如何返回Guzzle JSON响应

我正在使用Guzzle使返回JSON的异步请求。调用工作正常，响应正常，但是:

$client = new Client();
    $promise = $client->requestAsync($requestType ,$this->url.$resource, // endpoint
        [
            'auth' => [ // credentials
                $this->username, 
                $this->password
            ],
            'json' => $payload, // the package
            'curl' => [ // some curl options
                CURLOPT_HTTPAUTH => CURLAUTH_BASIC,
                CURLOPT_RETURNTRANSFER => true,
            ],
            'headers' => [ // custom headers
                'Accept' =>  'application/json',
                'Content-Type' => 'application/json'
            ]
        ]
    );
    $response = $promise->wait();
    echo $response->getStatusCode().'<br /><br />';
    // Error handling
    if($response->getStatusCode() != 200){
        // Error Handling
    }else{
        echo $response->getBody(true);
    }

如果我回显response->getBody()，我看到JSON字符串，但如果我把它分配给一个属性，print_r，或返回它，我得到:

GuzzleHttp'Psr7'Stream Object ( [stream:GuzzleHttp'Psr7'Stream:private] => Resource id #245 [size:GuzzleHttp'Psr7'Stream:private] => [seekable:GuzzleHttp'Psr7'Stream:private] => 1 [readable:GuzzleHttp'Psr7'Stream:private] => 1 [writable:GuzzleHttp'Psr7'Stream:private] => 1 [uri:GuzzleHttp'Psr7'Stream:private] => php://temp [customMetadata:GuzzleHttp'Psr7'Stream:private] => Array ( ) )

我需要使用JSON来验证来自服务的响应。我该怎么做呢?我已经通读了文档，但是我明显遗漏了什么吗?

基本上沿着分配json getBody输出的行说$json:

if($json->first_field > 0)

感谢任何帮助。关于