From fb5558da811a49031922ee5582f61ac1d9b08d3c Mon Sep 17 00:00:00 2001
From: Tim Culverhouse <tim@timculverhouse.com>
Date: Sun, 24 Jul 2022 10:13:43 -0500
Subject: [PATCH] seqmap: sync seqNum to uid after expunge

This patch updates the seqNums after an Expunge operation. When an
expunge operation occurs, the seqNum of the deleted message is reported.
The Imap spec [0] states that an immediate decrement of all seqnums greater
than the deleted occurs, even before the next reporting of an expunge
update.

[0]: https://datatracker.ietf.org/doc/html/rfc3501#section-7.4.1

Fixes: https://todo.sr.ht/~rjarry/aerc/61
Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Signed-off-by: Robin Jarry <robin@jarry.cc>
---
 worker/imap/seqmap.go      | 16 ++++++++++++++--
 worker/imap/seqmap_test.go |  9 ++++++---
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/worker/imap/seqmap.go b/worker/imap/seqmap.go
index 2752cc8..093bbc5 100644
--- a/worker/imap/seqmap.go
+++ b/worker/imap/seqmap.go
@@ -1,6 +1,8 @@
 package imap
 
-import "sync"
+import (
+	"sync"
+)
 
 type SeqMap struct {
 	lock sync.Mutex
@@ -35,7 +37,17 @@ func (s *SeqMap) Pop(seqnum uint32) (uint32, bool) {
 	s.lock.Lock()
 	uid, found := s.m[seqnum]
 	if found {
-		delete(s.m, seqnum)
+		m := make(map[uint32]uint32)
+		for s, u := range s.m {
+			if s > seqnum {
+				// All sequence numbers greater than the removed one must be decremented by one
+				// https://datatracker.ietf.org/doc/html/rfc3501#section-7.4.1
+				m[s-1] = u
+			} else if s < seqnum {
+				m[s] = u
+			}
+		}
+		s.m = m
 	}
 	s.lock.Unlock()
 	return uid, found
diff --git a/worker/imap/seqmap_test.go b/worker/imap/seqmap_test.go
index 0ee0738..0fa8711 100644
--- a/worker/imap/seqmap_test.go
+++ b/worker/imap/seqmap_test.go
@@ -39,12 +39,15 @@ func TestSeqMap(t *testing.T) {
 	assert.Equal(found, true)
 	assert.Equal(seqmap.Size(), 2)
 
+	// Repop the same seqnum should work because of the syncing
 	_, found = seqmap.Pop(1)
-	assert.Equal(found, false)
-	assert.Equal(seqmap.Size(), 2)
+	assert.Equal(found, true)
+	assert.Equal(seqmap.Size(), 1)
 
+	// sync means we already have a 1. This is replacing that UID so the size
+	// shouldn't increase
 	seqmap.Put(1, 7331)
-	assert.Equal(seqmap.Size(), 3)
+	assert.Equal(seqmap.Size(), 1)
 
 	seqmap.Clear()
 	assert.Equal(seqmap.Size(), 0)