Check data transmission integrity by using CRC-64

Operation instructions

• The PutObject, AppendObject, PostObject, and MultipartUploadPart operations return the corresponding CRC-64 value. The client can obtain the CRC-64 value returned by the server after the upload is complete and can check it against the value calculated on the local machine.
• When the MultipartComplete operation is called, the CRC-64 value of the entire object is returned if each part has a CRC-64 value. However, if a part is uploaded before the CRC-64 goes online, the CRC-64 value is returned.
• The GetObject, HeadObject, and GetObjectMeta operations return the corresponding CRC-64 value (if any). After the GetObject operation is complete, the client can obtain the CRC-64 value returned by the server and check it against the value calculated on the local machine.
  Note The GET request that includes the Range header returns the CRC-64 value of the entire object.
• The newly generated object or part may not have the CRC-64 value after copy related operations such as CopyObject and UploadPartCopy are complete.

Examples

The following code provides an example on how to use Python to use CRC-64 values to verify data transmission integrity:

1. Calculate the CRC-64 value.

   import oss2
   from oss2.models import PartInfo
   import os
   import crcmod
   import random
   import string
   do_crc64 = crcmod.mkCrcFun(0x142F0E1EBA9EA3693L, initCrc=0L, xorOut=0xffffffffffffffffL, rev=True)
   def check_crc64(local_crc64, oss_crc64, msg="check crc64"):
   if local_crc64 ! = oss_crc64:
   print "{0} check crc64 failed. local:{1}, oss:{2}.".format(msg, local_crc64, oss_crc64)
   return False
   else:
   print "{0} check crc64 ok.".format(msg)
   return True
   def random_string(length):
   return ''.join(random.choice(string.lowercase) for i in range(length))
   bucket = oss2.Bucket(oss2.Auth(access_key_id, access_key_secret), endpoint, bucket_name)

2. Verify CRC-64 values for PutObject.

   content = random_string(1024)
    key = 'normal-key'
    result = bucket.put_object(key, content)
    oss_crc64 = result.headers.get('x-oss-hash-crc64ecma', '')
    local_crc64 = str(do_crc64(content))
    check_crc64(local_crc64, oss_crc64, "put object")

3. Verify CRC-64 values for GetObject.

   result = bucket.get_object(key)
    oss_crc64 = result.headers.get('x-oss-hash-crc64ecma', '')
    local_crc64 = str(do_crc64(result.resp.read()))
    check_crc64(local_crc64, oss_crc64, "get object")

4. Verify CRC-64 values for UploadPart and MultipartComplete.

   part_info_list = []
    key = "multipart-key"
    result = bucket.init_multipart_upload(key)
    upload_id = result.upload_id
    part_1 = random_string(1024 * 1024)
    result = bucket.upload_part(key, upload_id, 1, part_1)
    oss_crc64 = result.headers.get('x-oss-hash-crc64ecma', '')
    local_crc64 = str(do_crc64(part_1))
    # Check whether the uploaded part_1 data is complete
    check_crc64(local_crc64, oss_crc64, "upload_part object 1")
    part_info_list.append(PartInfo(1, result.etag, len(part_1)))
    part_2 = random_string(1024 * 1024)
    result = bucket.upload_part(key, upload_id, 2, part_2)
    oss_crc64 = result.headers.get('x-oss-hash-crc64ecma', '')
    local_crc64 = str(do_crc64(part_2))
    # Check whether the uploaded part_2 data is complete
    check_crc64(local_crc64, oss_crc64, "upload_part object 2")
    part_info_list.append(PartInfo(2, result.etag, len(part_2)))
    result = bucket.complete_multipart_upload(key, upload_id, part_info_list)
    oss_crc64 = result.headers.get('x-oss-hash-crc64ecma', '')
    local_crc64 = str(do_crc64(part_2, do_crc64(part_1)))
    # Check whether the final object in OSS is consistent with the local file
    check_crc64(local_crc64, oss_crc64, "complete object")

OSS SDK support

The following table describes OSS SDKs, some of which support CRC-64 for downloads and uploads.