imap: fix data race on seqMap array

There are concurrent threads that are accessing and modifying
IMAPWorker.seqMap (the mapping of sequence numbers to message UIDs).
This can lead to crashes when trying to add and remove a message ID.

panic: runtime error: index out of range [391] with length 390

goroutine 1834 [running]:
git.sr.ht/~rjarry/aerc/logging.PanicHandler()
	logging/panic-logger.go:47 +0x6de
panic({0xa41760, 0xc0019b3290})
	/usr/lib/golang/src/runtime/panic.go:838 +0x207
git.sr.ht/~rjarry/aerc/worker/imap.(*IMAPWorker).handleFetchMessages.func1()
	worker/imap/fetch.go:214 +0x185
created by git.sr.ht/~rjarry/aerc/worker/imap.(*IMAPWorker).handleFetchMessages
	worker/imap/fetch.go:209 +0x12b

Use a map which makes more sense than a simple array for random access
operations. Also, it allows better typing for the key values. Protect
the map with a mutex. Add internal API to access the map. Add basic unit
tests to ensure that concurrent access works.

Fixes: https://todo.sr.ht/~rjarry/aerc/49
Signed-off-by: Robin Jarry <robin@jarry.cc>
Acked-by: Moritz Poldrack <moritz@poldrack.dev>

worker/imap/fetch.go

@@ -211,7 +211,7 @@ func (imapw *IMAPWorker) handleFetchMessages(
 
 		var reterr error
 		for _msg := range messages {
-			imapw.seqMap[_msg.SeqNum-1] = _msg.Uid
+			imapw.seqMap.Put(_msg.SeqNum, _msg.Uid)
 			err := procFunc(_msg)
 			if err != nil {
 				if reterr == nil {

worker/imap/flags.go

@@ -2,6 +2,7 @@ package imap
 
 import (
 	"fmt"
+
 	"github.com/emersion/go-imap"
 
 	"git.sr.ht/~rjarry/aerc/logging"
@@ -26,9 +27,11 @@ func (imapw *IMAPWorker) handleDeleteMessages(msg *types.DeleteMessages) {
 		defer logging.PanicHandler()
 
 		for seqNum := range ch {
-			i := seqNum - 1
-			deleted = append(deleted, imapw.seqMap[i])
-			imapw.seqMap = append(imapw.seqMap[:i], imapw.seqMap[i+1:]...)
+			if uid, found := imapw.seqMap.Pop(seqNum); !found {
+				imapw.worker.Logger.Printf("handleDeleteMessages unknown seqnum: %v", seqNum)
+			} else {
+				deleted = append(deleted, uid)
+			}
 		}
 		done <- nil
 	}()

worker/imap/open.go

@@ -61,9 +61,7 @@ func (imapw *IMAPWorker) handleFetchDirectoryContents(
 		}, nil)
 	} else {
 		imapw.worker.Logger.Printf("Found %d UIDs", len(uids))
-		if len(imapw.seqMap) < len(uids) {
-			imapw.seqMap = make([]uint32, len(uids))
-		}
+		imapw.seqMap.Clear()
 		imapw.worker.PostMessage(&types.DirectoryContents{
 			Message: types.RespondTo(msg),
 			Uids:    uids,
@@ -113,7 +111,7 @@ func (imapw *IMAPWorker) handleDirectoryThreaded(
 		aercThreads, count := convertThreads(threads, nil)
 		sort.Sort(types.ByUID(aercThreads))
 		imapw.worker.Logger.Printf("Found %d threaded messages", count)
-		imapw.seqMap = make([]uint32, count)
+		imapw.seqMap.Clear()
 		imapw.worker.PostMessage(&types.DirectoryThreaded{
 			Message: types.RespondTo(msg),
 			Threads: aercThreads,

worker/imap/seqmap.go

@@ -0,0 +1,48 @@
+package imap
+
+import "sync"
+
+type SeqMap struct {
+	lock sync.Mutex
+	// map of IMAP sequence numbers to message UIDs
+	m map[uint32]uint32
+}
+
+func (s *SeqMap) Size() int {
+	s.lock.Lock()
+	size := len(s.m)
+	s.lock.Unlock()
+	return size
+}
+
+func (s *SeqMap) Get(seqnum uint32) (uint32, bool) {
+	s.lock.Lock()
+	uid, found := s.m[seqnum]
+	s.lock.Unlock()
+	return uid, found
+}
+
+func (s *SeqMap) Put(seqnum, uid uint32) {
+	s.lock.Lock()
+	if s.m == nil {
+		s.m = make(map[uint32]uint32)
+	}
+	s.m[seqnum] = uid
+	s.lock.Unlock()
+}
+
+func (s *SeqMap) Pop(seqnum uint32) (uint32, bool) {
+	s.lock.Lock()
+	uid, found := s.m[seqnum]
+	if found {
+		delete(s.m, seqnum)
+	}
+	s.lock.Unlock()
+	return uid, found
+}
+
+func (s *SeqMap) Clear() {
+	s.lock.Lock()
+	s.m = make(map[uint32]uint32)
+	s.lock.Unlock()
+}

