Phase 4: sync

Implements PLAN.md Phase 4: the read model. /sync, /messages and /context,
the filters that narrow them, and the streams a response carries that are
not room events — typing, receipts, presence and to-device messages. With
this a client can be used against Warp, which is milestone M1.

The one architectural choice is that the syncapi has no copy of the rooms:
it reads them through the roomserver. Dendrite gives its syncapi its own
tables and feeds them from the output stream, which is right for a design
where the two can be separate processes, and Dendrite's could be. Warp is
one process by decision, and there the copy buys nothing and costs the
hardest class of bug a homeserver has — a read model that disagrees with
the room, where a client is shown a message that was rejected and the only
way to find out is to compare two tables. So the roomserver grew a read
model (stream.go, roomsync.go, visibility.go) rather than exporting its
store: reading an event means parsing it under its room's version, and a
second copy of the version registry, the parser and the client projection
would be a second place for them to disagree.

syncapi: stream tokens naming a position in each of five independent
streams, so a client that has seen receipt 7 but only event 4 can say so in
one opaque string. A token with fewer positions than this build writes is
accepted and the rest read as zero, which is what lets a token stored
before a stream existed go on working. The PDU position comes from
MAX(stream_ordering) and not from the counter row the other four use: the
counter is advanced inside the writing transaction, so a token taken from
it would name a position whose event no reader can see yet, and the event
would be skipped for good once that transaction committed.

Long polling goes through a notifier that wakes by room and by user rather
than globally — an event wakes the listeners of its room, a membership
event also wakes the user it names, so an invite reaches a client that is
not in the room yet. A wake-up is only ever a hint: the listener re-reads
the streams and decides for itself what changed, which is what makes it
safe for the notifier to hold no state about what each client has seen. The
listener registers before the read, so an event landing in between leaves
the channel signalled and the sync reads again rather than blocking on a
change it just missed. EventPersisted must not block, because it is called
with the room's write lock still held.

"Something happened" is not "a token moved". A stream can move without this
user being concerned by it, and returning on every such move would turn a
long poll back into a busy loop. The same trap caught presence twice over:
a client says it is still online by syncing, so ?set_presence= makes every
sync a presence write, and a stream that moved each time would wake every
peer, which would sync, which would move it again. SetPresence therefore
reports whether anything a peer would notice actually changed, and a write
that only refreshes the last-active timestamp leaves the stream alone.

Timeline windows are named by their two ends and a direction, Low exclusive
and High inclusive in both directions, rather than by "from" and "to" as
the wire format spells them. Each of those would otherwise be the low bound
in one direction and the high bound in the other, which is exactly the
off-by-one every pagination bug is made of; the handlers translate once and
nothing below them thinks about it again. A sync's timeline is read
backwards and reported forwards, because a client wants the newest events
of the window it missed — a forward read with a limit hands it the oldest
and then calls the rest a gap.

visibility: history visibility is now a span rather than a yes or no, which
is what Phase 3 deferred here. A user who has left a room is served the
room as it was when they left — their state reads, their members and their
timeline — instead of being refused, and is bounded above at their own
membership event so a kicked client cannot go on streaming. Their span is
found from their own member events, so a user who joined, left and rejoined
sees their latest span. ?at= on /members is honoured for the same reason.
What is left is that the span is computed from the room's current
history_visibility where the spec judges each event by the one in force
when it was sent; that is a state read per event and belongs with open
question 1.

Typing is held in memory and nowhere else: notifications expire in seconds,
are worthless across a restart, and arrive one per keystroke-burst per
room, so persisting them would be the busiest table in the database holding
the least valuable data in it. Receipts only ever advance, compared on the
position of the event acknowledged rather than on arrival, because two of a
user's clients read at different speeds and the slower one must not drag
the marker backwards. To-device queues are per device and drained by the
next sync rather than by the one that delivered them, so a client that
crashes in between gets the batch again — the right way round, since a lost
key share leaves a message permanently undecryptable and a duplicate is
ignored. A wildcard addressee is expanded when sent, not stored, because
"every device" means the ones that existed then.

Presence is off by default, which answers PLAN.md open question 3. It is
the noisiest thing in Matrix and the one genuinely fan-out notification
here; a private homeserver gains little from it. With it off the endpoints
refuse rather than disappearing, because a client that gets a 404 from
/presence concludes the server is too old to have it and stops asking.

storage: one migration per driver adding the receipt, to-device, presence
and filter tables with a counter row each, and a stream position on the
existing account data table rather than a parallel one — there is exactly
one current value per (user, room, type), and a second table would be a
second thing to keep in step. Account data is reported in an event list but
is not an event, so it gets its own response type: a room event with an
empty sender and no timestamp would make a client decide what that meant.

