Added automatic folding of long header lines

Fixes #53

message_test.go

@@ -7,6 +7,7 @@ import (
 	"io/ioutil"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strconv"
 	"strings"
 	"testing"
@@ -150,7 +151,8 @@ func TestAlternative(t *testing.T) {
 		to:   []string{"to@example.com"},
 		content: "From: from@example.com\r\n" +
 			"To: to@example.com\r\n" +
-			"Content-Type: multipart/alternative; boundary=_BOUNDARY_1_\r\n" +
+			"Content-Type: multipart/alternative;\r\n" +
+			" boundary=_BOUNDARY_1_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: text/plain; charset=UTF-8\r\n" +
@@ -180,7 +182,8 @@ func TestPartSetting(t *testing.T) {
 		to:   []string{"to@example.com"},
 		content: "From: from@example.com\r\n" +
 			"To: to@example.com\r\n" +
-			"Content-Type: multipart/alternative; boundary=_BOUNDARY_1_\r\n" +
+			"Content-Type: multipart/alternative;\r\n" +
+			" boundary=_BOUNDARY_1_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: text/plain; format=flowed; charset=UTF-8\r\n" +
@@ -216,7 +219,8 @@ func TestBodyWriter(t *testing.T) {
 		to:   []string{"to@example.com"},
 		content: "From: from@example.com\r\n" +
 			"To: to@example.com\r\n" +
-			"Content-Type: multipart/alternative; boundary=_BOUNDARY_1_\r\n" +
+			"Content-Type: multipart/alternative;\r\n" +
+			" boundary=_BOUNDARY_1_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: text/plain; charset=UTF-8\r\n" +
@@ -267,7 +271,8 @@ func TestAttachment(t *testing.T) {
 		to:   []string{"to@example.com"},
 		content: "From: from@example.com\r\n" +
 			"To: to@example.com\r\n" +
-			"Content-Type: multipart/mixed; boundary=_BOUNDARY_1_\r\n" +
+			"Content-Type: multipart/mixed;\r\n" +
+			" boundary=_BOUNDARY_1_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: text/plain; charset=UTF-8\r\n" +
@@ -298,7 +303,8 @@ func TestAttachmentsOnly(t *testing.T) {
 		to:   []string{"to@example.com"},
 		content: "From: from@example.com\r\n" +
 			"To: to@example.com\r\n" +
-			"Content-Type: multipart/mixed; boundary=_BOUNDARY_1_\r\n" +
+			"Content-Type: multipart/mixed;\r\n" +
+			" boundary=_BOUNDARY_1_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: application/pdf; name=\"test.pdf\"\r\n" +
@@ -331,7 +337,8 @@ func TestAttachments(t *testing.T) {
 		to:   []string{"to@example.com"},
 		content: "From: from@example.com\r\n" +
 			"To: to@example.com\r\n" +
-			"Content-Type: multipart/mixed; boundary=_BOUNDARY_1_\r\n" +
+			"Content-Type: multipart/mixed;\r\n" +
+			" boundary=_BOUNDARY_1_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: text/plain; charset=UTF-8\r\n" +
@@ -369,7 +376,8 @@ func TestEmbedded(t *testing.T) {
 		to:   []string{"to@example.com"},
 		content: "From: from@example.com\r\n" +
 			"To: to@example.com\r\n" +
-			"Content-Type: multipart/related; boundary=_BOUNDARY_1_\r\n" +
+			"Content-Type: multipart/related;\r\n" +
+			" boundary=_BOUNDARY_1_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: text/plain; charset=UTF-8\r\n" +
@@ -410,13 +418,16 @@ func TestFullMessage(t *testing.T) {
 		to:   []string{"to@example.com"},
 		content: "From: from@example.com\r\n" +
 			"To: to@example.com\r\n" +
-			"Content-Type: multipart/mixed; boundary=_BOUNDARY_1_\r\n" +
+			"Content-Type: multipart/mixed;\r\n" +
+			" boundary=_BOUNDARY_1_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
-			"Content-Type: multipart/related; boundary=_BOUNDARY_2_\r\n" +
+			"Content-Type: multipart/related;\r\n" +
+			" boundary=_BOUNDARY_2_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_2_\r\n" +
-			"Content-Type: multipart/alternative; boundary=_BOUNDARY_3_\r\n" +
+			"Content-Type: multipart/alternative;\r\n" +
+			" boundary=_BOUNDARY_3_\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_3_\r\n" +
 			"Content-Type: text/plain; charset=UTF-8\r\n" +
@@ -660,6 +671,32 @@ func mockCopyFileWithHeader(m *Message, name string, h map[string][]string) (str
 	return name, f, SetHeader(h)
 }
 
