# Merging Parts into a Complete Object

#### Functions

After uploading all parts for a multipart upload, you can use this operation to complete the multipart upload. Before performing this operation, you cannot download the uploaded data. When merging parts, you need to copy the additional message header information recorded during the initialization of the multipart upload task to the object metadata. The processing process is the same as that of the common upload object with these message headers. In the case of merging parts concurrently, the Last Write Win policy must be followed but the time for initiating Last Write is specified as the time when a part multipart upload is initiated.

If a multipart upload has not been aborted, the uploaded parts occupy your storage quota. After all parts in the multipart upload are merged to an object, only the object occupies your storage quota. If a part uploaded in a multipart upload is not used in any merging parts multipart uploads, the part will be deleted to release storage quota.

You can send a request for downloading all or some data of the generated multipart by specifying a range.

You can send a request for deleting all parts uploaded in a multipart upload. Deleted data cannot be restored.

The merged parts do not use the MD5 value of entire object as the ETag. Their ETag is calculated as follows: MD5(M1M2...MN)-N, where Mn is the MD5 value of part n (N is the total number of parts). As described in the Sample Request, there are three parts and each part has an MD5 value. The MD5 values of the three parts are recalculated to obtain a new MD5 value. Then -N is added to the right of the MD5 value to get the ETag of the combined parts. In this example, -N is -3.

If the response to an object merge request times out and error 500 or 503 is returned, you can first obtain the object metadata of the multipart upload task. Then, check whether the value of header x-obs-uploadId in the response is the same as the ID of this multipart upload task. If they are the same, object parts have been successfully merged on the server and you do not need to try again. For details, see Consistency of Concurrent Operations.

#### Versioning

If a bucket has versioning enabled, a unique version ID is generated for an object created from a multipart upload in this bucket and the version ID is returned in response header x-obs-version-id. If versioning is suspended for a bucket, the object version obtained after the merge is null. For details about the versioning statuses of a bucket, see Configuring Versioning for a Bucket.

If 10 parts are uploaded but only nine parts are selected for merge, the parts that are not merged will be automatically deleted by the system. The parts that are not merged cannot be restored after being deleted. Before combining the parts, adopt the interface used to list the parts that have been uploaded to check all parts to ensure that no part is missed.

#### Request Syntax

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    POST /ObjectName?uploadId=uploadID HTTP/1.1
    Host: bucketname.obs.region.example.com
    Date: date
    Content-Length: length
    Authorization: authorization
    <CompleteMultipartUpload>
        <Part>
            <PartNumber>partNum</PartNumber>
            <ETag>etag</ETag>
        </Part>
        <Part>
            <PartNumber>partNum</PartNumber>
            <ETag>etag</ETag>
        </Part>
        <Part>
            <PartNumber>partNum</PartNumber>
            <ETag>etag</ETag>
        </Part>
    </CompleteMultipartUpload>

#### Request Parameters

This request uses parameters to specify the ID of a multipart upload whose parts will be merged. Table 1 describes the parameters.

Table 1 Request parameters
Parameter | Description | Mandatory
--- | --- | ---
uploadId | Indicates a multipart upload. Type: string | Yes

#### Request Headers

This request uses common headers. For details, see Table 3.

#### Request Elements

This request uses elements to specify the list of parts to be merged. Table 2 describes the elements.

Table 2 Request Elements
Element | Description | Mandatory
--- | --- | ---
CompleteMultipartUpload | List of parts to be combined Type: XML | Yes
PartNumber | Part number Type: integer | Yes
ETag | ETag value returned upon successful upload of a part. It is the unique identifier of the part content. This parameter is used to verify data consistency when parts are merged. Type: string | Yes

#### Response Syntax

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    HTTP/1.1 status_code
    Date: date
    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <CompleteMultipartUploadResult xmlns="http://obs.region.example.com/doc/2015-06-30/">
        <Location>http://example-Bucket.obs.region.example.com/example-Object</Location>
        <Bucket>bucketname</Bucket>
        <Key>ObjectName</Key>
        <ETag>ETag</ETag>
    </CompleteMultipartUploadResult>

#### Response Headers

The response to the request uses common headers. For details, see Table 1.

In addition to the common response headers, the following message headers may also be used. For details, see Table 3.

