fix: part boundray and message encoding

msgwriter.go

@@ -138,6 +138,10 @@ func (mw *msgWriter) writeMsg(msg *Msg) {
 	if msg.hasMixed() {
 		mw.stopMP()
 	}
+
+	if msg.hasSMime() {
+		mw.stopMP()
+	}
 }
 
 // writeGenHeader writes out all generic headers to the msgWriter
@@ -341,7 +345,7 @@ func (mw *msgWriter) writeBody(writeFunc func(io.Writer) (int64, error), encodin
 		encodedWriter = quotedprintable.NewWriter(&writeBuffer)
 	} else if encoding == EncodingB64 && !singingWithSMime {
 		encodedWriter = base64.NewEncoder(base64.StdEncoding, &lineBreaker)
-	} else if encoding == NoEncoding {
+	} else if encoding == NoEncoding || singingWithSMime {
 		_, err = writeFunc(&writeBuffer)
 		if err != nil {
 			mw.err = fmt.Errorf("bodyWriter function: %w", err)

sime.go

@@ -16,6 +16,9 @@ var (
 	// ErrInvalidKeyPair should be used if key pair is invalid
 	ErrInvalidKeyPair = errors.New("invalid key pair")
 
+	// ErrInvalidCertificate should be used if a certificate is invalid
+	ErrInvalidCertificate = errors.New("invalid certificate")
+
 	// ErrCouldNotInitialize should be used if the signed data could not initialize
 	ErrCouldNotInitialize = errors.New("could not initialize signed data")
 
@@ -46,7 +49,7 @@ func newSMime(keyPair *tls.Certificate) (*SMime, error) {
 	for _, cert := range keyPair.Certificate[1:] {
 		c, err := x509.ParseCertificate(cert)
 		if err != nil {
-			return nil, err
+			return nil, ErrInvalidCertificate
 		}
 		parentCertificates = append(parentCertificates, c)
 	}
@@ -102,8 +105,10 @@ func encodeToPEM(msg []byte) (*string, error) {
 	}
 
 	r := arrayBuffer.String()
-	r = strings.ReplaceAll(r, "-----BEGIN -----\n", "")
+	r = strings.TrimPrefix(r, "-----BEGIN -----")
-	r = strings.ReplaceAll(r, "-----END -----\n", "")
+	r = strings.Trim(r, "\n")
+	r = strings.TrimSuffix(r, "-----END -----")
+	r = strings.Trim(r, "\n")
 
 	return &r, nil
 }