Object Storage Service:Check data integrity by using CRC-64

Usage notes

• The PutObject, AppendObject, PostObject, and MultipartUploadPart operations return a CRC-64 value. After an upload is complete, you can retrieve the CRC-64 value from the server and compare it with the value that you calculated locally.

• When you call the CompleteMultipartUpload operation, the CRC-64 value for the entire object is returned only if all of its parts have a CRC-64 value. If any part lacks a CRC-64 value, the CRC-64 value for the complete object is not returned. For example, if a part was uploaded before this feature was available, it will not have a CRC-64 value.

• The GetObject, HeadObject, and GetObjectMeta operations return the object's CRC-64 value, if available. After a GetObject operation completes, you can retrieve the CRC-64 value from the server and compare it with a locally calculated value.

  Note

  A GET request with a Range header returns the CRC-64 value of the entire object.

• For copy operations, such as CopyObject and UploadPartCopy, the new object or part is not guaranteed to have a CRC-64 value.

Examples

The following Python code provides an example of how to verify data integrity using CRC-64 values.

import oss2 from oss2.credentials import EnvironmentVariableCredentialsProvider import crcmod import random import string from oss2.models import PartInfo # Obtain access credentials from environment variables. Before you run this sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. auth = oss2.ProviderAuth(EnvironmentVariableCredentialsProvider()) # Specify the endpoint for the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. # Specify the bucket name in yourBucketName. bucket = oss2.Bucket(auth, 'https://oss-cn-hangzhou.aliyuncs.com', 'yourBucketName') # Create a CRC-64 check function. do_crc64 = crcmod.mkCrcFun(0x142F0E1EBA9EA3693, initCrc=0, xorOut=0xffffffffffffffff, rev=True) # Check the CRC-64 and print the result. 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 # Generate a random string of a specified length. def random_string(length): return ''.join(random.choice(string.ascii_lowercase) for i in range(length)) # Generate a random string named content with a length of 1024. content = random_string(1024) # Set the object path. key = 'normal-key' # Verify PutObject. result = bucket.put_object(key, content) oss_crc64 = result.headers.get('x-oss-hash-crc64ecma', '') local_crc64 = str(do_crc64(oss2.to_bytes(content))) check_crc64(local_crc64, oss_crc64, "put object") # Verify 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") # Verify UploadPart and Complete. 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(oss2.to_bytes(part_1))) # Check the data integrity of uploaded part 1. 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(oss2.to_bytes(part_2))) # Check the data integrity of uploaded part 2. 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(oss2.to_bytes(part_2), do_crc64(oss2.to_bytes(part_1)))) # Check whether the final object on OSS is consistent with the local file. check_crc64(local_crc64, oss_crc64, "complete object")

OSS SDK support

Some OSS SDKs support CRC-64 data integrity checks for uploads and downloads. See the following table for examples.