worker/imap/seqmap_test.go

@@ -0,0 +1,78 @@
+package imap
+
+import (
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSeqMap(t *testing.T) {
+	var seqmap SeqMap
+	var uid uint32
+	var found bool
+	assert := assert.New(t)
+
+	assert.Equal(seqmap.Size(), 0)
+
+	_, found = seqmap.Get(42)
+	assert.Equal(found, false)
+
+	_, found = seqmap.Pop(0)
+	assert.Equal(found, false)
+
+	seqmap.Put(1, 1337)
+	seqmap.Put(2, 42)
+	seqmap.Put(3, 1107)
+	assert.Equal(seqmap.Size(), 3)
+
+	_, found = seqmap.Pop(0)
+	assert.Equal(found, false)
+
+	uid, found = seqmap.Get(1)
+	assert.Equal(uid, uint32(1337))
+	assert.Equal(found, true)
+
+	uid, found = seqmap.Pop(1)
+	assert.Equal(uid, uint32(1337))
+	assert.Equal(found, true)
+	assert.Equal(seqmap.Size(), 2)
+
+	_, found = seqmap.Pop(1)
+	assert.Equal(found, false)
+	assert.Equal(seqmap.Size(), 2)
+
+	seqmap.Put(1, 7331)
+	assert.Equal(seqmap.Size(), 3)
+
+	seqmap.Clear()
+	assert.Equal(seqmap.Size(), 0)
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		time.Sleep(20 * time.Millisecond)
+		seqmap.Put(42, 1337)
+		time.Sleep(20 * time.Millisecond)
+		seqmap.Put(43, 1107)
+	}()
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for _, found := seqmap.Pop(43); !found; _, found = seqmap.Pop(43) {
+			time.Sleep(1 * time.Millisecond)
+		}
+	}()
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for _, found := seqmap.Pop(42); !found; _, found = seqmap.Pop(42) {
+			time.Sleep(1 * time.Millisecond)
+		}
+	}()
+	wg.Wait()
+
+	assert.Equal(seqmap.Size(), 0)
+}

worker/imap/worker.go

@@ -61,8 +61,7 @@ type IMAPWorker struct {
 	selected *imap.MailboxStatus
 	updates  chan client.Update
 	worker   *types.Worker
-	// Map of sequence numbers to UIDs, index 0 is seq number 1
-	seqMap []uint32
+	seqMap   SeqMap
 
 	idler    *idler
 	observer *observer
@@ -212,12 +211,6 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 
 func (w *IMAPWorker) handleImapUpdate(update client.Update) {
 	w.worker.Logger.Printf("(= %T", update)
-	checkBounds := func(idx, size int) bool {
-		if idx < 0 || idx >= size {
-			return false
-		}
-		return true
-	}
 	switch update := update.(type) {
 	case *client.MailboxUpdate:
 		status := update.Mailbox
@@ -238,11 +231,12 @@ func (w *IMAPWorker) handleImapUpdate(update client.Update) {
 	case *client.MessageUpdate:
 		msg := update.Message
 		if msg.Uid == 0 {
-			if ok := checkBounds(int(msg.SeqNum)-1, len(w.seqMap)); !ok {
-				w.worker.Logger.Println("MessageUpdate error: index out of range")
+			if uid, found := w.seqMap.Get(msg.SeqNum); !found {
+				w.worker.Logger.Printf("MessageUpdate unknown seqnum: %v", msg.SeqNum)
 				return
+			} else {
+				msg.Uid = uid
 			}
-			msg.Uid = w.seqMap[msg.SeqNum-1]
 		}
 		w.worker.PostMessage(&types.MessageInfo{
 			Info: &models.MessageInfo{
@@ -254,16 +248,13 @@ func (w *IMAPWorker) handleImapUpdate(update client.Update) {
 			},
 		}, nil)
 	case *client.ExpungeUpdate:
-		i := update.SeqNum - 1
-		if ok := checkBounds(int(i), len(w.seqMap)); !ok {
-			w.worker.Logger.Println("ExpungeUpdate error: index out of range")
-			return
+		if uid, found := w.seqMap.Pop(update.SeqNum); !found {
+			w.worker.Logger.Printf("ExpungeUpdate unknown seqnum: %v", update.SeqNum)
+		} else {
+			w.worker.PostMessage(&types.MessagesDeleted{
+				Uids: []uint32{uid},
+			}, nil)
 		}
-		uid := w.seqMap[i]
-		w.seqMap = append(w.seqMap[:i], w.seqMap[i+1:]...)
-		w.worker.PostMessage(&types.MessagesDeleted{
-			Uids: []uint32{uid},
-		}, nil)
 	}
 }