fix: handle nested multipart/alternative, fixes #1

Author: abhidg

extract_body.go

@@ -48,16 +48,16 @@ func extractBodyAsMarkdown(msg *mail.Message) (string, error) {
 			if perr == io.EOF {
 				break
 			}
+			pct := part.Header.Get("Content-Type")
+			pcte := part.Header.Get("Content-Transfer-Encoding")
+			ptype, pparams, _ := mime.ParseMediaType(pct)
 			if perr != nil {
 				return "", perr
 			}
 			// skip attachments
 			if disp := strings.ToLower(part.Header.Get("Content-Disposition")); strings.HasPrefix(disp, "attachment") {
 				continue
 			}
-			pct := part.Header.Get("Content-Type")
-			pcte := part.Header.Get("Content-Transfer-Encoding")
-			ptype, _, _ := mime.ParseMediaType(pct)
 			switch ptype {
 			case "text/plain":
 				b, e := readAndDecodePart(part, pct, pcte)
@@ -71,6 +71,9 @@ func extractBodyAsMarkdown(msg *mail.Message) (string, error) {
 					return "", e
 				}
 				firstHTML = string(b)
+			case "multipart/alternative":
+				mr = multipart.NewReader(part, pparams["boundary"])
+				continue
 			default:
 				return "", errors.New("no text part found")
 			}

main.go

@@ -115,3 +115,26 @@ func main() {
 	initS3()
 	lambda.Start(handler)
 }
+
+func debugMain() {
+	if len(os.Args) < 2 {
+		fmt.Println("usage: ./ticket-dispatcher <filename>")
+		return
+	}
+	file, err := os.Open(os.Args[1])
+	if err != nil {
+		log.Fatalf("error opening file: %v", err)
+	}
+	defer file.Close()
+
+	msg, err := mail.ReadMessage(file)
+	if err != nil {
+		log.Fatalf("error parsing email: %v", err)
+	}
+	body, err := extractBodyAsMarkdown(msg)
+	if err != nil {
+		log.Fatalf("error extracting body: %v", err)
+	} else {
+		fmt.Println(body)
+	}
+}