How to get the generated query string of wp_remote_get?

While the other answers are pretty good in providing an answer to your question (how to get the generated url), i will answer what i guess you really want to know (how do i get it to call thirdparty.com?foo=bar with wp_remote_get)

The Answer is: the $args array you use to transmit the url parameters won't work like this. If you have to transmit a POST request with wp_remote_post, you would use the body argument like your example. However, to wp_remote_get thirdparty.com?foo=bar, you simply do

wp_remote_get('http://thirdparty.com?foo=bar');

if you want to get fancy and use an array, you can also do this:

$url = "http://thirdparty.com";
$data = array('foo' => 'bar');
$query_url = $url.'?'.http_build_query($data);
$response = wp_remote_get($query_url);

Happy Coding!

This is a task for Xdebug. I'd recommend to use it together with PHPStorm.

Then you'll need to set a breakpoint exactly at the moment you build the query or when you post the request. Then you can inspect what exactly is going on.

Following is a sample chain I used to post something successfully, which results in a query that simply looks like the following which then get appended to the $url below. I found it important to format the query with PHP_QUERY_RFC3986 using PHP's http_build_query() so it gets encoded properly.

The query:

foo=foovalue&bar=barvalue

The complete sample:

// Build the URL query to be append to the POST request URL.
$data = [
  'foo' => $foo,
  'bar' => $bar,
];

$query = http_build_query($data, NULL, '&', PHP_QUERY_RFC3986);

// The POST request URL.
$url = 'https://example.com/index.php/fooBar/save2?' . $query;

$args = [
  'headers' => ['Content-Type' => 'application/x-www-form-urlencoded'],
  'method'  => 'POST',
];

// Post the request.
$response = wp_remote_request($url, $args);

//Check for success
if (!is_wp_error($response) && ($response['response']['code'] === 200 || $response['response']['code'] === 201)) {
  return $response['body'];
}

You can have a look into the classes inside wp-includes/class-http that handle the actual request. There are various hooks like http_api_curl you could hook into to see what is actually requested.