Get Blob Metadata

Artikkeli
11/07/2023

The Get Blob Metadata operation returns all user-defined metadata for the specified blob or snapshot.

Request

You can construct the Get Blob Metadata request as follows. We recommend that you use HTTPS. Replace myaccount with the name of your storage account.

GET or HEAD method request URI	HTTP version
`https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=metadata` `https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=metadata&snapshot=<DateTime>` `https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=metadata&versionid=<DateTime>`	HTTP/1.1

Emulated storage service request

When you're making a request against the emulated storage service, specify the emulator hostname and Azure Blob Storage port as 127.0.0.1:10000, followed by the emulated storage account name:

GET or HEAD method request URI	HTTP version
`http://127.0.0.1:10000/devstoreaccount1/mycontainer/myblob?comp=metadata`	HTTP/1.1

For more information, see Use the Azurite emulator for local Azure Storage development.

URI parameters

You can specify the following additional parameters on the request URI:

Parameter	Description
`snapshot`	Optional. The snapshot parameter is an opaque `DateTime` value that, when present, specifies the blob snapshot to retrieve. For more information about working with blob snapshots, see Create a snapshot of a blob.
`versionid`	Optional. Version 2019-12-12 and later. The `versionid` parameter is an opaque `DateTime` value that, when present, specifies the version of the blob to retrieve.
`timeout`	Optional. The `timeout` parameter is expressed in seconds. For more information, see Set timeouts for Blob Storage operations.

Request headers

The required and optional request headers are described in the following table:

Request header	Description
`Authorization`	Required. Specifies the authorization scheme, account name, and signature. For more information, see Authorize requests to Azure Storage.
`Date` or `x-ms-date`	Required. Specifies the Coordinated Universal Time (UTC) for the request. For more information, see Authorize requests to Azure Storage.
`x-ms-version`	Required for all authorized requests. Optional for anonymous requests. Specifies the version of the operation to use for this request. For more information, see Versioning for the Azure Storage services.
`x-ms-lease-id:<ID>`	Optional. If this header is specified, the `Get Blob Metadata` operation is performed only if both of the following conditions are met: - The blob's lease is currently active. - The lease ID that's specified in the request matches the lease ID of the blob. If either of these conditions is not met, the request fails, and the `Get Blob Metadata` operation fails with status code 412 (Precondition Failed).
`x-ms-client-request-id`	Optional. Provides a client-generated, opaque value with a 1-kibibyte (KiB) character limit that's recorded in the logs when logging is configured. We highly recommend that you use this header to correlate client-side activities with requests that the server receives. For more information, see Monitor Azure Blob Storage.

This operation also supports the use of conditional headers to get the blob's metadata operation only if a specified condition is met. For more information, see Specify conditional headers for Blob Storage operations.

Request headers (customer-provided encryption keys)

As of version 2019-02-02, you can specify the following headers on the request to read a blob that's encrypted with a customer-provided key. Encryption with a customer-provided key (and the corresponding set of headers) is optional. If a blob has previously been encrypted with a customer-provided key, these headers must be included on the request so that the read operation can be completed successfully.

Request header	Description
`x-ms-encryption-key`	Required. The Base64-encoded AES-256 encryption key.
`x-ms-encryption-key-sha256`	Optional. The Base64-encoded SHA256 hash of the encryption key.
`x-ms-encryption-algorithm: AES256`	Required. Specifies the algorithm to use for encryption. The value of this header must be `AES256`.

Request body

None.

Response

The response includes an HTTP status code and a set of response headers.

Status code

A successful operation returns status code 200 (OK).

For information about status codes, see Status and error codes.

Response headers

The response for this operation includes the following headers. The response may also include additional standard HTTP headers. All standard headers conform to the HTTP/1.1 protocol specification.

