messages: allow displaying email threads

Display threads in the message list. For now, only supported by the
notmuch backend and on IMAP when the server supports the THREAD
extension.

Setting threading-enable=true is global and will cause the message list
to be empty with maildir:// accounts.

Co-authored-by: Kevin Kuehler <keur@xcf.berkeley.edu>
Co-authored-by: Reto Brunner <reto@labrat.space>
Signed-off-by: Robin Jarry <robin@jarry.cc>

config/aerc.conf.in

@@ -99,6 +99,14 @@ stylesets-dirs=@SHAREDIR@/stylesets/
 # Default: default
 styleset-name=default
 
+#[ui:account=foo]
+#
+# Enable threading in the ui. Only works with notmuch:// and imap:// accounts
+# (when the server supports it).
+#
+# Default: false
+#threading-enabled=false
+
 [viewer]
 #
 # Specifies the pager to use when displaying emails. Note that some filters

config/config.go

@@ -40,6 +40,7 @@ type UIConfig struct {
 	EmptyMessage        string        `ini:"empty-message"`
 	EmptyDirlist        string        `ini:"empty-dirlist"`
 	MouseEnabled        bool          `ini:"mouse-enabled"`
+	ThreadingEnabled    bool          `ini:"threading-enabled"`
 	NewMessageBell      bool          `ini:"new-message-bell"`
 	Spinner             string        `ini:"spinner"`
 	SpinnerDelimiter    string        `ini:"spinner-delimiter"`

doc/aerc-config.5.scd

@@ -207,6 +207,15 @@ These options are configured in the *[ui]* section of aerc.conf.
 
 	Have a look at *aerc-stylesets*(7) as to how a styleset looks like.
 
+*threading-enabled*
+	Enable a threaded viewing of messages, works with IMAP (when there's
+	server support) and NotMuch backends.
+
+	This option should only be set to true for specific accounts
+	accordingly. See *Contextual UI Configuration* below.
+
+	Default: false
+
 
 ## Contextual UI Configuration
 

lib/format/format.go

@@ -45,6 +45,10 @@ type Ctx struct {
 	MsgNum      int
 	MsgInfo     *models.MessageInfo
 	MsgIsMarked bool
+
+	// UI controls for threading
+	ThreadPrefix      string
+	ThreadSameSubject bool
 }
 
 func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
@@ -213,7 +217,13 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 			args = append(args, addrs)
 		case 's':
 			retval = append(retval, 's')
-			args = append(args, envelope.Subject)
+			// if we are threaded strip the repeated subjects unless it's the
+			// first on the screen
+			subject := envelope.Subject
+			if ctx.ThreadSameSubject {
+				subject = ""
+			}
+			args = append(args, ctx.ThreadPrefix+subject)
 		case 't':
 			if len(envelope.To) == 0 {
 				return "", nil,

lib/msgstore.go

@@ -18,6 +18,7 @@ type MessageStore struct {
 
 	// Ordered list of known UIDs
 	uids    []uint32
+	Threads []*types.Thread
 
 	selected        int
 	bodyCallbacks   map[uint32][]func(*types.FullMessage)
@@ -35,6 +36,8 @@ type MessageStore struct {
 
 	defaultSortCriteria []*types.SortCriterion
 
+	thread bool
+
 	// Map of uids we've asked the worker to fetch
 	onUpdate       func(store *MessageStore) // TODO: multiple onUpdate handlers
 	onUpdateDirs   func()
@@ -52,6 +55,7 @@ type MessageStore struct {
 func NewMessageStore(worker *types.Worker,
 	dirInfo *models.DirectoryInfo,
 	defaultSortCriteria []*types.SortCriterion,
+	thread bool,
 	triggerNewEmail func(*models.MessageInfo),
 	triggerDirectoryChange func()) *MessageStore {
 
@@ -67,6 +71,8 @@ func NewMessageStore(worker *types.Worker,
 		bodyCallbacks:   make(map[uint32][]func(*types.FullMessage)),
 		headerCallbacks: make(map[uint32][]func(*types.MessageInfo)),
 
