Auto-generate username if none provided during registration

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

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

@@ -49,12 +49,16 @@ const selectAccountByLocalpartSQL = "" +
 const selectPasswordHashSQL = "" +
 	"SELECT password_hash FROM account_accounts WHERE localpart = $1"
 
+const selectAllLocalpartSQL = "" +
+	"SELECT localpart FROM account_accounts"
+
 // TODO: Update password
 
 type accountsStatements struct {
 	insertAccountStmt            *sql.Stmt
 	selectAccountByLocalpartStmt *sql.Stmt
 	selectPasswordHashStmt       *sql.Stmt
+	selectAllLocalpartStmt       *sql.Stmt
 	serverName                   gomatrixserverlib.ServerName
 }
 
@@ -72,6 +76,9 @@ func (s *accountsStatements) prepare(db *sql.DB, server gomatrixserverlib.Server
 	if s.selectPasswordHashStmt, err = db.Prepare(selectPasswordHashSQL); err != nil {
 		return
 	}
+	if s.selectAllLocalpartStmt, err = db.Prepare(selectAllLocalpartSQL); err != nil {
+		return
+	}
 	s.serverName = server
 	return
 }
@@ -123,6 +130,31 @@ func (s *accountsStatements) selectAccountByLocalpart(
 	return &acc, err
 }
 
+func (s *accountsStatements) selectAllLocalparts(ctx context.Context) ([]string, error) {
+	var localparts []string
+
+	stmt := s.selectAllLocalpartStmt
+	rows, err := stmt.QueryContext(ctx)
+
+	if err != nil {
+		return nil, err
+	}
+
+	for rows.Next() {
+		var t string
+		err := rows.Scan(&t)
+
+		if err != nil {
+			return nil, err
+		}
+
+		localparts = append(localparts, t)
+	}
+
+	// Ensure that rows is closed in case of error.
+	return localparts, rows.Close()
+}
+
 func makeUserID(localpart string, server gomatrixserverlib.ServerName) string {
 	return fmt.Sprintf("@%s:%s", localpart, string(server))
 }

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

@@ -358,3 +358,10 @@ func (d *Database) CheckAccountAvailability(ctx context.Context, localpart strin
 	}
 	return false, err
 }
+
+// GetAllLocalparts returns an slice header containing all localparts in database.
+// If no records exist it returns an empty slice.
+// Returns an error if something goes wrong.
+func (d *Database) GetAllLocalparts(ctx context.Context) ([]string, error) {
+	return d.accounts.selectAllLocalparts(ctx)
+}

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

@@ -27,6 +27,7 @@ import (
 	"net/url"
 	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -237,6 +238,38 @@ func validateRecaptcha(
 	return nil
 }
 
+// generates username for registration if none provided.
+// Sequentially checks for available username and returns the lowest available one.
+func generateUsername(
+	ctx context.Context, accountDB *accounts.Database, cfg *config.Dendrite,
+) (string, error) {
+	numericLps := make(map[string]bool)
+
+	// re matches localparts with only digits
+	re := regexp.MustCompile(`\A\d+\z`)
+	localparts, err := accountDB.GetAllLocalparts(ctx)
+
+	if err != nil {
+		return "", err
+	}
+
+	for _, lp := range localparts {
+		if re.MatchString(lp) {
+			// Length == 2 implies there is a matched localpart
+			numericLps[lp] = true
+		}
+	}
+
+	for i := 1; ; i++ {
+		lp := strconv.Itoa(i)
+		if _, ok := numericLps[lp]; !ok && !UsernameMatchesExclusiveNamespace(
+			cfg, lp,
+		) {
+			return lp, nil
+		}
+	}
+}
+
 // UsernameIsWithinApplicationServiceNamespace checks to see if a username falls
 // within any of the namespaces of a given Application Service. If no
 // Application Service is given, it will check to see if it matches any
@@ -269,6 +302,17 @@ func UsernameIsWithinApplicationServiceNamespace(
 	return false
 }
 
+// UsernameMatchesExclusiveNamespace will check if a given username matches
+// an exclusive namespace. localpart should not match Application Service namespace.
+func UsernameMatchesExclusiveNamespace(
+	cfg *config.Dendrite,
+	username string,
+) bool {
+	// Check namespaces and see if there's a match
+	matchCount := countMatchingNamespaces(cfg, username)
+	return matchCount > 0
+}
+
 // UsernameMatchesMultipleExclusiveNamespaces will check if a given username matches
 // more than one exclusive namespace. More than one is not allowed
 func UsernameMatchesMultipleExclusiveNamespaces(
@@ -276,6 +320,15 @@ func UsernameMatchesMultipleExclusiveNamespaces(
 	username string,
 ) bool {
 	// Check namespaces and see if more than one match
+	matchCount := countMatchingNamespaces(cfg, username)
+	return matchCount > 1
+}
+
+func countMatchingNamespaces(
+	cfg *config.Dendrite,
+	username string,
+) int {
+	// Check namespaces and count matches
 	matchCount := 0
 	for _, appservice := range cfg.Derived.ApplicationServices {
 		for _, namespaceSlice := range appservice.NamespaceMap {
@@ -287,7 +340,7 @@ func UsernameMatchesMultipleExclusiveNamespaces(
 			}
 		}
 	}
-	return matchCount > 1
+	return matchCount
 }
 
 // validateApplicationService checks if a provided application service token
@@ -361,6 +414,16 @@ func Register(
 		sessionID = util.RandomString(sessionIDLength)
 	}
 
+	// auto generate a numeric username if r.Username empty
+	if r.Username == "" {
+		var err error
+		r.Username, err = generateUsername(req.Context(), accountDB, cfg)
+
+		if err != nil {
+			return jsonerror.InternalServerError()
+		}
+	}
+
 	// If no auth type is specified by the client, send back the list of available flows
 	if r.Auth.Type == "" {
 		return util.JSONResponse{