Correctly create new device when device_id is passed to /login (#753)

Fixes https://github.com/matrix-org/dendrite/issues/401

Currently when passing a `device_id` parameter to `/login`, which is [supposed](https://matrix.org/docs/spec/client_server/unstable#post-matrix-client-r0-login) to return a device with that ID set, it instead just generates a random `device_id` and hands that back to you.

The code was already there to do this correctly, it looks like it had just been broken during some change. Hopefully sytest will prevent this from becoming broken again.

clientapi/auth/storage/devices/devices_table.go

@@ -169,6 +169,8 @@ func (s *devicesStatements) selectDeviceByToken(
 	return &dev, err
 }
 
+// selectDeviceByID retrieves a device from the database with the given user
+// localpart and deviceID
 func (s *devicesStatements) selectDeviceByID(
 	ctx context.Context, localpart, deviceID string,
 ) (*authtypes.Device, error) {

clientapi/auth/storage/devices/storage.go

@@ -84,7 +84,7 @@ func (d *Database) CreateDevice(
 	if deviceID != nil {
 		returnErr = common.WithTransaction(d.db, func(txn *sql.Tx) error {
 			var err error
-			// Revoke existing token for this device
+			// Revoke existing tokens for this device
 			if err = d.devices.deleteDevice(ctx, txn, *deviceID, localpart); err != nil {
 				return err
 			}

clientapi/routing/login.go

@@ -18,7 +18,6 @@ import (
 	"net/http"
 
 	"context"
-	"database/sql"
 
 	"github.com/matrix-org/dendrite/clientapi/auth"
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
@@ -44,8 +43,10 @@ type flow struct {
 type passwordRequest struct {
 	User     string `json:"user"`
 	Password string `json:"password"`
+	// Both DeviceID and InitialDisplayName can be omitted, or empty strings ("")
+	// Thus a pointer is needed to differentiate between the two
 	InitialDisplayName *string `json:"initial_device_display_name"`
-	DeviceID           string  `json:"device_id"`
+	DeviceID           *string `json:"device_id"`
 }
 
 type loginResponse struct {
@@ -110,7 +111,7 @@ func Login(
 			return httputil.LogThenError(req, err)
 		}
 
-		dev, err := getDevice(req.Context(), r, deviceDB, acc, localpart, token)
+		dev, err := getDevice(req.Context(), r, deviceDB, acc, token)
 		if err != nil {
 			return util.JSONResponse{
 				Code: http.StatusInternalServerError,
@@ -134,20 +135,16 @@ func Login(
 	}
 }
 
-// check if device exists else create one
+// getDevice returns a new or existing device
 func getDevice(
 	ctx context.Context,
 	r passwordRequest,
 	deviceDB *devices.Database,
 	acc *authtypes.Account,
-	localpart, token string,
+	token string,
 ) (dev *authtypes.Device, err error) {
-	dev, err = deviceDB.GetDeviceByID(ctx, localpart, r.DeviceID)
-	if err == sql.ErrNoRows {
-		// device doesn't exist, create one
 	dev, err = deviceDB.CreateDevice(
-			ctx, acc.Localpart, nil, token, r.InitialDisplayName,
+		ctx, acc.Localpart, r.DeviceID, token, r.InitialDisplayName,
 	)
-	}
 	return
 }

clientapi/routing/register.go

@@ -121,7 +121,10 @@ type registerRequest struct {
 	// user-interactive auth params
 	Auth authDict `json:"auth"`
 
+	// Both DeviceID and InitialDisplayName can be omitted, or empty strings ("")
+	// Thus a pointer is needed to differentiate between the two
 	InitialDisplayName *string `json:"initial_device_display_name"`
+	DeviceID           *string `json:"device_id"`
 
 	// Prevent this user from logging in
 	InhibitLogin common.WeakBoolean `json:"inhibit_login"`
@@ -626,7 +629,7 @@ func handleApplicationServiceRegistration(
 	// application service registration is entirely separate.
 	return completeRegistration(
 		req.Context(), accountDB, deviceDB, r.Username, "", appserviceID,
-		r.InhibitLogin, r.InitialDisplayName,
+		r.InhibitLogin, r.InitialDisplayName, r.DeviceID,
 	)
 }
 
@@ -646,7 +649,7 @@ func checkAndCompleteFlow(
 		// This flow was completed, registration can continue
 		return completeRegistration(
 			req.Context(), accountDB, deviceDB, r.Username, r.Password, "",
-			r.InhibitLogin, r.InitialDisplayName,
+			r.InhibitLogin, r.InitialDisplayName, r.DeviceID,
 		)
 	}
 
@@ -697,10 +700,10 @@ func LegacyRegister(
 			return util.MessageResponse(http.StatusForbidden, "HMAC incorrect")
 		}
 
-		return completeRegistration(req.Context(), accountDB, deviceDB, r.Username, r.Password, "", false, nil)
+		return completeRegistration(req.Context(), accountDB, deviceDB, r.Username, r.Password, "", false, nil, nil)
 	case authtypes.LoginTypeDummy:
 		// there is nothing to do
-		return completeRegistration(req.Context(), accountDB, deviceDB, r.Username, r.Password, "", false, nil)
+		return completeRegistration(req.Context(), accountDB, deviceDB, r.Username, r.Password, "", false, nil, nil)
 	default:
 		return util.JSONResponse{
 			Code: http.StatusNotImplemented,
@@ -738,13 +741,19 @@ func parseAndValidateLegacyLogin(req *http.Request, r *legacyRegisterRequest) *u
 	return nil
 }
 
+// completeRegistration runs some rudimentary checks against the submitted
+// input, then if successful creates an account and a newly associated device
+// We pass in each individual part of the request here instead of just passing a
+// registerRequest, as this function serves requests encoded as both
+// registerRequests and legacyRegisterRequests, which share some attributes but
+// not all
 func completeRegistration(
 	ctx context.Context,
 	accountDB *accounts.Database,
 	deviceDB *devices.Database,
 	username, password, appserviceID string,
 	inhibitLogin common.WeakBoolean,
-	displayName *string,
+	displayName, deviceID *string,
 ) util.JSONResponse {
 	if username == "" {
 		return util.JSONResponse{
@@ -773,6 +782,9 @@ func completeRegistration(
 		}
 	}
 
+	// Increment prometheus counter for created users
+	amtRegUsers.Inc()
+
 	// Check whether inhibit_login option is set. If so, don't create an access
 	// token or a device for this user
 	if inhibitLogin {
@@ -793,8 +805,7 @@ func completeRegistration(
 		}
 	}
 
-	// TODO: Use the device ID in the request.
-	dev, err := deviceDB.CreateDevice(ctx, username, nil, token, displayName)
+	dev, err := deviceDB.CreateDevice(ctx, username, deviceID, token, displayName)
 	if err != nil {
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
@@ -802,9 +813,6 @@ func completeRegistration(
 		}
 	}
 
-	// Increment prometheus counter for created users
-	amtRegUsers.Inc()
-
 	return util.JSONResponse{
 		Code: http.StatusOK,
 		JSON: registerResponse{

testfile

@@ -149,3 +149,5 @@ Typing events appear in incremental sync
 Typing events appear in gapped sync
 Inbound federation of state requires event_id as a mandatory paramater
 Inbound federation of state_ids requires event_id as a mandatory paramater
+POST /register returns the same device_id as that in the request
+POST /login returns the same device_id as that in the request