Deliberately missing, each named in docs/sync.md: notification counts (they
need push rules, Phase 8), device lists (the keyserver, Phase 7), anything
remote (Phase 5), threads (Phase 10). device_lists is sent as two empty
lists because a client reads a missing one as malformed; the notification
counts are left out entirely, because a zero there is a claim and an absent
field is not.

Tested through HTTP rather than against the builder, because what is worth
pinning down is the response a client sees — which section a room lands in,
whether a token handed back can be handed in again, whether paging
terminates and loses nothing. The storage tests run against both SQL
drivers; the notifier has its own tests for the concurrent case. A live
server was driven end to end, which is what caught the two bugs the unit
tests had missed: a backwards /messages page must be in reverse
chronological order, and `start` must name where the page began rather than
position zero when ?from= was omitted.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

server/internal/setup/phase1_test.go

@@ -74,11 +74,13 @@ func TestClientAPIIsWiredUp(t *testing.T) {
 		t.Fatalf("registration returned no access token: %s", rec.Body.String())
 	}
 
+	// /sync is not in this list: it belongs to the syncapi, which needs
+	// the roomserver, which needs a signing key this server was started
+	// without. TestSyncIsWiredUp covers it.
 	for _, path := range []string{
 		"/_matrix/client/v3/account/whoami",
 		"/_matrix/client/v3/capabilities",
 		"/_matrix/client/v3/devices",
-		"/_matrix/client/v3/sync",
 	} {
 		if rec := getWithToken(t, srv, path, token); rec.Code != http.StatusOK {
 			t.Errorf("GET %s = %d, want 200 (body: %s)", path, rec.Code, rec.Body.String())

