Overview
Errors may occur when data is transferred between the client and the server. COS can not only verify data integrity through MD5 and custom attributes, but also the CRC64 check code. COS will calculate the CRC64 of the newly uploaded object and store the result as object attributes. It will carry x-cos-hash-crc64ecma in the returned response header, which indicates the CRC64 value of the uploaded object calculated according to ECMA-182 standard. If an object already has a CRC64 value stored before this feature is activated, COS will not calculate its CRC64 value, nor will it be returned when the object is obtained.
Description
APIs that currently support CRC64 include:
APIs for simple upload
Multipart upload APIs
Upload Part: you can compare and verify the CRC64 value returned by COS against the value calculated locally. Complete Multipart Upload: returns a CRC64 value for the entire object only if each part has a CRC64 attribute. Otherwise, no value is returned. When you call the PUT Object - Copy, the CRC64 value is returned only if the source object has one. The HEAD Object and GET Object operations return the CRC64 value provided the object has one. You can compare and verify the CRC64 value returned by COS against that calculated locally. API Samples
Upload Part response
The following example shows the response to an Upload Part request. The x-cos-hash-crc64ecma
header represents the CRC64 value of a part, which you can compare against the locally calculated CRC64 value to verify the part integrity.
HTTP/1.1 200 OK
content-length: 0
connection: close
date: Thu, 05 Dec 2019 01:58:03 GMT
etag: "358e8c8b1bfa35ee3bd44cb3d2cc416b"
server: tencent-cos
x-cos-hash-crc64ecma: 15060521397700495958
x-cos-request-id: NWRlODY0MmJfMjBiNDU4NjRfNjkyZl80ZjZi****
Complete Multipart Upload response
The following example shows the response to a Complete Multipart Upload request. The x-cos-hash-crc64ecma
header represents the CRC64 value of an entire object, which you can compare against the locally calculated CRC64 value to verify the object integrity.
HTTP/1.1 200 OK
content-type: application/xml
transfer-encoding: chunked
connection: close
date: Thu, 05 Dec 2019 02:01:17 GMT
server: tencent-cos
x-cos-hash-crc64ecma: 15060521397700495958
x-cos-request-id: NWRlODY0ZWRfMjNiMjU4NjRfOGQ4Ml81MDEw****
[Object Content]
SDK Samples
Python SDK
The following example uses the Python SDK to verify object integrity. The complete sample code is as follows.
Note:
The code is based on Python 2.7. For more information on how to use the Python SDK, see Object Operations. 1. Initialization configuration
Configure user attributes, including SecretId, SecretKey, and region, and create a client object.
from qcloud_cos import CosConfig
from qcloud_cos import CosS3Client
from qcloud_cos import CosServiceError
from qcloud_cos import CosClientError
import sys
import logging
import hashlib
import crcmod
logging.basicConfig(level=logging.INFO, stream=sys.stdout)
secret_id = COS_SECRETID
secret_key = COS_SECRETKEY
region = 'ap-beijing'
token = None
config = CosConfig(Region=region, SecretId=secret_id, SecretKey=secret_key, Token=token)
client = CosS3Client(config)
2. Calculate the object checksum
Simulate object parts and calculate the checksum of the entire object.
OBJECT_PART_SIZE = 1024 * 1024
OBJECT_TOTAL_SIZE = OBJECT_PART_SIZE * 1 + 123
object_body = '1' * OBJECT_TOTAL_SIZE
c64 = crcmod.mkCrcFun(0x142F0E1EBA9EA3693, initCrc=0, xorOut=0xffffffffffffffff, rev=True)
local_crc64 =str(c64(object_body))
3. Initialize the multipart upload
response = client.create_multipart_upload(
Bucket='examplebucket-1250000000',
Key='exampleobject',
StorageClass='STANDARD',
)
upload_id = response['UploadId']
4. Upload the object using multipart upload
During a multipart upload, an object is divided into multiple (up to 10,000) parts for upload. The size of each part ranges from 1 MB to 5 GB, except the last part can be less than 1 MB. When uploading parts, configure the PartNumber of each part and calculate its corresponding CRC64 value. After the parts are successfully uploaded, check the returned CRC64 value with the locally calculated value to verify the object integrity.
part_list = list()
position = 0
left_size = OBJECT_TOTAL_SIZE
part_number = 0
while left_size > 0:
part_number += 1
if left_size >= OBJECT_PART_SIZE:
body = object_body[position:position+OBJECT_PART_SIZE]
else:
body = object_body[position:]
position += OBJECT_PART_SIZE
left_size -= OBJECT_PART_SIZE
local_part_crc_64 = c64(body)
response = client.upload_part(
Bucket='examplebucket-1250000000',
Key='exampleobject',
Body=body,
PartNumber=part_number,
UploadId=upload_id,
)
part_crc_64 = response['x-cos-hash-crc64ecma']
if local_part_crc64 != part_crc_64:
print 'crc64 check FAIL'
exit(-1)
etag = response['ETag']
part_list.append({'ETag' : etag, 'PartNumber' : part_number})
5. Complete the multipart upload
After all parts are successfully uploaded, you need to complete the multipart upload. Then, you can verify the CRC64 value returned by COS against that of the local object.
response = client.complete_multipart_upload(
Bucket='examplebucket-1250000000',
Key=‘exampleobject’,
UploadId=upload_id,
MultipartUpload={
'Part' : part_list
},
)
crc64ecma = response['x-cos-hash-crc64ecma']
if crc64ecma != local_crc64:
print 'check crc64 Failed'
exit(-1)
Java SDK
You are advised to use advanced APIs of the Java SDK to upload objects. For more information, please see Object Operations. Calculating CRC64 locally
String calculateCrc64(File localFile) throws IOException {
CRC64 crc64 = new CRC64();
try (FileInputStream stream = new FileInputStream(localFile)) {
byte[] b = new byte[1024 * 1024];
while (true) {
final int read = stream.read(b);
if (read <= 0) {
break;
}
crc64.update(b, read);
}
}
return Long.toUnsignedString(crc64.getValue());
}
Getting CRC64 of a COS file and verifying it with the local one
ObjectMetadata cosMeta = COSClient().getObjectMetadata(bucketName, cosFilePath);
String cosCrc64 = cosMeta.getCrc64Ecma();
String localCrc64 = calculateCrc64(localFile);
if (cosCrc64.equals(localCrc64)) {
System.out.println("ok");
} else {
System.out.println("fail");
}
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