Merge pull request #77 from wneessen/feature/76-ability-for-preformated-headers

Add SetHeaderPreformatted() method

msg.go

@@ -77,6 +77,11 @@ type Msg struct {
 	// genHeader is a slice of strings that the different generic mail Header fields
 	genHeader map[Header][]string
 
+	// preformHeader is a slice of strings that the different generic mail Header fields
+	// of which content is already preformated and will not be affected by the automatic line
+	// breaks
+	preformHeader map[Header]string
+
 	// mimever represents the MIME version
 	mimever MIMEVersion
 
@@ -100,6 +105,7 @@ func NewMsg(o ...MsgOption) *Msg {
 		charset:       CharsetUTF8,
 		encoding:      EncodingQP,
 		genHeader:     make(map[Header][]string),
+		preformHeader: make(map[Header]string),
 		mimever:       Mime10,
 	}
 
@@ -194,6 +200,24 @@ func (m *Msg) SetHeader(h Header, v ...string) {
 	m.genHeader[h] = v
 }
 
+// SetHeaderPreformatted sets a generic header field of the Msg which content is
+// already preformated.
+//
+// This method does not take a slice of values but only a single value. This is
+// due to the fact, that we do not perform any content alteration and expect the
+// user has already done so
+//
+// **Please note:** This method should be used only as a last resort. Since the
+// user is respondible for the formating of the message header, go-mail cannot
+// guarantee the fully compliance with the RFC 2822. It is recommended to use
+// SetHeader instead.
+func (m *Msg) SetHeaderPreformatted(h Header, v string) {
+	if m.preformHeader == nil {
+		m.preformHeader = make(map[Header]string)
+	}
+	m.preformHeader[h] = v
+}
+
 // SetAddrHeader sets an address related header field of the Msg
 func (m *Msg) SetAddrHeader(h AddrHeader, v ...string) error {
 	if m.addrHeader == nil {

msg_test.go

@@ -255,7 +255,7 @@ func TestApplyMiddlewares(t *testing.T) {
 	}
 }
 
-// TestMsg_SetHEader tests Msg.SetHeader
+// TestMsg_SetHeader tests Msg.SetHeader
 func TestMsg_SetHeader(t *testing.T) {
 	tests := []struct {
 		name   string
@@ -289,6 +289,46 @@ func TestMsg_SetHeader(t *testing.T) {
 	}
 }
 
+// TestMsg_SetHeaderPreformatted tests Msg.SetHeaderPreformatted
+func TestMsg_SetHeaderPreformatted(t *testing.T) {
+	tests := []struct {
+		name   string
+		header Header
+		value  string
+	}{
+		{"set subject", HeaderSubject, "This is Subject"},
+		{"set content-language", HeaderContentLang, fmt.Sprintf("%s, %s, %s, %s",
+			"en", "de", "fr", "es")},
+		{"set subject with newline", HeaderSubject, "This is Subject\r\n with 2nd line"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m := &Msg{}
+			m.SetHeaderPreformatted(tt.header, tt.value)
+			m = NewMsg()
+			m.SetHeaderPreformatted(tt.header, tt.value)
+			if m.preformHeader[tt.header] == "" {
+				t.Errorf("SetHeaderPreformatted() failed. Tried to set header %s, but it is empty", tt.header)
+			}
+			if m.preformHeader[tt.header] != tt.value {
+				t.Errorf("SetHeaderPreformatted() failed. Expected: %q, got: %q", tt.value,
+					m.preformHeader[tt.header])
+			}
+			buf := bytes.Buffer{}
+			_, err := m.WriteTo(&buf)
+			if err != nil {
+				t.Errorf("failed to write message to memory: %s", err)
+				return
+			}
+			if !strings.Contains(buf.String(), fmt.Sprintf("%s: %s%s", tt.header, tt.value, SingleNewLine)) {
+				t.Errorf("SetHeaderPreformatted() failed. Unable to find correctly formated header in " +
+					"mail message output")
+			}
+		})
+	}
+}
+
 // TestMsg_AddTo tests the Msg.AddTo method
 func TestMsg_AddTo(t *testing.T) {
 	a := []string{"address1@example.com", "address2@example.com"}

msgwriter.go

@@ -62,6 +62,7 @@ func (mw *msgWriter) writeMsg(m *Msg) {
 	m.addDefaultHeader()
 	m.checkUserAgent()
 	mw.writeGenHeader(m)
+	mw.writePreformattedGenHeader(m)
 
 	// Set the FROM header (or envelope FROM if FROM is empty)
 	hf := true
@@ -132,6 +133,13 @@ func (mw *msgWriter) writeGenHeader(m *Msg) {
 	}
 }
 
+// writePreformatedHeader writes out all preformated generic headers to the msgWriter
+func (mw *msgWriter) writePreformattedGenHeader(m *Msg) {
+	for k, v := range m.preformHeader {
+		mw.writeString(fmt.Sprintf("%s: %s%s", k, v, SingleNewLine))
+	}
+}
+
 // startMP writes a multipart beginning
 func (mw *msgWriter) startMP(mt MIMEType, b string) {
 	mp := multipart.NewWriter(mw)