Before you upload an object to OSS by using resumable upload, you can specify a folder for the checkpoint file that stores resumable upload records. If a file fails to be uploaded because the network is abnormal or the program stops responding, the upload task is resumed from the position recorded in the checkpoint file to upload remaining bytes.

Background information

During resumable upload, the upload progress is recorded in a checkpoint file. If the upload of a part fails, the next upload starts from the position recorded in the checkpoint file. The checkpoint file is deleted after resumable upload is complete.

You can use client.ResumableUploadObject to perform resumable upload. The following table describes the parameters you can configure for UploadObjectRequest.

Parameter Description Required Default value Configuration method
bucket The name of the bucket. Yes None Constructor
key The name of the object. Yes None
filePath The name of the local file to upload. No None
partSize The size of each part. Valid values: 100 KB to 5 GB. No 8 MB setPartSize
threadNum The number of parts you upload simultaneously. No 3 Constructor or setThreadNum
checkpointDir The checkpoint file that records the upload results of each part. This file stores information about upload progress. If you fail to upload a part, the part upload continues based on the recorded progress. After the entire local file is uploaded, this file is deleted. No The same directory as that of DownloadFile Constructor or setCheckpointDir

For more information about how to perform resumable upload, see Multipart upload and resumable upload. For the complete code, visit GitHub.

Sample code

The following code provides an example on how to perform resumable upload by using multipart upload.

#include <alibabacloud/oss/OssClient.h>
using namespace AlibabaCloud::OSS;

int main(void)
     /* Initialize the OSS account information. */
    std::string AccessKeyId = "yourAccessKeyId";
    std::string AccessKeySecret = "yourAccessKeySecret";
    std::string Endpoint = "yourEndpoint";
    std::string BucketName = "yourBucketName";
    std::string ObjectName = "yourObjectName";
    std::string UploadFilePath = "yourUploadfilePath";
    std::string CheckpointFilePath = "yourCheckpointFilepath"

    /* Initialize network resources. */

    ClientConfiguration conf;
    OssClient client(Endpoint, AccessKeyId, AccessKeySecret, conf);

    /* Start resumable upload. */
    UploadObjectRequest request(BucketName, ObjectName, UploadFilePath, CheckpointFilePath);
    auto outcome = client.ResumableUploadObject(request);

    if (! outcome.isSuccess()) {
        /* Handle exceptions. */
        std::cout << "ResumableUploadObject fail" <<
        ",code:" << outcome.error().Code() <<
        ",message:" << outcome.error().Message() <<
        ",requestId:" << outcome.error().RequestId() << std::endl;
        return -1;

    /* Release network resources. */
    return 0;