How to modify parameters in Guzzle middleware? - middleware

Question

I want to write a middleware for Guzzle that adds a specific key to the form_params and populates it with a value. In the docs I have read how to modify the headers but have not found anything about other properties of the $request object. Following the example from the docs this is what I have:
$key = 'asdf';
$stack = new HandlerStack();
$stack->setHandler(new CurlHandler());
$stack->push(Middleware::mapRequest(function (RequestInterface $request) use ($key) {
// TODO: Modify the $request so that
// $form_params['api_key'] == 'default_value'
return $request;
}));
$client = new Client(array(
'handler' => $stack
));
The middleware should modify the request so that this:
$client->post('example', array(
'form_params' => array(
'foo' => 'some_value'
)
));
has the same effect as this:
$client->post('example', array(
'form_params' => array(
'foo' => 'some_value',
'api_key' => 'default_value'
)
));

Answer 1

Having done something similar to this, I can say it is very easy.
If you reference GuzzleHttp\Client two things happen when you pass an array into the request in the 'form_params' input option. First, the contents of the array become the body of the request after being urlencoded using http_build query() and secondly, the 'Content-Type' header is set to 'x-www-form-urlencoded'
The snippet below is akin to what you are looking for.
$stack->push(Middleware::mapRequest(function (RequestInterface $request) {
// perform logic
return new GuzzleHttp\Psr7\Request(
$request->getMethod(),
$request->getUri(),
$request->getHeaders(),
http_build_query($added_parameters_array) . '&' . $request->getBody()->toString()
);
}));