Cloud Storage for Firebase allows you to list the contents of your
Cloud Storage bucket. The SDKs return both the items and the prefixes of
objects under the current Cloud Storage reference.
Projects that use the List API require Cloud Storage for Firebase
Rules version 2. If you have an existing Firebase project, follow the steps in
the
Security Rules Guide
.
list()
uses the
Google Cloud Storage List API
.
In Cloud Storage for Firebase, we use
/
as a delimiter, which allows us to
emulate file system semantics. To allow for efficient traversal of large,
hierarchical Cloud Storage buckets, the List API returns prefixes and
items separately. For example, if you upload one file
/images/uid/file1
,
root.child('images').listAll()
will return
/images/uid
as a prefix.
root.child('images/uid').listAll()
will return the file as an item.
The Cloud Storage for Firebase SDK does not return object paths that contain two
consecutive
/
s or end with a
/
. For example, consider a bucket that has the
following objects:
correctPrefix/happyItem
wrongPrefix//sadItem
lonelyItem/
The list operations on items in this bucket will give the following results:
- The list operation at the root returns the references to
correctPrefix
,
wrongPrefix
and
lonelyItem
as
prefixes
.
- The list operation at the
correctPrefix/
returns the references to
correctPrefix/happyItem
as
items
.
- The list operation at the
wrongPrefix/
doesn't return any references
because
wrongPrefix//sadItem
contains two consecutive
/
s.
- The list operation at the
lonelyItem/
doesn't return any references
because the object
lonelyItem/
ends with
/
.
List all files
You can use
listAll
to fetch all results for a directory.
This is best used for small directories as all results are buffered in memory.
The operation also may not return a consistent snapshot if objects are added or
removed during the process.
For a large list, use the paginated
list()
method as
listAll()
buffers all
results in memory.
The following example demonstrates
listAll
.
final storageRef = FirebaseStorage.instance.ref().child("files/uid");
final listResult = await storageRef.listAll();
for (var prefix in listResult.prefixes) {
// The prefixes under storageRef.
// You can call listAll() recursively on them.
}
for (var item in listResult.items) {
// The items under storageRef.
}
Paginate list results
The
list()
API places a limit on the number of results it returns.
list()
provides a consistent pageview and exposes a pageToken that allows control over
when to fetch additional results.
The pageToken encodes the path and version of the last item returned in the
previous result. In a subsequent request using the pageToken, items that come
after the pageToken are shown.
The following example demonstrates paginating a result:
Stream<ListResult> listAllPaginated(Reference storageRef) async* {
String? pageToken;
do {
final listResult = await storageRef.list(ListOptions(
maxResults: 100,
pageToken: pageToken,
));
yield listResult;
pageToken = listResult.nextPageToken;
} while (pageToken != null);
}
Handle errors
list()
and
listAll()
fail if you haven't upgraded
the Security Rules to version 2. Upgrade your Security Rules if you see this
error:
Listing objects in a bucket is disallowed for rules_version = "1".
Please update storage security rules to rules_version = "2" to use list.
Other possible errors may indicate the user does not have the right permission.
More information on errors can be found in the
Handle Errors
page.