feat: base server-side message deletion on force_encryption

don't use `is_chatmail` for determining whether to delete messages on the server:
whether a downloaded message may be dropped from the relay
depends on whether another device still needs it (BccSelf)
and on whether plaintext mail is allowed (ForceEncryption).

src/download.rs

@@ -6,7 +6,6 @@ use anyhow::{Result, anyhow, bail, ensure};
 use deltachat_derive::{FromSql, ToSql};
 use serde::{Deserialize, Serialize};
 
-use crate::config::Config;
 use crate::context::Context;
 use crate::imap::session::Session;
 use crate::log::warn;
@@ -164,8 +163,7 @@ pub(crate) async fn download_msg(
         .fetch_single_msg(context, &server_folder, server_uid, rfc724_mid)
         .await?;
 
-    let bcc_self = context.get_config_bool(Config::BccSelf).await?;
+    if ephemeral::should_delete_all_downloaded_messages(context).await? {
-    if ephemeral::should_delete_all_downloaded_messages(bcc_self, session.is_chatmail()) {
         // Now that the message was downloaded, it likely needs to be deleted;
         // trigger a re-check by interrupting the inbox folder.
         // This is mainly needed to make the tests pass;

src/ephemeral.rs

@@ -654,12 +654,11 @@ pub(crate) async fn ephemeral_loop(context: &Context, interrupt_receiver: Receiv
 pub(crate) async fn delete_expired_imap_messages(
     context: &Context,
     transport_id: u32,
-    is_chatmail: bool,
 ) -> Result<()> {
     let now = time();
 
     let bcc_self = context.get_config_bool(Config::BccSelf).await?;
-    if should_delete_all_downloaded_messages(bcc_self, is_chatmail) {
+    if should_delete_all_downloaded_messages(context).await? {
         // This is the only device using this relay.
         // Mark all downloaded messages for deletion, because they are not needed anymore.
         //
@@ -708,7 +707,7 @@ pub(crate) async fn delete_expired_imap_messages(
             )
             .await?;
     } else {
-        // Single device.
+        // Single device, but unencrypted messages are allowed.
         // Delete all expired and encrypted messages.
         context
             .sql
@@ -736,8 +735,9 @@ pub(crate) async fn delete_expired_imap_messages(
     Ok(())
 }
 
-pub(crate) fn should_delete_all_downloaded_messages(bcc_self: bool, is_chatmail: bool) -> bool {
+pub(crate) async fn should_delete_all_downloaded_messages(context: &Context) -> Result<bool> {
-    !bcc_self && is_chatmail
+    Ok(!context.get_config_bool(Config::BccSelf).await?
+        && context.get_config_bool(Config::ForceEncryption).await?)
 }
 
 /// Start ephemeral timers for seen messages if they are not started

src/ephemeral/ephemeral_tests.rs

@@ -509,7 +509,7 @@ async fn test_delete_expired_imap_messages() -> Result<()> {
             .await?;
     }
 
-    for (is_chatmail, other_transport, bcc_self) in [
+    for (force_encryption, other_transport, bcc_self) in [
         (false, false, false),
         (false, false, true),
         (false, true, false),
@@ -520,10 +520,12 @@ async fn test_delete_expired_imap_messages() -> Result<()> {
         (true, true, true),
     ] {
         println!(
-            "Testing combination is_chatmail={is_chatmail}, other_transport={other_transport}, bcc_self={bcc_self}"
+            "Testing combination force_encryption={force_encryption}, other_transport={other_transport}, bcc_self={bcc_self}"
         );
 
         t.set_config_bool(Config::BccSelf, bcc_self).await?;
+        t.set_config_bool(Config::ForceEncryption, force_encryption)
+            .await?;
 
         delete_expired_imap_messages(
             &t,
@@ -532,7 +534,6 @@ async fn test_delete_expired_imap_messages() -> Result<()> {
             } else {
                 transport_id
             },
-            is_chatmail,
         )
         .await?;
 
@@ -548,7 +549,7 @@ async fn test_delete_expired_imap_messages() -> Result<()> {
         assert_eq!(is_deleted(&t, "no_expire@localhost").await?, !bcc_self);
         assert_eq!(
             is_deleted(&t, "no_expire_unencrypted@localhost").await?,
-            is_chatmail && !bcc_self
+            force_encryption && !bcc_self
         );
         assert_eq!(is_deleted(&t, "future@localhost").await?, !bcc_self);
         assert_eq!(is_deleted(&t, "expired_post@localhost").await?, true);
@@ -563,9 +564,10 @@ async fn test_delete_expired_imap_messages() -> Result<()> {
         reset_targets(&t).await;
     }
 
-    // With BccSelf=true, non-expired messages are kept even if `is_chatmail` is true
+    // With BccSelf=true, non-expired messages are kept even if `force_encryption` is true
     t.set_config_bool(Config::BccSelf, true).await?;
-    delete_expired_imap_messages(&t, transport_id, true).await?;
+    t.set_config_bool(Config::ForceEncryption, true).await?;
+    delete_expired_imap_messages(&t, transport_id).await?;
     assert_eq!(is_deleted(&t, "expired@localhost").await?, true);
     assert_eq!(is_deleted(&t, "no_expire@localhost").await?, false);
     assert_eq!(is_deleted(&t, "done_pre@localhost").await?, false);

src/imap.rs

@@ -452,7 +452,7 @@ impl Imap {
 
         // Mark expired messages for deletion. Note that `delete_expired_imap_messages` is
         // not well optimized and should not be called before fetching.
-        delete_expired_imap_messages(context, session.transport_id(), session.is_chatmail())
+        delete_expired_imap_messages(context, session.transport_id())
             .await
             .context("delete_expired_imap_messages")?;