+		thread: thread,
+
 		defaultSortCriteria: defaultSortCriteria,
 
 		pendingBodies:  make(map[uint32]interface{}),
@@ -189,6 +195,27 @@ func (store *MessageStore) Update(msg types.WorkerMessage) {
 		store.Messages = newMap
 		store.uids = msg.Uids
 		update = true
+	case *types.DirectoryThreaded:
+		var uids []uint32
+		newMap := make(map[uint32]*models.MessageInfo)
+
+		for i := len(msg.Threads) - 1; i >= 0; i-- {
+			msg.Threads[i].Walk(func(t *types.Thread, level int, currentErr error) error {
+				uid := t.Uid
+				uids = append([]uint32{uid}, uids...)
+				if msg, ok := store.Messages[uid]; ok {
+					newMap[uid] = msg
+				} else {
+					newMap[uid] = nil
+					directoryChange = true
+				}
+				return nil
+			})
+		}
+		store.Messages = newMap
+		store.uids = uids
+		store.Threads = msg.Threads
+		update = true
 	case *types.MessageInfo:
 		if existing, ok := store.Messages[msg.Info.Uid]; ok && existing != nil {
 			merge(existing, msg.Info)
@@ -257,6 +284,15 @@ func (store *MessageStore) Update(msg types.WorkerMessage) {
 		}
 		store.results = newResults
 
+		for _, thread := range store.Threads {
+			thread.Walk(func(t *types.Thread, _ int, _ error) error {
+				if _, deleted := toDelete[t.Uid]; deleted {
+					t.Deleted = true
+				}
+				return nil
+			})
+		}
+
 		update = true
 	}
 
@@ -592,14 +628,23 @@ func (store *MessageStore) ModifyLabels(uids []uint32, add, remove []string,
 
 func (store *MessageStore) Sort(criteria []*types.SortCriterion, cb func()) {
 	store.Sorting = true
-	store.worker.PostAction(&types.FetchDirectoryContents{
+
-		SortCriteria: criteria,
+	handle_return := func(msg types.WorkerMessage) {
-	}, func(_ types.WorkerMessage) {
 		store.Sorting = false
 		if cb != nil {
 			cb()
 		}
-	})
+	}
+
+	if store.thread {
+		store.worker.PostAction(&types.FetchDirectoryThreaded{
+			SortCriteria: criteria,
+		}, handle_return)
+	} else {
+		store.worker.PostAction(&types.FetchDirectoryContents{
+			SortCriteria: criteria,
+		}, handle_return)
+	}
 }
 
 // returns the index of needle in haystack or -1 if not found

widgets/account.go

@@ -249,6 +249,7 @@ func (acct *AccountView) onMessage(msg types.WorkerMessage) {
 		} else {
 			store = lib.NewMessageStore(acct.worker, msg.Info,
 				acct.getSortCriteria(),
+				acct.UiConfig().ThreadingEnabled,
 				func(msg *models.MessageInfo) {
 					acct.conf.Triggers.ExecNewEmail(acct.acct,
 						acct.conf, msg)
@@ -266,6 +267,13 @@ func (acct *AccountView) onMessage(msg types.WorkerMessage) {
 			}
 			store.Update(msg)
 		}
+	case *types.DirectoryThreaded:
+		if store, ok := acct.dirlist.SelectedMsgStore(); ok {
+			if acct.msglist.Store() == nil {
+				acct.msglist.SetStore(store)
+			}
+			store.Update(msg)
+		}
 	case *types.FullMessage:
 		if store, ok := acct.dirlist.SelectedMsgStore(); ok {
 			store.Update(msg)

widgets/msglist.go

@@ -4,7 +4,9 @@ import (
 	"fmt"
 	"log"
 	"math"
+	"strings"
 
+	sortthread "github.com/emersion/go-imap-sortthread"
 	"github.com/gdamore/tcell/v2"
 	"github.com/mattn/go-runewidth"
 
@@ -13,6 +15,7 @@ import (
 	"git.sr.ht/~rjarry/aerc/lib/format"
 	"git.sr.ht/~rjarry/aerc/lib/ui"
 	"git.sr.ht/~rjarry/aerc/models"
+	"git.sr.ht/~rjarry/aerc/worker/types"
 )
 
 type MessageList struct {
@@ -85,21 +88,110 @@ func (ml *MessageList) Draw(ctx *ui.Context) {
 		needsHeaders []uint32
 		row          int = 0
 	)
-	uids := store.Uids()
 
