如何使用表单上传_对象存储(OSS)-阿里云帮助中心

OSS表单上传允许网页应用通过标准HTML表单直接将文件上传至OSS。这种方式下，在前端页面选择文件后，浏览器发起POST请求直接将文件传输到OSS服务器，而无需经过网站服务器中转，减轻了服务器的压力，提高了文件上传的效率和稳定性。

使用限制

通过表单上传的方式上传的Object大小不能超过5 GB。

使用场景

表单上传广泛应用于Web应用程序，包括但不限于以下几个方面：

用户资料上传：注册账号时上传头像、身份证照片或其他身份验证材料。在个人中心修改信息时上传新的头像或背景图。
文件分享与存储：在网盘服务、协同办公平台等通过表单上传各种格式的文件，如文档、图片、音频、视频等至云端进行存储和共享。
内容创作与发布：在博客、论坛、问答社区等平台编写文章并通过表单上传图片、附件等作为内容补充。
电商管理：商家在电商平台后台上传商品图片、详细描述文件、资质证书等；买家在购买过程中上传发票需求或其他证明材料。
在线教育平台：学生在提交作业或项目时上传文档、PPT、视频等作业文件；教师在课程建设时上传教学资料、课件等。
求职招聘网站：求职者上传简历、作品集等求职材料；企业发布职位时上传公司LOGO、招聘信息文件等。
问卷调查与反馈：填写在线调查问卷时上传附加的证据文件或说明文档。
软件开发协作：在代码托管平台如GitHub、GitLab等上传代码文件或项目文档。

方案概述

您可以在服务端生成PostObject所需的Post签名、PostPolicy等信息，然后客户端可以凭借这些信息，在一定的限制下不依赖OSS SDK直接上传文件。您可以借助服务端生成的PostPolicy限制客户端上传的文件，例如限制文件大小、文件类型。此方案适用于通过HTML表单上传的方式上传文件。需要注意的是，此方案不支持基于分片上传大文件、基于分片断点续传的场景。更多信息，请参见PostObject。

服务端通过Post签名和Post Policy授权客户端上传文件到OSS的过程如下。

客户端向业务服务器请求Post签名和Post Policy等信息。
业务服务器生成并返回Post签名和Post Policy等信息给客户端。
客户端使用Post签名和Post Policy等信息调用PostObject通过HTML表单的方式上传文件到OSS。
OSS返回成功响应给客户端。

操作步骤

服务端生成Post签名和Post Policy等信息。

示例工程：postsignature.zip

示例代码

服务端生成Post签名和Post Policy等信息的示例代码如下：

说明

当前代码支持一键部署，您可以直接在函数计算FC中一键部署本代码。oss-upload-post-signature-app

Python

import os
from hashlib import sha1 as sha
import json
import base64
import hmac
import datetime
import time

# 配置环境变量OSS_ACCESS_KEY_ID。
access_key_id = os.environ.get('OSS_ACCESS_KEY_ID')
# 配置环境变量OSS_ACCESS_KEY_SECRET。
access_key_secret = os.environ.get('OSS_ACCESS_KEY_SECRET')
# 将<YOUR_BUCKET>替换为Bucket名称。
bucket = '<YOUR_BUCKET>'
# host的格式为bucketname.endpoint。将<YOUR_BUCKET>替换为Bucket名称。将<YOUR_ENDPOINT>替换为OSS Endpoint，例如oss-cn-hangzhou.aliyuncs.com。
host = 'https://<YOUR_BUCKET>.<YOUR_ENDPOINT>'
# 指定上传到OSS的文件前缀。
upload_dir = 'user-dir-prefix/'
# 指定过期时间，单位为秒。
expire_time = 3600


def generate_expiration(seconds):
    """
    通过指定有效的时长（秒）生成过期时间。
    :param seconds: 有效时长（秒）。
    :return: ISO8601 时间字符串，如："2014-12-01T12:00:00.000Z"。
    """
    now = int(time.time())
    expiration_time = now + seconds
    gmt = datetime.datetime.utcfromtimestamp(expiration_time).isoformat()
    gmt += 'Z'
    return gmt


