType)
+		w.writeString("\r\n")
 	} else {
-		h := make(map[string][]string)
+		w.createPart(map[string][]string{
-		h["Content-Type"] = []string{contentType}
+			"Content-Type": []string{contentType},
-		w.createPart(h)
+		})
 	}
 	w.depth++
 }
 
 func (w *messageWriter) createPart(h map[string][]string) {
-	// No need to check the error since the underlying writer is a bytes.Buffer
+	w.partWriter, w.err = w.writers[w.depth-1].CreatePart(h)
-	w.partWriter, _ = w.writers[w.depth-1].CreatePart(h)
 }
 
 func (w *messageWriter) closeMultipart() {
@@ -131,20 +122,53 @@ func (w *messageWriter) addFiles(files []*File, isAttachment bool) {
 				h["Content-ID"] = []string{"<" + f.Name + ">"}
 			}
 		}
-
+		w.writeHeaders(h)
-		w.write(h, f.Content, Base64)
+		w.writeBody(f.Content, Base64)
 	}
 }
 
-func (w *messageWriter) write(h map[string][]string, body []byte, enc Encoding) {
+func (w *messageWriter) Write(p []byte) (int, error) {
-	w.writeHeader(h)
+	if w.err != nil {
-	w.writeBody(body, enc)
+		return 0, errors.New("gomail: cannot write as writer is in error")
+	}
+
+	var n int
+	n, w.err = w.w.Write(p)
+	w.n += int64(n)
+	return n, w.err
 }
 
-func (w *messageWriter) writeHeader(h map[string][]string) {
+func (w *messageWriter) writeString(s string) {
+	n, _ := io.WriteString(w.w, s)
+	w.n += int64(n)
+}
+
+func (w *messageWriter) writeStrings(a []string, sep string) {
+	if len(a) > 0 {
+		w.writeString(a[0])
+		if len(a) == 1 {
+			return
+		}
+	}
+	for _, s := range a[1:] {
+		w.writeString(sep)
+		w.writeString(s)
+	}
+}
+
+func (w *messageWriter) writeHeader(k string, v ...string) {
+	w.writeString(k)
+	w.writeString(": ")
+	w.writeStrings(v, ", ")
+	w.writeString("\r\n")
+}
+
+func (w *messageWriter) writeHeaders(h map[string][]string) {
 	if w.depth == 0 {
-		for field, value := range h {
+		for k, v := range h {
-			w.header[field] = value
+			if k != "Bcc" {
+				w.writeHeader(k, v...)
+			}
 		}
 	} else {
 		w.createPart(h)
@@ -154,30 +178,25 @@ func (w *messageWriter) writeHeader(h map[string][]string) {
 func (w *messageWriter) writeBody(body []byte, enc Encoding) {
 	var subWriter io.Writer
 	if w.depth == 0 {
-		subWriter = w.buf
+		w.writeString("\r\n")
+		subWriter = w.w
 	} else {
 		subWriter = w.partWriter
 	}
 
-	// The errors returned by writers are not checked since these writers cannot
-	// return errors.
 	if enc == Base64 {
-		writer := base64.NewEncoder(base64.StdEncoding, newBase64LineWriter(subWriter))
+		wc := base64.NewEncoder(base64.StdEncoding, newBase64LineWriter(subWriter))
-		writer.Write(body)
+		wc.Write(body)
-		writer.Close()
+		wc.Close()
 	} else if enc == Unencoded {
 		subWriter.Write(body)
 	} else {
-		writer := quotedprintable.NewWriter(subWriter)
+		wc := quotedprintable.NewWriter(subWriter)
-		writer.Write(body)
+		wc.Write(body)
-		writer.Close()
+		wc.Close()
 	}
 }
 