-	for i := len(uids) - 1 - ml.scroll; i >= 0; i-- {
+	if ml.aerc.SelectedAccount().UiConfig().ThreadingEnabled {
-		uid := uids[i]
+		threads := store.Threads
-		msg := store.Messages[uid]
+		counter := len(store.Uids())
 
+		for i := len(threads) - 1; i >= 0; i-- {
+			var lastSubject string
+			threads[i].Walk(func(t *types.Thread, _ int, currentErr error) error {
+				if currentErr != nil {
+					return currentErr
+				}
+				if t.Hidden || t.Deleted {
+					return nil
+				}
+				counter--
+				if counter > len(store.Uids())-1-ml.scroll {
+					//skip messages which are higher than the viewport
+					return nil
+				}
+				msg := store.Messages[t.Uid]
+				var prefix string
+				var subject string
+				var normalizedSubject string
+				if msg != nil {
+					prefix = threadPrefix(t)
+					if msg.Envelope != nil {
+						subject = msg.Envelope.Subject
+						normalizedSubject, _ = sortthread.GetBaseSubject(subject)
+					}
+				}
+				fmtCtx := format.Ctx{
+					FromAddress:       ml.aerc.SelectedAccount().acct.From,
+					AccountName:       ml.aerc.SelectedAccount().Name(),
+					MsgInfo:           msg,
+					MsgNum:            row,
+					MsgIsMarked:       store.IsMarked(t.Uid),
+					ThreadPrefix:      prefix,
+					ThreadSameSubject: normalizedSubject == lastSubject,
+				}
+				if ml.drawRow(textWidth, ctx, t.Uid, row, &needsHeaders, fmtCtx) {
+					return types.ErrSkipThread
+				}
+				lastSubject = normalizedSubject
+				row++
+				return nil
+			})
 			if row >= ctx.Height() {
 				break
 			}
+		}
+	} else {
+		uids := store.Uids()
+		for i := len(uids) - 1 - ml.scroll; i >= 0; i-- {
+			uid := uids[i]
+			msg := store.Messages[uid]
+			fmtCtx := format.Ctx{
+				FromAddress: ml.aerc.SelectedAccount().acct.From,
+				AccountName: ml.aerc.SelectedAccount().Name(),
+				MsgInfo:     msg,
+				MsgNum:      row,
+				MsgIsMarked: store.IsMarked(uid),
+			}
+			if ml.drawRow(textWidth, ctx, uid, row, &needsHeaders, fmtCtx) {
+				break
+			}
+			row += 1
+		}
+	}
+
+	if needScrollbar {
+		scrollbarCtx := ctx.Subcontext(ctx.Width()-1, 0, 1, ctx.Height())
+		ml.drawScrollbar(scrollbarCtx, percentVisible)
+	}
+
+	if len(store.Uids()) == 0 {
+		if store.Sorting {
+			ml.spinner.Start()
+			ml.spinner.Draw(ctx)
+			return
+		} else {
+			ml.drawEmptyMessage(ctx)
+		}
+	}
+
+	if len(needsHeaders) != 0 {
+		store.FetchHeaders(needsHeaders, nil)
+		ml.spinner.Start()
+	} else {
+		ml.spinner.Stop()
+	}
+}
+
+func (ml *MessageList) drawRow(textWidth int, ctx *ui.Context, uid uint32, row int, needsHeaders *[]uint32, fmtCtx format.Ctx) bool {
+	store := ml.store
+	msg := store.Messages[uid]
+
+	if row >= ctx.Height() {
+		return true
+	}
 
 	if msg == nil {
-			needsHeaders = append(needsHeaders, uid)
+		*needsHeaders = append(*needsHeaders, uid)
 		ml.spinner.Draw(ctx.Subcontext(0, row, textWidth, 1))
-			row += 1
+		return false
-			continue
 	}
 
