Get Block List¶

The Get Block List operation retrieves the list of blocks that have been uploaded as part of a block blob.

Two block lists are maintained for a blob:

Committed Block List: The list of blocks that have been successfully committed to a given blob with Put Block List.
Uncommitted Block List: The list of blocks that have been uploaded for a blob using Put Block, but are not yet committed. These blocks are stored in Azure in association with a blob, but do not yet form part of the blob.

You can call Get Block List to return the committed block list, the uncommitted block list, or both.

Request¶

The Get Block List request may be constructed as follows. HTTPS is recommended. Replace myaccount with the name of your storage account, and example.com with your endpoint’s domain name or IP address.

Method	Request URI	HTTP Version
GET	`https://myaccount.blob.example.com/mycontainer/myblob?comp=blocklist`	HTTP/1.1

URI Parameters¶

The following additional parameters may be specified on the request URI.

URI Parameter	Description
`snapshot`	Not applicable (Zenko version 2.3.13 does not support snapshots).
`blocklisttype`	Specifies whether to return the list of committed blocks, the list of uncommitted blocks, or both lists together. Valid values are `committed`, `uncommitted`, or `all`. If you omit this parameter, `Get Block List` returns the list of committed blocks.
`timeout`	Optional. The `timeout` parameter is expressed in seconds. For more information, see Setting Timeouts for Blob Service Operations.

Request Headers¶

The following table describes required and optional request headers.

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`	Not applicable (Zenko version 2.3.13 does not support leasing).
`x-ms-client-request-id`	Optional. Provides a client-generated, opaque value with a 1 KB character limit that is recorded in the analytics logs when storage analytics logging is enabled. Use this header to correlate client-side activities with requests received by the server. For more information, see Azure Storage Analytics Logging and Windows Azure Logging: Using Logs to Track Storage Requests.

Request Body¶

None

Sample Request¶

The following sample request URI returns the committed block list for a blob named MOV1.avi:

GET http://myaccount.blob.example.com/movies/MOV1.avi?comp=blocklist&blocklisttype=committed HTTP/1.1

The following sample request URI returns both the committed and uncommitted block lists:

GET http://myaccount.blob.example.com/movies/MOV1.avi?comp=blocklist&blocklisttype=all HTTP/1.1

Response¶

The response includes an HTTP status code, a set of response headers, and a response body containing the list of blocks.

Status Codes¶

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
`Last-Modified`	The date/time the blob was last modified. The date format follows RFC 1123. See Representation of date/time values in headers for more information. This header is returned only if the blob has committed blocks. Any operation that modifies the blob, including updates to the blob’s metadata or properties, changes the blob’s last-modified time.
`ETag`	The ETag for the blob. This header is returned only if the blob has committed blocks.
`Content-Type`	The MIME content type of the blob. The default value is `application/xml`.
`x-ms-blob-content-length`	The size of the blob in bytes.
`x-ms-request-id`	This header uniquely identifies the request that was made and can be used for troubleshooting the request. For more information, see Troubleshooting API operations.
`x-ms-version`	Indicates the version of the Blob service used to execute the request. Only the committed block list can be returned via an anonymous request.
`Date`	A UTC date/time value generated by the service that indicates the time at which the response was initiated.
`x-ms-client-request-id`	This header can be used to troubleshoot requests and corresponding responses. The value of this header is equal to the value of the `x-ms-client-request-id` header if it is present in the request and the value is at most 1024 visible ASCII characters. If the `x-ms-client-request-id` header is not present in the request, this header will not be present in the response.

This operation also supports the use of conditional headers to get the block list only if a specified condition is met. For more information, see Specifying conditional headers for Blob service operations.

