Virtual hosting schema and logic changes (#2876)

Note that virtual users cannot federate correctly yet.

userapi/storage/sqlite3/deltas/2022110411000001_server_names.go

@@ -0,0 +1,28 @@
+package deltas
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/lib/pq"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// I know what you're thinking: you're wondering "why doesn't this use $1
+// and pass variadic parameters to ExecContext?" — the answer is because
+// PostgreSQL doesn't expect the table name to be specified as a substituted
+// argument in that way so it results in a syntax error in the query.
+
+func UpServerNamesPopulate(ctx context.Context, tx *sql.Tx, serverName gomatrixserverlib.ServerName) error {
+	for _, table := range serverNamesTables {
+		q := fmt.Sprintf(
+			"UPDATE %s SET server_name = %s WHERE server_name = '';",
+			pq.QuoteIdentifier(table), pq.QuoteLiteral(string(serverName)),
+		)
+		if _, err := tx.ExecContext(ctx, q); err != nil {
+			return fmt.Errorf("write server names to %q error: %w", table, err)
+		}
+	}
+	return nil
+}