Add additional error handling to email message sending. (#1639)

* Adding additional error handling to email message sending.

* Adding additional error handling to email message sending.

* Fixing issue with err being lost in the defer.

* Moving defers to be queued up earlier to ensure they get called.

* Fixed closing encoder to use defer pattern that matches the others.

internal/post/message.go

@@ -12,6 +12,8 @@ import (
 	"mime/quotedprintable"
 	"net/textproto"
 	"time"
+
+	"github.com/zeebo/errs"
 )
 
 // Message is RFC compliant email message
@@ -35,8 +37,11 @@ type Part struct {
 	Content     string
 }
 
+// Error is the default message errs class
+var Error = errs.Class("Email message error")
+
 // Bytes builds message and returns result as bytes
-func (msg *Message) Bytes() []byte {
+func (msg *Message) Bytes() (data []byte, err error) {
 	// always returns nil error on read and write, so most of the errors can be ignored
 	var body bytes.Buffer
 
@@ -62,6 +67,7 @@ func (msg *Message) Bytes() []byte {
 	// multipart upload
 	case len(msg.Parts) > 0:
 		wr := multipart.NewWriter(&body)
+		defer func() { err = errs.Combine(err, wr.Close()) }()
 
 		fmt.Fprintf(&body, "Content-Type: multipart/alternative;")
 		fmt.Fprintf(&body, "\tboundary=\"%v\"\r\n", wr.Boundary())
@@ -70,14 +76,21 @@ func (msg *Message) Bytes() []byte {
 		var sub io.Writer
 
 		if len(msg.PlainText) > 0 {
-			sub, _ = wr.CreatePart(textproto.MIMEHeader{
+			sub, err := wr.CreatePart(textproto.MIMEHeader{
 				"Content-Type":              []string{"text/plain; charset=UTF-8; format=flowed"},
 				"Content-Transfer-Encoding": []string{"quoted-printable"},
 			})
+			if err != nil {
+				return nil, Error.Wrap(err)
+			}
 
 			enc := quotedprintable.NewWriter(sub)
-			_, _ = enc.Write([]byte(msg.PlainText))
-			_ = enc.Close()
+			defer func() { err = errs.Combine(err, enc.Close()) }()
+
+			_, err = enc.Write([]byte(msg.PlainText))
+			if err != nil {
+				return nil, Error.Wrap(err)
+			}
 		}
 
 		for _, part := range msg.Parts {
@@ -93,18 +106,20 @@ func (msg *Message) Bytes() []byte {
 			fmt.Fprint(sub, part.Content)
 		}
 
-		_ = wr.Close()
 	// fallback if there are no parts, write PlainText with appropriate Content-Type
 	default:
 		fmt.Fprintf(&body, "Content-Type: text/plain; charset=UTF-8; format=flowed\r\n")
 		fmt.Fprintf(&body, "Content-Transfer-Encoding: quoted-printable\r\n\r\n")
 
 		enc := quotedprintable.NewWriter(&body)
-		_, _ = enc.Write([]byte(msg.PlainText))
-		_ = enc.Close()
+		defer func() { err = errs.Combine(err, enc.Close()) }()
+
+		if _, err := enc.Write([]byte(msg.PlainText)); err != nil {
+			return nil, Error.Wrap(err)
+		}
 	}
 
-	return tocrlf(body.Bytes())
+	return tocrlf(body.Bytes()), nil
 }
 
 func tocrlf(data []byte) []byte {

internal/post/sender.go

@@ -76,7 +76,12 @@ func (sender *SMTPSender) SendEmail(msg *Message) error {
 		err = errs.Combine(err, data.Close())
 	}()
 
-	_, err = data.Write(msg.Bytes())
+	mess, err := msg.Bytes()
+	if err != nil {
+		return err
+	}
+
+	_, err = data.Write(mess)
 	if err != nil {
 		return err
 	}