This tutorial aims to solve the problem that the backend cannot receive data correctly when sending a POST request through Content-Type: application/json in Yii2 application. By default, Yii2's request component only parses traditional form data such as application/x-www-form-urlencoded. To ensure that JSON data is correctly identified and processed, developers need to add yii\web\JsonParser to the request component in the Yii2 configuration file, so that the framework can automatically parse the JSON request body and successfully obtain the submitted data in the controller.

Problem Description: JSON POST data reception is empty

When developing web applications, front-end and back-end separation architectures often send JSON format data through JavaScript fetch or XMLHttpRequest. However, in the Yii2 framework, even if the front-end request status code is 200, the Yii::$app->request->post() method in the back-end controller may not be able to obtain the expected JSON data, but instead return a null value.

Here is an example of a typical JavaScript front-end sending JSON data:

 let csrfToken = document.querySelector("meta[name='csrf-token']").content;
let csrfParam = document.querySelector("meta[name='csrf-param']").content;

fetch("http://site.se/react/save-babysitter", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "Accept": "application/json",
    "csrf-param": csrfParam, // CSRF Parameters "X-CSRF-Token": csrfToken // CSRF Token
  },
  body: JSON.stringify({
    'id': e.id, // Sample data: id
    'name': this.state.ChangeName // Sample data: name
  })
}).then(response => response.json())
  .then((data) => console.log(data));

The corresponding Yii2 backend controller code may look like this:

 public function actionSaveBabysitter() {
    $request = Yii::$app->request;
    $name = $request->post('name'); // At this time, the $name variable may be empty // In the original question, try to json_decode the empty value, resulting in an error // echo json_decode($name); 

    // In fact, it should be to check whether $name has received correctly if (empty($name)) {
        return $this->asJson(['status' => 'error', 'message' => 'Name is empty']);
    } else {
        return $this->asJson(['status' => 'success', 'received_name' => $name]);
    }
}

In this case, although the HTTP status code is 200, $request->post('name') cannot get the name value sent by the front-end.

Root Cause Analysis

The Yii2 framework's request component yii\web\Request By default, only the data in the $_POST global variable is parsed. Web servers (such as Apache or Nginx) usually only parse request body data with Content-Type application/x-www-form-urlencoded or multipart/form-data into $_POST global variables.

When the current side uses Content-Type: application/json to send data, the request body content is the original JSON string, which the web server will not automatically parse and fill in $_POST. Therefore, $_POST remains empty, and Yii2's $request->post() method naturally cannot obtain any data.

Solution: Configure the JSON request parser

In order for Yii2 to correctly identify and parse request bodies of application/json type, we need to add a JSON parser for the request component in Yii2's application configuration file (usually config/web.php).

The specific operation is to add the parsers attribute in the request configuration under the components array, and specify that the parser corresponding to application/json is yii\web\JsonParser.

 // config/web.php
Return [
    'id' => 'your-app-id',
    // ... Other configurations...
    'components' => [
        'request' => [
            'cookieValidationKey' => 'your-secret-key', // Please make sure to set a safe key
            'parsers' => [
                'application/json' => 'yii\web\JsonParser',
                // If you need to support other Content-Types, you can also add // 'application/xml' => 'yii\web\XmlParser',
            ],
            // ... other configurations of the request component...
        ],
        // ...Other components...
    ],
    // ... Other configurations...
];

Through the above configuration, when Yii2 receives a request with Content-Type application/json, yii\web\JsonParser will automatically intervene, parse the JSON string in the request body into a PHP array or object, and fill it into the Yii::$app->request->bodyParams property.

Correct access to JSON data

After the configuration is complete, in the controller, you can get parsed JSON data through Yii::$app->request->post() or Yii::$app->request->getBodyParam() just like accessing normal POST data.

 public function actionSaveBabysitter() {
    $request = Yii::$app->request;

    // At this time, Yii2 has automatically parsed the JSON request body// You can directly obtain the specific parameter $id = $request->post('id'); 
    $name = $request->post('name');

    // Or get all parsed parameter arrays through getBodyParams() // $data = $request->getBodyParams();
    // $id = $data['id'] ?? null;
    // $name = $data['name'] ?? null;

    if (empty($id) || empty($name)) {
        Yii::error("Received empty data: ID={$id}, Name={$name}", __METHOD__);
        return $this->asJson(['status' => 'error', 'message' => 'ID or Name cannot be empty.']);
    }

    // Example: Process data and return a response // For example, save to a database and other operations // ...

    return $this->asJson(['status' => 'success', 'received_id' => $id, 'received_name' => $name]);
}

Notes and summary

1. The importance of Content-Type: When the front-end sends a request, it is important to make sure that the Content-Type in the headers is set to application/json, which is the key for the back-end parser to correctly identify and process JSON data.
2. CSRF protection: Yii2's CSRF protection mechanism is still effective even if it is a JSON request. It is the correct way to send CSRF tokens through csrf-param and X-CSRF-Token in front-end JS code. Yii2 will automatically verify these tokens based on configuration.
3. Data verification: Even if the data is successfully received, it is necessary to strictly verify and filter the received data on the backend to prevent malicious input and security vulnerabilities.
4. getBodyParams() and post(): Yii::$app->request->post() method After the JSON parser is configured, it will automatically find the value of the corresponding key from the parsed bodyParams. Therefore, in general, just use the post() method directly. If you need to get all parsed parameter arrays, you can use getBodyParams().
5. Other parsers: If your application also needs to handle other non-standard form types request bodies (such as XML), you can also configure the corresponding parsers in parsers.

Through the above configuration, Yii2 applications will be able to seamlessly process JSON format POST requests sent by the front-end, ensuring the correct transmission and processing of data, thereby improving the efficiency of front-end collaboration and application robustness.

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