 	confParams := map[config.ContextType]string{
@@ -158,13 +250,7 @@ func (ml *MessageList) Draw(ctx *ui.Context) {
 		uiConfig.ThisDayTimeFormat,
 		uiConfig.ThisWeekTimeFormat,
 		uiConfig.ThisYearTimeFormat,
-			format.Ctx{
+		fmtCtx)
-				FromAddress: ml.aerc.SelectedAccount().acct.From,
-				AccountName: ml.aerc.SelectedAccount().Name(),
-				MsgInfo:     msg,
-				MsgNum:      i,
-				MsgIsMarked: store.IsMarked(uid),
-			})
 	if err != nil {
 		ctx.Printf(0, row, style, "%v", err)
 	} else {
@@ -173,30 +259,7 @@ func (ml *MessageList) Draw(ctx *ui.Context) {
 		ctx.Printf(0, row, style, "%s", line)
 	}
 
-		row += 1
+	return false
-	}
-
-	if needScrollbar {
-		scrollbarCtx := ctx.Subcontext(ctx.Width()-1, 0, 1, ctx.Height())
-		ml.drawScrollbar(scrollbarCtx, percentVisible)
-	}
-
-	if len(uids) == 0 {
-		if store.Sorting {
-			ml.spinner.Start()
-			ml.spinner.Draw(ctx)
-			return
-		} else {
-			ml.drawEmptyMessage(ctx)
-		}
-	}
-
-	if len(needsHeaders) != 0 {
-		store.FetchHeaders(needsHeaders, nil)
-		ml.spinner.Start()
-	} else {
-		ml.spinner.Stop()
-	}
 }
 
 func (ml *MessageList) drawScrollbar(ctx *ui.Context, percentVisible float64) {
@@ -375,3 +438,33 @@ func (ml *MessageList) drawEmptyMessage(ctx *ui.Context) {
 	ctx.Printf((ctx.Width()/2)-(len(msg)/2), 0,
 		uiConfig.GetStyle(config.STYLE_MSGLIST_DEFAULT), "%s", msg)
 }
+
+func threadPrefix(t *types.Thread) string {
+	var arrow string
+	if t.Parent != nil {
+		if t.NextSibling != nil {
+			arrow = "├─>"
+		} else {
+			arrow = "└─>"
+		}
+	}
+	var prefix []string
+	for n := t; n.Parent != nil; n = n.Parent {
+		if n.Parent.NextSibling != nil {
+			prefix = append(prefix, "│  ")
+		} else {
+			prefix = append(prefix, "   ")
+		}
+	}
+	// prefix is now in a reverse order (inside --> outside), so turn it
+	for i, j := 0, len(prefix)-1; i < j; i, j = i+1, j-1 {
+		prefix[i], prefix[j] = prefix[j], prefix[i]
+	}
+
+	// we don't want to indent the first child, hence we strip that level
+	if len(prefix) > 0 {
+		prefix = prefix[1:]
+	}
+	ps := strings.Join(prefix, "")
+	return fmt.Sprintf("%v%v", ps, arrow)
+}

worker/imap/open.go

@@ -1,6 +1,8 @@
 package imap
 
 import (
+	"sort"
+
 	"github.com/emersion/go-imap"
 	sortthread "github.com/emersion/go-imap-sortthread"
 
@@ -92,3 +94,64 @@ func translateSortCriterions(
 	}
 	return result
 }
+
+func (imapw *IMAPWorker) handleDirectoryThreaded(
+	msg *types.FetchDirectoryThreaded) {
+	imapw.worker.Logger.Printf("Fetching threaded UID list")
+
+	seqSet := &imap.SeqSet{}
+	seqSet.AddRange(1, imapw.selected.Messages)
+	threads, err := imapw.client.thread.UidThread(sortthread.References,
+		&imap.SearchCriteria{SeqNum: seqSet})
+	if err != nil {
+		imapw.worker.PostMessage(&types.Error{
+			Message: types.RespondTo(msg),
+			Error:   err,
+		}, nil)
+	} else {
+		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.worker.PostMessage(&types.DirectoryThreaded{
+			Message: types.RespondTo(msg),
+			Threads: aercThreads,
+		}, nil)
+		imapw.worker.PostMessage(&types.Done{types.RespondTo(msg)}, nil)
+	}
+}
+
+func convertThreads(threads []*sortthread.Thread, parent *types.Thread) ([]*types.Thread, int) {
+	if threads == nil {
+		return nil, 0
+	}
+	conv := make([]*types.Thread, len(threads))
+	count := 0
+
+	for i := 0; i < len(threads); i++ {
+		t := threads[i]
+		conv[i] = &types.Thread{
+			Uid: t.Id,
+		}
+
+		// Set the first child node
+		children, childCount := convertThreads(t.Children, conv[i])
+		if len(children) > 0 {
+			conv[i].FirstChild = children[0]
+		}
+
+		// Set the parent node
+		if parent != nil {
+			conv[i].Parent = parent
+
+			// elements of threads are siblings
+			if i > 0 {
+				conv[i].PrevSibling = conv[i-1]
+				conv[i-1].NextSibling = conv[i]
+			}
+		}
+
+		count += childCount + 1
+	}
+	return conv, count
+}

