Do not try to redownload the message in case of any error

Since switch to async we don't have spurious "database is busy"
errors anymore. Since an error is irrecoverable in most cases,
we can skip the message. The cost of this is we may
accidentally skip a correct message if I/O fails, but
the advantage is that we are guaranteed to never confuse
irrecoverable error with recoverable one and get stuck in
infinite loop redownloading the same message over and over.

src/receive_imf.rs

@@ -28,7 +28,7 @@ use crate::message::{
     self, rfc724_mid_exists, Message, MessageState, MessengerMessage, MsgId, Viewtype,
 };
 use crate::mimeparser::{
-    parse_message_ids, AvatarAction, MailinglistType, MimeMessage, ParserError, SystemMessage,
+    parse_message_ids, AvatarAction, MailinglistType, MimeMessage, SystemMessage,
 };
 use crate::param::{Param, Params};
 use crate::peerstate::{Peerstate, PeerstateKeyType, PeerstateVerifiedStatus};
@@ -72,15 +72,13 @@ pub async fn receive_imf(
 
 /// Receive a message and add it to the database.
 ///
-/// Returns an error on recoverable errors, e.g. database errors. In this case,
-/// message parsing should be retried later.
+/// Returns an error on database failure or if the message is broken,
+/// e.g. has nonstandard MIME structure.
 ///
-/// If message itself is wrong, logs
-/// the error and returns success:
-/// - If possible, creates a database entry to prevent the message from being
-///   downloaded again, sets `chat_id=DC_CHAT_ID_TRASH` and returns `Ok(Some(…))`
-/// - If the message is so wrong that we didn't even create a database entry,
-///   returns `Ok(None)`
+/// If possible, creates a database entry to prevent the message from being
+/// downloaded again, sets `chat_id=DC_CHAT_ID_TRASH` and returns `Ok(Some(…))`.
+/// If the message is so wrong that we didn't even create a database entry,
+/// returns `Ok(None)`.
 ///
 /// If `is_partial_download` is set, it contains the full message size in bytes.
 /// Do not confuse that with `replace_partial_download` that will be set when the full message is loaded later.
@@ -101,9 +99,8 @@ pub(crate) async fn receive_imf_inner(
 
     let mut mime_parser =
         match MimeMessage::from_bytes_with_partial(context, imf_raw, is_partial_download).await {
-            Err(ParserError::Malformed(err)) => {
+            Err(err) => {
                 warn!(context, "receive_imf: can't parse MIME: {}", err);
-
                 let msg_ids;
                 if !rfc724_mid.starts_with(GENERATED_PREFIX) {
                     let row_id = context
@@ -127,7 +124,6 @@ pub(crate) async fn receive_imf_inner(
                     needs_delete_job: false,
                 }));
             }
-            Err(ParserError::Sql(err)) => return Err(err),
             Ok(mime_parser) => mime_parser,
         };
 
@@ -2309,7 +2305,7 @@ mod tests {
                     \n\
                     hello\x00";
         let mimeparser = MimeMessage::from_bytes_with_partial(&context.ctx, &raw[..], None).await;
-        assert!(matches!(mimeparser, Err(ParserError::Malformed(_))));
+        assert!(mimeparser.is_err());
     }
 
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]