转换base64字符串时出错

Question

我正在尝试将base64字符串转换为HTML代码，该代码是通过WinRT中的Gmail Api从电子邮件中获取的。 但是问题是当将base64字符串转换为字节数组时，会抛出FormatException。此外，当我在base64decode网站上对其进行解码时，它也会完美地解码base64字符串。

这是我尝试解码的base64字符串：

PGltZyBzcmM9Imh0dHA6Ly9jY3Byb21haWwuY29tOjgxODEvYWRtaW1wLmpzcD9pZD1UaUUtbldrcGhESUJuaHNUS2t0NENpclQzTHVvY09ZOVV2czJDb1lFbGo4YjZJWjl0TWp6SzNvRUpERkVHZnBnIiBib3JkZXI9IjAiIGhlaWdodD0iMCIgd2lkdGg9IjAiPjxkaXYgc3R5bGU9IndpZHRoOjYwMHB4OyAgZm9udC1mYW1pbHk6QXJpYWwsIEhlbHZldGljYSwgc2Fucy1zZXJpZjsgZm9udC1zaXplOiAxOHB4OyBsaW5lLWhlaWdodDoyMnB4OyB0ZXh0LWFsaWduOiBjZW50ZXI7Ij4gIDxmb250IHN0eWxlPSJmb250LXdlaWdodDogYm9sZDsgZm9udC1zaXplOiAyMHB4OyBjb2xvcjogcmVkOyI-IEdST1cgWU9VUiBPV04gSEFJUiBGT1IgSlVTVCAxIFJTLjwvZm9udD4gIDxicj4gIDxicj4gIDxmb250IHN0eWxlPSJjb2xvcjpncmVlbjtmb250LXdlaWdodDogYm9sZDsiPkludGVyZXN0IEZyZWUgRU1JPGJyPjxicj4xIFJzLiBEb3duIFBheW1lbnQ8L2ZvbnQ-ICA8YnI-ICA8YnI-ICA8YSBocmVmPSJodHRwOi8vY2Nwcm9tYWlsLmNvbTo4MTgxL3RyYWNrLmpzcD9pZD1UaUUtbldrcGhESUJuaHNUS2t0NENpclQzTHVvY09ZOVV2czJDb1lFbGo4YjZJWjl0TWp6SzNvRUpERkVHZnBnIiBzdHlsZT0iY29sb3I6IGJsdWU7IGJhY2tncm91bmQtY29sb3I6IHllbGxvdzsiPkdldCBZb3VyIEFwcG9pbnRtZW50IE5vdzwvYT4gIDxicj4gIDxicj4gPC9kaXY-PGJyLz48ZGl2IHN0eWxlPSJmb250LXNpemU6OXB4O3dpZHRoOjYwMHB4 O21hcmdpbi1sZWZ0OiAxNTBweDsiPjxhIGhyZWY9Imh0dHA6Ly9jY3Byb21haWwuY29tOjgxODEvdHJhY2suanNwP2lkPVRpRS1uV2twaERJQm5oc1RLa3Q0Q2lyVDNMdW9jT1k5VXZzMkNvWUVsajhiNklaOXRNanpLM29FSkRGRUdmcGcmdT1hIj5DbGljayBIZXJlPC9hPiB0byB1bnN1YnNjcmliZSBmcm9tIHRoaXMgbmV3c2xldHRlci48YnIvPjwvZGl2Pg0K

