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:
https://gist.github.com/nextend/8c0d752024bac9c0a030d5ba022dfac9
There is a chunk which is not written into the stream. The output is the following:
/ 1160
Chunk #4430: 781473d903bedf95d8a07d34974ac548 1160
Good md5: 231732259d67fe83ed6fc02d7ad9be57
Stream md5: 4a3b968a44c585a2883e687d61c251fb
Memory md5: 231732259d67fe83ed6fc02d7ad9be57
The return value of fwrite() for this chunk is NULL.
Previous Comments:
------------------------------------------------------------------------
[2021-10-13 16:35:59] roland at nextendweb dot com
The following gist works like a charm and the md5 of the data is fine without the PHP stream write:
https://gist.github.com/nextend/61bb5a8b36ea126f3e95297f3f7de10e
I tried, but it takes forever to finish:
for ($len = 0; $len < $data_length; ) {
$len += fwrite($this->stream_handle, substr($data, $len));
}
------------------------------------------------------------------------
[2021-10-13 08:15:11] roland at nextendweb dot com
Thank you for your tips!
As you wrote CURLOPT_BUFFERSIZE is just a request and not an order, so it might happen that a part
of the response is missing and this is why the md5 hashes are different for several chunks. So I can
see why my check of the chunk's md5 hashes might not the right tool for debugging this.
Expected response at buffersize 4:
aaaa
bbbb
cccc
dddd
-> response hash OK
Valid response at buffersize 4:
aaaa
bbb -> chunk hash mismatch
bcccc -> chunk hash mismatch
dddd
-> response hash OK
Not valid response at buffersize 4:
aaaa
bb -> chunk hash mismatch
ccc -> chunk hash mismatch
dddd
-> response hash FAIL
I think the latter happens, but I will do more debugging with the length of the chunks.
Currently I do not have access to the server which produced this error, but will try to get one. We
know about 10 different servers which produced this and they are were the very same response MD5
hash, so it could not be a coincident.
------------------------------------------------------------------------
[2021-10-12 18:49:18] requinix@php.net
Can you modify your script to also include the data length in the log output?
After doing that and running the script (and if seeing the length doesn't identify the
problem), can you additionally modify the fwrite() statement to be a loop:
for ($len = 0; $len < $data_length; ) {
$len += fwrite($this->stream_handle, substr($data, $len));
}
This is because fwrite() does not guarantee to write its entire string at once, and will return the
number of bytes it actually wrote. This is almost never an issue with writing to a local file,
though...
Back to the data length. The output shows those 40 chunks *present* but with different hashes. Your
original report said that 1160 bytes were *missing*. Does that mean you're seeing two different
behaviors between the WP code and your script?
Because if cURL is giving the write function 1160 bytes, that means your original report had a
problem with the callback 1 time while your new script had a problem with the callback 40 times.
Speaking of, note that the buffer size is "a request, not an order", so the chunks
received by the callback may not be exactly that size.
https://curl.se/libcurl/c/CURLOPT_BUFFERSIZE.html
------------------------------------------------------------------------
[2021-10-12 13:51:27] roland at nextendweb dot com
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
------------------------------------------------------------------------
[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.
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