+func TestLineLength(t *testing.T) {
+	switch runtime.Version()[:5] {
+	case "go1.2", "go1.3", "go1.4", "go1.5":
+		t.Skip("Only pass with Go 1.6+")
+	}
+
+	m := NewMessage()
+	m.SetAddressHeader("From", "from@example.com", "Señor From")
+	m.SetHeader("Subject", "{$firstname} Bienvendio a Apostólica, aquí inicia el camino de tu")
+	m.SetBody("text/plain", strings.Repeat("a", 100))
+
+	buf := new(bytes.Buffer)
+	m.WriteTo(buf)
+	n := 0
+	for _, b := range buf.Bytes() {
+		if b == '\n' {
+			n = 0
+		} else {
+			n++
+			if n == 80 {
+				t.Errorf("A line is too long:\n%s", buf.Bytes())
+			}
+		}
+	}
+}
+
 func BenchmarkFull(b *testing.B) {
 	discardFunc := SendFunc(func(from string, to []string, m io.WriterTo) error {
 		_, err := m.WriteTo(ioutil.Discard)

mime.go

@@ -5,6 +5,7 @@ package gomail
 import (
 	"mime"
 	"mime/quotedprintable"
+	"strings"
 )
 
 var newQPWriter = quotedprintable.NewWriter
@@ -16,4 +17,5 @@ type mimeEncoder struct {
 var (
 	bEncoding     = mimeEncoder{mime.BEncoding}
 	qEncoding     = mimeEncoder{mime.QEncoding}
+	lastIndexByte = strings.LastIndexByte
 )

mime_go14.go

@@ -13,4 +13,13 @@ type mimeEncoder struct {
 var (
 	bEncoding     = mimeEncoder{quotedprintable.BEncoding}
 	qEncoding     = mimeEncoder{quotedprintable.QEncoding}
+	lastIndexByte = func(s string, c byte) int {
+		for i := len(s) - 1; i >= 0; i-- {
+
+			if s[i] == c {
+				return i
+			}
+		}
+		return -1
+	}
 )

writeto.go

@@ -7,6 +7,7 @@ import (
 	"mime"
 	"mime/multipart"
 	"path/filepath"
+	"strings"
 	"time"
 )
 
@@ -78,7 +79,7 @@ type messageWriter struct {
 
 func (w *messageWriter) openMultipart(mimeType string) {
 	mw := multipart.NewWriter(w)
-	contentType := "multipart/" + mimeType + "; boundary=" + mw.Boundary()
+	contentType := "multipart/" + mimeType + ";\r\n boundary=" + mw.Boundary()
 	w.writers[w.depth] = mw
 
 	if w.depth == 0 {
@@ -163,17 +164,87 @@ func (w *messageWriter) writeString(s string) {
 
 func (w *messageWriter) writeHeader(k string, v ...string) {
 	w.writeString(k)
+	if len(v) == 0 {
+		w.writeString(":\r\n")
+		return
+	}
 	w.writeString(": ")
-	if len(v) > 0 {
+
-		w.writeString(v[0])
+	// Max header line length is 78 characters in RFC 5322 and 76 characters
-		for _, s := range v[1:] {
+	// in RFC 2047. So for the sake of simplicity we use the 76 characters
+	// limit.
+	charsLeft := 76 - len(k) - len(": ")
+
+	for i, s := range v {
+		// If the line is already too long, insert a newline right away.
+		if charsLeft < 1 {
+			if i == 0 {
+				w.writeString("\r\n ")
+			} else {
+				w.writeString(",\r\n ")
+			}
+			charsLeft = 75
+		} else if i != 0 {
 			w.writeString(", ")
+			charsLeft -= 2
+		}
+
+		// While the header content is too long, fold it by inserting a newline.
+		for len(s) > charsLeft {
+			s = w.writeLine(s, charsLeft)
+			charsLeft = 75
+		}
 		w.writeString(s)
+		if i := lastIndexByte(s, '\n'); i != -1 {
+			charsLeft = 75 - (len(s) - i - 1)
+		} else {
+			charsLeft -= len(s)
 		}
 	}
 	w.writeString("\r\n")
 }
 
+func (w *messageWriter) writeLine(s string, charsLeft int) string {
+	// If there is already a newline before the limit. Write the line.
+	if i := strings.IndexByte(s, '\n'); i != -1 && i < charsLeft {
+		w.writeString(s[:i+1])
+		return s[i+1:]
+	}
+
+	for i := charsLeft - 1; i >= 0; i-- {
+		if s[i] == ' ' {
+			w.writeString(s[:i])
+			w.writeString("\r\n ")
+			return s[i+1:]
+		}
+	}
+
+	// No space found so insert a newline if it was not the start of the
+	// line.
+	if charsLeft != 75 {
+		w.writeString("\r\n ")
+		return s
+	}
+
+	// We could not insert a newline cleanly so look for a space or a newline
+	// even if it is after the limit.
+	for i := 75; i < len(s); i++ {
+		if s[i] == ' ' {
+			w.writeString(s[:i])
+			w.writeString("\r\n ")
+			return s[i+1:]
+		}
+		if s[i] == '\n' {
+			w.writeString(s[:i+1])
+			return s[i+1:]
+		}
+	}
+
+	// Too bad, no space or newline in the whole string. Just write everything.
+	w.writeString(s)
+	return ""
+}
+
 func (w *messageWriter) writeHeaders(h map[string][]string) {
 	if w.depth == 0 {
 		for k, v := range h {