Table 3 Additional response header parameters
Header | Description
--- | ---
x-obs-version-id | Version of the object after parts being merged. Type: string
x-obs-server-side-encryption | This header is included in a response if SSE-KMS is used. Type: string Example: x-obs-server-side-encryption:kms

x-obs-server-side-encryption-kms-key-id

Indicates the master key ID. This header is included in a response if SSE-KMS is used.

Type: string

Format: regionID:domainID:key/key_id

regionID is the ID of the region to which the key belongs. domainID is the account ID of the tenant to which the key belongs. key_id is the key ID used in this encryption.

Example: x-obs-server-side-encryption-kms-key-id:region:domainiddomainiddomainiddoma0001:key/4f1cd4de-ab64-4807-920a-47fc42e7f0d0

x-obs-server-side-encryption-customer-algorithm | Indicates an encryption algorithm. This header is included in a response if SSE-C is used. Type: string Example: x-obs-server-side-encryption-customer-algorithm:AES256

#### Response Elements

This response uses elements to return the result of merging parts. Table 4 describes the elements.

Table 4 Response elements
Element | Description
--- | ---
Location | URL of the object after parts being merged. Type: string
Bucket | Bucket in which parts are combined Type: string
Key | Indicates the key of the generated object. Type: string
ETag | The result calculated based on the ETag of each part is the unique identifier of the object content. Type: string

#### Error Responses

1. If no message body exists, OBS returns 400 Bad Request.
2. If the message body format is incorrect, OBS returns 400 Bad Request.
3. If the part information in the message body is not sorted by part sequence number, OBS returns 400 Bad Request and the error code is InvalidPartOrder.
4. If the AK or signature is invalid, OBS returns 403 Forbidden and the error code is AccessDenied.
5. If the requested bucket does not exist, OBS returns 404 Not Found and the error code is NoSuchBucket.
6. If the requested multipart upload does not exist, OBS returns 404 Not Found and error code NoSuchUpload.
7. If the user is not the initiator of the task, OBS returns 403 Forbidden and the error code is AccessDenied.
8. If the request part list contains a part that does not exist, OBS returns 400 Bad Request and the error code is InvalidPart.
9. If the Etag of the part contained in the request part list is incorrect, OBS returns 400 Bad Request and the error code is InvalidPart.
10. If the size of a part other than the last part is smaller than 100 KB, OBS returns 400 Bad Request.
11. If the size of the object is greater than 48.8 TB after parts being merged, OBS returns status code 400 Bad Request.

Other errors are included in Table 2.

#### Sample Request

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    POST /object02?uploadId=00000163D46218698DF407362295674C HTTP/1.1
    User-Agent: curl/7.29.0
    Host: examplebucket.obs.region.example.com
    Accept: */*
    Date: WED, 01 Jul 2015 05:23:46 GMT
    Authorization: OBS H4IPJX0TQTHTHEBQQCEC:dOfK9iILcKxo58tRp3fWeDoYzKA=
    Content-Length: 422

    <?xml version="1.0" encoding="utf-8"?>
    <CompleteMultipartUpload>
      <Part>
        <PartNumber>1</PartNumber>
        <ETag>a54357aff0632cce46d942af68356b38</ETag>
      </Part>
      <Part>
        <PartNumber>2</PartNumber>
        <ETag>0c78aef83f66abc1fa1e8477f296d394</ETag>
      </Part>
      <Part>
        <PartNumber>3</PartNumber>
        <ETag>acbd18db4cc2f85cedef654fccc4a4d8</ETag>
      </Part>
    </CompleteMultipartUpload>

#### Sample Response

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    HTTP/1.1 200 OK
    Server: OBS
    x-obs-request-id: 8DF400000163D4625BE3075019BD02B8
    x-obs-id-2: 32AAAQAAEAABAAAQAAEAABAAAQAAEAABCSN8D1AfQcIvyGBZ9+Ee+jU6zv1iYdO4
    Content-Type: application/xml
    Date: WED, 01 Jul 2015 05:23:46 GMT
    Content-Length: 326

    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <CompleteMultipartUploadResult xmlns="http://obs.example.com/doc/2015-06-30/">
      <Location>/examplebucket/object02</Location>
      <Bucket>examplebucket</Bucket>
      <Key>object02</Key>
      <ETag>"03f814825e5a691489b947a2e120b2d3-3"</ETag>
    </CompleteMultipartUploadResult>

Parent topic: Operations on Multipart Upload