Sync refactor — Part 1 (#1688)

* It's half-alive

* Wakeups largely working

* Other tweaks, typing works

* Fix bugs, add receipt stream

* Delete notifier, other tweaks

* Dedupe a bit, add a template for the invite stream

* Clean up, add templates for other streams

* Don't leak channels

* Bring forward some more PDU logic, clean up other places

* Add some more wakeups

* Use addRoomDeltaToResponse

* Log tweaks, typing fixed?

* Fix timed out syncs

* Don't reset next batch position on timeout

* Add account data stream/position

* End of day

* Fix complete sync for receipt, typing

* Streams package

* Clean up a bit

* Complete sync send-to-device

* Don't drop errors

* More lightweight notifications

* Fix typing positions

* Don't advance position on remove again unless needed

* Device list updates

* Advance account data position

* Use limit for incremental sync

* Limit fixes, amongst other things

* Remove some fmt.Println

* Tweaks

* Re-add notifier

* Fix invite position

* Fixes

* Notify account data without advancing PDU position in notifier

* Apply account data position

* Get initial position for account data

* Fix position update

* Fix complete sync positions

* Review comments @Kegsay

* Room consumer parameters

syncapi/types/provider.go

@@ -0,0 +1,53 @@
+package types
+
+import (
+	"context"
+	"time"
+
+	userapi "github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+)
+
+type SyncRequest struct {
+	Context       context.Context
+	Log           *logrus.Entry
+	Device        *userapi.Device
+	Response      *Response
+	Filter        gomatrixserverlib.EventFilter
+	Since         StreamingToken
+	Limit         int
+	Timeout       time.Duration
+	WantFullState bool
+
+	// Updated by the PDU stream.
+	Rooms map[string]string
+}
+
+type StreamProvider interface {
+	Setup()
+
+	// Advance will update the latest position of the stream based on
+	// an update and will wake callers waiting on StreamNotifyAfter.
+	Advance(latest StreamPosition)
+
+	// CompleteSync will update the response to include all updates as needed
+	// for a complete sync. It will always return immediately.
+	CompleteSync(ctx context.Context, req *SyncRequest) StreamPosition
+
+	// IncrementalSync will update the response to include all updates between
+	// the from and to sync positions. It will always return immediately,
+	// making no changes if the range contains no updates.
+	IncrementalSync(ctx context.Context, req *SyncRequest, from, to StreamPosition) StreamPosition
+
+	// LatestPosition returns the latest stream position for this stream.
+	LatestPosition(ctx context.Context) StreamPosition
+}
+
+type PartitionedStreamProvider interface {
+	Setup()
+	Advance(latest LogPosition)
+	CompleteSync(ctx context.Context, req *SyncRequest) LogPosition
+	IncrementalSync(ctx context.Context, req *SyncRequest, from, to LogPosition) LogPosition
+	LatestPosition(ctx context.Context) LogPosition
+}