Add test for EMLToMsgFromString with embedded content

The new test ensures that the EMLToMsgFromString function properly handles an EML that contains embedded content. The expected subject content and number of embedded objects are checked to confirm correct parsing.

eml.go

@@ -70,6 +70,7 @@ func EMLToMsgFromFile(filePath string) (*Msg, error) {
 	if err = parseEMLBodyParts(parsedMsg, bodybuf, msg); err != nil {
 		return msg, fmt.Errorf("failed to parse EML body parts: %w", err)
 	}
+	//fmt.Printf("FOO: %+v\n", msg)
 
 	return msg, nil
 }
@@ -159,6 +160,10 @@ func parseEMLHeaders(mailHeader *netmail.Header, msg *Msg) error {
 	// Extract common headers
 	for _, header := range commonHeaders {
 		if value := mailHeader.Get(header.String()); value != "" {
+			if strings.EqualFold(header.String(), HeaderContentType.String()) &&
+				strings.HasPrefix(value, TypeMultipartMixed.String()) {
+				continue
+			}
 			msg.SetGenHeader(header, value)
 		}
 	}
@@ -184,9 +189,10 @@ func parseEMLBodyParts(parsedMsg *netmail.Message, bodybuf *bytes.Buffer, msg *M
 			return fmt.Errorf("failed to parse plain body: %w", err)
 		}
 	case strings.EqualFold(mediatype, TypeMultipartAlternative.String()),
-		strings.EqualFold(mediatype, TypeMultipartMixed.String()):
+		strings.EqualFold(mediatype, TypeMultipartMixed.String()),
+		strings.EqualFold(mediatype, TypeMultipartRelated.String()):
 		if err = parseEMLMultipart(params, bodybuf, msg); err != nil {
-			return fmt.Errorf("failed to parse multipart/alternative body: %w", err)
+			return fmt.Errorf("failed to parse multipart body: %w", err)
 		}
 	default:
 	}
@@ -242,9 +248,27 @@ ReadNextPart:
 		return fmt.Errorf("failed to get next part of multipart message: %w", err)
 	}
 	for err == nil {
+		// Multipart/related parts need to be parsed seperately
+		if contentTypeSlice, ok := multiPart.Header[HeaderContentType.String()]; ok && len(contentTypeSlice) == 1 {
+			contentType, _ := parseMultiPartHeader(contentTypeSlice[0])
+			if strings.EqualFold(contentType, TypeMultipartRelated.String()) {
+				relatedPart := &netmail.Message{
+					Header: netmail.Header(multiPart.Header),
+					Body:   multiPart,
+				}
+				relatedBuf := &bytes.Buffer{}
+				if _, err = relatedBuf.ReadFrom(multiPart); err != nil {
+					return fmt.Errorf("failed to read related multipart message to buffer: %w", err)
+				}
+				if err := parseEMLBodyParts(relatedPart, relatedBuf, msg); err != nil {
+					return fmt.Errorf("failed to parse related multipart body: %w", err)
+				}
+			}
+		}
+
 		// Content-Disposition header means we have an attachment or embed
 		if contentDisposition, ok := multiPart.Header[HeaderContentDisposition.String()]; ok {
-			if err := parseEMLAttachmentEmbed(contentDisposition, multiPart, msg); err != nil {
+			if err = parseEMLAttachmentEmbed(contentDisposition, multiPart, msg); err != nil {
 				return fmt.Errorf("failed to parse attachment/embed: %w", err)
 			}
 			goto ReadNextPart
@@ -261,6 +285,9 @@ ReadNextPart:
 			return fmt.Errorf("failed to get content-type from part")
 		}
 		contentType, optional := parseMultiPartHeader(multiPartContentType[0])
+		if strings.EqualFold(contentType, TypeMultipartRelated.String()) {
+			goto ReadNextPart
+		}
 		part := msg.newPart(ContentType(contentType))
 		if charset, ok := optional["charset"]; ok {
 			part.SetCharset(Charset(charset))
@@ -316,7 +343,7 @@ func parseEMLContentTypeCharset(mailHeader *netmail.Header, msg *Msg) {
 			msg.SetCharset(Charset(charset))
 		}
 		msg.setEncoder()
-		if contentType != "" {
+		if contentType != "" && !strings.EqualFold(contentType, TypeMultipartMixed.String()) {
 			msg.SetGenHeader(HeaderContentType, contentType)
 		}
 	}

eml_test.go

@@ -152,6 +152,33 @@ ICAgc2V2ZXJhbAogICAgICAgICAgICBuZXdsaW5lcwoJICAgICAgICAgICAgYW5kCgkgICAgc3Bh
 Y2VzCiAgICAgaW4KICBpdAouCgpBcyB3ZWxsIGFzIGFuIGVtb2ppOiDwn5mCCg==
 
