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Blob snapshots

Snapshots preserve a blob's state at a specific point in time. They are created explicitly by an application, unlike blob versions, which Azure creates automatically when versioning is enabled.

Create A Snapshot​

Create a read-only snapshot of the current base blob:

use AzureOss\Storage\Blob\Models\CreateSnapshotOptions;

$snapshotInfo = $blob->createSnapshot(new CreateSnapshotOptions(
    metadata: ['purpose' => 'before-migration'],
));

$snapshot = $blob->withSnapshot($snapshotInfo->snapshot);
$content = $snapshot->downloadStreaming()->content->getContents();

When metadata is empty, Azure copies the base blob's metadata to the snapshot. Conditions such as an expected ETag can be supplied through the options:

use AzureOss\Storage\Blob\Models\BlobRequestConditions;
use AzureOss\Storage\Blob\Models\CreateSnapshotOptions;

$snapshotInfo = $blob->createSnapshot(new CreateSnapshotOptions(
    conditions: new BlobRequestConditions(ifMatch: $expectedETag),
));

BlobSnapshotInfo contains the opaque snapshot identifier, ETag, last-modified time, encryption state, and the version identifier returned when account versioning is enabled.

Work With A Snapshot​

Snapshots are immutable. A snapshot client can download content, read properties, act as a copy source, or delete that individual snapshot:

$snapshot = $blob->withSnapshot($snapshotId);

$content = $snapshot->downloadStreaming()->content->getContents();
$snapshot->delete();

withSnapshot() returns a new client and does not modify the original client. Use withSnapshot(null) to derive a client without the snapshot selector.

Generate A Snapshot SAS​

Calling generateSasUri() on a snapshot client creates a snapshot-specific SAS (sr=bs) and preserves the snapshot selector in the URI:

use AzureOss\Storage\Blob\Sas\BlobSasBuilder;
use AzureOss\Storage\Blob\Sas\BlobSasPermissions;

$snapshotSas = $snapshot->generateSasUri(
    BlobSasBuilder::new()
        ->setPermissions(new BlobSasPermissions(read: true))
        ->setExpiresOn((new DateTimeImmutable)->modify('+5 minutes')),
);