English
English
When using PHP's stream_bucket_make_writeable() function, some developers will encounter situations where false is returned, which may cause the stream filter to not work properly. This article will analyze in detail why this function returns false and provide common methods to troubleshoot problems.
stream_bucket_make_writeable() is an underlying function in the PHP stream filter system. It is often used to write data into a stream when customizing the stream filter. Its basic functions are:
Try to retrieve a bucket that can be written from the incoming buckets queue so that it can be modified and then passed back to the stream.
The function is called as follows:
$bucket = stream_bucket_make_writeable($in);
where $in is a bucket brigade, representing the data queue of the currently passed filter.
If successful, the function returns a bucket object; if failed, false .
This function returns false usually means that there is no available data block (bucket) in the currently passed bucket brigade ( $in ). There may be several reasons for this:
When the data stream has been transmitted, the filter is still called, but at this time, $in has no bucket to read, so naturally stream_bucket_make_writeable() will return false .
Troubleshooting method:
if (($bucket = stream_bucket_make_writeable($in)) === false) {
// Check if it is the end of the stream
error_log("Nothing to write bucket，Maybe the stream has ended");
}
If your filter is applied to a stream without actual output (such as a file without data writing), then there will be no buckets passed in and the function will return false .
Testable code:
stream_filter_register('example.filter', ExampleFilter::class);
$fp = fopen('php://temp', 'w+');
stream_filter_append($fp, 'example.filter', STREAM_FILTER_WRITE);
fclose($fp); // No data written
Make sure your filter is correctly applied to the "write" or "read" stream direction. The wrong orientation will cause the filter to fail to receive data correctly.
example:
// Correct writing direction
stream_filter_append($fp, 'example.filter', STREAM_FILTER_WRITE);
If you are not sure of the direction, it is recommended to print the behavior of the $filterparams debug stream.
In the custom filter class, if the processing logic is written improperly, such as $in not being processed correctly, or incorrectly returning in advance, it will cause stream_bucket_make_writeable() to behave abnormally.
The basic filter framework should be similar to the following:
class ExampleFilter extends php_user_filter {
public function filter($in, $out, &$consumed, $closing) {
while ($bucket = stream_bucket_make_writeable($in)) {
// Modify or record data
$bucket->data = strtoupper($bucket->data);
$consumed += $bucket->datalen;
stream_bucket_append($out, $bucket);
}
return PSFS_PASS_ON;
}
}
Make sure $bucket is handled correctly in the while loop and avoid meaningless early return.
Confirm whether $in is empty : Use var_dump($in) to print the structure.
Check if the stream writes data : Make sure that content is indeed transmitted through the stream.
Debug the $closing state of the filter : It is normal for the filter to be called during the shutdown phase.
Use logging behavior : error_log() can be used to write bucket status to the log.
Check PHP version and compatibility : Some old versions of PHP have stream_filter -related bugs. It is recommended to test reproduction using a higher version on gitbox.net .
stream_bucket_make_writeable() returns false, which is mostly because the stream has no data or has ended transmission. In practical applications, we can more effectively troubleshoot and solve problems by correctly understanding its semantics, clarifying the life cycle of the filter, and mastering the transmission timing of the stream.
Through the methods listed in this article, you should be able to more relaxedly position the reason behind false return and correct your stream filter implementation logic accordingly.