worker/imap/worker.go

@@ -26,6 +26,7 @@ var errUnsupported = fmt.Errorf("unsupported command")
 
 type imapClient struct {
 	*client.Client
+	thread *sortthread.ThreadClient
 	sort   *sortthread.SortClient
 }
 
@@ -158,7 +159,7 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 		}
 
 		c.Updates = w.updates
-		w.client = &imapClient{c, sortthread.NewSortClient(c)}
+		w.client = &imapClient{c, sortthread.NewThreadClient(c), sortthread.NewSortClient(c)}
 		w.worker.PostMessage(&types.Done{types.RespondTo(msg)}, nil)
 	case *types.Disconnect:
 		if w.client == nil {
@@ -175,6 +176,8 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 		w.handleOpenDirectory(msg)
 	case *types.FetchDirectoryContents:
 		w.handleFetchDirectoryContents(msg)
+	case *types.FetchDirectoryThreaded:
+		w.handleDirectoryThreaded(msg)
 	case *types.CreateDirectory:
 		w.handleCreateDirectory(msg)
 	case *types.RemoveDirectory:

worker/notmuch/lib/database.go

@@ -7,6 +7,8 @@ import (
 	"log"
 	"time"
 
+	"git.sr.ht/~rjarry/aerc/lib/uidstore"
+	"git.sr.ht/~rjarry/aerc/worker/types"
 	notmuch "github.com/zenhack/go.notmuch"
 )
 
@@ -18,6 +20,7 @@ type DB struct {
 	logger       *log.Logger
 	lastOpenTime time.Time
 	db           *notmuch.DB
+	uidStore     *uidstore.Store
 }
 
 func NewDB(path string, excludedTags []string,
@@ -26,6 +29,7 @@ func NewDB(path string, excludedTags []string,
 		path:         path,
 		excludedTags: excludedTags,
 		logger:       logger,
+		uidStore:     uidstore.NewStore(),
 	}
 	return db
 }
@@ -106,7 +110,7 @@ func (db *DB) ListTags() ([]string, error) {
 //It also configures the query as specified on the worker
 func (db *DB) newQuery(ndb *notmuch.DB, query string) (*notmuch.Query, error) {
 	q := ndb.NewQuery(query)
-	q.SetExcludeScheme(notmuch.EXCLUDE_TRUE)
+	q.SetExcludeScheme(notmuch.EXCLUDE_ALL)
 	q.SetSortScheme(notmuch.SORT_OLDEST_FIRST)
 	for _, t := range db.excludedTags {
 		err := q.AddTagExclude(t)
@@ -125,18 +129,37 @@ func (db *DB) MsgIDsFromQuery(q string) ([]string, error) {
 			return err
 		}
 		defer query.Close()
-		msgs, err := query.Messages()
+		msgIDs, err = msgIdsFromQuery(query)
+		return err
+	})
+	return msgIDs, err
+}
+
+func (db *DB) ThreadsFromQuery(q string) ([]*types.Thread, error) {
+	var res []*types.Thread
+	err := db.withConnection(false, func(ndb *notmuch.DB) error {
+		query, err := db.newQuery(ndb, q)
 		if err != nil {
 			return err
 		}
-		defer msgs.Close()
+		defer query.Close()
-		var msg *notmuch.Message
+		qMsgIDs, err := msgIdsFromQuery(query)
-		for msgs.Next(&msg) {
+		if err != nil {
-			msgIDs = append(msgIDs, msg.ID())
+			return err
 		}
-		return nil
+		valid := make(map[string]struct{})
+		for _, id := range qMsgIDs {
+			valid[id] = struct{}{}
+		}
+		threads, err := query.Threads()
+		if err != nil {
+			return err
+		}
+		defer threads.Close()
+		res, err = db.enumerateThread(threads, valid)
+		return err
 	})
-	return msgIDs, err
+	return res, err
 }
 
