如何获取前端提交来得json格式数据

composer.json

{
  "require": {
    "guzzlehttp/guzzle": "~6.0"
  }
}

composer install

index.php 访问该页面 请求后台接口

<?php

require "./vendor/autoload.php";


use GuzzleHttpClient;

$baseurl = "http://wang.com/json.php";



$client = new Client();

$response = $client->request('POST', $baseurl, [
	'json' => ['foo' => 'bar']
]);

echo $response->getBody();

echo $response->getHeader('Content-Length');

当我使用  form表单格式请求 或者get query 

$client->request('GET', 'http://httpbin.org', [
    'query' => ['foo' => 'bar']
]);

$res = $client->request('POST', 'http://localhost:9999/form.php', [
    'form_params' => [
        'field_name' => 'abc',
        'other_field' => '123',
        'nested_field' => [
            'nested' => 'hello'
        ]
    ]

后台都能通过 $_GET $_POST拿到数据 

但是 改为json请求就拿不到 

结果发现 获取json请求内容要换种 

var_dump(file_get_contents('php://input'));
echo json_encode(['code'=>200,'msg'=>'success']);