You can specify one or more conditions to download objects. If the specified conditions are met, the object is downloaded. If the specified conditions are not met, an error is returned and the object is not downloaded.
Usage notes
When you use packaging tools such as Webpack and Browserify, install OSS SDK for Browser.js by running the npm install ali-oss command.
If you want to access an OSS bucket from a browser but no CORS rules are configured for the bucket, the browser rejects the request. Therefore, you must configure CORS rules for a bucket if you want to access the bucket from a browser. For more information, see Installation.
In most cases, OSS SDK for Browser.js is used in browsers. To prevent your AccessKey pair from being exposed, we recommend that you use temporary access credentials obtained from Security Token Service (STS) to access OSS.
The temporary access credentials consist of an AccessKey pair and a security token. The AccessKey pair consists of an AccessKey ID and an AccessKey secret. For more information about how to obtain temporary access credentials, see Use STS for temporary access authorization.
Sample code
The following sample code provides an example on how to perform conditional download:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Document</title>
</head>
<body>
<button id='upload'>Upload</button>
<button id='download'>Download</button>
<!-- Import the SDK file -->
<script type="text/javascript" src="https://gosspublic.alicdn.com/aliyun-oss-sdk-6.16.0.min.js"></script>
<script type="text/javascript">
const client = new OSS({
// Specify the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the region to oss-cn-hangzhou.
region: 'yourRegion',
// Specify the temporary AccessKey pair obtained from STS. The AccessKey pair consists of an AccessKey ID and an AccessKey secret.
accessKeyId: 'yourAccessKeyId',
accessKeySecret: 'yourAccessKeySecret',
// Specify the security token that you obtained from STS.
stsToken: 'yourSecurityToken',
// Specify the name of the bucket. Example: examplebucket.
bucket: "examplebucket",
});
const download = document.getElementById('download')
const upload = document.getElementById('upload')
// Upload the object.
upload.addEventListener('click', () => {
// Specify the content of the object to upload.
const file = new Blob(['examplecontent'])
// Specify the full path of the object. Example: exampledir/exampleobject.txt.
const fileName = 'exampledir/exampleobject.txt'
const result = client.put(fileName, file).then(r => console.log(r))
})
// Download the object.
download.addEventListener('click', () => {
// Specify the data range of the object to download.
const start = 1, end = 5
client.get('exampledir/exampleobject.txt', {
headers: {
// Set the If-Modified-Since header in the request. If the value of this header is earlier than the time when the uploaded object is last modified, the object is downloaded. // If the value of the If-Modified-Since header is equal to or later than the time when the uploaded object is last modified, OSS returns 304 Not Modified.
"If-Modified-Since": new Date("1970-01-01").toGMTString()
// Set the If-Unmodified-Since header in the request. If the value of this header is equal to or later than the time when the uploaded object is last modified, the object is downloaded. If the value of the If-Unmodified-Since header is earlier than the time when the uploaded object is last modified, OSS returns 412 Precondition Failed.
//"If-Unmodified-Since": new Date(1970-01-01).toGMTString()
// Set the If-Match header to an ETag value. If the specified ETag value matches the ETag of the object, the object is downloaded. If the specified ETag value does not match the ETag of the object, OSS returns 412 Precondition Failed.
//"If-Match": '5B3C1A2E0563E1B002CC607C****'
// Set the If-Match header to an ETag value. If the specified ETag value does not match the ETag of the object, the object is downloaded. If the specified ETag value matches the ETag of the object, OSS returns 304 Not Modified.
//"If-None-Match": '5B3C1A2E0563E1B002CC607C****'
},
}).then(r => {
if (r.content.length > 0) {
const newBlob = new Blob([r.content], { type: r.res.headers['content-type'] });
const link = document.createElement('a')
link.href = window.URL.createObjectURL(newBlob)
link.download = 'foo.txt'
link.click()
window.URL.revokeObjectURL(link.href)
} else {
console.log ('Error code', r.res.status)
console.log ('No eligible objects to download')
}
})
})
</script>
</body>
</html>