def generate_signature(access_key_secret, expiration, conditions, policy_extra_props=None):
    """
    生成签名字符串Signature。
    :param access_key_secret: 有权限访问目标Bucket的AccessKeySecret。
    :param expiration: 签名过期时间，按照ISO8601标准表示，并需要使用UTC时间，格式为yyyy-MM-ddTHH:mm:ssZ。示例值："2014-12-01T12:00:00.000Z"。
    :param conditions: 策略条件，用于限制上传表单时允许设置的值。
    :param policy_extra_props: 额外的policy参数，后续如果policy新增参数支持，可以在通过dict传入额外的参数。
    :return: signature，签名字符串。
    """
    policy_dict = {
        'expiration': expiration,
        'conditions': conditions
    }
    if policy_extra_props is not None:
        policy_dict.update(policy_extra_props)
    policy = json.dumps(policy_dict).strip()
    policy_encode = base64.b64encode(policy.encode())
    h = hmac.new(access_key_secret.encode(), policy_encode, sha)
    sign_result = base64.b64encode(h.digest()).strip()
    return sign_result.decode()

def generate_upload_params():
    policy = {
        # 有效期。
        "expiration": generate_expiration(expire_time),
        # 约束条件。
        "conditions": [
            # 未指定success_action_redirect时，上传成功后的返回状态码，默认为 204。
            ["eq", "$success_action_status", "200"],
            # 表单域的值必须以指定前缀开始。例如指定key的值以user/user1开始，则可以写为["starts-with", "$key", "user/user1"]。
            ["starts-with", "$key", upload_dir],
            # 限制上传Object的最小和最大允许大小，单位为字节。
            ["content-length-range", 1, 1000000],
            # 限制上传的文件为指定的图片类型
            ["in", "$content-type", ["image/jpg", "image/png"]]
        ]
    }
    signature = generate_signature(access_key_secret, policy.get('expiration'), policy.get('conditions'))
    response = {
        'policy': base64.b64encode(json.dumps(policy).encode('utf-8')).decode(),
        'ossAccessKeyId': access_key_id,
        'signature': signature,
        'host': host,
        'dir': upload_dir
        # 可以在这里再自行追加其他参数
    }
    return json.dumps(response)

Java

import com.aliyun.help.demo.uploading_to_oss_directly_postsignature.config.OssConfig;
import com.aliyun.oss.ClientException;
import com.aliyun.oss.OSS;
import com.aliyun.oss.OSSException;
import com.aliyun.oss.common.utils.BinaryUtil;
import com.aliyun.oss.model.MatchMode;
import com.aliyun.oss.model.PolicyConditions;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.codehaus.jettison.json.JSONObject;
import java.util.Date;
import com.aliyun.oss.OSSClientBuilder;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Bean;
import javax.annotation.PreDestroy;

@Controller
public class PostSignatureController {
    @Autowired
    private OSS ossClient;

    @Autowired
    private OssConfig ossConfig;

    @GetMapping("/get_post_signature_for_oss_upload")
    @ResponseBody
    public String generatePostSignature() {
        JSONObject response = new JSONObject();
        try {
            long expireEndTime = System.currentTimeMillis() + ossConfig.getExpireTime() * 1000;
            Date expiration = new Date(expireEndTime);
            PolicyConditions policyConds = new PolicyConditions();
            policyConds.addConditionItem(PolicyConditions.COND_CONTENT_LENGTH_RANGE, 0, 1048576000);
            policyConds.addConditionItem(MatchMode.StartWith, PolicyConditions.COND_KEY, ossConfig.getDir());
            String postPolicy = ossClient.generatePostPolicy(expiration, policyConds);
            byte[] binaryData = postPolicy.getBytes("utf-8");
            String encodedPolicy = BinaryUtil.toBase64String(binaryData);
            String postSignature = ossClient.calculatePostSignature(postPolicy);
            response.put("ossAccessKeyId", ossConfig.getAccessKeyId());
            response.put("policy", encodedPolicy);
            response.put("signature", postSignature);
            response.put("dir", ossConfig.getDir());
            response.put("host", ossConfig.getHost());
        } catch (
    OSSException oe) {
        System.out.println("Caught an OSSException, which means your request made it to OSS, "
                + "but was rejected with an error response for some reason.");
        // 假设此方法存在
        System.out.println("HTTP Status Code: " + oe.getRawResponseError()); 
        System.out.println("Error Message: " + oe.getErrorMessage());
        System.out.println("Error Code:       " + oe.getErrorCode());
        System.out.println("Request ID:      " + oe.getRequestId());
        System.out.println("Host ID:           " + oe.getHostId());
    } catch (ClientException ce) {
        System.out.println("Caught an ClientException, which means the client encountered "
                + "a serious internal problem while trying to communicate with OSS, "
                + "such as not being able to access the network.");
        System.out.println("Error Message: " + ce.getMessage());
    } finally {
        if (ossClient != null) {
            ossClient.shutdown();
        }
        return response.toString();
    }
  }
}

