add body length tag

dkim.go

@@ -168,6 +168,15 @@ func Sign(email *bytes.Reader, options sigOptions) (*bytes.Reader, error) {
 		h2 = sha256.New()
 		h3 = crypto.SHA256
 	}
+
+	// if l tag (body length)
+	if options.BodyLength != 0 {
+		if uint(len(body)) < options.BodyLength {
+			return nil, ErrBadDKimTagLBodyTooShort
+		}
+		body = body[0:options.BodyLength]
+	}
+
 	h1.Write(body)
 	bodyHash = base64.StdEncoding.EncodeToString(h1.Sum(nil))
 

dkimHeader.go

@@ -199,7 +199,6 @@ func NewDkimHeaderBySigOptions(options sigOptions) *DkimHeader {
 		h.SignatureTimestamp = time.Now()
 	}
 	if options.SignatureExpireIn > 0 {
-		fmt.Println(options.SignatureExpireIn)
 		h.SignatureExpiration = time.Now().Add(time.Duration(options.SignatureExpireIn) * time.Second)
 	}
 	h.CopiedHeaderFileds = options.CopiedHeaderFileds
@@ -253,6 +252,16 @@ func (d *DkimHeader) GetHeaderBase(bodyHash string) string {
 		subh += " x=" + fmt.Sprintf("%d", ts) + ";"
 	}
 
+	// body length
+	if d.BodyLength != 0 {
+		bodyLengthStr := fmt.Sprintf("%d", d.BodyLength)
+		if len(subh)+len(bodyLengthStr)+4 > MaxHeaderLineLength {
+			h += subh + FWS
+			subh = ""
+		}
+		subh += " l=" + bodyLengthStr + ";"
+	}
+
 	// Headers
 	if len(subh)+len(d.Headers)+4 > MaxHeaderLineLength {
 		h += subh + FWS
@@ -287,7 +296,6 @@ func (d *DkimHeader) GetHeaderBase(bodyHash string) string {
 		}
 	}
 	h += subh + ";" + FWS + "b="
-
 	return h
 }
 

dkim_test.go

@@ -174,6 +174,7 @@ func Test_Sign(t *testing.T) {
 	options.Selector = selector
 	options.AddSignatureTimestamp = true
 	options.SignatureExpireIn = 3600
+	options.BodyLength = 5
 	options.Headers = []string{"from"}
 	emailReader, err := Sign(emailReader, options)
 	assert.NoError(t, err)

errors.go

@@ -28,4 +28,7 @@ var (
 
 	// ErrBadMailFormatHeaders
 	ErrBadMailFormatHeaders = errors.New("bad mail format found in headers")
+
+	// ErrBadDKimTagLBodyTooShort
+	ErrBadDKimTagLBodyTooShort = errors.New("bad tag l or bodyLength option. Body length < l value")
 )