fix: ignore html/* MIME parts

HTML parts have text/html MIME type.
html/* is not a registered MIME type: https://www.iana.org/assignments/media-types

src/mimeparser.rs

@@ -1364,7 +1364,7 @@ impl MimeMessage {
                         self.do_add_single_part(part);
                         return Ok(true);
                     }
-                    mime::TEXT | mime::HTML => {
+                    mime::TEXT => {
                         let decoded_data = match mail.get_body() {
                             Ok(decoded_data) => decoded_data,
                             Err(err) => {

src/mimeparser/mimeparser_tests.rs

@@ -2228,3 +2228,27 @@ async fn test_load_shared_secrets_with_legacy_state() -> Result<()> {
 
     Ok(())
 }
+
+/// Tests that MIME parts with html/* MIME type are ignored.
+///
+/// HTML parts should have a text/html MIME type.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_ignore_html_mime_parts() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let encrypted_msg = test_utils::encrypt_raw_message(
+        bob,
+        &[alice],
+        include_bytes!("../../test-data/message/html_html_mime.eml"),
+    )
+    .await?;
+
+    let msg = MimeMessage::from_bytes(alice, encrypted_msg.as_bytes()).await?;
+    assert_eq!(msg.parts.len(), 1);
+    assert_eq!(msg.parts[0].typ, Viewtype::Text);
+    assert_eq!(msg.parts[0].mimetype, Some(mime::TEXT_PLAIN));
+    assert_eq!(msg.parts[0].msg, "Here is a text part.");
+
+    Ok(())
+}

test-data/message/html_html_mime.eml

@@ -0,0 +1,31 @@
+From: Bob <bob@example.net>
+Subject: Message with invalid HTML mime types
+To: alice@example.org
+Message-ID: <html-html-test@localhost>
+Date: Thu, 17 Dec 2020 15:38:45 +0100
+MIME-Version: 1.0
+Content-Type: multipart/mixed;
+ boundary="------------MESSAGE_BOUNDARY"
+Content-Language: en-US
+Chat-Version: 1.0
+
+This is a multi-part message in MIME format.
+--------------MESSAGE_BOUNDARY
+Content-Type: html/plain; charset=utf-8
+Content-Transfer-Encoding: 7bit
+
+This should be ignored.
+
+--------------MESSAGE_BOUNDARY
+Content-Type: html/html; charset=utf-8
+Content-Transfer-Encoding: 7bit
+
+And this should be ignored too.
+
+--------------MESSAGE_BOUNDARY
+Content-Type: text/plain; charset=utf-8
+Content-Transfer-Encoding: 7bit
+
+Here is a text part.
+
+--------------MESSAGE_BOUNDARY--