@Configuration
public class OssConfig {
    /**
     * 将 <YOUR-ENDPOINT> 替换为 Endpoint，例如 oss-cn-hangzhou.aliyuncs.com
     */
    private String endpoint = "<YOUR-ENDPOINT>";
    /**
     * 将 <YOUR-BUCKET> 替换为 Bucket 名称
     */
    private String bucket = "<YOUR-BUCKET>";
    /**
     * 指定上传到 OSS 的文件前缀
     */
    private String dir = "user-dir-prefix/";
    /**
     * 指定过期时间，单位为秒
     */
    private long expireTime = 3600;
    /**
     * 构造 host
     */
    private String host = "http://" + bucket + "." + endpoint;
    /**
     * 通过环境变量 ALIBABA_CLOUD_ACCESS_KEY_ID 设置 accessKeyId
     */
    private String accessKeyId = System.getenv("ALIBABA_CLOUD_ACCESS_KEY_ID");
    /**
     * 通过环境变量 ALIBABA_CLOUD_ACCESS_KEY_SECRET 设置 accessKeySecret
     */
    private String accessKeySecret = System.getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET");

    private OSS ossClient;
    @Bean
    public OSS getOssClient() {
        ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);
        return ossClient;
    }
    @Bean
    public String getHost() {
        return host;
    }
    @Bean
    public String getAccessKeyId() {
        return accessKeyId;
    }
    @Bean
    public long getExpireTime() {
        return expireTime;
    }
    @Bean
    public String getDir() {
        return dir;
    }

    @PreDestroy
    public void onDestroy() {
        ossClient.shutdown();
    }
}

Go

package main

import (
    "crypto/hmac"
    "crypto/sha1"
    "encoding/base64"
    "encoding/json"
    "fmt"
    "io"
    "net/http"
    "os"
    "time"
)

var (
    // 配置环境变量ALIBABA_CLOUD_ACCESS_KEY_ID。
    accessKeyId = os.Getenv("ALIBABA_CLOUD_ACCESS_KEY_ID")
    // 配置环境变量ALIBABA_CLOUD_ACCESS_KEY_SECRET。
    accessKeySecret = os.Getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET")
    // host的格式为bucketname.endpoint。将${your-bucket}替换为Bucket名称。将${your-endpoint}替换为OSS Endpoint，例如oss-cn-hangzhou.aliyuncs.com。
    host = "http://${your-bucket}.${your-endpoint}"
    // 指定上传到OSS的文件前缀。
    uploadDir = "user-dir-prefix/"
    // 指定过期时间，单位为秒。
    expireTime = int64(3600)
)

type ConfigStruct struct {
    Expiration string     `json:"expiration"`
    Conditions [][]string `json:"conditions"`
}
type PolicyToken struct {
    AccessKeyId string `json:"ossAccessKeyId"`
    Host        string `json:"host"`
    Signature   string `json:"signature"`
    Policy      string `json:"policy"`
    Directory   string `json:"dir"`
}