 --45c75ff528359022eb03679fbe91877d75343f2e1f8193e349deffa33ff7--`
+	exampleMailPlainB64WithEmbed = `Date: Wed, 01 Nov 2023 00:00:00 +0000
+MIME-Version: 1.0
+Message-ID: <1305604950.683004066175.AAAAAAAAaaaaaaaaB@go-mail.dev>
+Subject: Example mail // plain text base64 with embed
+User-Agent: go-mail v0.4.1 // https://github.com/wneessen/go-mail
+X-Mailer: go-mail v0.4.1 // https://github.com/wneessen/go-mail
+From: "Toni Tester" <go-mail@go-mail.dev>
+To: <go-mail+test@go-mail.dev>
+Cc: <go-mail+cc@go-mail.dev>
+Content-Type: multipart/related;
+ boundary=ffbcfb94b44e5297325102f6ced05b3b37f1d70fc38a5e78dc73c1a8434b
+
+--ffbcfb94b44e5297325102f6ced05b3b37f1d70fc38a5e78dc73c1a8434b
+Content-Transfer-Encoding: quoted-printable
+Content-Type: text/plain; charset=UTF-8
+
+This is a test body string
+--ffbcfb94b44e5297325102f6ced05b3b37f1d70fc38a5e78dc73c1a8434b
+Content-Disposition: inline; filename="pixel.png"
+Content-Id: <pixel.png>
+Content-Transfer-Encoding: base64
+Content-Type: image/png; name="pixel.png"
+
+iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVQIW2NgYGD4DwABBAEAwS2O
+UAAAAABJRU5ErkJggg==
+
+--ffbcfb94b44e5297325102f6ced05b3b37f1d70fc38a5e78dc73c1a8434b--`
 )
 
 func TestEMLToMsgFromString(t *testing.T) {
@@ -278,18 +305,20 @@ func TestEMLToMsgFromStringWithAttachment(t *testing.T) {
 		t.Errorf("EMLToMsgFromString of EML with attachment failed: expected no. of attachments: %d, but got: %d",
 			1, len(msg.attachments))
 	}
-	contentTypeHeader := msg.GetGenHeader(HeaderContentType)
+}
-	if len(contentTypeHeader) != 1 {
+
-		t.Errorf("EMLToMsgFromString of EML with attachment failed: expected no. of content-type header: %d, "+
+func TestEMLToMsgFromStringWithEmbed(t *testing.T) {
-			"but got: %d", 1, len(contentTypeHeader))
+	wantSubject := "Example mail // plain text base64 with embed"
+	msg, err := EMLToMsgFromString(exampleMailPlainB64WithEmbed)
+	if err != nil {
+		t.Errorf("EML with embed failed: %s", err)
 	}
-	contentTypeSplit := strings.SplitN(contentTypeHeader[0], "; ", 2)
+	if subject := msg.GetGenHeader(HeaderSubject); len(subject) > 0 && !strings.EqualFold(subject[0], wantSubject) {
-	if len(contentTypeSplit) != 2 {
+		t.Errorf("EMLToMsgFromString of EML with embed failed: expected subject: %s, but got: %s",
-		t.Error("failed to split Content-Type header")
+			wantSubject, subject[0])
-		return
 	}
-	if !strings.EqualFold(contentTypeSplit[0], "multipart/mixed") {
+	if len(msg.embeds) != 1 {
-		t.Errorf("EMLToMsgFromString of EML with attachment failed: expected content-type: %s, "+
+		t.Errorf("EMLToMsgFromString of EML with embed failed: expected no. of embeds: %d, but got: %d",
-			"but got: %s", "multipart/mixed", contentTypeSplit[0])
+			1, len(msg.attachments))
 	}
 }