Use IMAP BINARY (RFC3516) extension to fetch message/part bodies (experimental)

CHANGELOG

@@ -1,6 +1,7 @@
 CHANGELOG Roundcube Webmail
 ===========================
 
+- Use IMAP BINARY (RFC3516) extension to fetch message/part bodies
 - Fix invalid error message on deleting mail from read only folder (#1488694)
 - Fix error where session wasn't updated after folder rename/delete (#1488692)
 - Replace data URIs of images (pasted in HTML editor) with inline attachments (#1488502)

program/include/rcube_imap_generic.php

@@ -2402,10 +2402,13 @@ class rcube_imap_generic
             $mode = 0;
         }
 
+        // Use BINARY extension when possible (and safe)
+        $binary     = $mode && preg_match('/^[0-9.]+$/', $part) && $this->hasCapability('BINARY');
+        $fetch_mode = $binary ? 'BINARY' : 'BODY';
+
         // format request
-        $reply_key = '* ' . $id;
         $key       = $this->nextTag();
-        $request   = $key . ($is_uid ? ' UID' : '') . " FETCH $id (BODY.PEEK[$part])";
+        $request   = $key . ($is_uid ? ' UID' : '') . " FETCH $id ($fetch_mode.PEEK[$part])";
 
         // send request
         if (!$this->putLine($request)) {
@@ -2413,6 +2416,10 @@ class rcube_imap_generic
             return false;
         }
 
+        if ($binary) {
+            $mode = -1;
+        }
+
         // receive reply line
         do {
             $line = rtrim($this->readLine(1024));
@@ -2457,13 +2464,13 @@ class rcube_imap_generic
             $prev     = '';
 
             while ($bytes > 0) {
-                $line = $this->readLine(4096);
+                $line = $this->readLine(8192);
 
                 if ($line === NULL) {
                     break;
                 }
 
-                $len  = strlen($line);
+                $len = strlen($line);
 
                 if ($len > $bytes) {
                     $line = substr($line, 0, $bytes);