How to Output Custom HTTP Body with CakePHP 3.4?

Outputting Custom HTTP Body with CakePHP 3.4

CakePHP 3.4 introduces a stricter approach to header handling, prohibiting the direct echoing of data within controllers. Attempting to echo content, as seen below, results in the error "Unable to emit headers":

<code class="php">public function test() {
    $this->autoRender = false;
    echo json_encode(['method' => __METHOD__, 'class' => get_called_class()]);
}</code>

Why CakePHP Complains

This practice is discouraged in CakePHP for several reasons:

• It can lead to unrecognized data in testing environments.
• It interferes with the ability to set proper headers.
• It may result in truncated data.

Proper Output Methods

There are two recommended approaches for sending custom output:

1. Configure the Response Object:

   Using the PSR-7 compliant interface:

   <code class="php">$content = json_encode(['method' => __METHOD__, 'class' => get_called_class()]);
   
   $this->response = $this->response->withStringBody($content);
   $this->response = $this->response->withType('json');
   
   return $this->response;</code>

   Using the deprecated interface:

   <code class="php">$content = json_encode(['method' => __METHOD__, 'class' => get_called_class()]);
   
   $this->response->body($content);
   $this->response->type('json');
   
   return $this->response;</code>

2. Use a Serialized View:

   <code class="php">$content = ['method' => __METHOD__, 'class' => get_called_class()];
   
   $this->set('content', $content);
   $this->set('_serialize', 'content');</code>

   This method requires the Request Handler component and appropriate URL mapping to utilize JSON rendering.

Reference Material

For more information, refer to the following resources:

• Cookbook: Controllers > Controller Actions
• Cookbook: Request & Response Objects > Setting the Body
• Cookbook: Views > JSON and XML views
• PHP FIG Standards: PSR-7 HTTP message interfaces

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