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MDL-69355 file: Do not attempt to set headers after output started

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It was found out that in certain situations there may be some content
in to output handlers buffers. Let's allow that to happen given that:

* default handler's buffer is not sent as a part of the file and an
  error is reported into the server log.
* other handlers' buffer is sent with the assumption that it is required
  for the correct serving of the file.
This commit is contained in:
David Mudrák 2020-09-17 11:37:54 +02:00
parent d4d798e684
commit af30f18a19
1 changed files with 15 additions and 11 deletions
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26
lib/filelib.php
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@ -2234,23 +2234,27 @@ function readfile_accel($file, $mimetype, $accelerate) {
}
}
if ($filesize > 10000000) {
// for large files try to flush and close all buffers to conserve memory
while(@ob_get_level()) {
if (!@ob_end_flush()) {
break;
}
}
}
// Send this header after we have flushed the buffers so that if we fail
// later can remove this because it wasn't sent.
header('Content-Length: ' . $filesize);
if (!empty($_SERVER['REQUEST_METHOD']) and $_SERVER['REQUEST_METHOD'] === 'HEAD') {
exit;
}
while (ob_get_level()) {
$handlerstack = ob_list_handlers();
$activehandler = array_pop($handlerstack);
if ($activehandler === 'default output handler') {
// We do not expect any content in the buffer when we are serving files.
$buffercontents = ob_get_clean();
if ($buffercontents !== '') {
error_log('Non-empty default output handler buffer detected while serving the file ' . $file);
}
} else {
// Some handlers such as zlib output compression may have file signature buffered - flush it.
ob_end_flush();
}
}
// send the whole file content
if (is_object($file)) {
$file->readfile();