Object Storage Service:Conditional download

Usage notes

• Before you run the sample code in this topic, you must create an OSSClient instance by using methods such as using a custom domain name or Security Token Service (STS). For more information, see Initialization.

  Note

  The region of the bucket is determined by the endpoint specified for initialization.

• To download an object, you must have the ossGetObject permission. For more information, see Attach a custom policy to a RAM user.

Examples

The following sample code provides an example on how to download the exampleobject.txt object from the exampledir directory of the examplebucket bucket. Multiple conditions are specified for the download:

OSSGetObjectRequest *get = [OSSGetObjectRequest new];
// Specify the name of the bucket. For more information about bucket naming, see Bucket naming conventions. 
get.bucketName = @"examplebucket";
// Specify the full path of the object. Do not include the bucket name in the full path of the object. For more information about the naming conventions for objects, see Object naming conventions. 
get.objectKey = @"exampledir/exampleobject.txt";
NSMutableDictionary *headerFields = [NSMutableDictionary dictionary];
// Set If-Modified-Since to Fri, 13 Oct 2021 14:47:53 GMT. 
[headerFields setValue:@"Fri, 13 Oct 2021 14:47:53 GMT" forKey:@"If-Modified-Since"];
// Specify that the object is downloaded only when its last modified time is the specified time or earlier. 
[headerFields setValue:[[NSDate new] oss_asStringValue] forKey:@"If-Unmodified-Since"];
// Specify that the object is downloaded only if its entity tag (ETag) is not the specified ETag. 
[headerFields setValue:@"5B3C1A2E0563E1B002CC607C****" forKey:@"If-None-Match"];
// Specify that the object is downloaded only if its ETag is the same as the specified ETag. 
[headerFields setValue:@"fba9dede5f27731c9771645a3986****" forKey:@"If-Match"];
get.headerFields = headerFields;

[[[client getObject:get] continueWithBlock:^id _Nullable(OSSTask * _Nonnull task) {
    if (!task.error) {
        NSLog(@"get object success!");
    } else {
        NSLog(@"get object error: %@", task.error);
    }
    return nil;
}] waitUntilFinished];

References

• For more information about the API operation that you can call to perform conditional download, see GetObject.

• For more information about how to initialize an OSSClient instance, see Initialization.