Response header	Description
`x-ms-meta-name:value`	Returns a metadata value for the container.
`Last-Modified`	The date/time that the blob was last modified. The date format follows RFC 1123. For more information, see Represent date/time values in headers. Any operation that modifies the blob, including an update of the blob's metadata or properties, changes the last modified time of the blob.
`ETag`	The ETag for the blob. If the request version is 2011-08-18 or later, the ETag value is enclosed in quotation marks.
`x-ms-request-id`	This header uniquely identifies the request that was made, and you can use it to troubleshoot the request. For more information, see Troubleshoot API operations.
`x-ms-version`	Indicates the Blob Storage version that's being used to execute the request. This header is returned for requests that are made against version 2009-09-19 and later. This header is also returned for anonymous requests without a specified version if the container was marked for public access by using Blob Storage version 2009-09-19.
`Date`	The UTC date/time value that's generated by the service, which indicates the time when the response was initiated.
`x-ms-client-request-id`	Can be used to troubleshoot requests and their corresponding responses. The value of this header is equal to the value of the `x-ms-client-request-id` header if it's present in the request and the value is no more than 1,024 visible ASCII characters. If the `x-ms-client-request-id` header isn't present in the request, the header isn't present in the response.

Response body

None.

Authorization

Authorization is required when calling any data access operation in Azure Storage. You can authorize the Get Blob Metadata operation as described below.

Important

Microsoft recommends using Microsoft Entra ID with managed identities to authorize requests to Azure Storage. Microsoft Entra ID provides superior security and ease of use compared to Shared Key authorization.

Azure Storage supports using Microsoft Entra ID to authorize requests to blob data. With Microsoft Entra ID, you can use Azure role-based access control (Azure RBAC) to grant permissions to a security principal. The security principal may be a user, group, application service principal, or Azure managed identity. The security principal is authenticated by Microsoft Entra ID to return an OAuth 2.0 token. The token can then be used to authorize a request against the Blob service.

To learn more about authorization using Microsoft Entra ID, see Authorize access to blobs using Microsoft Entra ID.

Permissions

Listed below are the RBAC action necessary for a Microsoft Entra user, group, managed identity, or service principal to call the Get Blob Metadata operation, and the least privileged built-in Azure RBAC role that includes this action:

Azure RBAC action: Microsoft.Storage/storageAccounts/blobServices/containers/blobs/read
Least privileged built-in role: Storage Blob Data Reader

To learn more about assigning roles using Azure RBAC, see Assign an Azure role for access to blob data.

A shared access signature (SAS) provides secure delegated access to resources in a storage account. With a SAS, you have granular control over how a client can access data. You can specify what resource the client may access, what permissions they have to those resources, and how long the SAS is valid.

The Get Blob Metadata operation supports three types of shared access signatures: user delegation SAS, service SAS, and account SAS.

As a security best practice, we recommend that you use Microsoft Entra credentials rather than the storage account key, which can be more easily compromised. If your application design requires shared access signatures, use Microsoft Entra credentials to create a user delegation SAS, when possible.

When Shared Key access is disallowed for the storage account, a service SAS token or an account SAS token will not be permitted on a request to Blob Storage. To learn more, see Understand how disallowing Shared Key affects SAS tokens.

User delegation SAS

A user delegation SAS is secured with Microsoft Entra credentials and also by the permissions specified for the SAS.

Calling the Get Blob Metadata operation using a SAS token delegated to a container or blob resource requires the Read (r) permission as part of the user delegation SAS token.

To learn more about the user delegation SAS, see Create a user delegation SAS.

Service SAS

A service SAS is secured with the storage account key. A service SAS delegates access to a resource in a single Azure Storage service, such as blob storage.

Calling the Get Blob Metadata operation using a SAS token delegated to a container or blob resource requires the Read (r) permission as part of the service SAS token.

To learn more about the service SAS, see Create a service SAS.

Account SAS

An account SAS is secured with the storage account key. An account SAS delegates access to resources in one or more of the storage services. All of the operations available via a service or user delegation SAS are also available via an account SAS.

The following table indicates the signed resource type and signed permissions to specify when delegating access:

Operation	Signed service	Signed resource type	Signed permission
Get Blob Metadata	Blob (b)	Object (o)	Read (r)

To learn more about the account SAS, see Create an account SAS.

Remarks

None. See billing information for details on how this operation affects costs.

Billing

Pricing requests can originate from clients that use Blob Storage APIs, either directly through the Blob Storage REST API, or from an Azure Storage client library. These requests accrue charges per transaction. The type of transaction affects how the account is charged. For example, read transactions accrue to a different billing category than write transactions. The following table shows the billing category for Get Blob Metadata requests based on the storage account type:

Operation	Storage account type	Billing category
Get Blob Metadata	Premium block blob Standard general-purpose v2	Other operations
Get Blob Metadata	Standard general-purpose v1	Read operations

To learn about pricing for the specified billing category, see Azure Blob Storage Pricing.

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