-func (w *messageWriter) export() *mail.Message {
-	return &mail.Message{Header: w.header, Body: w.buf}
-}
-
 // As required by RFC 2045, 6.7. (page 21) for quoted-printable, and
 // RFC 2045, 6.8. (page 25) for base64.
 const maxLineLen = 76
@@ -207,3 +226,6 @@ func (w *base64LineWriter) Write(p []byte) (int, error) {
 
 	return n + len(p), nil
 }
+
+// Stubbed out for testing.
+var now = time.Now

message_test.go

@@ -1,9 +1,9 @@
 package gomail
 
 import (
+	"bytes"
 	"encoding/base64"
 	"io"
-	"io/ioutil"
 	"path/filepath"
 	"regexp"
 	"strconv"
@@ -476,7 +476,7 @@ func testMessage(t *testing.T, msg *Message, bCount int, want *message) {
 }
 
 func stubSendMail(t *testing.T, bCount int, want *message) SendFunc {
-	return func(from string, to []string, msg io.Reader) error {
+	return func(from string, to []string, msg io.WriterTo) error {
 		if from != want.from {
 			t.Fatalf("Invalid from, got %q, want %q", from, want.from)
 		}
@@ -495,11 +495,12 @@ func stubSendMail(t *testing.T, bCount int, want *message) SendFunc {
 			}
 		}
 
-		content, err := ioutil.ReadAll(msg)
+		buf := new(bytes.Buffer)
+		_, err := msg.WriteTo(buf)
 		if err != nil {
 			t.Error(err)
 		}
-		got := string(content)
+		got := buf.String()
 		wantMsg := string("Mime-Version: 1.0\r\n" +
 			"Date: Wed, 25 Jun 2014 17:46:00 +0000\r\n" +
 			want.content)
@@ -580,7 +581,7 @@ func getBoundaries(t *testing.T, count int, msg string) []string {
 var boundaryRegExp = regexp.MustCompile("boundary=(\\w+)")
 
 func BenchmarkFull(b *testing.B) {
-	emptyFunc := func(from string, to []string, msg io.Reader) error {
+	emptyFunc := func(from string, to []string, msg io.WriterTo) error {
 		return nil
 	}
 

send.go

@@ -1,20 +1,17 @@
 package gomail
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/mail"
-	"strings"
 )
 
 // Sender is the interface that wraps the Send method.
 //
 // Send sends an email to the given addresses.
 type Sender interface {
-	Send(from string, to []string, msg io.Reader) error
+	Send(from string, to []string, msg io.WriterTo) error
 }
 
 // SendCloser is the interface that groups the Send and Close methods.
@@ -27,10 +24,10 @@ type SendCloser interface {
 // The SendFunc type is an adapter to allow the use of ordinary functions as
 // email senders. If f is a function with the appropriate signature, SendFunc(f)
 // is a Sender object that calls f.
-type SendFunc func(from string, to []string, msg io.Reader) error
+type SendFunc func(from string, to []string, msg io.WriterTo) error
 
 // Send calls f(from, to, msg).
-func (f SendFunc) Send(from string, to []string, msg io.Reader) error {
+func (f SendFunc) Send(from string, to []string, msg io.WriterTo) error {
 	return f(from, to, msg)
 }
 
@@ -46,64 +43,39 @@ func Send(s Sender, msg ...*Message) error {
 }
 
 func send(s Sender, msg *Message) error {
-	message := msg.Export()
+	from, err := msg.getFrom()
-
-	from, err := getFrom(message)
-	if err != nil {
-		return err
-	}
-	to, err := getRecipients(message)
 	if err != nil {
 		return err
 	}
 
-	h := flattenHeader(message)
+	to, err := msg.getRecipients()
-	body, err := ioutil.ReadAll(message.Body)
 	if err != nil {
 		return err
 	}
 
