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unpack('N', substr($data, 0, 4))[1])方法无法使用

### 问题描述
unpack('N', substr($data, 0, 4))[1])方法无法使用

### Swoole版本，PHP版本，以及操作系统版本信息
swoole=>Version => 4.5.2
PHP 7.1.32 (cli) (built: Jul  9 2020 23:58:07) ( NTS )
CentOS Linux release 7.3.1611 (Core)

### 相关代码
```php
class TcpClient
{
    function tcp_pack(string $data)
    {
        return pack('N', strlen($data)) . $data;
    }

function tcp_unpack(string $data)
    {
        return substr($data, 4, unpack('N', substr($data, 0, 4))[1]);
    }

/**
     * TcpClient constructor.
     */
    public function __construct()
    {
        $this->exec();
    }

public function exec()
    {
        Co\run(function () {
         
            $tcpOptions = [
                'open_length_check' => true,
                'package_max_length' => 80 * 1024,//80k
                'package_length_type' => 'N',
                'package_length_offset' => 0,
                'package_body_offset' => 4,
                'log_level' => SWOOLE_LOG_ERROR
            ];
            go(function () use ($tcpOptions) {
                //tcp
                $tcp_client = new Swoole\Coroutine\Client(SWOOLE_TCP);
                $tcp_client->set($tcpOptions);

if (!$tcp_client->connect('127.0.0.1', 9503, 0.5)) {
                    echo "connect failed. Error: {$tcp_client->errCode}\n";
                }
                $tcp_client->send($this->tcp_pack('SwoolefefefewTCP'));
                var_dump($this->tcp_unpack($tcp_client->recv()));
            });
        });

}
}

new TcpClient();
```

### 你期待的结果是什么？实际看到的错误信息又是什么？
期待结果，可以正常请求server端数据返回；
PHP Warning:  unpack(): Type n: not enough input, need 2, have 0 in TcpClient.php on line 19
一直提示unpack()方法错误，不知道要怎么修改了

发布于6年前 · 0 次浏览 · 来自提问

xiaoqiang111