fix threading in interation with non-delta-clients

threading was broken in core43 as this flags unencrypted messages as errors
and errors are not replied-to.

the fix is not to mark missing signatures for unencrypted messages as errors.

Author: r10s

src/mimeparser.rs

@@ -127,69 +127,74 @@ impl MimeMessage {
         let mail_raw;
         let mut gossipped_addr = Default::default();
 
-        let (mail, signatures) = match e2ee::try_decrypt(context, &mail, message_time).await {
-            Ok((raw, signatures)) => {
-                if let Some(raw) = raw {
-                    // Encrypted, but maybe unsigned message. Only if
-                    // `signatures` set is non-empty, it is a valid
-                    // autocrypt message.
-
-                    mail_raw = raw;
-                    let decrypted_mail = mailparse::parse_mail(&mail_raw)?;
-                    if std::env::var(crate::DCC_MIME_DEBUG).is_ok() {
-                        info!(context, "decrypted message mime-body:");
-                        println!("{}", String::from_utf8_lossy(&mail_raw));
-                    }
-
-                    // Handle any gossip headers if the mail was encrypted.  See section
-                    // "3.6 Key Gossip" of https://autocrypt.org/autocrypt-spec-1.1.0.pdf
-                    // but only if the mail was correctly signed:
-                    if !signatures.is_empty() {
-                        let gossip_headers =
-                            decrypted_mail.headers.get_all_values("Autocrypt-Gossip");
-                        gossipped_addr =
-                            update_gossip_peerstates(context, message_time, &mail, gossip_headers)
-                                .await?;
-                    }
-
-                    // let known protected headers from the decrypted
-                    // part override the unencrypted top-level
-
-                    // Signature was checked for original From, so we
-                    // do not allow overriding it.
-                    let mut throwaway_from = from.clone();
-
-                    // We do not want to allow unencrypted subject in encrypted emails because the user might falsely think that the subject is safe.
-                    // See https://github.com/deltachat/deltachat-core-rust/issues/1790.
-                    headers.remove("subject");
+        let (mail, signatures, warn_empty_signature) =
+            match e2ee::try_decrypt(context, &mail, message_time).await {
+                Ok((raw, signatures)) => {
+                    if let Some(raw) = raw {
+                        // Encrypted, but maybe unsigned message. Only if
+                        // `signatures` set is non-empty, it is a valid
+                        // autocrypt message.
+
+                        mail_raw = raw;
+                        let decrypted_mail = mailparse::parse_mail(&mail_raw)?;
+                        if std::env::var(crate::DCC_MIME_DEBUG).is_ok() {
+                            info!(context, "decrypted message mime-body:");
+                            println!("{}", String::from_utf8_lossy(&mail_raw));
+                        }
 
-                    MimeMessage::merge_headers(
-                        context,
-                        &mut headers,
-                        &mut recipients,
-                        &mut throwaway_from,
-                        &mut chat_disposition_notification_to,
-                        &decrypted_mail.headers,
-                    );
+                        // Handle any gossip headers if the mail was encrypted.  See section
+                        // "3.6 Key Gossip" of https://autocrypt.org/autocrypt-spec-1.1.0.pdf
+                        // but only if the mail was correctly signed:
+                        if !signatures.is_empty() {
+                            let gossip_headers =
+                                decrypted_mail.headers.get_all_values("Autocrypt-Gossip");
+                            gossipped_addr = update_gossip_peerstates(
+                                context,
+                                message_time,
+                                &mail,
+                                gossip_headers,
+                            )
+                            .await?;
+                        }
 
-                    (decrypted_mail, signatures)
-                } else {
-                    // Message was not encrypted
-                    (mail, signatures)
+                        // let known protected headers from the decrypted
+                        // part override the unencrypted top-level
+
+                        // Signature was checked for original From, so we
+                        // do not allow overriding it.
+                        let mut throwaway_from = from.clone();
+
+                        // We do not want to allow unencrypted subject in encrypted emails because the user might falsely think that the subject is safe.
+                        // See https://github.com/deltachat/deltachat-core-rust/issues/1790.
+                        headers.remove("subject");
+
+                        MimeMessage::merge_headers(
+                            context,
+                            &mut headers,
+                            &mut recipients,
+                            &mut throwaway_from,
+                            &mut chat_disposition_notification_to,
+                            &decrypted_mail.headers,
+                        );
+
+                        (decrypted_mail, signatures, true)
+                    } else {
+                        // Message was not encrypted
+                        (mail, signatures, false)
+                    }
                 }
-            }
-            Err(err) => {
-                // continue with the current, still encrypted, mime tree.
-                // unencrypted parts will be replaced by an error message
-                // that is added as "the message" to the chat then.
-                //
-                // if we just return here, the header is missing
-                // and the caller cannot display the message
-                // and try to assign the message to a chat
-                warn!(context, "decryption failed: {}", err);
-                (mail, Default::default())
-            }
-        };
+                Err(err) => {
+                    // continue with the current, still encrypted, mime tree.
+                    // unencrypted parts will be replaced by an error message
+                    // that is added as "the message" to the chat then.
+                    //
+                    // if we just return here, the header is missing
+                    // and the caller cannot display the message
+                    // and try to assign the message to a chat
+                    warn!(context, "decryption failed: {}", err);
+                    (mail, Default::default(), true)
+                }
+            };
 
         let mut parser = MimeMessage {
             parts: Vec::new(),
@@ -215,7 +220,7 @@ impl MimeMessage {
         parser.heuristically_parse_ndn(context).await;
         parser.parse_headers(context)?;
 
-        if parser.signatures.is_empty() {
+        if warn_empty_signature && parser.signatures.is_empty() {
             for part in parser.parts.iter_mut() {
                 part.error = "No valid signature".to_string();
             }