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/storage/sqlstore/timeline.go

@@ -0,0 +1,331 @@
+package sqlstore
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+
+	"github.com/dariuszjaniak/warp/server/internal/storage"
+)
+
+// The stream reads of the room store: the queries the sync API and
+// /messages are built on.
+//
+// They live apart from the rest of the room store because they are the only
+// queries in it that are about *order* rather than about identity. Every
+// other read answers "what is the state of this room" or "what is this
+// event"; these answer "what happened between here and there", which is a
+// different access pattern and the one the (room_id, stream_ordering) index
+// exists for.
+
+const selectMaxStreamOrderingSQL = `
+	SELECT COALESCE(MAX(stream_ordering), 0) FROM roomserver_events`
+
+// MaxStreamOrdering implements storage.RoomStore.
+//
+// It reads the events table rather than the counter in
+// roomserver_sequences. The counter is advanced inside the writing
+// transaction and is therefore already at the new value while that
+// transaction is still open; a sync token taken from it would name a
+// position whose event no reader can see yet, and the event would be
+// skipped for good once the transaction committed.
+func (s *Rooms) MaxStreamOrdering(ctx context.Context) (int64, error) {
+	var top int64
+	if err := s.db.QueryRowContext(ctx, s.q(selectMaxStreamOrderingSQL)).Scan(&top); err != nil {
+		return 0, fmt.Errorf("read the top of the event stream: %w", err)
+	}
+	return top, nil
+}
+
+// MembershipsForUser implements storage.RoomStore.
+func (s *Rooms) MembershipsForUser(ctx context.Context, userID string, memberships []string) ([]storage.SyncMembership, error) {
+	query := `
+		SELECT cs.room_id, cs.membership, cs.event_id, e.stream_ordering
+		FROM roomserver_current_state cs
+		JOIN roomserver_events e ON e.event_id = cs.event_id
+		WHERE cs.event_type = 'm.room.member' AND cs.state_key = ?`
+	args := []any{userID}
+	if len(memberships) > 0 {
+		query += ` AND cs.membership IN (` + placeholders(len(memberships)) + `)`
+		for _, m := range memberships {
+			args = append(args, m)
+		}
+	}
+	query += ` ORDER BY cs.room_id`
+
+	rows, err := s.db.QueryContext(ctx, s.q(query), args...)
+	if err != nil {
+		return nil, fmt.Errorf("read the memberships of %q: %w", userID, err)
+	}
+	defer func() { _ = rows.Close() }()
+
+	var out []storage.SyncMembership
+	for rows.Next() {
+		var m storage.SyncMembership
+		if err := rows.Scan(&m.RoomID, &m.Membership, &m.EventID, &m.StreamOrdering); err != nil {
+			return nil, fmt.Errorf("read the memberships of %q: %w", userID, err)
+		}
+		out = append(out, m)
+	}
+	return out, rows.Err()
+}
+
+var selectUserMembershipEventsSQL = `
+	SELECT ` + eventColumns + `
+	FROM roomserver_events e
+	WHERE e.room_id = ? AND e.event_type = 'm.room.member' AND e.state_key = ?
+	ORDER BY e.stream_ordering`
+
+// UserMembershipEvents implements storage.RoomStore.
+func (s *Rooms) UserMembershipEvents(ctx context.Context, roomID, userID string) ([]storage.StoredEvent, error) {
+	rows, err := s.db.QueryContext(ctx, s.q(selectUserMembershipEventsSQL), roomID, userID)
+	if err != nil {
+		return nil, fmt.Errorf("read the membership events of %q in %q: %w", userID, roomID, err)
+	}
+	events, err := scanEvents(rows)
+	if err != nil {
+		return nil, fmt.Errorf("read the membership events of %q in %q: %w", userID, roomID, err)
+	}
+	return events, nil
+}
+
+// Timeline implements storage.RoomStore.
