使用預先簽署的 URL 上傳檔案

使用預先簽署的 URL，用戶端可以直接將檔案上傳到與 S3 相容的雲端儲存伺服器 (S3)，而無需向使用者公開 S3 憑證。

本指南說明如何使用 presignedPutObject API 從 MinIO JavaScript 程式庫產生預先簽署的 URL。這透過 JavaScript 範例來展示，其中 Express Node.js 伺服器公開一個端點以產生預先簽署的 URL，而用戶端 Web 應用程式使用該 URL 將檔案上傳到 MinIO 伺服器。

建立伺服器
建立用戶端 Web 應用程式

1. 建立伺服器

伺服器由一個 Express Node.js 伺服器組成，該伺服器公開一個名為 /presignedUrl 的端點。此端點使用 Minio.Client 物件產生一個短暫的預先簽署 URL，可用於將檔案上傳到 Minio 伺服器。

// In order to use the MinIO JavaScript API to generate the pre-signed URL, begin by instantiating
// a `Minio.Client` object and pass in the values for your server.
// The example below uses values for play.min.io:9000

const Minio = require('minio')

var client = new Minio.Client({
    endPoint: 'play.min.io',
    port: 9000,
    useSSL: true,
    accessKey: 'Q3AM3UQ867SPQQA43P2F',
    secretKey: 'zuf+tfteSlswRu7BJ86wekitnifILbZam1KYY3TG'
})

// Instantiate an `express` server and expose an endpoint called `/presignedUrl` as a `GET` request that
// accepts a filename through a query parameter called `name`. For the implementation of this endpoint,
// invoke [`presignedPutObject`](https://minio.dev.org.tw/docs/minio/linux/developers/javascript/API.html#presignedPutObjectt) 
// on the `Minio.Client` instance to generate a pre-signed URL, and return that URL in the response:

// express is a small HTTP server wrapper, but this works with any HTTP server
const server = require('express')()

server.get('/presignedUrl', (req, res) => {
    client.presignedPutObject('uploads', req.query.name, (err, url) => {
        if (err) throw err
        res.end(url)
    })
})

server.get('/', (req, res) => {
    res.sendFile(__dirname + '/index.html');
})

server.listen(8080)

2. 建立用戶端 Web 應用程式

用戶端 Web 應用程式的使用者介面包含一個選取器欄位，允許使用者選取要上傳的檔案，以及一個按鈕，用於叫用一個名為 upload 的 onclick 處理常式。

<input type="file" id="selector" multiple>
<button onclick="upload()">Upload</button>

<div id="status">No uploads</div>

<script type="text/javascript">
  // `upload` iterates through all files selected and invokes a helper function called `retrieveNewURL`.
  function upload() {
        // Get selected files from the input element.
        var files = document.querySelector("#selector").files;
        for (var i = 0; i < files.length; i++) {
            var file = files[i];
            // Retrieve a URL from our server.
            retrieveNewURL(file, (file, url) => {
                // Upload the file to the server.
                uploadFile(file, url);
            });
        }
    }

    // `retrieveNewURL` accepts the name of the current file and invokes the `/presignedUrl` endpoint to
    // generate a pre-signed URL for use in uploading that file: 
    function retrieveNewURL(file, cb) {
        fetch(`/presignedUrl?name=${file.name}`).then((response) => {
            response.text().then((url) => {
                cb(file, url);
            });
        }).catch((e) => {
            console.error(e);
        });
    }

    // ``uploadFile` accepts the current filename and the pre-signed URL. It then uses `Fetch API`
    // to upload this file to S3 at `play.min.io:9000` using the URL:
    function uploadFile(file, url) {
        if (document.querySelector('#status').innerText === 'No uploads') {
            document.querySelector('#status').innerHTML = '';
        }
        fetch(url, {
            method: 'PUT',
            body: file
        }).then(() => {
            // If multiple files are uploaded, append upload status on the next line.
            document.querySelector('#status').innerHTML += `<br>Uploaded ${file.name}.`;
        }).catch((e) => {
            console.error(e);
        });
    }
</script>

注意： 這使用 File API、QuerySelector API、fetch API 和 Promise API。