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简介

通常情况下，应用程序上传文件到AWS S3，会使用aws-sdk，但是有些情况下，客户端应用会有安装限制，比如不能安装aws-sdk，此时我们就需要通过其他方式实现文件上传与下载。

这里我们提供一个服务端，在服务端安装aws-sdk。对于文件上传，服务端通过aws-sdk生成一个upload policy，然后将这个upload policy返回给客户端，客户端通过这个upload policy上传文件。对于文件下载，服务端通过aws-sdk生成一个presigned url，然后将这个presigned url返回给客户端，客户端通过这个presigned url下载文件。

文件上传

服务端安装aws-sdk

npm install @aws-sdk/client-s3 
npm install @aws-sdk/s3-request-presigner
npm install @aws-sdk/s3-presigned-post

服务端生成upload policy

在服务端的 controller 里添加一个路由产生并返回 upload policy

import { S3Client } from "@aws-sdk/client-s3";
import { createPresignedPost } from '@aws-sdk/s3-presigned-post';
import { Conditions } from "@aws-sdk/s3-presigned-post/dist-types/types";...app.get("/s3/getUploadPolicy", async (req: Request, res: Response) => {const bucket = req.query.bucket?.toString();const key = req.query.key?.toString();const id = req.query.id?.toString();if (bucket && key) {const fields = {'x-amz-meta-uuid': '' + id};const conditions: Conditions[] = [['starts-with', '$key', key],['content-length-range', 16, 10 * 1024 * 1024],['starts-with', '$Content-Type', '']];const params = {Bucket: bucket,Key: key,Conditions: conditions,Fields: fields,Expires: 10 * 60 * 60,};const client = new S3Client();const policy = await createPresignedPost(client, params);res.json({ policy: policy });} else {res.json({ error: 'error' });}
});

客户端上传文件

客户端上传需要使用form-data库做表单提交，因此需要先安装form-data库

npm install form-data

客户端上传代码如下：

import * as FormData from 'form-data';
import { createReadStream } from "fs";async function testForUpload(bucket: string, key: string, id: string, file: string) {// http://localhost:3000/s3/getUploadPolicy?bucket=mybucket&key=abc.tar.gz&uuid=12345const url = `http://localhost:3000/s3/getUploadPolicy?bucket=${bucket}&key=${key}&uuid=${id}`;const response = await fetch(url);const policy = await response.json();console.log(policy);const form = new FormData();form.append('key', policy.fields.key);form.append('Content-Type', 'application/gzip');form.append('X-Amz-Credential', policy.fields['X-Amz-Credential']);form.append('X-Amz-Algorithm', policy.fields['X-Amz-Algorithm']);form.append('X-Amz-Date', policy.fields['X-Amz-Date']);form.append('Policy', policy.fields.Policy);form.append('X-Amz-Signature', policy.fields['X-Amz-Signature']);form.append('x-amz-meta-uuid', policy.fields['x-amz-meta-uuid']);form.append('file', createReadStream(file));await form.submit(policy.url);
}
// testForUpload('mybucket', 'abc.tar.gz', '12345', '/Volumes/mydisk/test/abc.tar.gz');

• 客户端代码首先调用服务端接口获取upload policy，请求的时候传递bucket、key和id，服务端会根据这些参数生成upload policy；
• 然后客户端使用form-data库生成一个form，将参数、policy和文件添加到form中，然后将form提交到服务端返回的url；

文件下载

服务端安装aws-sdk

npm install @aws-sdk/client-s3 
npm install @aws-sdk/s3-request-presigner
npm install @aws-sdk/s3-presigned-post

服务端生成签名的文件下载链接

在服务端的 controller 里添加一个路由产生并返回签名的文件访问url

import {S3Client,GetObjectCommand,
} from "@aws-sdk/client-s3";
import {getSignedUrl} from '@aws-sdk/s3-request-presigner';...app.get("/s3/getDownloadUrl", async (req: Request, res: Response) => {const bucket = req.query.bucket?.toString();const key = req.query.key?.toString();if (bucket && key) {const client = new S3Client();const url = await getSignedUrl(client,new GetObjectCommand({Bucket: bucket,Key: key,}),{expiresIn: 10 * 60 * 60,});res.json({ url: url });} else {res.json({ error: 'error' });}
});

然后客户端请求此链接，并添加bucket和key参数，比如http://localhost:3000/s3/getDownloadUrl?bucket=mybucket&key=abc.tar.gz，即可获取签名的文件下载链接。