func getGMTISO8601(expireEnd int64) string {
    return time.Unix(expireEnd, 0).UTC().Format("2006-01-02T15:04:05Z")
}
func getPolicyToken() string {
    now := time.Now().Unix()
    expireEnd := now + expireTime
    tokenExpire := getGMTISO8601(expireEnd)
    var config ConfigStruct
    config.Expiration = tokenExpire
    var condition []string
    condition = append(condition, "starts-with")
    condition = append(condition, "$key")
    condition = append(condition, uploadDir)
    config.Conditions = append(config.Conditions, condition)
    result, err := json.Marshal(config)
    if err != nil {
    fmt.Println("callback json err:", err)
    return ""
    }
    encodedResult := base64.StdEncoding.EncodeToString(result)
    h := hmac.New(sha1.New, []byte(accessKeySecret))
    io.WriteString(h, encodedResult)
    signedStr := base64.StdEncoding.EncodeToString(h.Sum(nil))
    policyToken := PolicyToken{
    AccessKeyId: accessKeyId,
    Host:        host,
    Signature:   signedStr,
    Policy:      encodedResult,
    Directory:   uploadDir,
    }
    response, err := json.Marshal(policyToken)
    if err != nil {
    fmt.Println("json err:", err)
    return ""
    }
    return string(response)
}
func handler(w http.ResponseWriter, r *http.Request) {
    if r.URL.Path == "/" {
    http.ServeFile(w, r, "templates/index.html")
    return
    } else if r.URL.Path == "/get_post_signature_for_oss_upload" {
    policyToken := getPolicyToken()
    w.Header().Set("Content-Type", "application/json")
    w.Write([]byte(policyToken))
    return
    }
    http.NotFound(w, r)
}
func main() {
    http.HandleFunc("/", handler)
    http.ListenAndServe(":8080", nil)
}

PHP

<?php
function gmt_iso8601($time)
{
    return str_replace('+00:00', '.000Z', gmdate('c', $time));
}

// 从环境变量中获取访问凭证。运行本示例代码之前，请确保已设置环境变量ALIBABA_CLOUD_ACCESS_KEY_ID和ALIBABA_CLOUD_ACCESS_KEY_SECRET。
$accessKeyId = getenv("ALIBABA_CLOUD_ACCESS_KEY_ID");
$accessKeySecret = getenv("ALIBABA_CLOUD_ACCESS_KEY_SECRET");
// $host的格式为<YOUR-BUCKET>.<YOUR-ENDPOINT>'，请替换为您的真实信息。
$host = 'http://<YOUR-BUCKET>.<YOUR-ENDPOINT>';
// 用户上传文件时指定的前缀。
$dir = 'user-dir-prefix/';          

$now = time();
//设置该policy超时时间是10s. 即这个policy过了这个有效时间，将不能访问。
$expire = 30;  
$end = $now + $expire;
$expiration = gmt_iso8601($end);

//最大文件大小.用户可以自己设置。
$condition = array(0 => 'content-length-range', 1 => 0, 2 => 1048576000);
$conditions[] = $condition;

// 表示用户上传的数据，必须是以$dir开始，不然上传会失败，这一步不是必须项，只是为了安全起见，防止用户通过policy上传到别人的目录。
$start = array(0 => 'starts-with', 1 => '$key', 2 => $dir);
$conditions[] = $start;


$arr = array('expiration' => $expiration, 'conditions' => $conditions);
$policy = json_encode($arr);
$base64_policy = base64_encode($policy);
$string_to_sign = $base64_policy;
$signature = base64_encode(hash_hmac('sha1', $string_to_sign, $accessKeySecret, true));

$response = array();
$response['ossAccessKeyId'] = $accessKeyId;
$response['host'] = $host;
$response['policy'] = $base64_policy;
$response['signature'] = $signature;
$response['dir'] = $dir;  
echo json_encode($response);

Node.js

const express = require("express");
const { Buffer } = require("buffer");
const OSS = require("ali-oss");
const app = express();
const path = require("path");
const config = {
  // 配置环境变量ALIBABA_CLOUD_ACCESS_KEY_ID。
  accessKeyId: process.env.ALIBABA_CLOUD_ACCESS_KEY_ID,
  // 配置环境变量ALIBABA_CLOUD_ACCESS_KEY_SECRET。
  accessKeySecret: process.env.ALIBABA_CLOUD_ACCESS_KEY_SECRET,
  // 将<YOUR-BUCKET>替换为Bucket名称。
  bucket: "<YOUR-BUCKET>",
  // 指定上传到OSS的文件前缀。
  dir: "prefix/",
};

app.use(express.static(path.join(__dirname, "templates")));

