A couple of high level questions about the API. Let's take this code from the PR description:

$bucket = $client->selectDatabase('test_db')->selectGridFSBucket();
$bucket->registerAsDefaultStreamWrapper();
file_put_contents("gridfs://test_db/fs.files/filename.txt", 'Hello GridFS!');

If we're already registering a bucket as the default stream wrapper, why does the URI still contain the database and bucket names? The bucket instance is tied to a client, database, and bucket, so I'd expect to use something like this:

file_put_contents('gridfs://filename.txt', 'Hello GridFS!');

This might create conflicts with us using GridFS internally. However, we could work around that by allowing to registerer a new stream wrapper for each bucket:

$client->selectDatabase('test_db')->selectGridFSBucket()->registerStreamWrapper('foo');
$client->selectDatabase('test_db')->selectGridFSBucket(['name' => 'cache'])->registerStreamWrapper('cache');
file_put_contents('foo://filename.txt', 'Hello GridFS!'); // Writes to the fs.files collection
file_put_contents('cache://filename.txt', 'Hello GridFS!'); // Writes to the cache.files collection

Not only would this make accessing files easier, but it would also allow for using more than a single bucket if users so desire.

I'm thinking to an other path pattern: gridfs://<bucket-alias>/<filename>

• <bucket-alias>: name associated with a closure that get the context from the stream_open data ($path, $mode, $options).
• <filename> : the path associated to the file

The context resolver will be a map instead of a single closure.

We can reuse the same StreamWrapper class and the same protocol gridfs.

This CI failure looks relevant:

1) MongoDB\Tests\GridFS\StreamWrapperFunctionalTest::testOpenSpecificRevision
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'version 1'
+'version 0'
/home/runner/work/mongo-php-library/mongo-php-library/tests/GridFS/StreamWrapperFunctionalTest.php:300

I noticed some other CI failures related to Atlas Search spec tests failing to match error messages, but that's probably related to DRIVERS-2794 as it only fails on mongodb-latest.