Javascript 为什么在ajax请求中会出现与内容类型相关的JSON错误？

在尝试向我的PHP API发出ajax请求（使用Angularjs）时，我遇到以下错误

SyntaxError: Unexpected token n in JSON at position 24

我非常感谢你的帮助。谢谢

以下是我的代码：

var data = {"username":"sarahexample", "password":"5f4dcc3b5aa765d61d8327deb882cf99"};
$http({
    method: 'POST',
    url: 'http://localhost/API/auth',
    data : JSON.stringify(data)
}).then(function successCallback(response) {
   console.log(response);
}, function errorCallback(response) {
   console.log(response);
});

下面是PHP auth函数，它在请求端点时执行

protected function auth($parameters) {
    if ($this->method == 'POST') {
        //echo the POST data back to the client side to test it's working
        //This works when I take out the php Content-Type header
        echo json_encode($_POST);
    } else {
        //echo "Only accepts POST requests";
    }
 }

在我的PHPAPI中，我有下面的标题（，当去掉它时，一切正常，但是我希望它与标题一起工作

我尝试在上面的标题中留下，并在ajax请求中添加

contentType:'application/json'

，如下所示（但这并没有解决json错误）：

在控制台的“网络”选项卡中：

Request URL:http://localhost/API/auth
Request Method:POST
Status Code:200 OK
Remote Address:[::1]:80
Referrer Policy:no-referrer-when-downgrade

Response Headers
view source
Access-Control-Allow-Methods:*
Access-Control-Allow-Origin:*
Connection:Keep-Alive
Content-Length:6
Content-Type:application/json
Date:Thu, 28 Sep 2017 17:17:31 GMT
Keep-Alive:timeout=5, max=100
Server:Apache/2.4.27 (Win64) PHP/5.6.31
X-Powered-By:PHP/5.6.31

Request Headers
view source
Accept:application/json, text/plain, */*
Accept-Encoding:gzip, deflate, br
Accept-Language:en-US,en;q=0.8
Cache-Control:no-cache
Connection:keep-alive
Content-Length:73
Content-Type:application/json
Host:localhost
Origin:http://localhost
Pragma:no-cache
Referer:http://localhost/phonegap_tut/


Request Payload
view source
{username: "sarahexample", password: "5f4dcc3b5aa765d61d8327deb882cf99"}
password
:
"5f4dcc3b5aa765d61d8327deb882cf99"
username
:
"sarahexample"

---

正确的方法是在echo之前检查JSON输出

// Check if your JSON conversion succeed

$json = json_encode($_POST);
if ($json === false) {
    // JSONify the error message:
    $json = json_encode(array("jsonError", json_last_error_msg()));
    if ($json === false) {
        // This should not happen, but we go all the way now:
        $json = '{"jsonError": "unknown"}';
    }
    // Set HTTP response status code to: 500 - Internal Server Error
    http_response_code(500);
}
echo $json;

---

我发现了错误发生的原因。这是几件事的结合

首先，我犯了一个愚蠢的错误，我不小心重复了两次数据：

我有一个名为MyAPI.php的类，它包含auth方法。我在这里回显数据，而我本应该在另一个名为api.php的脚本中再次回显数据时将其返回。这是在服务器返回的JSON数据的末尾添加null

下面是我的新auth函数：

protected function auth($parameters) {
    if ($this->method == 'POST') {
        //need to get the POST data this way because we have the Content-Type header set to application/json, so $_POST will no longer be populated
        $rawPostData = file_get_contents('php://input');
        //return the data because we will echo it from the api.php script
        return $rawPostData;
    }else{
        $errorMessage = array("error" => "Only accepts POST requests");
        return json_encode($errorMessage);
    }
}

下面是一个名为api.php的脚本，它响应了结果

<?php       
    require_once 'MyAPI.class.php';

    try {
        $API = new MyAPI($_REQUEST, $_SERVER['HTTP_ORIGIN']);
        echo $API->processAPI();
    } catch (Exception $e) {
        echo json_encode(Array('error' => $e->getMessage()));
    }
 ?>

---

作为请求主体发送的实际JSON负载是什么…？这些症状表明您没有返回有效的JSON。如果指定从服务器返回json，则如果希望能够读取客户端响应，则必须在成功和出错时都返回json。@NeilHibbert，谢谢。对不起，我错漏了。我在JSON Payloads中编辑了我的问题。我猜您在PHP中使用的是不正确的，这导致将PHP错误返回给客户端，该错误不是有效的JSON。我们需要查看实际发送的内容，而不是您打算发送的内容。

protected function auth($parameters) {
    if ($this->method == 'POST') {
        //need to get the POST data this way because we have the Content-Type header set to application/json, so $_POST will no longer be populated
        $rawPostData = file_get_contents('php://input');
        //return the data because we will echo it from the api.php script
        return $rawPostData;
    }else{
        $errorMessage = array("error" => "Only accepts POST requests");
        return json_encode($errorMessage);
    }
}

<?php       
    require_once 'MyAPI.class.php';

    try {
        $API = new MyAPI($_REQUEST, $_SERVER['HTTP_ORIGIN']);
        echo $API->processAPI();
    } catch (Exception $e) {
        echo json_encode(Array('error' => $e->getMessage()));
    }
 ?>

var data = {"username":"sarahexample","password":"5f4dcc3b5aa765d61d8327deb882cf99"};
    $http({
        method: 'POST',
        url: 'http://localhost/API/auth',
        data : JSON.stringify(data),
        headers: {
           'Content-Type': 'application/json;charset=utf-8'
        },
        responseType:'json'
    }).then(function successCallback(response) {
        console.log('success');
        if(response.data.hasOwnProperty('error')){
            console.log(response.data.error);

        }else{
            console.log(response.data.username);
        }   
    }, function errorCallback(response) {
        console.log("error");
        console.log(response);

    });