+func (s *Rooms) Timeline(ctx context.Context, req storage.TimelineRequest) ([]storage.StoredEvent, error) {
+	if req.Limit <= 0 {
+		return nil, nil
+	}
+
+	conditions := []string{`e.room_id = ?`}
+	args := []any{req.RoomID}
+	if req.Low > 0 {
+		conditions = append(conditions, `e.stream_ordering > ?`)
+		args = append(args, req.Low)
+	}
+	if req.High > 0 {
+		conditions = append(conditions, `e.stream_ordering <= ?`)
+		args = append(args, req.High)
+	}
+
+	// The order decides which end the LIMIT trims: reading backwards keeps
+	// the newest of the window, which is what a timeline is.
+	order := `ASC`
+	if req.Direction == storage.DirectionBackward {
+		order = `DESC`
+	}
+
+	if clause, filterArgs := filterConditions(req.Filter); clause != "" {
+		conditions = append(conditions, clause)
+		args = append(args, filterArgs...)
+	}
+	args = append(args, req.Limit)
+
+	query := `SELECT ` + eventColumns + `
+		FROM roomserver_events e
+		WHERE ` + strings.Join(conditions, " AND ") + `
+		ORDER BY e.stream_ordering ` + order + `
+		LIMIT ?`
+
+	rows, err := s.db.QueryContext(ctx, s.q(query), args...)
+	if err != nil {
+		return nil, fmt.Errorf("read the timeline of %q: %w", req.RoomID, err)
+	}
+	events, err := scanEvents(rows)
+	if err != nil {
+		return nil, fmt.Errorf("read the timeline of %q: %w", req.RoomID, err)
+	}
+	return events, nil
+}
+
+// filterConditions renders the part of an event filter the store applies in
+// SQL, as a WHERE fragment and its arguments.
+//
+// The exclusions are ANDed in after the inclusions, which is what makes
+// not_types win over types for an event matching both — the behaviour the
+// spec requires.
+func filterConditions(f storage.TimelineFilter) (string, []any) {
+	var (
+		clauses []string
+		args    []any
+	)
+	add := func(column string, patterns []string, negate bool) {
+		if len(patterns) == 0 {
+			return
+		}
+		clause, clauseArgs := patternMatch(column, patterns)
+		if negate {
+			clause = `NOT (` + clause + `)`
+		}
+		clauses = append(clauses, clause)
+		args = append(args, clauseArgs...)
+	}
+	add(`e.event_type`, f.Types, false)
+	add(`e.event_type`, f.NotTypes, true)
+	add(`e.sender`, f.Senders, false)
+	add(`e.sender`, f.NotSenders, true)
+
+	if len(clauses) == 0 {
+		return "", nil
+	}
+	return strings.Join(clauses, " AND "), args
+}
+
+// patternMatch renders "this column matches any of these patterns".
+//
+// A filter pattern may end in '*', which the spec defines as matching any
+// suffix — "m.room.*" is how a client asks for every room event type. Exact
+// patterns go into one IN list so that the common case is a single indexed
+// lookup; a wildcard becomes a LIKE with an explicit escape character, so
+// that a '%' or '_' inside the pattern is matched literally rather than
+// being read as a LIKE wildcard of its own.
+func patternMatch(column string, patterns []string) (string, []any) {
+	var (
+		exact    []string
+		wildcard []string
+		args     []any
+	)
+	for _, p := range patterns {
+		if prefix, isWildcard := strings.CutSuffix(p, "*"); isWildcard {
+			wildcard = append(wildcard, prefix)
+			continue
+		}
+		exact = append(exact, p)
+	}
+
+	var parts []string
+	if len(exact) > 0 {
+		parts = append(parts, column+` IN (`+placeholders(len(exact))+`)`)
+		for _, p := range exact {
+			args = append(args, p)
+		}
+	}
+	for _, prefix := range wildcard {
+		parts = append(parts, column+` LIKE ? ESCAPE '\'`)
+		args = append(args, escapeLike(prefix)+`%`)
+	}
+	return strings.Join(parts, " OR "), args
+}
+
+// escapeLike makes a literal string safe to embed in a LIKE pattern that
+// declares '\' as its escape character.
+func escapeLike(s string) string {
+	var b strings.Builder
+	b.Grow(len(s))
+	for _, r := range s {
+		if r == '\\' || r == '%' || r == '_' {
+			b.WriteRune('\\')
+		}
+		b.WriteRune(r)
+	}
+	return b.String()
+}
+
+// RoomsWithEvents implements storage.RoomStore.