app.get("/get_post_signature_for_oss_upload", async (req, res) => {
  const client = new OSS(config);
  const date = new Date();
  // 设置签名的有效期，单位为秒。
  date.setSeconds(date.getSeconds() + 3600);
  const policy = {
    expiration: date.toISOString(),
    conditions: [
      // 设置上传文件的大小限制。
      ["content-length-range", 0, 1048576000],
      // 限制可上传的Bucket。
      { bucket: client.options.bucket },
    ],
  };
  const formData = await client.calculatePostSignature(policy);
  const host = `http://${config.bucket}.${
    (await client.getBucketLocation()).location
  }.aliyuncs.com`.toString();
  const params = {
    policy: formData.policy,
    signature: formData.Signature,
    ossAccessKeyId: formData.OSSAccessKeyId,
    host,
    dir: config.dir,
  };
  res.json(params);
});

app.get(/^(.+)*\.(html|js)$/i, async (req, res) => {
  res.sendFile(path.join(__dirname, "./templates", req.originalUrl));
});

app.listen(8000, () => {
  console.log("http://127.0.0.1:8000");
});

Ruby

require 'sinatra'
require 'base64'
require 'open-uri'
require 'cgi'
require 'openssl'
require 'json'
require 'sinatra/reloader'
require 'sinatra/content_for'

# 设置public文件夹路径为当前文件夹下的templates文件夹
set :public_folder, File.dirname(__FILE__) + '/templates'

# 配置环境变量ALIBABA_CLOUD_ACCESS_KEY_ID。
$access_key_id = ENV['ALIBABA_CLOUD_ACCESS_ID']
# 配置环境变量ALIBABA_CLOUD_ACCESS_KEY_SECRET。
$access_key_secret = ENV['ALIBABA_CLOUD_ACCESS_SECRET']

# $host的格式为<bucketname>.<endpoint>，请替换为您的真实信息。
$host = 'http://<bucketname>.<endpoint>';

# 用户上传文件时指定的前缀。
$upload_dir = 'user-dir-prefix/'
# 过期时间，单位为秒。
$expire_time = 30
$server_ip = "0.0.0.0"
$server_port = 8000

if ARGV.length == 1 
  $server_port = ARGV[0]
elsif ARGV.length == 2
  $server_ip = ARGV[0]
  $server_port = ARGV[1]
end

puts "App server is running on: http://#{$server_ip}:#{$server_port}"

def hash_to_jason(source_hash)
  jason_string = source_hash.to_json;    

  jason_string.gsub!("\":[", "\": [")
  jason_string.gsub!("\",\"", "\", \"")
  jason_string.gsub!("],\"", "], \"")
  jason_string.gsub!("\":\"", "\": \"")

  jason_string
end


def get_token()
  expire_syncpoint = Time.now.to_i + $expire_time
  expire = Time.at(expire_syncpoint).utc.iso8601()
  response.headers['expire'] = expire
  policy_dict = {}
  condition_arrary = Array.new
  array_item = Array.new
  array_item.push('starts-with')
  array_item.push('$key')
  array_item.push($upload_dir)
  condition_arrary.push(array_item)
  policy_dict["conditions"] = condition_arrary
  policy_dict["expiration"] = expire
  policy = hash_to_jason(policy_dict)
  policy_encode = Base64.strict_encode64(policy).chomp;
  h = OpenSSL::HMAC.digest('sha1', $access_key_secret, policy_encode)
  hs = Digest::MD5.hexdigest(h)
  sign_result = Base64.strict_encode64(h).strip()
  token_dict = {}
  token_dict['ossAccessKeyId'] = $access_key_id
  token_dict['host'] = $host
  token_dict['policy'] = policy_encode
  token_dict['signature'] = sign_result 
  token_dict['expire'] = expire_syncpoint
  token_dict['dir'] = $upload_dir
  result = hash_to_jason(token_dict)
  result
end

set :bind, $server_ip
set :port, $server_port

get '/get_post_signature_for_oss_upload' do
  token = get_token()
  puts "Token: #{token}"
  token
end

get '/*' do
  puts "********************* GET "
  send_file File.join(settings.public_folder, 'index.html')
end

end

if ARGV.length == 1 
  $server_port = ARGV[0]
elsif ARGV.length == 2
  $server_ip = ARGV[0]
  $server_port = ARGV[1]
end

