Auto-generate username if none provided during registration

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

@@ -38,6 +38,8 @@ CREATE TABLE IF NOT EXISTS account_accounts (
     -- TODO:
     -- is_guest, is_admin, upgraded_ts, devices, any email reset stuff?
 );
+-- Create sequence for autogenerated numeric usernames
+CREATE SEQUENCE IF NOT EXISTS numeric_username_seq START 1;
 `
 
 const insertAccountSQL = "" +
@@ -49,13 +51,17 @@ const selectAccountByLocalpartSQL = "" +
 const selectPasswordHashSQL = "" +
 	"SELECT password_hash FROM account_accounts WHERE localpart = $1"
 
+const selectNewNumericLocalpartSQL = "" +
+	"SELECT nextval('numeric_username_seq')"
+
 // TODO: Update password
 
 type accountsStatements struct {
-	insertAccountStmt            *sql.Stmt
-	selectAccountByLocalpartStmt *sql.Stmt
-	selectPasswordHashStmt       *sql.Stmt
-	serverName                   gomatrixserverlib.ServerName
+	insertAccountStmt             *sql.Stmt
+	selectAccountByLocalpartStmt  *sql.Stmt
+	selectPasswordHashStmt        *sql.Stmt
+	selectNewNumericLocalpartStmt *sql.Stmt
+	serverName                    gomatrixserverlib.ServerName
 }
 
 func (s *accountsStatements) prepare(db *sql.DB, server gomatrixserverlib.ServerName) (err error) {
@@ -72,6 +78,9 @@ func (s *accountsStatements) prepare(db *sql.DB, server gomatrixserverlib.Server
 	if s.selectPasswordHashStmt, err = db.Prepare(selectPasswordHashSQL); err != nil {
 		return
 	}
+	if s.selectNewNumericLocalpartStmt, err = db.Prepare(selectNewNumericLocalpartSQL); err != nil {
+		return
+	}
 	s.serverName = server
 	return
 }
@@ -121,3 +130,10 @@ func (s *accountsStatements) selectAccountByLocalpart(
 	}
 	return
 }
+
+func (s *accountsStatements) selectNewNumericLocalpart(
+	ctx context.Context,
+) (id int64, err error) {
+	err = s.selectNewNumericLocalpartStmt.QueryRowContext(ctx).Scan(&id)
+	return
+}

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

@@ -267,6 +267,13 @@ func (d *Database) GetAccountDataByType(
 	)
 }
 
+// GetNewNumericLocalpart generates and returns a new unused numeric localpart
+func (d *Database) GetNewNumericLocalpart(
+	ctx context.Context,
+) (int64, error) {
+	return d.accounts.selectNewNumericLocalpart(ctx)
+}
+
 func hashPassword(plaintext string) (hash string, err error) {
 	hashBytes, err := bcrypt.GenerateFromPassword([]byte(plaintext), bcrypt.DefaultCost)
 	return string(hashBytes), err

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

@@ -27,6 +27,7 @@ import (
 	"net/url"
 	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -403,6 +404,23 @@ func Register(
 		sessionID = util.RandomString(sessionIDLength)
 	}
 
+	// Don't allow numeric usernames less than MAX_INT64.
+	if _, err := strconv.ParseInt(r.Username, 10, 64); err == nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.InvalidUsername("Numeric user IDs are reserved"),
+		}
+	}
+	// Auto generate a numeric username if r.Username is empty
+	if r.Username == "" {
+		id, err := accountDB.GetNewNumericLocalpart(req.Context())
+		if err != nil {
+			return httputil.LogThenError(req, err)
+		}
+
+		r.Username = strconv.FormatInt(id, 10)
+	}
+
 	// If no auth type is specified by the client, send back the list of available flows
 	if r.Auth.Type == "" {
 		return util.JSONResponse{