From 70e5bef61a007c7f654b24f02d729d0eb1a5fe98 Mon Sep 17 00:00:00 2001
From: Yuan-Yi Chang <changyy.csie@gmail.com>
Date: Thu, 5 Sep 2019 23:42:40 +0800
Subject: [PATCH] Try to help #1824

---
 examples/smtp_reduce_mime_encoding.phps | 234 ++++++++++++++++++++++++
 src/PHPMailer.php                       |  37 +++-
 2 files changed, 266 insertions(+), 5 deletions(-)
 create mode 100644 examples/smtp_reduce_mime_encoding.phps

diff --git a/examples/smtp_reduce_mime_encoding.phps b/examples/smtp_reduce_mime_encoding.phps
new file mode 100644
index 0000000000..dd4b8d9ebd
--- /dev/null
+++ b/examples/smtp_reduce_mime_encoding.phps
@@ -0,0 +1,234 @@
+<?php
+/**
+ * This example shows sending mail per receiver and reduce MIME encode.
+ */
+
+//Import the PHPMailer class into the global namespace
+use PHPMailer\PHPMailer\PHPMailer;
+
+//SMTP needs accurate times, and the PHP time zone MUST be set
+//This should be done in your php.ini, but this is how to do it if you don't have access to that
+date_default_timezone_set('Etc/UTC');
+
+require '../vendor/autoload.php';
+
+
+$receiver_count = 1000;
+
+$receiver_list = [];
+for ($i=0 ; $i<$receiver_count ; ++$i)
+	$receiver_list[] = 'whoto'.$i.'@example.com';
+
+echo "Genrate $receiver_count receivers: ".count($receiver_list)."\n";
+
+echo "Sending $receiver_count mails with creating a new PHPMailer instance: ";
+
+$start = microtime(true);
+foreach ($receiver_list as $receiver) {
+
+    //Create a new PHPMailer instance
+    $mail = new PHPMailer;
+    //Tell PHPMailer to use SMTP
+    $mail->isSMTP();
+    //Enable SMTP debugging
+    // 0 = off (for production use)
+    // 1 = client messages
+    // 2 = client and server messages
+    $mail->SMTPDebug = 0;
+    //Set the hostname of the mail server
+    $mail->Host = 'mail.example.com';
+    //Set the SMTP port number - likely to be 25, 465 or 587
+    $mail->Port = 25;
+    //Whether to use SMTP authentication
+    $mail->SMTPAuth = true;
+    //Username to use for SMTP authentication
+    $mail->Username = 'yourname@example.com';
+    //Password to use for SMTP authentication
+    $mail->Password = 'yourpassword';
+    //Set who the message is to be sent from
+    $mail->setFrom('from@example.com', 'First Last');
+    //Set an alternative reply-to address
+    $mail->addReplyTo('replyto@example.com', 'First Last');
+    //Set who the message is to be sent to
+    $mail->addAddress($receiver);
+    //Set the subject line
+    $mail->Subject = 'Hi '.$receiver.'!';
+    //Read an HTML message body from an external file, convert referenced images to embedded,
+    //convert HTML into a basic plain-text alternative body
+    $mail->msgHTML(str_replace( '<h1>This is a test of PHPMailer.</h1>', '<h1>Hi '.$receiver.'</h1>', file_get_contents('contents.html')), __DIR__);
+    //Replace the plain text body with one created manually
+    $mail->AltBody = 'This is a plain-text message body for '.$receiver;
+    //Attach an image file
+    $mail->addAttachment('images/phpmailer_mini.png');
+
+    //Build the mail content
+    $mail->preSend(); 
+    unset($mail);
+}
+$cost = microtime(true) - $start;
+
+echo $cost." sec\n";
+
+echo "Sending $receiver_count mails with only one PHPMailer instance: ";
+
+$start = microtime(true);
+{
+    //Create a new PHPMailer instance
+    $mail = new PHPMailer;
+    //Tell PHPMailer to use SMTP
+    $mail->isSMTP();
+    //Enable SMTP debugging
+    // 0 = off (for production use)
+    // 1 = client messages
+    // 2 = client and server messages
+    $mail->SMTPDebug = 0;
+    //Set the hostname of the mail server
+    $mail->Host = 'mail.example.com';
+    //Set the SMTP port number - likely to be 25, 465 or 587
+    $mail->Port = 25;
+    //Whether to use SMTP authentication
+    $mail->SMTPAuth = true;
+    //Username to use for SMTP authentication
+    $mail->Username = 'yourname@example.com';
+    //Password to use for SMTP authentication
+    $mail->Password = 'yourpassword';
