AppendObject

An object created with the AppendObject operation is an appendable object, and an object uploaded with the PutObject operation is a normal object.

Association with other operations

Request syntax

POST /ObjectName? append&position=Position HTTP/1.1
Content-Length：ContentLength
Content-Type: ContentType
Host: BucketName.oss.aliyuncs.com
Date: GMT Date
Authorization: SignatureValue

Parameters in an AppendObject request

An AppendObject request must include the append and position parameters, which are both CanonicalizedResource and must be included in the signature.

• append

  This parameter indicates that the request is sent to perform an AppendObject operation.

• position

  This parameter specifies the position from where the append operation starts. The value of position in the first AppendObject operation must be 0, and the value of position in the subsequent operation is the current object length. For example, if the value of position specified in the first AppendObject request is 0, and the value of content-length is 65536, the value of position specified in the second AppendObject request must be set to 65536.

  Each time after an AppendObject operation succeeds, x-oss-next-append-position in the response header specifies the position of the next AppendObject request.

  Note the following when setting position:

  • If the value of position is 0 and an object with the same name does not exist, you can set headers (such as x-oss-server-side-encryption) in the AppendObject request in the same way as you do in a PutObject request. If you add a correct x-oss-server-side-encryption header in an AppendObject request in which the value of position is 0, the x-oss-server-side-encryption header is also included in the response header. You can initiate a CopyObject request to modify the metadata of the object in subsequent operations.
  • If the value of position is 0 and an appendable object with the same name does not exist, or if the length of an appendable object with the same name is 0, the AppendObject operation is successful. Otherwise, the system determines that the position and object length do not match and returns a PositionNotEqualToLength error code.
  • The length limit of an object generated by an AppendObject operation is the same as that of an object generated by a PutObject operation. Each time after an AppendObject operation is performed, the last modification time of this object is updated.
  • If the position value is correct and content with a length of 0 is appended to an existing appendable object, the status of the object does not change.

Request headers

Response headers

CRC64 calculation method

The CRC value of an appendable object is calculated according to ECMA-182. You can calculate the CRC64 in the following methods:

• Calculate using boost CRC module:

  typedef boost::crc_optimal<64, 0x42F0E1EBA9EA3693ULL, 0xffffffffffffffffULL, 0xffffffffffffffffULL, true, true> boost_ecma;
  
  uint64_t do_boost_crc(const char* buffer, int length)
  {
      boost_ecma crc;
      crc.process_bytes(buffer, length);
      return crc.checksum();
  }

• Calculate using the Python crcmod:

  do_crc64 = crcmod.mkCrcFun(0x142F0E1EBA9EA3693L, initCrc=0L, xorOut=0xffffffffffffffffL, rev=True)
  
  print do_crc64(“123456789”)

Example

Request example:

POST /oss.jpg? append&position=0 HTTP/1.1 
Host: oss-example.oss.aliyuncs.com 
Cache-control: no-cache 
Expires: Wed, 08 Jul 2015 16:57:01 GMT 
Content-Encoding: utf-8 
x-oss-storage-class: Archive
Content-Disposition: attachment;filename=oss_download.jpg 
Date: Wed, 08 Jul 2015 06:57:01 GMT 
Content-Type: image/jpg 
Content-Length: 1717 
Authorization: OSS qn6qrrqxo2oawuk53otfjbyc:kZoYNv66bsmc10+dcGKw5x2PRrk=  
[1717 bytes of object data]

Response example:

HTTP/1.1 200 OK
Date: Wed, 08 Jul 2015 06:57:01 GMT
ETag: "0F7230CAA4BE94CCBDC99C5500000000"
Connection: keep-alive
Content-Length: 0  
Server: AliyunOSS
x-oss-hash-crc64ecma: 14741617095266562575
x-oss-next-append-position: 1717
x-oss-request-id: 559CC9BDC755F95A64485981

Error messages