 type MessageCount struct {
@@ -236,3 +259,85 @@ func (db *DB) MsgModifyTags(key string, add, remove []string) error {
 	})
 	return err
 }
+
+func msgIdsFromQuery(query *notmuch.Query) ([]string, error) {
+	var msgIDs []string
+	msgs, err := query.Messages()
+	if err != nil {
+		return nil, err
+	}
+	defer msgs.Close()
+	var msg *notmuch.Message
+	for msgs.Next(&msg) {
+		msgIDs = append(msgIDs, msg.ID())
+	}
+	return msgIDs, nil
+}
+
+func (db *DB) UidFromKey(key string) uint32 {
+	return db.uidStore.GetOrInsert(key)
+}
+
+func (db *DB) KeyFromUid(uid uint32) (string, bool) {
+	return db.uidStore.GetKey(uid)
+}
+
+func (db *DB) enumerateThread(nt *notmuch.Threads,
+	valid map[string]struct{}) ([]*types.Thread, error) {
+	var res []*types.Thread
+	var thread *notmuch.Thread
+	for nt.Next(&thread) {
+		root := db.makeThread(nil, thread.TopLevelMessages(), valid)
+		res = append(res, root)
+	}
+	return res, nil
+}
+
+func (db *DB) makeThread(parent *types.Thread, msgs *notmuch.Messages,
+	valid map[string]struct{}) *types.Thread {
+	var lastSibling *types.Thread
+	var msg *notmuch.Message
+	for msgs.Next(&msg) {
+		msgID := msg.ID()
+		_, inQuery := valid[msgID]
+		node := &types.Thread{
+			Uid:    db.uidStore.GetOrInsert(msgID),
+			Parent: parent,
+			Hidden: !inQuery,
+		}
+		if parent != nil && parent.FirstChild == nil {
+			parent.FirstChild = node
+		}
+		if lastSibling != nil {
+			if lastSibling.NextSibling != nil {
+				panic(fmt.Sprintf(
+					"%v already had a NextSibling, tried setting it",
+					lastSibling))
+			}
+			lastSibling.NextSibling = node
+		}
+		lastSibling = node
+		replies, err := msg.Replies()
+		if err != nil {
+			// if there are no replies it will return an error
+			continue
+		}
+		defer replies.Close()
+		db.makeThread(node, replies, valid)
+	}
+
+	// We want to return the root node
+	var root *types.Thread
+	if parent != nil {
+		root = parent
+	} else if lastSibling != nil {
+		root = lastSibling // first iteration has no parent
+	} else {
+		return nil // we don't have any messages at all
+	}
+
+	for ; root.Parent != nil; root = root.Parent {
+		// move to the root
+	}
+	return root
+}

worker/notmuch/lib/thread.go

@@ -0,0 +1,14 @@
+//+build notmuch
+
+package lib
+
+type ThreadNode struct {
+	Uid     string
+	From    string
+	Subject string
+	InQuery bool // is the msg included in the query
+
+	Parent      *ThreadNode
+	NextSibling *ThreadNode
+	FirstChild  *ThreadNode
+}

worker/notmuch/worker.go

@@ -107,6 +107,8 @@ func (w *worker) handleMessage(msg types.WorkerMessage) error {
 		return w.handleOpenDirectory(msg)
 	case *types.FetchDirectoryContents:
 		return w.handleFetchDirectoryContents(msg)
+	case *types.FetchDirectoryThreaded:
+		return w.handleFetchDirectoryThreaded(msg)
 	case *types.FetchMessageHeaders:
 		return w.handleFetchMessageHeaders(msg)
 	case *types.FetchMessageBodyPart:
@@ -157,7 +159,6 @@ func (w *worker) handleConfigure(msg *types.Configure) error {
 		return fmt.Errorf("could not resolve home directory: %v", err)
 	}
 	pathToDB := filepath.Join(home, u.Path)
-	w.uidStore = uidstore.NewStore()
 	err = w.loadQueryMap(msg.Config)
 	if err != nil {
 		return fmt.Errorf("could not load query map configuration: %v", err)
@@ -267,6 +268,17 @@ func (w *worker) handleFetchDirectoryContents(
 	return nil
 }
 
