Retain Guzzle Session During Batch Operations

On a Drupal 7 site, I am using the Batch API to perform operations on many entities, one at a time. During a typical operation, the D7 site uses Guzzle to make a POST call to a Drupal 8 site. The D7 Batch callback looks like this:

function example_operation($foo, &$context) {

  // Login to Drupal 8.
  // ...

  // Make POST call to Drupal 8.
  // ...

  // Logout from Drupal 8.
  // ...

}

The D7 client uses a Guzzle client and cookie jar to authenticate with the D8 server (REST+cookies), with no issues. Great!

Now imagine running this on 100K+ entities, that’s an awful lot of logging in and out unnecessarily, wasting a whole bunch of time and resources. So I figure, let’s login once on the first operation, retain that session for each operation, then logout when finished. Sounds reasonable.

I thought I’d use D7 Batch API’s $context['results'] array to hang onto the cookie jar and D8 rest tokens, that way each operation would have access to them, no problem, or so I thought. Take a look at this attempt in the D7 Batch callbacks:

function example_operation($foo, &$context) {

  $jar = NULL;
  $csrfToken = NULL;

  // Login to Drupal 8 (first time only)
  if (!isset($context['results']['jar'])) {

    // Login to Drupal 8.
    // ...

    // Set aside cookie jar and tokens.
    $context['results']['jar'] = $jar;
    $context['results']['csrf_token'] = $csrfToken;
    $context['results']['logout_token'] = $logoutToken;

  }
  else {

    // We've already logged in, grab the cookie jar and token.
    $jar = $context['results']['jar'];
    $csrfToken = $context['results']['csrf_token'];

  }

  // Make POST call to Drupal 8 (using cookie jar and token).
  // ...

}

function example_finished($success, $results, $operations) {

  // Pull out cookie jar and tokens.
  $jar = $results['jar'];
  $csrfToken = $results['csrf_token'];
  $logoutToken = $results['logout_token'];

  // Logout from Drupal 8 (using cookie jar and tokens)
  // ...

}

This approach works fine on the first operation only. Then on the second operation, the tokens are available in $context['results'] as expected, but the cookie jar always comes through as a __PHP_Incomplete_Class Object, and then if I try using it with the Guzzle client a cookies must be an instance of GuzzleHttpCookieCookieJarInterface is thrown.

How do you retain a Guzzle session between batch operations in Drupal 7?

• Perhaps $context['results'] cannot contain "complex" class/objects like a Guzzle cookie jar
• I tried using the cookies request option when instantiating the Guzzle client, but that breaks any authenticated POST calls (including the first operation)
• Maybe the way D7’s batch http requests work, it starts confusing the client/cookies/etc

$context['results']['jar'] = $jar->toArray();

$jar = CookieJar::fromArray($context['results']['jar'], 'domain.com');