如何解码 GMail API 返回的 message.parts？

Question

我正在使用 Gmail API 从服务器获取一些邮件。它 returns 一个长 json 数组。这是相关部分：

"parts": [
   {
    "partId": "0",
    "mimeType": "text/plain",
    "filename": "",
    "headers": [
     {
      "name": "Content-Type",
      "value": "text/plain; charset=UTF-8"
     }
    ],
    "body": {
     "size": 91,
     "data": "dGVzdA0KLS0NCkRhd2lkIChSZXluZXZhbikgU2VyYWZpbg0KKmh0dHA6Ly93d3cucmV5bmV2YW4uY29tLyA8aHR0cDovL3d3dy5yZXluZXZhbi5jb20vPioNCg=="
    }
   },
   {
    "partId": "1",
    "mimeType": "text/html",
    "filename": "",
    "headers": [
     {
      "name": "Content-Type",
      "value": "text/html; charset=UTF-8"
     },
     {
      "name": "Content-Transfer-Encoding",
      "value": "quoted-printable"
     }
    ],
    "body": {
     "size": 391,
     "data": "PGRpdiBkaXI9Imx0ciI-dGVzdDxiciBjbGVhcj0iYWxsIj48ZGl2PjxkaXYgY2xhc3M9ImdtYWlsX3NpZ25hdHVyZSI-PGRpdiBkaXI9Imx0ciI-PGRpdj48Zm9udCBmYWNlPSJjb21pYyBzYW5zIG1zLCBzYW5zLXNlcmlmIj4tLTwvZm9udD48L2Rpdj48Zm9udCBmYWNlPSJjb21pYyBzYW5zIG1zLCBzYW5zLXNlcmlmIj5EYXdpZCAoUmV5bmV2YW4pIFNlcmFmaW48L2ZvbnQ-PGRpdj48Zm9udCBmYWNlPSJjb21pYyBzYW5zIG1zLCBzYW5zLXNlcmlmIj48Yj48aT48YSBocmVmPSJodHRwOi8vd3d3LnJleW5ldmFuLmNvbS8iIHRhcmdldD0iX2JsYW5rIj5odHRwOi8vd3d3LnJleW5ldmFuLmNvbS88L2E-PC9pPjwvYj48L2ZvbnQ-PC9kaXY-PC9kaXY-PC9kaXY-PC9kaXY-DQo8L2Rpdj4NCg=="
    }
   }
  ]

我使用这段代码可以毫无问题地解析的第一个：

foreach (Match b in body)
{
    var raw = b.Groups[1].Value;
    var bytes = Convert.FromBase64String(raw);
    var s = Encoding.UTF8.GetString(bytes);
    bodyDecoded += s;
}

但第二个看起来与第一个不同，此代码抛出 FormatException。

我该怎么办？这还是base64吗？我应该删除破折号吗？

编辑：这是另一个字符串：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

eser 编辑

这就是我在答案中的代码产生的（已过滤）

XXXXXX, the XXXXXX 1 V SP 'Patch' has dropped – here's your purchase
link.
<https://launches.XXXXXXXX.com/>
XXXXXX 1 V SP 'Patch'

Sand
[image: Product image]

DROPS IN

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Please click the link below to join the queue for purchasing this product.
Remember to hurry - stock is allocated on a first come first serve basis.
Clicking this link does not guarantee purchase.
Click Here
<https://launches.XXXXXXX.com/#/checkout/XXXX/login>
END.
XXXXXXXXXXXXXXXXXXXXXx
XXXXXXXXXXXXXXXXXXXX
NE27 0QG
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info@XXXXXXX.com
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Answer 1

- 不是有效的 base64 字符...我不知道使用该字符的原因，但只需将 - 替换为 + 即可正确的 html..

string data = "PGRpdiBkaXI9Imx0ciI-dGVzdDxiciBjbGVhcj0iYWxsIj48ZGl2PjxkaXYgY2xhc3M9ImdtYWlsX3NpZ25hdHVyZSI-PGRpdiBkaXI9Imx0ciI-PGRpdj48Zm9udCBmYWNlPSJjb21pYyBzYW5zIG1zLCBzYW5zLXNlcmlmIj4tLTwvZm9udD48L2Rpdj48Zm9udCBmYWNlPSJjb21pYyBzYW5zIG1zLCBzYW5zLXNlcmlmIj5EYXdpZCAoUmV5bmV2YW4pIFNlcmFmaW48L2ZvbnQ-PGRpdj48Zm9udCBmYWNlPSJjb21pYyBzYW5zIG1zLCBzYW5zLXNlcmlmIj48Yj48aT48YSBocmVmPSJodHRwOi8vd3d3LnJleW5ldmFuLmNvbS8iIHRhcmdldD0iX2JsYW5rIj5odHRwOi8vd3d3LnJleW5ldmFuLmNvbS88L2E-PC9pPjwvYj48L2ZvbnQ-PC9kaXY-PC9kaXY-PC9kaXY-PC9kaXY-DQo8L2Rpdj4NCg==";

var base64 = Convert.FromBase64String(data.Replace("-", "+"));
var str = Encoding.UTF8.GetString(base64);

结果：

<div dir="ltr">test<br clear="all"><div><div class="gmail_signature"><div dir="ltr"><div><font face="comic sans ms, sans-serif">--</font></div><font face="comic sans ms, sans-serif">Dawid (Reynevan) Serafin</font><div><font face="comic sans ms, sans-serif"><b><i><a href="http://www.reynevan.com/" target="_blank">http://www.reynevan.com/</a></i></b></font></div></div></div></div> </div>

Answer 2

Google Gmail API 使用 Base64 编码的变体，在 URL 中使用是安全的。此方案用“-”字符替换“+”字符，用“/”字符替换“_”字符，并删除填充字符串末尾的任何尾随“=”字符。

详情和转换码请看下面问题： How to achieve Base64 URL safe encoding in C#?

如何解码 GMail API 返回的 message.parts？

How do I decode message.parts returned by GMail API?

c#

base64

json