Object Storage Service:Upload callbacks (C++ SDK)

Prerequisites

Before you begin, ensure that you have:

• An OSS bucket

• The OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables set with valid credentials

• A running callback server that accepts HTTP POST requests

Usage notes

• Examples in this topic use the public endpoint of the China (Hangzhou) region. To access OSS from other Alibaba Cloud services in the same region, use an internal endpoint instead. For more information, see Regions and endpoints.

• This topic creates the OSSClient instance using an OSS endpoint. To create an OSSClient using a custom domain name or Security Token Service (STS), see Create an OSSClient instance.

How it works

1. Configure a callback when submitting the upload request. Specify the callback URL, the callback body, and any custom variables.

2. OSS uploads the object. On success, OSS sends an HTTP POST request to your callback URL with the body you specified.

3. A failed callback does not affect the status of a successful file upload.

Configure an upload callback

The following example configures an upload callback for a PutObject request.

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

int main(void)
{
    /* Set the endpoint of the region where your bucket is located.
       For the China (Hangzhou) region: https://oss-cn-hangzhou.aliyuncs.com */
    std::string Endpoint = "yourEndpoint";
    /* Set the region ID. For the China (Hangzhou) region: cn-hangzhou */
    std::string Region = "yourRegion";
    /* Bucket name. Example: examplebucket */
    std::string BucketName = "examplebucket";
    /* Full path of the object, excluding the bucket name.
       Example: exampledir/exampleobject.txt */
    std::string ObjectName = "exampledir/exampleobject.txt";
    /* URL of your callback server */
    std::string ServerName = "https://example.aliyundoc.com:23450";

    /* Initialize network resources */
    InitializeSdk();

    ClientConfiguration conf;
    conf.signatureVersion = SignatureVersionType::V4;
    /* Read access credentials from environment variables.
       Set OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET before running this code. */
    auto credentialsProvider = std::make_shared<EnvironmentVariableCredentialsProvider>();
    OssClient client(Endpoint, credentialsProvider, conf);
    client.SetRegion(Region);

    std::shared_ptr<std::iostream> content = std::make_shared<std::stringstream>();
    *content << "Thank you for using Alibaba Cloud Object Storage Service!";

    /* Build the callback configuration */
    std::string callbackBody = "bucket=${bucket}&object=${object}&etag=${etag}&size=${size}&mimeType=${mimeType}&my_var1=${x:var1}";
    ObjectCallbackBuilder builder(ServerName, callbackBody, "", ObjectCallbackBuilder::Type::URL);
    std::string value = builder.build();

    /* Add a custom variable */
    ObjectCallbackVariableBuilder varBuilder;
    varBuilder.addCallbackVariable("x:var1", "value1");
    std::string varValue = varBuilder.build();

    /* Attach the callback config to the upload request */
    PutObjectRequest request(BucketName, ObjectName, content);
    request.MetaData().addHeader("x-oss-callback", value);
    request.MetaData().addHeader("x-oss-callback-var", varValue);
    auto outcome = client.PutObject(request);

    /* Release network resources */
    ShutdownSdk();
    return 0;
}

Callback parameters

System variables in the callback body

Use these variables in callbackBody to include object metadata in the callback request sent to your server.

What's next

• Callback — API reference for upload callbacks