+    //Set who the message is to be sent from
+    $mail->setFrom('from@example.com', 'First Last');
+    //Set an alternative reply-to address
+    $mail->addReplyTo('replyto@example.com', 'First Last');
+
+    //Attach an image file
+    $mail->addAttachment('images/phpmailer_mini.png');
+
+    foreach ($receiver_list as $receiver) {
+        //Reset addresses
+        $mail->clearAddresses();
+        //Set who the message is to be sent to
+        $mail->addAddress($receiver);
+        //Set the subject line
+        $mail->Subject = 'Hi '.$receiver.'!';
+        //Read an HTML message body from an external file, convert referenced images to embedded,
+        //convert HTML into a basic plain-text alternative body
+        $mail->msgHTML(str_replace( '<h1>This is a test of PHPMailer.</h1>', '<h1>Hi '.$receiver.'</h1>', file_get_contents('contents.html')), __DIR__);
+        //Replace the plain text body with one created manually
+        $mail->AltBody = 'This is a plain-text message body for '.$receiver;
+ 
+        //Build the mail content
+        $mail->preSend(); 
+    }
+}
+$cost = microtime(true) - $start;
+
+echo $cost." sec\n";
+//
+// ---
+//
+echo "Sending $receiver_count mails with creating a new PHPMailer instance and ReduceMIMEEncodeCacheStore: ";
+
+$start = microtime(true);
+$cacheLookupTable = [];
+foreach ($receiver_list as $receiver) {
+    //Create a new PHPMailer instance
+    $mail = new PHPMailer;
+    //Tell PHPMailer to use SMTP
+    $mail->isSMTP();
+    //Enable SMTP debugging
+    // 0 = off (for production use)
+    // 1 = client messages
+    // 2 = client and server messages
+    $mail->SMTPDebug = 0;
+    //Set the hostname of the mail server
+    $mail->Host = 'mail.example.com';
+    //Set the SMTP port number - likely to be 25, 465 or 587
+    $mail->Port = 25;
+    //Whether to use SMTP authentication
+    $mail->SMTPAuth = true;
+    //Username to use for SMTP authentication
+    $mail->Username = 'yourname@example.com';
+    //Password to use for SMTP authentication
+    $mail->Password = 'yourpassword';
+    //Set who the message is to be sent from
+    $mail->setFrom('from@example.com', 'First Last');
+    //Set an alternative reply-to address
+    $mail->addReplyTo('replyto@example.com', 'First Last');
+    //Set who the message is to be sent to
+    $mail->addAddress($receiver);
+    //Set the subject line
+    $mail->Subject = 'Hi '.$receiver.'!';
+    //Read an HTML message body from an external file, convert referenced images to embedded,
+    //convert HTML into a basic plain-text alternative body
+    $mail->msgHTML(str_replace( '<h1>This is a test of PHPMailer.</h1>', '<h1>Hi '.$receiver.'</h1>', file_get_contents('contents.html')), __DIR__);
+    //Replace the plain text body with one created manually
+    $mail->AltBody = 'This is a plain-text message body for '.$receiver;
+    //Attach an image file
+    $mail->addAttachment('images/phpmailer_mini.png');
+
+    //Set Reduce MIME Encode Cache Store
+    $mail->ReduceMIMEEncodeCacheStore = &$cacheLookupTable;
+
+    //Build the mail content
+    $mail->preSend(); 
+    unset($mail);
+}
+$cost = microtime(true) - $start;
+
+echo $cost." sec\n";
+//
+// ---
+//
+echo "Sending $receiver_count mails with only one PHPMailer instance and ReduceMIMEEncodeCacheStore: ";
+
+$start = microtime(true);
+$cacheLookupTable = [];
+{
+    //Create a new PHPMailer instance
+    $mail = new PHPMailer;
+    //Tell PHPMailer to use SMTP
+    $mail->isSMTP();
+    //Enable SMTP debugging
+    // 0 = off (for production use)
+    // 1 = client messages
+    // 2 = client and server messages
+    $mail->SMTPDebug = 0;
+    //Set the hostname of the mail server
+    $mail->Host = 'mail.example.com';
+    //Set the SMTP port number - likely to be 25, 465 or 587
+    $mail->Port = 25;
+    //Whether to use SMTP authentication
+    $mail->SMTPAuth = true;
+    //Username to use for SMTP authentication