server/internal/setup/phase4_test.go

@@ -0,0 +1,149 @@
+package setup_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"path/filepath"
+	"testing"
+
+	"github.com/dariuszjaniak/warp/server/internal/config"
+	"github.com/dariuszjaniak/warp/server/internal/matrix/signing"
+	"github.com/dariuszjaniak/warp/server/internal/setup"
+)
+
+// newSigningServer is newTestServer with a real signing key, which is what
+// the roomserver and therefore the syncapi need: a server started without
+// one has no rooms and so no stream to read.
+func newSigningServer(t *testing.T, tweak func(*config.Config)) *setup.Server {
+	t.Helper()
+
+	key, err := signing.Generate("test")
+	if err != nil {
+		t.Fatalf("signing.Generate: %v", err)
+	}
+	keyPath := filepath.Join(t.TempDir(), "signing.key")
+	if err := key.Save(keyPath); err != nil {
+		t.Fatalf("saving the signing key: %v", err)
+	}
+
+	cfg := config.Default()
+	cfg.Global.ServerName = "warp.example"
+	cfg.Global.PrivateKeyPath = keyPath
+	cfg.Database.ConnectionString = "file:" + t.Name() + "?mode=memory&cache=shared"
+	cfg.Registration.Enabled = true
+	// The limiter keys on the client address, and every httptest request
+	// comes from the same one.
+	cfg.ClientAPI.RateLimit.Enabled = false
+	if tweak != nil {
+		tweak(cfg)
+	}
+	if err := cfg.Validate(); err != nil {
+		t.Fatalf("test config is invalid: %v", err)
+	}
+
+	srv, err := setup.New(t.Context(), cfg, setup.Options{Logger: slog.New(slog.DiscardHandler)})
+	if err != nil {
+		t.Fatalf("setup.New: %v", err)
+	}
+	t.Cleanup(func() { _ = srv.Close() })
+	return srv
+}
+
+// registerThrough walks the registration flow and returns the access token.
+func registerThrough(t *testing.T, srv *setup.Server, localpart string) string {
+	t.Helper()
+
+	body := map[string]any{"username": localpart, "password": "sUp3rs3kr1t"}
+	rec := post(t, srv, "/_matrix/client/v3/register", body, "")
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("register status = %d, want 401 (body: %s)", rec.Code, rec.Body.String())
+	}
+	body["auth"] = map[string]any{
+		"type":    "m.login.dummy",
+		"session": decode[map[string]any](t, rec)["session"],
+	}
+
+	rec = post(t, srv, "/_matrix/client/v3/register", body, "")
+	if rec.Code != http.StatusOK {
+		t.Fatalf("register status = %d, want 200 (body: %s)", rec.Code, rec.Body.String())
+	}
+	token, _ := decode[map[string]any](t, rec)["access_token"].(string)
+	if token == "" {
+		t.Fatalf("registration returned no access token: %s", rec.Body.String())
+	}
+	return token
+}
+
+// put sends a JSON body with PUT through the fully wrapped handler.
+func put(t *testing.T, srv *setup.Server, path string, body any, token string) *httptest.ResponseRecorder {
+	t.Helper()
+
+	raw, err := json.Marshal(body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req := httptest.NewRequest(http.MethodPut, path, bytes.NewReader(raw))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer "+token)
+	rec := httptest.NewRecorder()
+	srv.Handler().ServeHTTP(rec, req)
+	return rec
+}
+
+// TestSyncIsWiredUp is the Phase 4 counterpart of TestClientAPIIsWiredUp:
+// it goes through the whole stack rather than a hand-built router, to catch
+// an endpoint that was written but never registered.
+func TestSyncIsWiredUp(t *testing.T) {
+	srv := newSigningServer(t, func(c *config.Config) { c.Sync.Presence = true })
+	token := registerThrough(t, srv, "alice")
+
+	if srv.Sync() == nil {
+		t.Fatal("a server with a signing key must have a syncapi")
+	}
+
+	rec := post(t, srv, "/_matrix/client/v3/createRoom", map[string]any{}, token)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("createRoom status = %d (body: %s)", rec.Code, rec.Body.String())
+	}
+	roomID, _ := decode[map[string]any](t, rec)["room_id"].(string)
+	if roomID == "" {
+		t.Fatalf("createRoom returned no room ID: %s", rec.Body.String())
+	}
+
+	for _, path := range []string{
+		"/_matrix/client/v3/sync",
+		"/_matrix/client/v3/rooms/" + roomID + "/messages?dir=b",
+		"/_matrix/client/v3/presence/@alice:warp.example/status",
+	} {
+		if rec := getWithToken(t, srv, path, token); rec.Code != http.StatusOK {
+			t.Errorf("GET %s = %d, want 200 (body: %s)", path, rec.Code, rec.Body.String())
+		}
+	}
+}
+
+// TestPresenceIsOffByDefault pins down PLAN.md open question 3: presence is
+// the noisiest thing in Matrix and a new install does not get it.
+func TestPresenceIsOffByDefault(t *testing.T) {
+	if config.Default().Sync.Presence {
+		t.Error("presence must be off in a default configuration")
+	}
+
+	srv := newSigningServer(t, nil)
+	token := registerThrough(t, srv, "alice")
+
+	// The endpoint is registered and refuses, rather than being absent: a
+	// client that gets a 404 concludes the server is too old to have
+	// presence and stops asking, where a refusal says it is switched off.
+	rec := put(t, srv, "/_matrix/client/v3/presence/@alice:warp.example/status",
+		map[string]any{"presence": "online"}, token)
+	if rec.Code != http.StatusForbidden {
+		t.Errorf("PUT /presence with presence off = %d, want 403 (body: %s)",
+			rec.Code, rec.Body.String())
+	}
+	if code, _ := decode[map[string]any](t, rec)["errcode"].(string); code != "M_FORBIDDEN" {
+		t.Errorf("errcode = %q, want M_FORBIDDEN", code)
+	}
+}

server/internal/setup/routes.go

@@ -12,10 +12,12 @@ import (
 //
 // Keep it honest: a version belongs here once the endpoints a client
 // actually uses from it work. Accounts, sessions, devices, profiles,
-// account data and — with Phase 3 — rooms all do. What is still missing is
-// the event stream: /sync returns an empty placeholder and there is no
-// /messages, so a client can create a room and send into it but cannot read
-// its history. The list grows when Phase 4 lands.
+// account data, rooms and — with Phase 4 — the event stream all do, which
+// is enough for a client to be used. What is still missing is end-to-end
+// encryption (Phase 7), media (Phase 6), push (Phase 8) and federation
+// (Phase 5); a client discovers each of those from the endpoint it needs
+// rather than from this list, which is why their absence does not make a
+// version listed here a lie.
 var SpecVersions = []string{"v1.13", "v1.14"}
 
