This article elaborates on the common problems and solutions of the backend failing to obtain the request body data correctly in the Yii2 framework when the current end sends a POST request with the application/json type. The core is that the default request parser of Yii2 does not process JSON format. It is necessary to enable automatic JSON data parsing by introducing yii\web\JsonParser into the application configuration to ensure that the backend controller can access POST data smoothly.

In modern web development, front-end separation architectures are becoming increasingly popular, and it has become standard practice for the front-end to send data to the back-end API interface in JSON format through asynchronous JavaScript (such as fetch or axios). However, when using the Yii2 framework as the backend, developers may encounter a common problem: even if the frontend successfully sends a POST request of Content-Type: application/json type, the backend cannot get any data through the Yii::$app->request->post() method, and the return result is null or empty.

Analysis of problem phenomenon and root causes

When the current side uses the fetch API and sets Content-Type to application/json, the data in the request body will be sent as the original JSON string. For example:

 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, // Yii2 CSRF parameter "X-CSRF-Token": csrfToken // Yii2 CSRF token},
  body: JSON.stringify({
    'id': 123,
    'name': 'Test Name'
  })
}).then(response => response.json())
  .then((data) => console.log(data));

In the Yii2 backend, if you try to get the data directly through Yii::$app->request->post('name') or Yii::$app->request->post(), you may find that the result is empty:

 public function actionSaveBabysitter()
{
    $request = Yii::$app->request;
    $postData = $request->post('name'); // At this time, $postData will be null

    // If you try to get all POST data// $allPostData = $request->post(); // At this time, $allPostData will be an empty array echo json_encode(['received_data' => $postData]);
    Yii::$app->end();
}

The reason for this problem is that the web server (such as Apache or Nginx) will only parse request bodies of two content types: application/x-www-form-urlencoded or multipart/form-data by default, and fill the parsed data into the $_POST global variable of PHP. For requests of application/json type, the request body content will not be automatically parsed to $_POST. By default, Yii2's request component's post() method mainly relies on $_POST or its internally configured parser. Since there is no default JSON parser, it is impossible to extract JSON data from the original request body.

Solution: Configure Yii2's JSON parser

In order for Yii2 to automatically parse request bodies of application/json type and make its data accessible through the Yii::$app->request->post() method, we need to add a JSON parser to the request component in the configuration of the Yii2 application (usually config/web.php or config/main.php).

Under the components configuration item, find or add the configuration of the request component and add the parsers property inside it:

 // config/web.php or config/main.php
Return [
    'components' => [
        'request' => [
            // !!! insert a secret key in the following (if it is empty) - this is required by cookie validation
            'cookieValidationKey' => 'your-secret-key',
            'enableCsrfValidation' => true, // Make sure CSRF verification is enabled 'parsers' => [
                'application/json' => 'yii\web\JsonParser',
                // If you need to deal with XML or other types, you can also add // 'application/xml' => 'yii\web\XmlParser',
            ],
            // ... Configuration of other request components],
        // ... Other component configuration],
    // ...Other top-level configurations];

Through the above configuration, when Yii2's request component receives a request with Content-Type application/json, it will automatically call yii\web\JsonParser to parse the JSON string in the request body. The parsed data can be accessed directly through the Yii::$app->request->post() method.

Backend correctly obtains JSON data

After configuring JsonParser, your controller code can obtain JSON data through the Yii::$app->request->post() method just like handling ordinary POST requests:

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

    // Get all parsed POST data $allPostData = $request->post();

    // Get a specific field, such as 'name'
    $name = $request->post('name');
    $id = $request->post('id');

    // You can perform business logic processing on $allPostData, $name, $id here // For example: save to the database, verify data, etc. // Return the response if ($name && $id) {
        return $this->asJson([
            'status' => 'success',
            'message' => 'Data received successfully!',
            'received_id' => $id,
            'received_name' => $name
        ]);
    } else {
        return $this->asJson([
            'status' => 'error',
            'message' => 'Missing required data.'
        ]);
    }
}

Things to note

1. CSRF token : When the front-end sends JSON data, if Yii2 enables CSRF verification (enableCsrfValidation is set to true), be sure to include the CSRF token in the request header. It is usually passed through X-CSRF-Token and csrf-param headers, as shown in the front-end code example.
2. Data access method : After configuring JsonParser, the Yii::$app->request->post() method will automatically return the parsed JSON data. There is no need to manually use file_get_contents('php://input') and json_decode() to get the original request body.
3. Error handling and data verification : Even if the data is successfully parsed, the received data still needs to be validated and filtered in the controller to ensure the validity and security of the data.
4. Content-Type Accuracy : When the front-end sends a request, the Content-Type header must be accurately set to application/json, otherwise the JsonParser will not be triggered.

Summarize

By adding yii\web\JsonParser to the request component in Yii2 application configuration, the backend cannot get data when sending POST requests in application/json format. This allows Yii2 to seamlessly interact with modern front-end frameworks and APIs, improving development efficiency and maintainability of code. Proper configuration of the parser and combined with proper CSRF processing is a key step in building a robust Yii2 API interface.

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