Help Center> Object Storage Service> Node.js> Object Download> Performing a Conditioned Download
Updated on 2023-11-09 GMT+08:00

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:

Parameter

Description

Format

IfModifiedSince

Returns the object if it is modified after the time specified by this parameter; otherwise, an error code is returned.

This parameter must conform to the HTTP time format specified in http://www.ietf.org/rfc/rfc2616.txt.

IfUnmodifiedSince

Returns the object if it remains unchanged since the time specified by this parameter; otherwise, an error code is returned.

This parameter must conform to the HTTP time format specified in http://www.ietf.org/rfc/rfc2616.txt.

IfMatch

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

Character string

IfNoneMatch

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

Character string

  • The ETag of the source object is the MD5 check value of the source object content.
  • 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 is as follows:

// Import the OBS library.
// Use npm to install the client.
var ObsClient = require('esdk-obs-nodejs');
// Use source codes to install the client.
// var ObsClient = require('./lib/obs');

// Create an instance of ObsClient.
var obsClient = new ObsClient({
       //Obtain an AK/SK pair using environment variables or import the AK/SK pair in other ways. Using hard coding may result in leakage.
       //Obtain an AK/SK pair on the management console. For details, see https://support.huaweicloud.com/intl/en-us/usermanual-ca/ca_01_0003.html.
       access_key_id: process.env.ACCESS_KEY_ID,
       secret_access_key: process.env.SECRET_ACCESS_KEY,
       server : 'https://your-endpoint'
});

obsClient.getObject({
       Bucket : 'bucketname',
       Key : 'objectname',
       IfModifiedSince : 'Wed, 04 Jul 2018 08:54:53 GMT'
}, (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.toString()); 
              }
       }
});