dendrite/src/github.com/matrix-org/dendrite/syncserver/sync/requestpool.go

package sync

import (
	"net/http"
	"strconv"
	"sync"
	"time"

	log "github.com/Sirupsen/logrus"
	"github.com/matrix-org/dendrite/clientapi/auth"
	"github.com/matrix-org/dendrite/clientapi/httputil"
	"github.com/matrix-org/dendrite/clientapi/jsonerror"
	"github.com/matrix-org/dendrite/syncserver/storage"
	"github.com/matrix-org/dendrite/syncserver/types"
	"github.com/matrix-org/gomatrixserverlib"
	"github.com/matrix-org/util"
)

const defaultSyncTimeout = time.Duration(30) * time.Second

type syncRequest struct {
	userID        string
	timeout       time.Duration
	since         types.StreamPosition
	wantFullState bool
}

// RequestPool manages HTTP long-poll connections for /sync
type RequestPool struct {
	db *storage.SyncServerDatabase
	// The latest sync stream position: guarded by 'cond'.
	currPos types.StreamPosition
	// A condition variable to notify all waiting goroutines of a new sync stream position
	cond *sync.Cond
}

// NewRequestPool makes a new RequestPool
func NewRequestPool(db *storage.SyncServerDatabase) (*RequestPool, error) {
	pos, err := db.SyncStreamPosition()
	if err != nil {
		return nil, err
	}
	return &RequestPool{db, types.StreamPosition(pos), sync.NewCond(&sync.Mutex{})}, nil
}

// OnIncomingSyncRequest is called when a client makes a /sync request. This function MUST be
// called in a dedicated goroutine for this request. This function will block the goroutine
// until a response is ready, or it times out.
func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request) util.JSONResponse {
	// Extract values from request
	logger := util.GetLogger(req.Context())
	userID, resErr := auth.VerifyAccessToken(req)
	if resErr != nil {
		return *resErr
	}
	since, err := getSyncStreamPosition(req.URL.Query().Get("since"))
	if err != nil {
		return util.JSONResponse{
			Code: 400,
			JSON: jsonerror.Unknown(err.Error()),
		}
	}
	timeout := getTimeout(req.URL.Query().Get("timeout"))
	fullState := req.URL.Query().Get("full_state")
	wantFullState := fullState != "" && fullState != "false"
	// TODO: Additional query params: set_presence, filter
	syncReq := syncRequest{
		userID:        userID,
		timeout:       timeout,
		since:         since,
		wantFullState: wantFullState,
	}
	logger.WithFields(log.Fields{
		"userID":  userID,
		"since":   since,
		"timeout": timeout,
	}).Info("Incoming /sync request")

	// Fork off 2 goroutines: one to do the work, and one to serve as a timeout.
	// Whichever returns first is the one we will serve back to the client.
	// TODO: Currently this means that cpu work is timed, which may not be what we want long term.
	timeoutChan := make(chan struct{})
	timer := time.AfterFunc(timeout, func() {
		close(timeoutChan) // signal that the timeout has expired
	})

	done := make(chan util.JSONResponse)
	go func() {
		syncData, err := rp.currentSyncForUser(syncReq)
		timer.Stop()
		var res util.JSONResponse
		if err != nil {
			res = httputil.LogThenError(req, err)
		} else {
			res = util.JSONResponse{
				Code: 200,
				JSON: syncData,
			}
		}
		done <- res
		close(done)
	}()

	select {
	case <-timeoutChan: // timeout fired
		return util.JSONResponse{
			Code: 200,
			JSON: []struct{}{}, // return empty array for now
		}
	case res := <-done: // received a response
		return res
	}
}

// OnNewEvent is called when a new event is received from the room server. Must only be
// called from a single goroutine, to avoid races between updates which could set the
// current position in the stream incorrectly.
func (rp *RequestPool) OnNewEvent(ev *gomatrixserverlib.Event, pos types.StreamPosition) {
	// update the current position in a guard and then notify all /sync streams
	rp.cond.L.Lock()
	rp.currPos = pos
	rp.cond.L.Unlock()

	rp.cond.Broadcast() // notify ALL waiting goroutines
}

func (rp *RequestPool) waitForEvents(req syncRequest) types.StreamPosition {
	// In a guard, check if the /sync request should block, and block it until we get a new position
	rp.cond.L.Lock()
	currentPos := rp.currPos
	for req.since == currentPos {
		// we need to wait for a new event.
		// TODO: This waits for ANY new event, we need to only wait for events which we care about.
		rp.cond.Wait() // atomically unlocks and blocks goroutine, then re-acquires lock on unblock
		currentPos = rp.currPos
	}
	rp.cond.L.Unlock()
	return currentPos
}

func (rp *RequestPool) currentSyncForUser(req syncRequest) (*types.Response, error) {
	currentPos := rp.waitForEvents(req)

	// TODO: handle ignored users

	// TODO: Implement https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L821
	// 1) Get the CURRENT joined room list for this user
	// 2) Get membership list changes for this user between the provided stream position and now.
	// 3) For each room which has membership list changes:
	//   a) Check if the room is 'newly joined' (insufficient to just check for a join event because we allow dupe joins).
	//      If it is, then we need to send the full room state down (and 'limited' is always true).
	//   b) Check if user is still CURRENTLY invited to the room. If so, add room to 'invited' block.
	//   c) Check if the user is CURRENTLY left/banned. If so, add room to 'archived' block. // Synapse has a TODO: How do we handle ban -> leave in same batch?
	// 4) Add joined rooms (joined room list)

	events, err := rp.db.EventsInRange(req.since, currentPos)
	if err != nil {
		return nil, err
	}

	res := types.NewResponse()
	// for now, dump everything as join timeline events
	for _, ev := range events {
		roomData := res.Rooms.Join[ev.RoomID()]
		roomData.Timeline.Events = append(roomData.Timeline.Events, ev)
		res.Rooms.Join[ev.RoomID()] = roomData
	}

	// Make sure we send the next_batch as a string. We don't want to confuse clients by sending this
	// as an integer even though (at the moment) it is.
	res.NextBatch = currentPos.String()
	return res, nil
}

func getTimeout(timeoutMS string) time.Duration {
	if timeoutMS == "" {
		return defaultSyncTimeout
	}
	i, err := strconv.Atoi(timeoutMS)
	if err != nil {
		return defaultSyncTimeout
	}
	return time.Duration(i) * time.Millisecond
}

func getSyncStreamPosition(since string) (types.StreamPosition, error) {
	if since == "" {
		return types.StreamPosition(0), nil
	}
	i, err := strconv.Atoi(since)
	if err != nil {
		return types.StreamPosition(0), err
	}
	return types.StreamPosition(i), nil
}