Fixing it is not possible in 5.4.
I propose to deprecate the possibility of sending a message with a closed generator in 6.4 and throw in 7.0. That way, we don't need to store the generator result and that avoids the memory leak.

@fabpot the issue is not just about sending a message with a closed generator. If you try to both access the string content and serialize the object, this will make 2 usages of the iterator, with the RawMessage being the one closing the generator in the first usage.

@stof Sure, but that's not something people will do. What would you suggest?

Isn't patching onlytoIterable() enough to fix the issue?

diff --git a/src/Symfony/Component/Mime/RawMessage.php b/src/Symfony/Component/Mime/RawMessage.phpindex d2a311daeb..14223d3d7f 100644--- a/src/Symfony/Component/Mime/RawMessage.php+++ b/src/Symfony/Component/Mime/RawMessage.php@@ -48,12 +48,9 @@ class RawMessage implements \Serializable             return;         }-        $message = '';         foreach ($this->message as $chunk) {-            $message .= $chunk;             yield $chunk;         }-        $this->message = $message;     }      /**

Transforming the generator to an array intoString() seems unavoidable, unless we forbid calling toString() more than once which sounds worse.