如何在golang中编码POST策略 - 基于浏览器的上传到Amazon S3？

Question

我正在尝试将图像文件上传到亚马逊S3。设置如下：

Web服务器：Golang 前端：简单的HTML表单进行测试

参考此文档：http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-post-example.html 我参考了上述文档中提供的示例，并尝试了这个：http://play.golang.org/p/3zn5fSDasK

  package main

  import "fmt"
  import "encoding/base64"

  func main() {
         bytePolicy := []byte(`{ 
                    "expiration": "2013-08-06T12:00:00.000Z",
                    "conditions": [
                             {"bucket": "examplebucket"},
                             ["starts-with", "$key", "user/user1/"],
                             {"acl": "public-read"},
                             {"success_action_redirect": "http://acl6.s3.amazonaws.com/successful_upload.html"},
                             ["starts-with", "$Content-Type", "image/"],
                             {"x-amz-meta-uuid": "14365123651274"},
                             ["starts-with", "$x-amz-meta-tag", ""],
                             {"x-amz-credential":"AKIAIOSFODNN7EXAMPLE/20130806/us-east-1/s3/aws4_request"},
                             {"x-amz-algorithm": "AWS4-HMAC-SHA256"},
                             {"x-amz-date": "20130806T000000Z" }
                      ]
                  }`)
        fmt.Println(base64.StdEncoding.EncodeToString(bytePolicy))
 }

我用这个方法得到的结果是：

   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

这是亚马逊教程链接上的 Base64 编码策略：

   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

为什么我的base64编码策略与亚马逊的不匹配？

- Tripti R

Answer 1

仅仅因为生成这些base64字符串的两个JSON源文本具有不同的缩进和内容，如下所示（它们并非逐个字符相等）。

解码这两个base64字符串，您将看到其中的差异。您可以使用程序（不一定是Go），也可以简单地使用在线服务，例如此网站。

您不必担心缩进，在JSON中它并不重要。但是，当您使用Base64编码文本时，它会编码源中包括用于缩进的空格和制表符的所有字符，因此不同的缩进将导致不同的Base64编码形式。

但是，在比较两个已解码的JSON文件时，还有其他的差异：

第一个：

"expiration": "2013-08-06T12:00:00.000Z"
"success_action_redirect": "http://acl6.s3.amazonaws.com/successful_upload.html"

第二个：

"expiration": "2013-08-07T12:00:00.000Z"
"success_action_redirect": "http://examplebucket.s3.amazonaws.com/successful_upload.html"

---

完整解码的JSON文本：

第一个：

{ 
                        "expiration": "2013-08-06T12:00:00.000Z",
                        "conditions": [
                                 {"bucket": "examplebucket"},
                                ["starts-with", "$key", "user/user1/"],
                                 {"acl": "public-read"},
                                 {"success_action_redirect": "http://acl6.s3.amazonaws.com/successful_upload.html"},
                                ["starts-with", "$Content-Type", "image/"],
                                {"x-amz-meta-uuid": "14365123651274"},
                                ["starts-with", "$x-amz-meta-tag", ""],

                                {"x-amz-credential":"AKIAIOSFODNN7EXAMPLE/20130806/us-east-1/s3/aws4_request"},
                                {"x-amz-algorithm": "AWS4-HMAC-SHA256"},
                               {"x-amz-date": "20130806T000000Z" }
                          ]
                    }

还有第二个：

{ "expiration": "2013-08-07T12:00:00.000Z",
  "conditions": [
    {"bucket": "examplebucket"},
    ["starts-with", "$key", "user/user1/"],
    {"acl": "public-read"},
    {"success_action_redirect": "http://examplebucket.s3.amazonaws.com/successful_upload.html"},
    ["starts-with", "$Content-Type", "image/"],
    {"x-amz-meta-uuid": "14365123651274"},
    ["starts-with", "$x-amz-meta-tag", ""],

    {"x-amz-credential": "AKIAIOSFODNN7EXAMPLE/20130806/us-east-1/s3/aws4_request"},
    {"x-amz-algorithm": "AWS4-HMAC-SHA256"},
    {"x-amz-date": "20130806T000000Z" }
  ]
}

- icza

---

谢谢！现在，我正在尝试创建此策略，并稍后使用我的Amazon访问密钥进行签名。我如何确保我的缩进和Amazon端生成的缩进相同？这样，最终，我的签名将与Amazon的签名匹配。 - Tripti R

@TriptiR 只需使用 Amazon 文本中所见的格式（例如，缩进2个空格，数组在一行中，':' 和 ',' 后面加上空格等）。 - icza

@TriptiR 修改了答案，除了缩进之外还有两个差异。 - icza

谢谢，因为更改问题本身是不合适的。即使在纠正了这个问题之后，我仍然无法让它工作。在创建POST策略的步骤中，有一个要求 - “使用UTF-8编码创建策略”。我相信，在这一点上我错过了什么。如何确保我的JSON策略是使用UTF-8编码创建的？ - Tripti R

@TriptiR 这只是指描述策略的JSON文本，需要在应用base64编码时将其转换/表示为UTF-8字节序列。但这正是Go在内存中存储字符串的方式。 - icza