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 error code will be returned and the download will fail.

You can set the following conditions:

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

Sample code:

// Create an instance of ObsClient.
var obsClient = new ObsClient({
    // Hard-coded or plaintext AK/SK are risky. For security purposes, encrypt your AK/SK and store them in the configuration file or environment variables. In this example, the AK/SK are stored in environment variables for identity authentication. Before running this example, configure environment variables AccessKeyID and SecretAccessKey.
    // The front-end code does not have the process environment variable, so you need to use a module bundler like webpack to define the process variable.
    // Obtain an AK/SK pair on the management console. For details, see https://support.huaweicloud.com/eu/usermanual-ca/ca_01_0003.html.
    access_key_id: process.env.AccessKeyID,
    secret_access_key: process.env.SecretAccessKey,
    // Replace the example endpoint with the actual one in your case.
    server: 'https://obs.eu-west-101.myhuaweicloud.eu'
});

obsClient.getObject({
       Bucket : 'bucketname',
       Key : 'objectname',
       IfModifiedSince : 'Thu, 31 Dec 2015 16:00:00 GMT'
}, function (err, result) {
       if(err){
              console.error('Error-->' + err);
       }else{
              console.log('Status-->' + result.CommonMsg.Status);
              if(result.CommonMsg.Status < 300 && result.InterfaceResult){
                   // Obtain the object content.
                   console.log('Object Content:'); 
                   console.log(result.InterfaceResult.Content); 
              }
       }
});