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CRC64 Check
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Last updated: 2024-02-02 12:12:58
CRC64 Check
Last updated: 2024-02-02 12:12:58
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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 PUT Object and POST Object: you can get the CRC64 check value for your object from the response headers.
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.
The Upload Part - Copy operation returns a corresponding CRC64 value.
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 Verification Methods

The default C++ SDK verification methods vary depending on APIs.
APIs for simple upload PUT Object: MD5 verification by default, with CRC64 verification unavailable.
APIs for multipart upload
Upload Part: MD5 verification by default, with CRC64 verification unavailable.
Complete Multipart Upload: CRC64 verification by default, with MD5 verification unavailable.

Sample 1. Multipart upload

qcloud_cos::CosConfig config("./config.json");
qcloud_cos::CosAPI cos(config);

std::string bucket_name = "examplebucket-1250000000"; // Change to the bucket name
std::string object_name = "exampleobject"; // Change to the object name
std::string local_file = "./test"; // Change to the local file name

qcloud_cos::MultiUploadObjectReq req(bucket_name, object_name, local_file); // CRC64 verification enabled by default
req.SetRecvTimeoutInms(1000 * 60);
qcloud_cos::MultiUploadObjectResp resp;
qcloud_cos::CosResult result = cos.MultiUploadObject(req, &resp); // Automatic verification of the CRC64 value
// The call is successful. You can call the resp member functions to get the return content.
if (result.IsSucc()) {
    // ...
} else {
    // You can call the CosResult member functions to get the error information, such as requestID.
}

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