src/vs/workbench/contrib/remote/browser/tunnelView.ts/validateInput
	function validateInput(remoteExplorerService: IRemoteExplorerService, value: string, canElevate: boolean): { content: string; severity: Severity } | null {
		const parsed = parseAddress(value);
		if (!parsed) {
			return { content: invalidPortString, severity: Severity.Error };
		} else if (parsed.port >= maxPortNumber) {
			return { content: invalidPortNumberString, severity: Severity.Error };
		} else if (canElevate && isPortPrivileged(parsed.port)) {
			return { content: requiresSudoString, severity: Severity.Info };
		} else if (mapHasAddressLocalhostOrAllInterfaces(remoteExplorerService.tunnelModel.forwarded, parsed.host, parsed.port)) {
			return { content: alreadyForwarded, severity: Severity.Error };
		}
		return null;
	}