Generate smaller device IDs

src/github.com/matrix-org/dendrite/clientapi/auth/auth.go

@@ -40,6 +40,9 @@ var UnknownDeviceID = "unknown-device"
 // 32 bytes => 256 bits
 var tokenByteLength = 32
 
+// The length of generated device IDs
+var deviceIDByteLength = 8
+
 // DeviceDatabase represents a device database.
 type DeviceDatabase interface {
 	// Look up the device matching the given access token.
@@ -89,7 +92,7 @@ func GenerateAccessToken() (string, error) {
 // GenerateDeviceID creates a new device id. Returns an error if failed to generate
 // random bytes.
 func GenerateDeviceID() (string, error) {
-	b := make([]byte, tokenByteLength)
+	b := make([]byte, deviceIDByteLength)
 	_, err := rand.Read(b)
 	if err != nil {
 		return "", err

src/github.com/matrix-org/dendrite/clientapi/auth/storage/devices/storage.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"database/sql"
 
+	"github.com/matrix-org/dendrite/clientapi/auth"
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
 	"github.com/matrix-org/dendrite/common"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -55,20 +56,42 @@ func (d *Database) GetDeviceByAccessToken(
 // If there is already a device with the same device ID for this user, that access token will be revoked
 // and replaced with the given accessToken. If the given accessToken is already in use for another device,
 // an error will be returned.
+// If no device ID is given one is generated.
 // Returns the device on success.
 func (d *Database) CreateDevice(
-	ctx context.Context, localpart, deviceID, accessToken string,
+	ctx context.Context, localpart string, deviceID *string, accessToken string,
 ) (dev *authtypes.Device, returnErr error) {
-	returnErr = common.WithTransaction(d.db, func(txn *sql.Tx) error {
-		var err error
-		// Revoke existing token for this device
-		if err = d.devices.deleteDevice(ctx, txn, deviceID, localpart); err != nil {
-			return err
-		}
+	if deviceID != nil {
+		returnErr = common.WithTransaction(d.db, func(txn *sql.Tx) error {
+			var err error
+			// Revoke existing token for this device
+			if err = d.devices.deleteDevice(ctx, txn, *deviceID, localpart); err != nil {
+				return err
+			}
 
-		dev, err = d.devices.insertDevice(ctx, txn, deviceID, localpart, accessToken)
-		return err
-	})
+			dev, err = d.devices.insertDevice(ctx, txn, *deviceID, localpart, accessToken)
+			return err
+		})
+	} else {
+		// We generate device IDs in a loop in case its already taken.
+		// We cap this at going round 5 times to ensure we don't spin forever
+		var newDeviceID string
+		for i := 1; i <= 5; i++ {
+			newDeviceID, returnErr = auth.GenerateDeviceID()
+			if returnErr != nil {
+				return
+			}
+
+			returnErr = common.WithTransaction(d.db, func(txn *sql.Tx) error {
+				var err error
+				dev, err = d.devices.insertDevice(ctx, txn, newDeviceID, localpart, accessToken)
+				return err
+			})
+			if returnErr == nil {
+				return
+			}
+		}
+	}
 	return
 }
 

src/github.com/matrix-org/dendrite/clientapi/readers/login.go

@@ -117,14 +117,9 @@ func Login(
 			httputil.LogThenError(req, err)
 		}
 
-		deviceID, err := auth.GenerateDeviceID()
-		if err != nil {
-			httputil.LogThenError(req, err)
-		}
-
 		// TODO: Use the device ID in the request
 		dev, err := deviceDB.CreateDevice(
-			req.Context(), acc.Localpart, deviceID, token,
+			req.Context(), acc.Localpart, nil, token,
 		)
 		if err != nil {
 			return util.JSONResponse{
@@ -139,7 +134,7 @@ func Login(
 				UserID:      dev.UserID,
 				AccessToken: dev.AccessToken,
 				HomeServer:  cfg.Matrix.ServerName,
-				DeviceID:    deviceID,
+				DeviceID:    dev.ID,
 			},
 		}
 	}

src/github.com/matrix-org/dendrite/clientapi/writers/register.go

@@ -290,7 +290,7 @@ func completeRegistration(
 	}
 
 	// // TODO: Use the device ID in the request.
-	dev, err := deviceDB.CreateDevice(ctx, username, auth.UnknownDeviceID, token)
+	dev, err := deviceDB.CreateDevice(ctx, username, nil, token)
 	if err != nil {
 		return util.JSONResponse{
 			Code: 500,

src/github.com/matrix-org/dendrite/cmd/create-account/main.go

@@ -87,7 +87,7 @@ func main() {
 	}
 
 	device, err := deviceDB.CreateDevice(
-		context.Background(), *username, "create-account-script", *accessToken,
+		context.Background(), *username, nil, *accessToken,
 	)
 	if err != nil {
 		fmt.Println(err.Error())