-	mail := bytes.NewReader(append(h, body...))
+	if err := s.Send(from, to, msg); err != nil {
-	if err := s.Send(from, to, mail); err != nil {
 		return err
 	}
 
 	return nil
 }
 
-func flattenHeader(msg *mail.Message) []byte {
+func (msg *Message) getFrom() (string, error) {
-	buf := getBuffer()
+	from := msg.header["Sender"]
-	defer putBuffer(buf)
+	if len(from) == 0 {
-
+		from = msg.header["From"]
-	for field, value := range msg.Header {
+		if len(from) == 0 {
-		if field != "Bcc" {
+			return "", errors.New(`gomail: invalid message, "From" field is absent`)
-			buf.WriteString(field)
-			buf.WriteString(": ")
-			buf.WriteString(strings.Join(value, ", "))
-			buf.WriteString("\r\n")
-		}
-	}
-	buf.WriteString("\r\n")
-
-	return buf.Bytes()
-}
-
-func getFrom(msg *mail.Message) (string, error) {
-	from := msg.Header.Get("Sender")
-	if from == "" {
-		from = msg.Header.Get("From")
-		if from == "" {
-			return "", errors.New("gomail: invalid message, \"From\" field is absent")
 		}
 	}
 
-	return parseAddress(from)
+	return parseAddress(from[0])
 }
 
-func getRecipients(msg *mail.Message) ([]string, error) {
+func (msg *Message) getRecipients() ([]string, error) {
 	var list []string
 	for _, field := range []string{"To", "Cc", "Bcc"} {
-		if addresses, ok := msg.Header[field]; ok {
+		if addresses, ok := msg.header[field]; ok {
 			for _, a := range addresses {
 				addr, err := parseAddress(a)
 				if err != nil {

send_test.go

@@ -1,8 +1,8 @@
 package gomail
 
 import (
+	"bytes"
 	"io"
-	"io/ioutil"
 	"reflect"
 	"testing"
 )
@@ -24,7 +24,7 @@ const (
 
 type mockSender SendFunc
 
-func (s mockSender) Send(from string, to []string, msg io.Reader) error {
+func (s mockSender) Send(from string, to []string, msg io.WriterTo) error {
 	return s(from, to, msg)
 }
 
@@ -60,7 +60,7 @@ func getTestMessage() *Message {
 }
 
 func stubSend(t *testing.T, wantFrom string, wantTo []string, wantBody string) mockSender {
-	return func(from string, to []string, msg io.Reader) error {
+	return func(from string, to []string, msg io.WriterTo) error {
 		if from != wantFrom {
 			t.Errorf("invalid from, got %q, want %q", from, wantFrom)
 		}
@@ -68,11 +68,12 @@ func stubSend(t *testing.T, wantFrom string, wantTo []string, wantBody string) m
 			t.Errorf("invalid to, got %v, want %v", to, wantTo)
 		}
 
-		content, err := ioutil.ReadAll(msg)
+		buf := new(bytes.Buffer)
+		_, err := msg.WriteTo(buf)
 		if err != nil {
 			t.Fatal(err)
 		}
-		compareBodies(t, string(content), wantBody)
+		compareBodies(t, buf.String(), wantBody)
 
 		return nil
 	}

smtp.go

@@ -122,7 +122,7 @@ type smtpSender struct {
 	smtpClient
 }
 
-func (c *smtpSender) Send(from string, to []string, msg io.Reader) error {
+func (c *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
 	if err := c.Mail(from); err != nil {
 		return err
 	}
@@ -138,7 +138,7 @@ func (c *smtpSender) Send(from string, to []string, msg io.Reader) error {
 		return err
 	}
 
-	if _, err = io.Copy(w, msg); err != nil {
+	if _, err = msg.WriteTo(w); err != nil {
 		w.Close()
 		return err
 	}

smtp_test.go

@@ -1,6 +1,7 @@
 package gomail
 
 import (
+	"bytes"
 	"crypto/tls"
 	"io"
 	"net"
@@ -173,15 +174,19 @@ func (c *mockClient) do(cmd string) {
 type mockWriter struct {
 	want string
 	c    *mockClient
+	buf  bytes.Buffer
 }
 
 func (w *mockWriter) Write(p []byte) (int, error) {
-	w.c.do("Write message")
+	if w.buf.Len() == 0 {
-	compareBodies(w.c.t, string(p), w.want)
+		w.c.do("Write message")
+	}
+	w.buf.Write(p)
 	return len(p), nil
 }
 
 func (w *mockWriter) Close() error {
+	compareBodies(w.c.t, w.buf.String(), w.want)
 	w.c.do("Close writer")
 	return nil
 }