Response Body¶

The format of the response body for a request that returns only committed blocks is as follows:

<?xml version="1.0" encoding="utf-8"?>
<BlockList>
  <CommittedBlocks>
    <Block>
      <Name>base64-encoded-block-id</Name>
      <Size>size-in-bytes</Size>
    </Block>
  <CommittedBlocks>
</BlockList>

The format of the response body for a request that returns both committed and uncommitted blocks is as follows:

<?xml version="1.0" encoding="utf-8"?>
<BlockList>
  <CommittedBlocks>
     <Block>
        <Name>base64-encoded-block-id</Name>
        <Size>size-in-bytes</Size>
     </Block>
  </CommittedBlocks>
  <UncommittedBlocks>
    <Block>
      <Name>base64-encoded-block-id</Name>
      <Size>size-in-bytes</Size>
    </Block>
  </UncommittedBlocks>
 </BlockList>

Sample Response¶

In the following example, the blocklisttype parameter was set to committed, so only the blob’s committed blocks are returned in the response.

HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/xml
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: 42da571d-34f4-4d3e-b53e-59a66cb36f23
Date: Sun, 25 Sep 2011 00:33:19 GMT

<?xml version="1.0" encoding="utf-8"?>
<BlockList>
  <CommittedBlocks>
    <Block>
      <Name>BlockId001</Name>
      <Size>4194304</Size>
    </Block>
    <Block>
      <Name>BlockId002</Name>
      <Size>4194304</Size>
    </Block>
  </CommittedBlocks>
</BlockList>

In this example, the blocklisttype parameter was set to all, and both the blob’s committed and uncommitted blocks are returned in the response.

HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/xml
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: 42da571d-34f4-4d3e-b53e-59a66cb36f23
Date: Sun, 25 Sep 2011 00:35:56 GMT

<?xml version="1.0" encoding="utf-8"?>
<BlockList>
  <CommittedBlocks>
    <Block>
      <Name>BlockId001</Name>
      <Size>4194304</Size>
    </Block>
    <Block>
      <Name>BlockId002</Name>
      <Size>4194304</Size>
    </Block>
  </CommittedBlocks>
  <UncommittedBlocks>
    <Block>
      <Name>BlockId003</Name>
      <Size>4194304</Size>
    </Block>
    <Block>
      <Name>BlockId004</Name>
      <Size>1024000</Size>
    </Block>
  </UncommittedBlocks>
</BlockList>

In this next example, the blocklisttype parameter was set to all, but the blob has not yet been committed, so the CommittedBlocks element is empty.

HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/xml
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: 42da571d-34f4-4d3e-b53e-59a66cb36f23
Date: Wed, 14 Sep 2011 00:40:22 GMT

<?xml version="1.0" encoding="utf-8"?>
<BlockList>
  <CommittedBlocks />
  <UncommittedBlocks>
    <Block>
      <Name>BlockId001</Name>
      <Size>1024</Size>
    </Block>
    <Block>
      <Name>BlockId002</Name>
      <Size>1024</Size>
    </Block>
    <Block>
      <Name>BlockId003</Name>
      <Size>1024</Size>
    </Block>
    <Block>
      <Name>BlockId004</Name>
      <Size>1024</Size>
    </Block>
  </UncommittedBlocks>
</BlockList>

Authorization¶

If the container’s ACL is set to allow anonymous access, any client may call Get Block List; however, only committed blocks can be accessed publicly. Access to the uncommitted block list is restricted to the account owner and to anyone using a Shared Access Signature that has permission to read this blob or its container.

Remarks¶

Call Get Block List to return the list of blocks that have been committed to a block blob, the list of blocks that have not yet been committed, or both lists. Use the blocklisttype parameter to specify which list of blocks to return. The list of committed blocks is returned in the same order they were committed by the Put Block List operation.

You can use the uncommitted block list to determine which blocks are missing from the blob in cases where calls to Put Block or Put Block List have failed. The list of uncommitted blocks is returned in alphabetical order. If a block ID has been uploaded more than once, only the most recently uploaded block appears in the list.

Note

When a blob has not yet been committed, calling Get Block List with blocklisttype=all returns the uncommitted blocks, and the CommittedBlocks element is empty.

Get Block List does not support concurrency when reading the list of uncommitted blocks. Calls to Get Block List where blocklisttype=uncommitted or blocklisttype=all have a lower maximum request rate than other read operations. For details on target throughput for read operations, see Azure Storage scalability and performance targets for storage accounts.