Using middleware to cross languages

Except in cases where you are trying to communicate between different versions of PHP, PSR-7 middleware will be of minimal use. Recall what the acronym stands for: PHP Standards Recommendations. Accordingly, if you need to make a request to an application written in another language, treat it as you would any other web service HTTP request.

How to do it...

In the case of PHP 4, you actually have a chance in that there is limited support for object-oriented programming. Accordingly, the best approach would be to downgrade the basic PSR-7 classes described in the first three recipes. There is not enough space to cover all the changes, but we present a potential PHP 4 version of Application\MiddleWare\ServerRequest. The first thing to note is that there are no namespaces! Accordingly, we use a classname with underscores, _, in place of namespace separators:
```
class Application_MiddleWare_ServerRequest
extends Application_MiddleWare_Request
implements Psr_Http_Message_ServerRequestInterface
{
```

All properties are identified in PHP 4 using the key word var:

var $serverParams;
var $cookies;
var $queryParams;
// not all properties are shown

The initialize() method is almost the same, except that syntax such as $this->getServerParams()['REQUEST_URI'] was not allowed in PHP 4. Accordingly, we need to split this out into a separate variable:

function initialize()
{
  $params = $this->getServerParams();
  $this->getCookieParams();
  $this->getQueryParams();
  $this->getUploadedFiles;
  $this->getRequestMethod();
  $this->getContentType();
  $this->getParsedBody();
  return $this->withRequestTarget($params['REQUEST_URI']);
}

All of the $_XXX super-globals were present in later versions of PHP 4:

function getServerParams()
{
  if (!$this->serverParams) {
      $this->serverParams = $_SERVER;
  }
  return $this->serverParams;
}
// not all getXXX() methods are shown to conserve space

The null coalesce operator was only introduced in PHP 7. We need to use isset(XXX) ? XXX : ''; instead:

function getRequestMethod()
{
  $params = $this->getServerParams();
  $method = isset($params['REQUEST_METHOD']) 
    ? $params['REQUEST_METHOD'] : '';
  $this->method = strtolower($method);
  return $this->method;
}

The JSON extension was not introduced until PHP 5. Accordingly, we need to be satisfied with raw input. We could also possibly use serialize() or unserialize() in place of json_encode() and json_decode():

function getParsedBody()
{
  if (!$this->parsedBody) {
      if (($this->getContentType() == 
           Constants::CONTENT_TYPE_FORM_ENCODED
           || $this->getContentType() == 
           Constants::CONTENT_TYPE_MULTI_FORM)
           && $this->getRequestMethod() == 
           Constants::METHOD_POST)
      {
          $this->parsedBody = $_POST;
      } elseif ($this->getContentType() == 
                Constants::CONTENT_TYPE_JSON
                || $this->getContentType() == 
                Constants::CONTENT_TYPE_HAL_JSON)
      {
          ini_set("allow_url_fopen", true);
          $this->parsedBody = 
            file_get_contents('php://stdin');
      } elseif (!empty($_REQUEST)) {
          $this->parsedBody = $_REQUEST;
      } else {
          ini_set("allow_url_fopen", true);
          $this->parsedBody = 
            file_get_contents('php://stdin');
      }
  }
  return $this->parsedBody;
}

The withXXX() methods work pretty much the same in PHP 4:

function withParsedBody($data)
{
  $this->parsedBody = $data;
  return $this;
}

Likewise, the withoutXXX() methods work the same as well:

function withoutAttribute($name)
{
  if (isset($this->attributes[$name])) {
      unset($this->attributes[$name]);
  }
  return $this;
}

}

For websites using other languages, we could use the PSR-7 classes to formulate requests and responses, but would then need to use an HTTP client to communicate with the other website. As an example, recall the demonstration of a Request discussed in the recipe Developing a PSR-7 request class from this chapter. Here is the example from the How it works... section:

$request = new Request(
  TARGET_WEBSITE_URL,
  Constants::METHOD_POST,
  new TextStream($contents),
  [Constants::HEADER_CONTENT_TYPE => 
  Constants::CONTENT_TYPE_FORM_ENCODED,
  Constants::HEADER_CONTENT_LENGTH => $body->getSize()]
);

$data = http_build_query(['data' => 
$request->getBody()->getContents()]);

$defaults = array(
  CURLOPT_URL => $request->getUri()->getUriString(),
  CURLOPT_POST => true,
  CURLOPT_POSTFIELDS => $data,
);
$ch = curl_init();
curl_setopt_array($ch, $defaults);
$response = curl_exec($ch);
curl_close($ch);

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Table of Contents for PHP 7: Real World Application Development

Using middleware to cross languages

How to do it...

Table of Contents for
PHP 7: Real World Application Development