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Fix quadratic memory usage in Structure::parsePart #612

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Fix quadratic memory usage in Structure::parsePart #612

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18 changes: 15 additions & 3 deletions src/Structure.php
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Original file line number Diff line number Diff line change
Expand Up @@ -103,11 +103,23 @@ public function findContentType(): void {
* @throws InvalidMessageDateException
*/
private function parsePart(string $context, int $part_number = 0): array {
// Optimize split of headers/body to avoid quadratic memory usage on large messages.
// The previous line-by-line substr loop could allocate huge intermediate strings (e.g. when body contains large attachments).
$headers = '';
$body = $context;
while (($pos = strpos($body, "\r\n")) > 0) {
$body = substr($body, $pos + 2);

$pos = strpos($context, "\r\n\r\n");
if ($pos !== false) {
// Keep the first CRLF (line terminator of last header) in headers, like legacy behavior.
$headers = substr($context, 0, $pos + 2);
$body = substr($context, $pos + 2);
} else {
while (($pos = strpos($body, "\r\n")) > 0) {
$body = substr($body, $pos + 2);
}
$headers = substr($context, 0, strlen($body) * -1);
}
$headers = substr($context, 0, strlen($body) * -1);

$body = substr($body, 0, -2);

$config = $this->header->getConfig();
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