Download Object

Download an Object

The SDKs present in the section will allow you to download a particular object, multiple objects, or version of the object. The Bucket reference used in the below code snippet is the component instance.

The first step of the download operation is a GET operation that retrieves the required object from the bucket.

To be able to download an object, the requester must have READ access permissions. However, owners of the bucket do have the option to grant READ access permissions to users, allowing them to download the object without using the required response headers.

If Versioning is enabled for your bucket, you need to pass the versionId to download the particular version of the object. If no versionId is passed, then by default, the latest version of the object will be downloaded.

If Versioning was enabled for a bucket, then disabled. By default, the principal first object will be downloaded. To ensure you download the latest version of this object, you need to pass the versionId param with the value “topVersion”.

    

        
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         const res = await bucket.getObject("sam/out/sample.txt");
// download the object to local machine
const files = fs.createWriteStream('filePath');
res.on('data', (data) => {
  files.write(data)
});
    

Download a Portion of the Object

The following SDK method is used with the range parameter. The range parameter allows you to download a specific range of bytes of an object.

    

        
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         const options = {
 'versionId': 'djkshr8374yiuhf48', // download the object with given versionId
 'range': '0-2000' // start and end range of the object in bytes
}
const res = await bucket.getObject("sam/out/sample.txt", options);
// download the object to your local machine
const files = fs.createWriteStream('filePath');
res.on('data', (data) => {
 files.write(data)
});
    

Download an Object Using Transfer Manager

In this section, we are going to go over SDK methods that will allow you to successfully download large objects from Stratus to your local system using Transfer Manager technique. Transfer Manager is an operation where the large object is split into multiple byte ranges using the start and end bytes range of the object. Each of the object’s parts is then returned as a stream, and they are downloaded to your local system.

Ensure the following packages are imported

    

        
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         const { TransferManager } = require('zcatalyst-sdk-node/lib/stratus');

    

Create Transfer Manager Instance

    

        
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          const transferManager = new TransferManager(bucket); // create transfer manager instance

    

Download Object as Iterable Part Streams

    

        
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         const partSize=50;
const getObjectRes = await transferManager.getIterableObject("sam/out/sample.txt",partSize);
// download the object to local machine
const file = fs.createWriteStream('filePath'); // create a file write stream
for await (const chunk of getObjectRes) {
 file.write(chunk);
}

    

Generate Object Parts for Download

In this SDK method we will download a portion of the object that falls under the required start and end range of bytes.

    

        
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         const file = fs.createWriteStream("filePath");
const partSize = 50;
const downloadRes = await transferManager.generatePartDownloaders("sam/out/sample.txt", file, partSize);
let partNum = 0;
while (partNum < downloadRes.length) {
	const objectPart = downloadRes[partNum++];
	const buffer = await objectPart(); // return the object part as stream
 // process the stream
}

    

Generate Presigned URL to Download an Object

Presigned URLs are secure URLs that authenticated users can share to their non-authenticated users. This URL will provide non-authenticated users with temporary authorization to access objects. The Bucket reference used in the below code snippet is the component instance.

Parameters Used

    

        
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         const signedURLRes = await bucket.generatePreSignedUrl("sam/out/sample.txt", 'GET', {
    'expiryIn': 100, // expiry time in seconds
    'activeFrom':'12334454327', // activate the url in the given date
    'versionId': '746398diij94839'
});
console.log(signedURLRes);

    

Example Response for Generating a Presigned URL for Download

    

        
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         {
  "signature": "https://sadi-development.zohostratus.com/_signed/text.txt?organizationId=96862383&stsCredential=96858154-96862383&stsDate=1747898364894&stsExpiresAfter=300&stsSignedHeaders=host&stsSignature=SFdW4woI5nXPCSCghrymsv06hM0cimwZpkFwHWngtto",
  "expiry_in_seconds": "100",
  "active_from": "12334454327"
}
    

Example Snippet Illustrating Usage of Presigned URL to Download an Object

    

        
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         const axios = require('axios');
const fs = require('fs');

// Replace with the actual pre-signed URL for your file.
const url = 'https://sadi-development.zohostratus.com/_signed/text.txt?organizationId=96862383&stsCredential=96858154-96862383&stsDate=1747898364894&stsExpiresAfter=300&stsSignedHeaders=host&stsSignature=SFdW4woI5nXPCSCghrymsv06hM0cimwZpkFwHWngtto';

(async () => {
  try {
    // Send GET request to download file as a stream
    const response = await axios.get(url, { responseType: 'stream' });

    // Create a writable stream to save the file locally
    const file = fs.createWriteStream('file_path'); // Replace with desired output path

    // ⛓ Pipe the response stream to the file stream
    response.data.pipe(file);

    // Notify when the file has been downloaded
    file.on('finish', () => {
      console.log('File downloaded successfully');
    });

    //  Handle any errors during writing
    file.on('error', (err) => {
      console.error('Error writing file:', err);
    });
  } catch (err) {
    console.error('Error downloading file:', err);
  }
})();