Unable to listUserMessages() - 500 Backend Error - php

Question

When using the below code to attempt to list messages received by a brand new gmail account I just set up, I get
[Google_Service_Exception] Error calling GET https://www.googleapis.com/gmail/v1/users/myGmailAccount%40gmail.com/messages: (500) Backend Error
I know the validation portion is working correctly because I'm able to make minor modifications and query the books api as shown in this example. Below is the code I'm using to attempt to query recent messages received...
const EMAIL = 'myGmailAccount#gmail.com';
private $permissions = [
'https://www.googleapis.com/auth/gmail.readonly'
];
private $serviceAccount = 'xxxxxxxxxxxxxxxxx#developer.gserviceaccount.com';
/** #var Google_Service_Gmail */
private $gmail = null;
/** #var null|string */
private static $serviceToken = null;
public function __construct()
{
$client = new Google_Client();
$client->setApplicationName($this->applicationName);
$this->gmail = new Google_Service_Gmail($client);
//authentication
if (isset(self::$serviceToken)) {
$client->setAccessToken(self::$serviceToken);
}
$credentials = new Google_Auth_AssertionCredentials(
$this->serviceAccount,
$this->permissions,
$this->getKey()
);
$client->setAssertionCredentials($credentials);
if($client->getAuth()->isAccessTokenExpired()) {
$client->getAuth()->refreshTokenWithAssertion($credentials);
}
self::$serviceToken = $client->getAccessToken();
}
public function getMessages()
{
$this->gmail->users_messages->listUsersMessages(self::EMAIL);
}
I have granted API access to gmail:
The 500 makes me believe this is an internal error with the gmail API or I'm missing something the PHP client isn't validating.

Answer 1

This one work for me. My understanding is service account doesn't have a mailbox and it's not too sure which mailbox it should work on. So you can't use listUsersMessages() function to get all messages.
So you will need to specify which email address that the service account need to work on.
Make sure that the scope has been allowed on Web App API to
1. Add this line:
$credentials->sub = self::EMAIL;
Before:
$client->setAssertionCredentials($credentials);
2. Then Update your getMessages() to:
$this->gmail->users_messages->listUsersMessages("me");
Hope this helps!

Answer 2

I imagine the account has logged in to the web interface already, right? Have you tried with a separate user? How about doing something like labels list instead? Did you try using the APIs explorer site? https://developers.google.com/apis-explorer/#p/gmail/v1/
Can you provide the first 5 digits of the developer's client ID (it's not secret anyway) so I can try to track down the error?

Answer 3

For this to work you have to impersonate an user account (the service account doesn't have a mailbox, as lthh89vt points out).
If you try to access the mailbox directly you will get the (500) Back End error.
The full code is:
$client_email = '1234567890-a1b2c3d4e5f6g7h8i#developer.gserviceaccount.com';
$private_key = file_get_contents('MyProject.p12');
$scopes = array('https://www.googleapis.com/auth/gmail.readonly');
$user_to_impersonate = 'user#example.org';
$credentials = new Google_Auth_AssertionCredentials(
$client_email,
$scopes,
$private_key,
'notasecret', // Default P12 password
'http://oauth.net/grant_type/jwt/1.0/bearer', // Default grant type
$user_to_impersonate,
);
$client = new Google_Client();
$client->setAssertionCredentials($credentials);
if ($client->getAuth()->isAccessTokenExpired()) {
$client->getAuth()->refreshTokenWithAssertion();
}
$service = new Google_Service_Gmail($client);
$results = $service->users_messages->listUsersMessages('me');
Full instructions can be found on Google APIs Client Library for PHP