$server_ip = "0.0.0.0"
$server_port = 8000

puts "App server is running on: http://#{$server_ip}:#{$server_port}"

set :bind, $server_ip
set :port, $server_port

get '/get_sts_token_for_oss_upload' do
  token = get_sts_token_for_oss_upload()
  response = {
    "AccessKeyId" => token["Credentials"]["AccessKeyId"],
    "AccessKeySecret" => token["Credentials"]["AccessKeySecret"],
    "SecurityToken" => token["Credentials"]["SecurityToken"]
  }
  response.to_json
end

get '/*' do
  puts "********************* GET "
  send_file File.join(settings.public_folder, 'index.html')
end

C#

using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.AspNetCore.Http;
using System.IO;
using System.Collections.Generic;
using System;
using System.Globalization;
using System.Text;
using System.Security.Cryptography;
using Newtonsoft.Json;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;

namespace YourNamespace
{
    public class Program
    {
        private ILogger<Program> _logger;
        // 配置环境变量ALIBABA_CLOUD_ACCESS_KEY_ID。
        public string AccessKeyId { get; set; } = Environment.GetEnvironmentVariable("ALIBABA_CLOUD_ACCESS_KEY_ID");
        // 配置环境变量ALIBABA_CLOUD_ACCESS_KEY_SECRET。
        public string AccessKeySecret { get; set; } = Environment.GetEnvironmentVariable("ALIBABA_CLOUD_ACCESS_KEY_SECRET");
        // host的格式为bucketname.endpoint。将<YOUR-BUCKET>替换为Bucket名称。将<YOUR-ENDPOINT>替换为OSS Endpoint，例如oss-cn-hangzhou.aliyuncs.com。
        public string Host { get; set; } = "<YOUR-BUCKET>.<YOUR-ENDPOINT>";
        // 指定上传到OSS的文件前缀。
        public string UploadDir { get; set; } = "user-dir-prefix/";
        // 指定过期时间，单位为秒。
        public int ExpireTime { get; set; } = 3600;
        public class PolicyConfig
        {
            public string expiration { get; set; }
            public List<List<object>> conditions { get; set; }
        }
        public class PolicyToken
        {
            public string Accessid { get; set; }
            public string Policy { get; set; }
            public string Signature { get; set; }
            public string Dir { get; set; }
            public string Host { get; set; }
            public string Expire { get; set; }
        }
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);
            var app = builder.Build();

            builder.Logging.AddConsole();
            var logger = builder.Services.BuildServiceProvider().GetRequiredService<ILogger<Program>>();

            app.UseStaticFiles(); 

            app.MapGet("/", async (context) =>
            {
                var filePath = Path.Combine(Directory.GetCurrentDirectory(), "templates/index.html");
                var htmlContent = await File.ReadAllTextAsync(filePath);
                await context.Response.WriteAsync(htmlContent);
                logger.LogInformation("GET request to root path");
            });

            app.MapGet("/get_post_signature_for_oss_upload", async (context) =>
            {
                var program = new Program(logger);
                var token = program.GetPolicyToken();

                logger.LogInformation($"Token: {token}");

                context.Response.ContentType = "application/json";
                await context.Response.WriteAsync(token);
            });

            app.Run();
        }

        public Program(ILogger<Program> logger)
        {
            _logger = logger;
        }

        private string ToUnixTime(DateTime dateTime)
        {
            return ((DateTimeOffset)dateTime).ToUnixTimeSeconds().ToString();
        }

        private string GetPolicyToken()
        {
            var expireDateTime = DateTime.Now.AddSeconds(ExpireTime);
            var config = new PolicyConfig
            {
                expiration = FormatIso8601Date(expireDateTime),
                conditions = new List<List<object>>()
            };
            config.conditions.Add(new List<object>
            {
                "content-length-range", 0, 1048576000
            });
            var policy = JsonConvert.SerializeObject(config);
            var policyBase64 = EncodeBase64("utf-8", policy);
            var signature = ComputeSignature(AccessKeySecret, policyBase64);
            var policyToken = new PolicyToken
            {
                Accessid = AccessKeyId,
                Host = Host,
                Policy = policyBase64,
                Signature = signature,
                Expire = ToUnixTime(expireDateTime),
                Dir = UploadDir
            };
            return JsonConvert.SerializeObject(policyToken);
        }

        private string FormatIso8601Date(DateTime dtime)
        {
            return dtime.ToUniversalTime().ToString("yyyy-MM-dd'T'HH:mm:ss.fff'Z'",
                                    CultureInfo.CurrentCulture);
        }

