fixing folders and image rendering in client

internal/mailview/mailview.go

@@ -30,6 +30,11 @@ type Attachment struct {
 	Filename    string
 	ContentType string
 	Data        []byte
+	// ContentID is the part's Content-Id header (RFC 2392), angle brackets stripped,
+	// or "" if absent. An HTML body referencing this part inline (<img src="cid:...">)
+	// only renders once that reference is resolved against this — see
+	// webui.inlineContentIDImages, the caller responsible for doing so.
+	ContentID string
 }
 
 // Message is the parsed result. TextBody/HTMLBody are independently populated when
@@ -114,11 +119,12 @@ func walkMultipart(m *Message, r io.Reader, boundary string) error {
 		if filename == "" {
 			filename = params["name"]
 		}
+		contentID := strings.Trim(part.Header.Get("Content-Id"), "<>")
 
 		switch {
 		case disp == "attachment" || (filename != "" && disp != "inline"):
 			m.Attachments = append(m.Attachments, Attachment{
-				Filename: filename, ContentType: contentTypeFor(mediaType, filename), Data: data,
+				Filename: filename, ContentType: contentTypeFor(mediaType, filename), Data: data, ContentID: contentID,
 			})
 		case mediaType == "text/html":
 			m.HTMLBody += string(data)
@@ -127,12 +133,15 @@ func walkMultipart(m *Message, r io.Reader, boundary string) error {
 				m.TextBody += "\n"
 			}
 			m.TextBody += string(data)
-		case filename != "":
-			// Inline non-text part (e.g. an embedded image) with no explicit
-			// disposition — still worth surfacing as a downloadable attachment
-			// rather than silently dropping it.
+		case filename != "" || contentID != "":
+			// Inline non-text part (e.g. an embedded image referenced by the HTML
+			// body via cid:) with no explicit disposition and possibly no filename
+			// either — still worth surfacing rather than silently dropping it.
+			if filename == "" {
+				filename = contentID
+			}
 			m.Attachments = append(m.Attachments, Attachment{
-				Filename: filename, ContentType: contentTypeFor(mediaType, filename), Data: data,
+				Filename: filename, ContentType: contentTypeFor(mediaType, filename), Data: data, ContentID: contentID,
 			})
 		}
 	}

internal/mailview/mailview_test.go

@@ -89,3 +89,49 @@ func TestParseNestedMultipartMixedWithAlternativeBody(t *testing.T) {
 		t.Fatalf("attachments = %+v", m.Attachments)
 	}
 }
+
+func TestParseInlineImageCapturesContentID(t *testing.T) {
+	raw := "" +
+		"From: a@example.com\r\nTo: b@example.com\r\nSubject: hi\r\n" +
+		"Content-Type: multipart/related; boundary=\"B\"\r\n\r\n" +
+		"--B\r\nContent-Type: text/html\r\n\r\n<p><img src=\"cid:img1@example.com\"></p>\r\n" +
+		"--B\r\nContent-Type: image/png\r\nContent-Disposition: inline; filename=\"header.png\"\r\n" +
+		"Content-Id: <img1@example.com>\r\n" +
+		"Content-Transfer-Encoding: BASE64\r\n\r\nSGVsbG8sIHdvcmxkIQ==\r\n" +
+		"--B--\r\n"
+	m, err := Parse([]byte(raw))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.TrimSpace(m.HTMLBody) != `<p><img src="cid:img1@example.com"></p>` {
+		t.Errorf("HTMLBody = %q", m.HTMLBody)
+	}
+	if len(m.Attachments) != 1 {
+		t.Fatalf("attachments = %+v", m.Attachments)
+	}
+	if m.Attachments[0].ContentID != "img1@example.com" {
+		t.Errorf("ContentID = %q, want angle brackets stripped", m.Attachments[0].ContentID)
+	}
+	if got := string(m.Attachments[0].Data); got != "Hello, world!" {
+		t.Errorf("attachment data = %q, want decoded base64", got)
+	}
+}
+
+func TestParseInlineImageWithNoFilenameStillCaptured(t *testing.T) {
+	raw := "" +
+		"From: a@example.com\r\nTo: b@example.com\r\nSubject: hi\r\n" +
+		"Content-Type: multipart/related; boundary=\"B\"\r\n\r\n" +
+		"--B\r\nContent-Type: text/html\r\n\r\n<p>hi</p>\r\n" +
+		"--B\r\nContent-Type: image/png\r\n" +
+		"Content-Id: <noname@example.com>\r\n\r\nrawbytes" +
+		"\r\n--B--\r\n"
+	m, err := Parse([]byte(raw))
+	if err != nil {
+		t.Fatal(err)
+	}
+	// No filename anywhere on the part — must not be silently dropped just because
+	// there's nothing to name it; falls back to the Content-Id itself.
+	if len(m.Attachments) != 1 || m.Attachments[0].ContentID != "noname@example.com" {
+		t.Fatalf("attachments = %+v", m.Attachments)
+	}
+}