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Performing a Conditioned Download

If you have any questions during development, post them on the Issues page of GitHub. For details about parameters and usage of each API, see the API Reference

When downloading an object, you can specify one or more conditions. Only when the conditions are met, the object will be downloaded. Otherwise, an exception indicating a download failure will be thrown.

You can set the following conditions:

Parameter

Description

Property in OBS .NET SDK

If-Modified-Since

Returns the object if it is modified after the time specified by this parameter; otherwise, an exception is thrown.

GetObjectRequest.IfModifiedSince

If-Unmodified-Since

Returns the object if it remains unchanged since the time specified by this parameter; otherwise, an exception is thrown.

GetObjectRequest.IfUnmodifiedSince

If-Match

Returns the source object if its ETag is the same as the one specified by this parameter; otherwise, an exception is thrown.

GetObjectRequest.IfMatch

If-None-Match

Returns the source object if its ETag is different from the one specified by this parameter; otherwise, an exception is thrown.

GetObjectRequest.IfNoneMatch
  • The ETag of an object is the MD5 check value of the object.
  • If the download request includes IfUnmodifiedSince or IfMatch and the specified condition is not met, an exception will be thrown with HTTP status code 412 Precondition Failed returned.
  • If the download request includes IfModifiedSince or IfNoneMatch and the specified condition is not met, an exception will be thrown with HTTP status code 304 Not Modified returned.

Sample code:

// Create an instance of ObsClient.
ObsClient client = new ObsClient("*** Provide your Access Key ***", "*** Provide your Secret Key ***", "https://your-endpoint");
// Download an object in conditioned mode.
try
{
    DateTime datetime = new DateTime(2018, 3, 10, 12, 00, 00);
    GetObjectRequest request = new GetObjectRequest()
    {
        BucketName = "bucketname",
        ObjectKey = "objectname",
        IfModifiedSince = datetime,
    };
    using (GetObjectResponse response = client.GetObject(request))
    {
        string dest = "savepath";
        if (!File.Exists(dest))
        {
            response.WriteResponseStreamToFile(dest);
        }
        Console.WriteLine("Get object response: {0}", response.StatusCode);
    }
}
catch (ObsException ex)
{
   Console.WriteLine("ErrorCode: {0}", ex.ErrorCode);
   Console.WriteLine("ErrorMessage: {0}", ex.ErrorMessage);
}
Parent topic: Object Download