        private string EncodeBase64(string codeType, string code)
        {
            string encode = "";
            byte[] bytes = Encoding.GetEncoding(codeType).GetBytes(code);
            try
            {
                encode = Convert.ToBase64String(bytes);
            }
            catch
            {
                encode = code;
            }
            return encode;
        }

        private string ComputeSignature(string key, string data)
        {
            using (var algorithm = new HMACSHA1(Encoding.UTF8.GetBytes(key)))
            {
                return Convert.ToBase64String(algorithm.ComputeHash(Encoding.UTF8.GetBytes(data)));
            }
        }
    }
}

客户端使用Post签名和Post Policy等信息调用PostObject通过HTML表单的方式上传文件到OSS。

以js为例：

<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>上传文件到OSS</title>
</head>
<body>
  <div class="container">
    <form>
      <div class="mb-3">
        <label for="file" class="form-label">选择文件</label>
        <input type="file" class="form-control" id="file" name="file" required>
      </div>
      <button type="submit" class="btn btn-primary">上传</button>
    </form>
  </div>
  <script type="text/javascript">
      const form = document.querySelector('form');
      const fileInput = document.querySelector('#file');
      form.addEventListener('submit', (event) => {
        event.preventDefault();
        let file = fileInput.files[0];
        let filename = fileInput.files[0].name;
        fetch('/get_post_signature_for_oss_upload', { method: 'GET' })
          .then(response => response.json())
          .then(data => {
            const formData = new FormData();
            formData.append('name',filename);
            formData.append('policy', data.policy);
            formData.append('OSSAccessKeyId', data.ossAccessKeyId);
            formData.append('success_action_status', '200');
            formData.append('signature', data.signature);
            formData.append('key', data.dir + filename);
            // file必须为最后一个表单域，除file以外的其他表单域无顺序要求。
            formData.append('file', file);
            fetch(data.host, { method: 'POST', body: formData},).then((res) => {
              console.log(res);
              alert('文件已上传');
            });
          })
          .catch(error => {
            console.log('Error occurred while getting OSS upload parameters:', error);
          });
      });
  </script>
</body>
</html>

注意事项

数据安全

防止覆盖同名Object

上传时默认会覆盖同名Object，您可以选择以下任意方式防止Object被意外覆盖。

开启版本控制功能
开启版本控制功能后，被覆盖的Object会以历史版本的形式保存下来。您可以随时恢复历史版本Object。更多信息，请参见版本控制介绍。
在上传请求中携带禁止覆盖同名Object的参数
在上传请求的Header中携带参数x-oss-forbid-overwrite，并指定其值为true。当您上传的Object在OSS中存在同名Object时，该Object会上传失败，并返回FileAlreadyExists错误。当不携带此参数或此参数的值为false时，同名Object会被覆盖。

授权上传

为了防止第三方用户未经授权在您的Bucket中上传数据，OSS提供了Bucket和Object级别的访问权限控制。更多信息，请参见访问控制。
使用签名URL授权第三方用户上传指定文件。签名URL允许第三方用户在没有安全凭证或者授权的情况下进行上传操作。第三方用户使用签名URL上传文件后，OSS将在指定的Bucket生成该文件。使用文件URL上传文件。

降低PUT类请求费用

如果要上传的文件数量较多，直接指定上传的文件类型为深度冷归档类型会造成较高的PUT类请求费用。建议您先将文件的存储类型指定为标准存储进行上传，然后通过生命周期规则将其转储为深度冷归档类型，从而降低PUT类请求费用。

避免影响OSS-HDFS服务

为避免影响OSS-HDFS服务的正常使用或者引发数据丢失的风险，在开通了OSS-HDFS服务的Bucket中，禁止以非OSS-HDFS服务提供的方式在OSS-HDFS的数据存储目录.dlsdata/中上传Object。

上传性能调优

如果您在上传大量Object时，在命名上使用了顺序前缀（如时间戳或字母顺序），可能会出现大量Object索引集中存储于存储空间中某个特定分区的情况，进而导致请求速率下降。建议您在上传大量Object时，不要使用顺序前缀的Object名称，而是将顺序前缀改为随机性前缀。具体操作，请参见OSS性能与扩展性最佳实践。