Add a show_message_size_by_attachment option.

This makes the message too large errors show the size as a "realistic" size more understandable by laypeople - i.e. it divides the message size limit by 1.33 to show the maximum size after base64-ing attachments, rather than the maximum size assume the whole message is text.

config/defaults.inc.php

@@ -587,6 +587,10 @@ $config['sendmail_delay'] = 0;
 // Size in bytes (possible unit suffix: K, M, G)
 $config['max_message_size'] = '100M';
 
+// Show message size by the attachable size in errors. i.e. the above limit
+// divided by 1.33 to account for base64 encoding.
+$config['show_message_size_by_attachment'] = false;
+
 // Maximum number of recipients per message (including To, Cc, Bcc).
 // Default: 0 (no limit)
 $config['max_recipients'] = 0;

program/steps/mail/attachments.inc

@@ -278,7 +278,11 @@ function rcmail_check_message_size($filesize, $filetype)
     $size  += $filesize * $multip;
 
     if ($size > $limit) {
-        $limit = $RCMAIL->show_bytes($limit);
+        if ($RCMAIL->config->get('show_message_size_by_attachment')) {
+            $limit = $RCMAIL->show_bytes($limit/1.33);
+        } else {
+            $limit = $RCMAIL->show_bytes($limit);
+        }
         return $RCMAIL->gettext(array('name' => 'msgsizeerror', 'vars' => array('size' => $limit)));
     }
 }

program/steps/mail/compose.inc

@@ -1136,7 +1136,11 @@ function rcmail_write_forward_attachments()
     }
 
     if ($size_errors) {
-        $limit = $RCMAIL->show_bytes($size_limit);
+        if ($RCMAIL->config->get('show_message_size_by_attachment')) {
+            $limit = $RCMAIL->show_bytes($size_limit/1.33);
+        } else {
+            $limit = $RCMAIL->show_bytes($size_limit);
+        }
         $error = $RCMAIL->gettext(array('name' => 'msgsizeerrorfwd', 'vars' => array('num' => $size_errors, 'size' => $limit)));
         $RCMAIL->output->add_script(sprintf("%s.display_message('%s', 'error');", rcmail_output::JS_OBJECT_NAME, rcube::JQ($error)), 'docready');
     }