+    $mail->Username = 'yourname@example.com';
+    //Password to use for SMTP authentication
+    $mail->Password = 'yourpassword';
+    //Set who the message is to be sent from
+    $mail->setFrom('from@example.com', 'First Last');
+    //Set an alternative reply-to address
+    $mail->addReplyTo('replyto@example.com', 'First Last');
+    //Attach an image file
+    $mail->addAttachment('images/phpmailer_mini.png');
+
+    //Set Reduce MIME Encode Cache Store
+    $mail->ReduceMIMEEncodeCacheStore = &$cacheLookupTable;
+
+    foreach ($receiver_list as $receiver) {
+        //Reset addresses
+        $mail->clearAddresses();
+        //Set who the message is to be sent to
+        $mail->addAddress($receiver);
+        //Set the subject line
+        $mail->Subject = 'Hi '.$receiver.'!';
+        //Read an HTML message body from an external file, convert referenced images to embedded,
+        //convert HTML into a basic plain-text alternative body
+        $mail->msgHTML(str_replace( '<h1>This is a test of PHPMailer.</h1>', '<h1>Hi '.$receiver.'</h1>', file_get_contents('contents.html')), __DIR__);
+        //Replace the plain text body with one created manually
+        $mail->AltBody = 'This is a plain-text message body for '.$receiver;
+ 
+        //Build the mail content
+        $mail->preSend(); 
+    }
+}
+$cost = microtime(true) - $start;
+
+echo $cost." sec\n";
+
+
diff --git a/src/PHPMailer.php b/src/PHPMailer.php
index 16359fabe5..1130d23095 100644
--- a/src/PHPMailer.php
+++ b/src/PHPMailer.php
@@ -420,6 +420,17 @@ class PHPMailer
      */
     protected $SingleToArray = [];
 
+    /**
+     * Whether to send the same message to each receiver 
+     * with small changes in mail content.
+     * Use a lookup table to reduce attachment encoding.
+     *
+     * Storage for attachment encoding.
+     *
+     * @var array
+     */
+    public $ReduceMIMEEncodeCacheStore = false;
+
     /**
      * Whether to generate VERP addresses on send.
      * Only applicable when sending via SMTP.
@@ -3031,12 +3042,28 @@ protected function encodeFile($path, $encoding = self::ENCODING_BASE64)
             if (!static::isPermittedPath($path) || !file_exists($path)) {
                 throw new Exception($this->lang('file_open') . $path, self::STOP_CONTINUE);
             }
-            $file_buffer = file_get_contents($path);
-            if (false === $file_buffer) {
-                throw new Exception($this->lang('file_open') . $path, self::STOP_CONTINUE);
+            $file_buffer = '';
+            if (is_array($this->ReduceMIMEEncodeCacheStore)) {
+                $cache_key = "$path\t$encoding";
+                if (isset($this->ReduceMIMEEncodeCacheStore[$cache_key])) {
+                    $file_buffer = $this->ReduceMIMEEncodeCacheStore[$cache_key];
+                    $this->edebug('encodeFile: use cache ['.$path.']['.$encoding.']');
+                } else {
+                    $file_buffer = file_get_contents($path);
+                    if (false === $file_buffer) {
+                        throw new Exception($this->lang('file_open') . $path, self::STOP_CONTINUE);
+                    }
+                    $file_buffer = $this->encodeString($file_buffer, $encoding);
+                    $this->ReduceMIMEEncodeCacheStore[$cache_key] = $file_buffer;
+                    $this->edebug('encodeFile: set cache ['.$path.']['.$encoding.']');
+                }
+            } else {
+                $file_buffer = file_get_contents($path);
+                if (false === $file_buffer) {
+                    throw new Exception($this->lang('file_open') . $path, self::STOP_CONTINUE);
+                }
+                $file_buffer = $this->encodeString($file_buffer, $encoding);
             }
-            $file_buffer = $this->encodeString($file_buffer, $encoding);
-
             return $file_buffer;
         } catch (Exception $exc) {
             $this->setError($exc->getMessage());