Bug #81516 [Com]: Curl used with CURLOPT_WRITEFUNCTION rarely corrupts the response

Edit report at https://bugs.php.net/bug.php?id=81516&edit=1 ID: 81516 Comment by: roland at nextendweb dot com Reported by: roland at nextendweb dot com Summary: Curl used with CURLOPT_WRITEFUNCTION rarely corrupts the response Status: Feedback Type: Bug Package: cURL related PHP Version: 7.4.24 Block user comment: N Private report: N New Comment: Also worth to mention that this issue does not happen when the server which serves the zip has HTTP/2 enabled. It happened only with HTTP/1.1 Previous Comments: ------------------------------------------------------------------------ [2021-10-12 12:57:56] roland at nextendweb dot com I was able to create a small test case which can reproduce the issue without WordPress. phpinfo(); -> https://gist.github.com/nextend/3905674a48c2da5c95dfea90b2115f82 PHP 7.4.24 cURL 7.71.0 Test code: https://gist.github.com/nextend/2819c93635c5f1c68c13cf1e28a2ef19 The problem happens at CURLOPT_BUFFERSIZE => 1160, 1160*2, 1160*3 1160*4 seems to work fine. See the md5 hash of the stream write data at 1160 buffer size. (Left is the normal server, right is the bad server) https://i.imgur.com/Jk0hzaM.png Between 3683 and 3711 the chunk's md5 are mismatching. If you want to I can send you the private url for the test in email. ------------------------------------------------------------------------ [2021-10-08 18:38:44] requinix@php.net Are you sure this is related to CURLOPT_WRITEFUNCTION? Can you confirm that stream_body is not being called for some chunk in the middle of the response? Would be nice if you could modify cURL.php to not need the write function, but with a casual glance at the code I don't think it would be easy. How about varying the buffer size to some fraction/multiple of 1160, like 580 or 2320? And, of course, are there any relevant differences in configuration between the servers? How about with the files or paths being written to? No offense but this doesn't really sound like a bug in PHP, or even in cURL itself, but rather some weird hiccup or fault with those specific servers. ------------------------------------------------------------------------ [2021-10-08 17:52:08] roland at nextendweb dot com Description: ------------ This issue happened through WordPress update system during plugin update. Our update url points to our private server and serving a zip file. We had tens of thousands updates for this very same file and there were only 2 sites which had this issue, so I think it is not related how we serve the file. The error is md5_mismatch: The checksum of the file (4a3b968a44c585a2883e687d61c251fb) does not match the expected checksum value (231732259d67fe83ed6fc02d7ad9be57). I started to debug this issue, I had the original zip file and the corrupted one which WordPress downloaded. I diffed the files and at some point it seems like some part is missing in the corrupted file. Like the stream lost a piece from the buffer. And it happens all the time on those servers. https://i.imgur.com/Nx0SKeK.png Curl transport handled this download, so I head over to /wp-includes/Requests/Transport/cURL.php: https://github.com/WordPress/WordPress/blob/master/wp-includes/Requests/Transport/cURL.php And when I removed CURLOPT_BUFFERSIZE or changed anything else (Requests::BUFFER_SIZE+1, Requests::BUFFER_SIZE-1), download_url function started to behave as it should and the file was not corrupted anymore. <?php curl_setopt($this->handle, CURLOPT_BUFFERSIZE, Requests::BUFFER_SIZE); Requests::BUFFER_SIZE value is 1160 in WordPress. Exactly one 1160 bytes block is missing in the middle of the file, which is the value of Requests::BUFFER_SIZE. https://i.imgur.com/KoWkzco.png Both site had the following configuration: WordPress 5.8.1 PHP 7.4.24 Curl 7.71.0 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=81516&edit=1