Add a `NextBatchStorer` interface to load/save next_batch tokens

Gets around cyclic dependencies.

src/github.com/matrix-org/go-neb/clients/clients.go

@@ -11,6 +11,31 @@ import (
 	"sync"
 )
 
+type nextBatchStore struct {
+	db *database.ServiceDB
+}
+
+func (s nextBatchStore) Save(userID, nextBatch string) {
+	if err := s.db.UpdateNextBatch(userID, nextBatch); err != nil {
+		log.WithFields(log.Fields{
+			log.ErrorKey: err,
+			"user_id":    userID,
+			"next_batch": nextBatch,
+		}).Error("Failed to persist next_batch token")
+	}
+}
+func (s nextBatchStore) Load(userID string) string {
+	token, err := s.db.LoadNextBatch(userID)
+	if err != nil {
+		log.WithFields(log.Fields{
+			log.ErrorKey: err,
+			"user_id":    userID,
+		}).Error("Failed to load next_batch token")
+		return ""
+	}
+	return token
+}
+
 // A Clients is a collection of clients used for bot services.
 type Clients struct {
 	db       *database.ServiceDB
@@ -213,15 +238,7 @@ func (c *Clients) newClient(config types.ClientConfig) (*matrix.Client, error) {
 	}
 
 	client := matrix.NewClient(homeserverURL, config.AccessToken, config.UserID)
-
-	client.OnSaveNextBatch(func(nextBatch string) {
-		if err := c.db.UpdateNextBatch(client.UserID, nextBatch); err != nil {
-			log.WithFields(log.Fields{
-				log.ErrorKey: err,
-				"next_batch": nextBatch,
-			}).Error("Failed to persist next_batch token")
-		}
-	})
+	client.NextBatch = nextBatchStore{c.db}
 
 	// TODO: Check that the access token is valid for the userID by peforming
 	// a request against the server.

src/github.com/matrix-org/go-neb/database/db.go

@@ -85,6 +85,15 @@ func (d *ServiceDB) UpdateNextBatch(userID, nextBatch string) (err error) {
 	return
 }
 
+// LoadNextBatch loads the next_batch token for the given user.
+func (d *ServiceDB) LoadNextBatch(userID string) (nextBatch string, err error) {
+	err = runTransaction(d.db, func(txn *sql.Tx) error {
+		nextBatch, err = selectNextBatchTxn(txn, userID)
+		return err
+	})
+	return
+}
+
 // LoadService loads a service from the database.
 // Returns sql.ErrNoRows if the service isn't in the database.
 func (d *ServiceDB) LoadService(serviceID string) (service types.Service, err error) {

src/github.com/matrix-org/go-neb/database/schema.go

@@ -138,6 +138,19 @@ func updateNextBatchTxn(txn *sql.Tx, userID, nextBatch string) error {
 	return err
 }
 
+const selectNextBatchSQL = `
+SELECT next_batch FROM matrix_clients WHERE user_id = $1
+`
+
+func selectNextBatchTxn(txn *sql.Tx, userID string) (string, error) {
+	var nextBatch string
+	row := txn.QueryRow(selectNextBatchSQL, userID)
+	if err := row.Scan(&nextBatch); err != nil {
+		return "", err
+	}
+	return nextBatch, nil
+}
+
 const selectServiceSQL = `
 SELECT service_type, service_user_id, service_json FROM services
 	WHERE service_id = $1

src/github.com/matrix-org/go-neb/matrix/matrix.go

@@ -31,6 +31,20 @@ var (
 	filterJSON = json.RawMessage(`{"room":{"timeline":{"limit":50}}}`)
 )
 
+// NextBatchStorer controls loading/saving of next_batch tokens for users
+type NextBatchStorer interface {
+	// Save a next_batch token for a given user. Best effort.
+	Save(userID, nextBatch string)
+	// Load a next_batch token for a given user. Return an empty string if no token exists.
+	Load(userID string) string
+}
+
+// noopNextBatchStore does not load or save next_batch tokens.
+type noopNextBatchStore struct{}
+
+func (s noopNextBatchStore) Save(userID, nextBatch string) {}
+func (s noopNextBatchStore) Load(userID string) string     { return "" }
+
 // Client represents a Matrix client.
 type Client struct {
 	HomeserverURL *url.URL
@@ -43,7 +57,7 @@ type Client struct {
 	syncingID     uint32 // Identifies the current Sync. Only one Sync can be active at any given time.
 	httpClient    *http.Client
 	filterID      string
-	nextBatchSaver func(string)
+	NextBatch     NextBatchStorer
 }
 
 func (cli *Client) buildURL(urlPath ...string) string {
@@ -200,9 +214,9 @@ func (cli *Client) Sync() {
 	}
 	cli.filterID = filterID
 	logger.WithField("filter", filterID).Print("Got filter ID")
-	nextToken := ""
+	nextToken := cli.NextBatch.Load(cli.UserID)
 
-	logger.Print("Starting sync")
+	logger.WithField("next_batch", nextToken).Print("Starting sync")
 
 	channel := make(chan syncHTTPResponse, 5)
 
@@ -249,9 +263,7 @@ func (cli *Client) Sync() {
 		// Save the token now *before* passing it through to the worker. This means it's possible
 		// to not process some events, but it means that we won't get constantly stuck processing
 		// a malformed/buggy event which keeps making us panic.
-		if cli.nextBatchSaver != nil {
-			cli.nextBatchSaver(nextToken)
-		}
+		cli.NextBatch.Save(cli.UserID, nextToken)
 
 		if !isFirstSync {
 			channel <- syncResponse
@@ -259,11 +271,6 @@ func (cli *Client) Sync() {
 	}
 }
 
-// OnSaveNextBatch is a function which can save the next_batch token passed to it
-func (cli *Client) OnSaveNextBatch(fn func(string)) {
-	cli.nextBatchSaver = fn
-}
-
 func (cli *Client) incrementSyncingID() uint32 {
 	cli.syncingMutex.Lock()
 	defer cli.syncingMutex.Unlock()
@@ -385,6 +392,7 @@ func NewClient(homeserverURL *url.URL, accessToken string, userID string) *Clien
 		Prefix:        "/_matrix/client/r0",
 	}
 	cli.Worker = newWorker(&cli)
+	cli.NextBatch = noopNextBatchStore{}
 	cli.Rooms = make(map[string]*Room)
 	cli.httpClient = &http.Client{}