 // UnstableFeatures advertises MSC support. Simplified Sliding Sync

server/internal/setup/server.go

@@ -25,6 +25,7 @@ import (
 	"github.com/dariuszjaniak/warp/server/internal/settings"
 	"github.com/dariuszjaniak/warp/server/internal/storage"
 	_ "github.com/dariuszjaniak/warp/server/internal/storage/drivers" // link in the storage drivers
+	"github.com/dariuszjaniak/warp/server/internal/syncapi"
 	"github.com/dariuszjaniak/warp/server/internal/userapi"
 )
 
@@ -41,6 +42,7 @@ type Server struct {
 
 	users     *userapi.API
 	rooms     *roomserver.API
+	sync      *syncapi.API
 	clientAPI *clientapi.ClientAPI
 	adminAPI  *adminapi.AdminAPI
 
@@ -149,21 +151,48 @@ func New(ctx context.Context, cfg *config.Config, opts Options) (*Server, error)
 	// and the Phase 1 tests start without a key, and then start without
 	// rooms — the C-S room endpoints answer M_UNRECOGNIZED rather than
 	// pretending to work.
+	//
+	// The syncapi comes with it, because a sync is almost entirely room
+	// reads: a server with no rooms has no stream to read, and /sync
+	// answering M_UNRECOGNIZED says so where an empty success would not.
+	//
+	// The notifier is built first and handed to both: it is the
+	// roomserver's emit stage and the syncapi's wake-up, which is exactly
+	// the seam Phase 3 left for this.
 	if s.signingKey != nil {
+		notifier := syncapi.NewNotifier()
+
 		s.rooms, err = roomserver.New(roomserver.Options{
 			ServerName:        cfg.Global.ServerName,
 			Store:             s.db.Rooms(),
 			Profiles:          s.users,
 			SigningKey:        s.signingKey,
 			FederationEnabled: settingsService.FederationEnabled,
+			Notifier:          notifier,
 			Logger:            log,
 		})
 		if err != nil {
 			_ = s.closeDB()
 			return nil, err
 		}
+
+		s.sync, err = syncapi.New(syncapi.Options{
+			ServerName:      cfg.Global.ServerName,
+			Rooms:           s.rooms,
+			Accounts:        s.users,
+			Store:           s.db.Sync(),
+			Notifier:        notifier,
+			PresenceEnabled: cfg.Sync.Presence,
+			TypingTimeout:   cfg.Sync.TypingTimeout,
+			LongPollTimeout: cfg.Sync.LongPollTimeout,
+			Logger:          log,
+		})
+		if err != nil {
+			_ = s.closeDB()
+			return nil, err
+		}
 	} else {
-		log.Warn("started without a signing key: rooms are unavailable")
+		log.Warn("started without a signing key: rooms and /sync are unavailable")
 	}
 
 	s.clientAPI, err = clientapi.New(clientapi.Options{
@@ -171,6 +200,7 @@ func New(ctx context.Context, cfg *config.Config, opts Options) (*Server, error)
 		ClientBaseURL:      cfg.ClientBaseURL(),
 		Users:              s.users,
 		Rooms:              s.rooms,
+		Sync:               s.sync,
 		Settings:           settingsService,
 		Federation:         s.federation,
 		Registration:       cfg.Registration,
@@ -252,6 +282,10 @@ func (s *Server) Users() *userapi.API { return s.users }
 // without a signing key.
 func (s *Server) Rooms() *roomserver.API { return s.rooms }
 
+// Sync exposes the syncapi component, or nil when the server started
+// without a signing key.
+func (s *Server) Sync() *syncapi.API { return s.sync }
+
 // SigningKey returns the server signing key, or nil when it was skipped.
 func (s *Server) SigningKey() *signing.KeyPair { return s.signingKey }
 
@@ -286,6 +320,7 @@ func (s *Server) Run(ctx context.Context) error {
 		"database", s.db.Driver(),
 		"federation", s.settings.FederationEnabled(),
 		"registration", s.settings.RegistrationEnabled(),
+		"presence", s.cfg.Sync.Presence,
 	)
 
 	errCh := make(chan error, 1)
@@ -321,6 +356,11 @@ func (s *Server) Run(ctx context.Context) error {
 
 // Close releases the resources New acquired.
 func (s *Server) Close() error {
+	if s.sync != nil {
+		// The typing tracker holds a timer per typing user; a server
+		// shutting down should not wait for them.
+		s.sync.Close()
+	}
 	return s.closeDB()
 }