imap: skip sync flags update if highest modseq has not increased

CHANGELOG.md

@@ -9,6 +9,7 @@
 - remove direct dependency on `byteorder` crate #3031
 - make it possible to cancel message sending by removing the message #3034,
   this was previosuly removed in 1.71.0 #2939
+- always skip Seen flag synchronization when there are no updates #3039
 
 ### Fixes
 - fix splitting off text from webxdc messages #3032

Cargo.lock

@@ -1090,6 +1090,7 @@ dependencies = [
  "hex",
  "humansize",
  "image",
+ "imap-proto",
  "kamadak-exif",
  "lettre_email",
  "libc",

Cargo.toml

@@ -38,6 +38,7 @@ escaper = "0.1"
 futures = "0.3"
 hex = "0.4.0"
 image = { version = "0.23.5", default-features=false, features = ["gif", "jpeg", "ico", "png", "pnm", "webp", "bmp"] }
+imap-proto = "0.14.3"
 kamadak-exif = "0.5"
 lettre_email = { git = "https://github.com/deltachat/lettre", branch = "master" }
 libc = "0.2"

src/imap.rs

@@ -1023,23 +1023,33 @@ impl Imap {
             .as_ref()
             .with_context(|| format!("No mailbox selected, folder: {}", folder))?;
 
-        // Check if the mailbox supports MODSEQ.
-        // We are not interested in actual value of HIGHESTMODSEQ.
-        if mailbox.highest_modseq.is_none() {
+        let remote_highest_modseq = if let Some(remote_highest_modseq) = mailbox.highest_modseq {
+            remote_highest_modseq
+        } else {
             info!(
                 context,
                 "Mailbox {} does not support mod-sequences, skipping flag synchronization.", folder
             );
             return Ok(());
+        };
+
+        let mut highest_modseq = get_modseq(context, folder)
+            .await
+            .with_context(|| format!("failed to get MODSEQ for folder {}", folder))?;
+        if highest_modseq >= remote_highest_modseq {
+            info!(
+                context,
+                "MODSEQ {} is already new, HIGHESTMODSEQ={}, skipping seen flag update",
+                highest_modseq,
+                remote_highest_modseq
+            );
+            return Ok(());
         }
 
         let mut updated_chat_ids = BTreeSet::new();
         let uid_validity = get_uidvalidity(context, folder)
             .await
             .with_context(|| format!("failed to get UID validity for folder {}", folder))?;
-        let mut highest_modseq = get_modseq(context, folder)
-            .await
-            .with_context(|| format!("failed to get MODSEQ for folder {}", folder))?;
         let mut list = session
             .uid_fetch("1:*", format!("(FLAGS) (CHANGEDSINCE {})", highest_modseq))
             .await
@@ -1074,6 +1084,10 @@ impl Imap {
             }
         }
 
+        if remote_highest_modseq > highest_modseq {
+            // We haven't seen the message with the highest MODSEQ, maybe it was deleted already.
+            highest_modseq = remote_highest_modseq;
+        }
         set_modseq(context, folder, highest_modseq)
             .await
             .with_context(|| format!("failed to set MODSEQ for folder {}", folder))?;
@@ -1570,6 +1584,23 @@ impl Imap {
         Ok(())
     }
 
+    /// Update HIGHESTMODSEQ on selected mailbox.
+    ///
+    /// Should be called when MODSEQ is seen on the response, such as IDLE response.
+    pub(crate) fn update_modseq(&mut self, modseq: u64) {
+        self.config.selected_mailbox =
+            self.config
+                .selected_mailbox
+                .as_ref()
+                .map(|mailbox| Mailbox {
+                    highest_modseq: Some(std::cmp::max(
+                        mailbox.highest_modseq.unwrap_or_default(),
+                        modseq,
+                    )),
+                    ..mailbox.clone()
+                });
+    }
+
     /// Return whether the server sent an unsolicited EXISTS response.
     /// Drains all responses from `session.unsolicited_responses` in the process.
     /// If this returns `true`, this means that new emails arrived and you should

src/imap/idle.rs

@@ -3,6 +3,7 @@ use super::Imap;
 use anyhow::{bail, Context as _, Result};
 use async_imap::extensions::idle::IdleResponse;
 use async_std::prelude::*;
+use imap_proto::types::{AttributeValue, Response};
 use std::time::{Duration, SystemTime};
 
 use crate::{context::Context, scheduler::InterruptInfo};
@@ -71,6 +72,13 @@ impl Imap {
             match fut.await {
                 Ok(Event::IdleResponse(IdleResponse::NewData(x))) => {
                     info!(context, "Idle has NewData {:?}", x);
+                    if let Response::Fetch(_message, attrs) = x.parsed() {
+                        for attr in attrs {
+                            if let AttributeValue::ModSeq(modseq) = attr {
+                                self.update_modseq(*modseq);
+                            }
+                        }
+                    }
                 }
                 Ok(Event::IdleResponse(IdleResponse::Timeout)) => {
                     info!(context, "Idle-wait timeout or interruption");