使用PHP中的GMail API发送电子邮件

我应该将邮件服务从旧项目替换为GMail。但是，该项目正在使用PHP，并且google文档页面中尚不提供有关PHP代码的文档。我想测试发送带有简单邮件正文的电子邮件，这是代码：

require_once __DIR__."/google-api-php-client-2.2.1/vendor/autoload.php";

define("APPLICATION_NAME", "Gmail API PHP Quickstart");
define("CREDENTIALS_PATH", "~/.credentials/gmail-php-quickstart.json");
define("CLIENT_SECRET_PATH", __DIR__."/client_secret.json");

// If modifying these scopes, delete your previously saved credentials
// at ~/.credentials/gmail-php-quickstart.json
define('SCOPES', implode(' ', array(
    Google_Service_Gmail::GMAIL_READONLY)
));

date_default_timezone_set('America/New_York'); // Prevent DateTime tz exception
/*
if (php_sapi_name() != 'cli') {
    throw new Exception('This application must be run on the command line.');
}
*/

/**
* Returns an authorized API client.
* @return Google_Client the authorized client object
*/
function getClient() {
    $client = new Google_Client();
    $client->setApplicationName(APPLICATION_NAME);
    $client->setScopes(SCOPES);
    $client->setAuthConfig(CLIENT_SECRET_PATH);
    $client->setAccessType('offline');

    // Load previously authorized credentials from a file.
    $credentialsPath = expandHomeDirectory(CREDENTIALS_PATH);
    if (file_exists($credentialsPath)) {
        $accessToken = json_decode(file_get_contents($credentialsPath), true);
    }
    else {
        // Request authorization from the user.
        $authUrl = $client->createAuthUrl();
        printf("Open the following link in your browser:\n%s\n", $authUrl);
        print 'Enter verification code: ';
        $authCode = trim(fgets(STDIN));

        // Exchange authorization code for an access token.
        $accessToken = $client->fetchAccessTokenWithAuthCode($authCode);

        // Store the credentials to disk.
        if(!file_exists(dirname($credentialsPath))) {
            mkdir(dirname($credentialsPath), 0700, true);
        }
        file_put_contents($credentialsPath, json_encode($accessToken));
        printf("Credentials saved to %s\n", $credentialsPath);
    }
    $client->setAccessToken($accessToken);

    // Refresh the token if it's expired.
    if ($client->isAccessTokenExpired()) {
        $client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
        file_put_contents($credentialsPath, json_encode($client->getAccessToken()));
    }
    return $client;
}

/**
* Expands the home directory alias '~' to the full path.
* @param string $path the path to expand.
* @return string the expanded path.
*/
function expandHomeDirectory($path) {
    $homeDirectory = getenv('HOME');
    if (empty($homeDirectory)) {
        $homeDirectory = getenv('HOMEDRIVE') . getenv('HOMEPATH');
    }
    return str_replace('~', realpath($homeDirectory), $path);
}

// Get the API client and construct the service object.
$client = getClient();
$service = new Google_Service_Gmail($client);

// Print the labels in the user's account.
$user = 'me';
$message = new Google_Service_Gmail_Message();
$messagePart = new Google_Service_Gmail_MessagePart();
$messagePartBody = new Google_Service_Gmail_MessagePartBody();
$messagePartHeader = new Google_Service_Gmail_MessagePartHeader();

$messagePartBody->setData("TEST BY FAROUK");

$messagePart->setHeader($messagePartHeader);
$messagePart->setBody($messagePartBody);
$message->setPayLoad($messagePart);

$service->users_messages->send($user, $message, null);

问题出在这部分，尚未完成：

$user = 'me';
$message = new Google_Service_Gmail_Message();
$messagePart = new Google_Service_Gmail_MessagePart();
$messagePartBody = new Google_Service_Gmail_MessagePartBody();
$messagePartHeader = new Google_Service_Gmail_MessagePartHeader();

$messagePartBody->setData("TEST BY ME");

$messagePart->setHeader($messagePartHeader);
$messagePart->setBody($messagePartBody);
$message->setPayLoad($messagePart);

$service->users_messages->send($user, $message, null);

我知道我必须创建这些类的对象，但是，我不知道应该使用它们的设置器在参数中设置什么样的数据。

请提供一个简单的代码以发送“ Hello world！” 到[email protected]之类的电子邮件地址。谢谢！