PHPMailer无法正确合并日志内容问题排查求助

问题背景 #

我编写了LogFileReader类用于读取当日更新的日志文件内容，并通过PHPMailer发送给自己复核。网页端可正常显示完整内容，但邮件中仅能收到硬编码的头部内容，日志内容丢失。

调试信息 #

开启PHPMailer调试后得到以下日志：

04-May-2023,18:06:13log_contents completed.
2023-05-04 09:06:13 Connection: opening to XXX.XXX:XXX, timeout=300, options=array ()
2023-05-04 09:06:13 Connection: opened
2023-05-04 09:06:13 SERVER -> CLIENT: 220 SPSVRMAILDB02.seapower.mo Microsoft ESMTP MAIL Service ready at Thu, 4 May 2023 18:07:07 +0900
2023-05-04 09:06:13 CLIENT -> SERVER: EHLO XX.DOMAIN.XXX
2023-05-04 09:06:13 SERVER -> CLIENT: 250-SPSVRMAILDB02.seapower.mo Hello [192.168.XXX.XX]250-SIZE 37748736250-PIPELINING250-DSN250-ENHANCEDSTATUSCODES250-8BITMIME250-BINARYMIME250 CHUNKING
2023-05-04 09:06:13 CLIENT -> SERVER: MAIL FROM:<XX@XXXXX.XXX>
2023-05-04 09:06:13 SERVER -> CLIENT: 250 2.1.0 Sender OK
2023-05-04 09:06:13 CLIENT -> SERVER: RCPT TO:<XX.XX@XX.XX>
2023-05-04 09:06:13 SERVER -> CLIENT: 250 2.1.5 Recipient OK
2023-05-04 09:06:13 CLIENT -> SERVER: X-Mailer: PHPMailer 5.2.28 (https://github.com/PHPMailer/PHPMailer)
2023-05-04 09:06:13 CLIENT -> SERVER: MIME-Version: 1.0
2023-05-04 09:06:13 CLIENT -> SERVER: Content-Type: multipart/alternative;
2023-05-04 09:06:13 CLIENT -> SERVER: boundary="b1_377eff022806XXXXXX3ea4f92bb02"
2023-05-04 09:06:13 CLIENT -> SERVER: Content-Transfer-Encoding: 8bit
2023-05-04 09:06:13 CLIENT -> SERVER:
2023-05-04 09:06:13 CLIENT -> SERVER: This is a multi-part message in MIME format.
2023-05-04 09:06:13 CLIENT -> SERVER:
2023-05-04 09:06:13 CLIENT -> SERVER: --b1_377eff022806cce60XXXXXXf92bb02
2023-05-04 09:06:13 CLIENT -> SERVER: Content-Type: text/plain; charset=us-ascii

已设置$mail->CharSet = "UTF-8"，但仍显示charset=us-ascii是否正常？

测试$mail->MsgHTML($log_contents)仍无效。

相关代码 #

LogFileReader类 #

define("TIMESTAMP", date("d-M-Y,H:i:s"));
class LogFileReader {
  private $dir; // Declare a property to store the current directory
  private $today;  // Declare a property to store today's date
  private $log_contents;  // Declare a property to store the log contents
  private $timestamp; // Declare a property to store system datetime
    // Declare a constructor that takes the directory as an argument
  public function __construct($dir) {
    // Assign the directory to the property
    $this->dir = $dir;
    // Get today's date and time in Y-m-d H:i:s format
    $this->today = date("Y-m-d");
    // Prepare params, timestamp with initiates.
    $this->timestamp = TIMESTAMP;
    $this->log_contents = " <h2>$this->timestamp daily cron job running.</h2><br>\n";
  }

    // Declare a method that reads and processes the files
  public function readFiles() {
    // List all the .txt files in the directory
    $files = glob($this->dir . "/*.txt");
    // Loop through the files and display their content after today's date and time
    foreach ($files as $file) {
      $this->log_contents .= "<h4>Filename: " . basename($file) . "</h4><br>\n";
      // Read the file content as an array of lines
      $file_content_lines = file($file);
      // Get the last 8 lines of the array
      $last_eight_lines = array_slice($file_content_lines, -8);
      // Filter out the lines that do not contain today's date and time or later
      foreach ($last_eight_lines as $line) {
        // If the line contains today's date and time or later, set the flag to true
        if (strpos($line, $this->today) !== false || strtotime($line) > strtotime($this->today)) {
          $flag = true;
        } // set flag for lines
        // If the flag is true, print the line
        if ($flag) {    $this->log_contents .= $line;    }
      }
      $this->log_contents .= " \n ---- ---- <hr>\n";
    }
  }

  // Declare a method that returns the log contents
  public function getLogContents() {
    return $this->log_contents;
  }
}

使用示例 #

// Create an instance of the FileReader class with the current directory
$log_files = new LogFileReader(getcwd());
// Call the readFiles method to process the files
$log_files->readFiles();
// Get and print the log contents
$log_contents = $log_files->getLogContents();

PHPMailer配置 #

if (!empty($log_contents)){ // after log_contents completed

  echo TIMESTAMP . "log_contents completed.<br/>\n"; // confirm log content completed.
  $email_content_head = "
  <h1>My Host XXXX daily crontab re-check</h1>
  <p>--- --- --- ---</p>
  "; // adding content head
  $emailContent = $email_content_head . $log_contents; // merge contents
// 此处无法正确合并内容

$mail->isHTML(true);                                  // Set email format to HTML
$mail->Subject = 'Our Host XXX.XXX.XXX daily crontab re-check';
$mail->Body    = $emailContent;
$mail->AltBody = 'This is the body in plain text for non-HTML mail clients';

已尝试添加：

$mail->CharSet = "UTF-8";                                // set email encode to UTF-8
$mail->Encoding = 'base64';                              // if UTF-8 not working

疑问 #

$log_contents在邮件中仍为空，var_dump显示其为string类型。请问我遗漏了什么？问题出在哪里？还有其他解决办法吗？

内容的提问来源于stack exchange，提问作者swlok