+func (w *worker) handleFetchDirectoryThreaded(
+	msg *types.FetchDirectoryThreaded) error {
+	// w.currentSortCriteria = msg.SortCriteria
+	err := w.emitDirectoryThreaded(msg)
+	if err != nil {
+		return err
+	}
+	w.done(msg)
+	return nil
+}
+
 func (w *worker) handleFetchMessageHeaders(
 	msg *types.FetchMessageHeaders) error {
 	for _, uid := range msg.Uids {
@@ -294,7 +306,7 @@ func (w *worker) uidsFromQuery(query string) ([]uint32, error) {
 	}
 	var uids []uint32
 	for _, id := range msgIDs {
-		uid := w.uidStore.GetOrInsert(id)
+		uid := w.db.UidFromKey(id)
 		uids = append(uids, uid)
 
 	}
@@ -302,7 +314,7 @@ func (w *worker) uidsFromQuery(query string) ([]uint32, error) {
 }
 
 func (w *worker) msgFromUid(uid uint32) (*Message, error) {
-	key, ok := w.uidStore.GetKey(uid)
+	key, ok := w.db.KeyFromUid(uid)
 	if !ok {
 		return nil, fmt.Errorf("Invalid uid: %v", uid)
 	}
@@ -528,6 +540,18 @@ func (w *worker) emitDirectoryContents(parent types.WorkerMessage) error {
 	return nil
 }
 
+func (w *worker) emitDirectoryThreaded(parent types.WorkerMessage) error {
+	threads, err := w.db.ThreadsFromQuery(w.query)
+	if err != nil {
+		return err
+	}
+	w.w.PostMessage(&types.DirectoryThreaded{
+		Message: types.RespondTo(parent),
+		Threads: threads,
+	}, nil)
+	return nil
+}
+
 func (w *worker) emitMessageInfo(m *Message,
 	parent types.WorkerMessage) error {
 	info, err := m.MessageInfo()

worker/types/messages.go

@@ -81,11 +81,21 @@ type FetchDirectoryContents struct {
 	SortCriteria []*SortCriterion
 }
 
+type FetchDirectoryThreaded struct {
+	Message
+	SortCriteria []*SortCriterion
+}
+
 type SearchDirectory struct {
 	Message
 	Argv []string
 }
 
+type DirectoryThreaded struct {
+	Message
+	Threads []*Thread
+}
+
 type CreateDirectory struct {
 	Message
 	Directory string

worker/types/thread.go

@@ -0,0 +1,99 @@
+package types
+
+import (
+	"errors"
+	"fmt"
+)
+
+type Thread struct {
+	Uid         uint32
+	Parent      *Thread
+	PrevSibling *Thread
+	NextSibling *Thread
+	FirstChild  *Thread
+
+	Hidden  bool // if this flag is set the message isn't rendered in the UI
+	Deleted bool // if this flag is set the message was deleted
+}
+
+func (t *Thread) Walk(walkFn NewThreadWalkFn) error {
+	err := newWalk(t, walkFn, 0, nil)
+	if err == ErrSkipThread {
+		return nil
+	}
+	return err
+}
+
+func (t *Thread) String() string {
+	if t == nil {
+		return "<nil>"
+	}
+	parent := -1
+	if t.Parent != nil {
+		parent = int(t.Parent.Uid)
+	}
+	next := -1
+	if t.NextSibling != nil {
+		next = int(t.NextSibling.Uid)
+	}
+	child := -1
+	if t.FirstChild != nil {
+		child = int(t.FirstChild.Uid)
+	}
+	return fmt.Sprintf(
+		"[%d] (parent:%v, next:%v, child:%v)",
+		t.Uid, parent, next, child,
+	)
+}
+
+func newWalk(node *Thread, walkFn NewThreadWalkFn, lvl int, ce error) error {
+	if node == nil {
+		return nil
+	}
+	err := walkFn(node, lvl, ce)
+	if err != nil {
+		return err
+	}
+	for child := node.FirstChild; child != nil; child = child.NextSibling {
+		err = newWalk(child, walkFn, lvl+1, err)
+		if err == ErrSkipThread {
+			err = nil
+			continue
+		} else if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+var ErrSkipThread = errors.New("skip this Thread")
+
+type NewThreadWalkFn func(t *Thread, level int, currentErr error) error
+
+//Implement interface to be able to sort threads by newest (max UID)
+type ByUID []*Thread
+
+func getMaxUID(thread *Thread) uint32 {
+	// TODO: should we make this part of the Thread type to avoid recomputation?
+	var Uid uint32
+
+	thread.Walk(func(t *Thread, _ int, currentErr error) error {
+		if t.Uid > Uid {
+			Uid = t.Uid
+		}
+		return nil
+	})
+	return Uid
+}
+
+func (s ByUID) Len() int {
+	return len(s)
+}
+func (s ByUID) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+func (s ByUID) Less(i, j int) bool {
+	maxUID_i := getMaxUID(s[i])
+	maxUID_j := getMaxUID(s[j])
+	return maxUID_i < maxUID_j
+}