+func (s *Rooms) RoomsWithEvents(ctx context.Context, roomIDs []string, from, to int64) ([]string, error) {
+	if len(roomIDs) == 0 {
+		return nil, nil
+	}
+
+	query := `
+		SELECT DISTINCT room_id FROM roomserver_events
+		WHERE room_id IN (` + placeholders(len(roomIDs)) + `) AND stream_ordering > ?`
+	args := make([]any, 0, len(roomIDs)+2)
+	for _, id := range roomIDs {
+		args = append(args, id)
+	}
+	args = append(args, from)
+	if to > 0 {
+		query += ` AND stream_ordering <= ?`
+		args = append(args, to)
+	}
+	query += ` ORDER BY room_id`
+
+	rows, err := s.db.QueryContext(ctx, s.q(query), args...)
+	if err != nil {
+		return nil, fmt.Errorf("find the rooms with events after %d: %w", from, err)
+	}
+	defer func() { _ = rows.Close() }()
+
+	var out []string
+	for rows.Next() {
+		var roomID string
+		if err := rows.Scan(&roomID); err != nil {
+			return nil, fmt.Errorf("find the rooms with events after %d: %w", from, err)
+		}
+		out = append(out, roomID)
+	}
+	return out, rows.Err()
+}
+
+const selectEventAtStreamSQL = `
+	SELECT e.event_id, e.event_type, e.state_key, e.state_before_id
+	FROM roomserver_events e
+	WHERE e.room_id = ? AND e.stream_ordering <= ?
+	ORDER BY e.stream_ordering DESC
+	LIMIT 1`
+
+const selectSnapshotEntriesSQL = `
+	SELECT se.event_type, se.state_key, se.event_id, ''
+	FROM roomserver_state_entries se
+	WHERE se.snapshot_id = ?
+	ORDER BY se.event_type, se.state_key`
+
+// StateAtStream implements storage.RoomStore.
+//
+// The state after a position is the snapshot recorded against the last
+// event at or before it, plus that event itself when it is a state event:
+// the snapshot is the state the event was authorised against, which is the
+// state *before* it.
+func (s *Rooms) StateAtStream(ctx context.Context, roomID string, pos int64) ([]storage.StateEntry, error) {
+	if pos <= 0 {
+		return nil, nil
+	}
+
+	var (
+		eventID    string
+		eventType  string
+		stateKey   sql.NullString
+		snapshotID int64
+	)
+	err := s.db.QueryRowContext(ctx, s.q(selectEventAtStreamSQL), roomID, pos).
+		Scan(&eventID, &eventType, &stateKey, &snapshotID)
+	switch {
+	case errors.Is(err, sql.ErrNoRows):
+		// Nothing had happened in the room by then, which for a position
+		// before its create event is the honest answer.
+		return nil, nil
+	case err != nil:
+		return nil, fmt.Errorf("read the state of %q at %d: %w", roomID, pos, err)
+	}
+
+	var entries []storage.StateEntry
+	if snapshotID != 0 {
+		rows, qErr := s.db.QueryContext(ctx, s.q(selectSnapshotEntriesSQL), snapshotID)
+		if qErr != nil {
+			return nil, fmt.Errorf("read the state of %q at %d: %w", roomID, pos, qErr)
+		}
+		if entries, err = scanStateEntries(rows); err != nil {
+			return nil, fmt.Errorf("read the state of %q at %d: %w", roomID, pos, err)
+		}
+	}
+	if stateKey.Valid {
+		entries = upsertStateEntry(entries, storage.StateEntry{
+			Type:     eventType,
+			StateKey: stateKey.String,
+			EventID:  eventID,
+		})
+	}
+	return entries, nil
+}
+
+// upsertStateEntry replaces the matching tuple in entries, or appends it.
+func upsertStateEntry(entries []storage.StateEntry, entry storage.StateEntry) []storage.StateEntry {
+	for i, existing := range entries {
+		if existing.Type == entry.Type && existing.StateKey == entry.StateKey {
+			entries[i] = entry
+			return entries
+		}
+	}
+	return append(entries, entry)
+}