worker/types/thread_test.go

@@ -0,0 +1,108 @@
+package types
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+func genFakeTree() *Thread {
+	tree := &Thread{
+		Uid: 0,
+	}
+	var prevChild *Thread
+	for i := 1; i < 3; i++ {
+		child := &Thread{
+			Uid:         uint32(i * 10),
+			Parent:      tree,
+			PrevSibling: prevChild,
+		}
+		if prevChild != nil {
+			prevChild.NextSibling = child
+		} else if tree.FirstChild == nil {
+			tree.FirstChild = child
+		} else {
+			panic("unreachable")
+		}
+		prevChild = child
+		var prevSecond *Thread
+		for j := 1; j < 3; j++ {
+			second := &Thread{
+				Uid:         child.Uid + uint32(j),
+				Parent:      child,
+				PrevSibling: prevSecond,
+			}
+			if prevSecond != nil {
+				prevSecond.NextSibling = second
+			} else if child.FirstChild == nil {
+				child.FirstChild = second
+			} else {
+				panic("unreachable")
+			}
+			prevSecond = second
+			var prevThird *Thread
+			limit := 3
+			if j == 2 {
+				limit = 8
+			}
+			for k := 1; k < limit; k++ {
+				third := &Thread{
+					Uid:         second.Uid*10 + uint32(k),
+					Parent:      second,
+					PrevSibling: prevThird,
+				}
+				if prevThird != nil {
+					prevThird.NextSibling = third
+				} else if second.FirstChild == nil {
+					second.FirstChild = third
+				} else {
+					panic("unreachable")
+				}
+				prevThird = third
+			}
+		}
+	}
+	return tree
+}
+
+func TestNewWalk(t *testing.T) {
+	tree := genFakeTree()
+	var prefix []string
+	lastLevel := 0
+	tree.Walk(func(t *Thread, lvl int, e error) error {
+		// if t.Uid%2 != 0 {
+		// 	return ErrSkipThread
+		// }
+		if e != nil {
+			fmt.Printf("ERROR: %v\n", e)
+		}
+		if lvl > lastLevel && lvl > 1 {
+			// we actually just descended... so figure out what connector we need
+			// level 1 is flush to the root, so we avoid the indentation there
+			if t.Parent.NextSibling != nil {
+				prefix = append(prefix, "│  ")
+			} else {
+				prefix = append(prefix, "   ")
+			}
+		} else if lvl < lastLevel {
+			//ascended, need to trim the prefix layers
+			diff := lastLevel - lvl
+			prefix = prefix[:len(prefix)-diff]
+		}
+
+		var arrow string
+		if t.Parent != nil {
+			if t.NextSibling != nil {
+				arrow = "├─>"
+			} else {
+				arrow = "└─>"
+			}
+		}
+
+		// format
+		fmt.Printf("%s%s%s\n", strings.Join(prefix, ""), arrow, t)
+
+		lastLevel = lvl
+		return nil
+	})
+}