编辑：这是我用来解码字符串的代码：

string raw = "PGltZyBzcmM9Imh0dHA6Ly9jY3Byb21haWwuY29tOjgxODEvYWRtaW1wLmpzcD9pZD1UaUUtbldrcGhESUJuaHNUS2t0NENpclQzTHVvY09ZOVV2czJDb1lFbGo4YjZJWjl0TWp6SzNvRUpERkVHZnBnIiBib3JkZXI9IjAiIGhlaWdodD0iMCIgd2lkdGg9IjAiPjxkaXYgc3R5bGU9IndpZHRoOjYwMHB4OyAgZm9udC1mYW1pbHk6QXJpYWwsIEhlbHZldGljYSwgc2Fucy1zZXJpZjsgZm9udC1zaXplOiAxOHB4OyBsaW5lLWhlaWdodDoyMnB4OyB0ZXh0LWFsaWduOiBjZW50ZXI7Ij4gIDxmb250IHN0eWxlPSJmb250LXdlaWdodDogYm9sZDsgZm9udC1zaXplOiAyMHB4OyBjb2xvcjogcmVkOyI-IEdST1cgWU9VUiBPV04gSEFJUiBGT1IgSlVTVCAxIFJTLjwvZm9udD4gIDxicj4gIDxicj4gIDxmb250IHN0eWxlPSJjb2xvcjpncmVlbjtmb250LXdlaWdodDogYm9sZDsiPkludGVyZXN0IEZyZWUgRU1JPGJyPjxicj4xIFJzLiBEb3duIFBheW1lbnQ8L2ZvbnQ-ICA8YnI-ICA8YnI-ICA8YSBocmVmPSJodHRwOi8vY2Nwcm9tYWlsLmNvbTo4MTgxL3RyYWNrLmpzcD9pZD1UaUUtbldrcGhESUJuaHNUS2t0NENpclQzTHVvY09ZOVV2czJDb1lFbGo4YjZJWjl0TWp6SzNvRUpERkVHZnBnIiBzdHlsZT0iY29sb3I6IGJsdWU7IGJhY2tncm91bmQtY29sb3I6IHllbGxvdzsiPkdldCBZb3VyIEFwcG9pbnRtZW50IE5vdzwvYT4gIDxicj4gIDxicj4gPC9kaXY-PGJyLz48ZGl2IHN0eWxlPSJmb250LXNpemU6OXB4O3dpZHRoOjYwMHB4O21hcmdpbi1sZWZ0OiAxNTBweDsiPjxhIGhyZWY9Imh0dHA6Ly9jY3Byb21haWwuY29tOjgxODEvdHJhY2suanNwP2lkPVRpRS1uV2twaERJQm5oc1RLa3Q0Q2lyVDNMdW9jT1k5VXZzMkNvWUVsajhiNklaOXRNanpLM29FSkRGRUdmcGcmdT1hIj5DbGljayBIZXJlPC9hPiB0byB1bnN1YnNjcmliZSBmcm9tIHRoaXMgbmV3c2xldHRlci48YnIvPjwvZGl2Pg0K";
string codedbody = raw.Replace("-", "+");
codedbody = raw.Replace("_", "/");
byte[] data = Convert.FromBase64String(codedbody);
string body = Encoding.UTF8.GetString(data);

Answer 1

怎么样

string input = "PGltZyBzcmM9Imh0dHA6Ly9jY3Byb21haWwuY29tOjgxODEvYWRtaW1wLmpzcD9pZD1UaUUtbldrcGhESUJuaHNUS2t0NENpclQzTHVvY09ZOVV2czJDb1lFbGo4YjZJWjl0TWp6SzNvRUpERkVHZnBnIiBib3JkZXI9IjAiIGhlaWdodD0iMCIgd2lkdGg9IjAiPjxkaXYgc3R5bGU9IndpZHRoOjYwMHB4OyAgZm9udC1mYW1pbHk6QXJpYWwsIEhlbHZldGljYSwgc2Fucy1zZXJpZjsgZm9udC1zaXplOiAxOHB4OyBsaW5lLWhlaWdodDoyMnB4OyB0ZXh0LWFsaWduOiBjZW50ZXI7Ij4gIDxmb250IHN0eWxlPSJmb250LXdlaWdodDogYm9sZDsgZm9udC1zaXplOiAyMHB4OyBjb2xvcjogcmVkOyI-IEdST1cgWU9VUiBPV04gSEFJUiBGT1IgSlVTVCAxIFJTLjwvZm9udD4gIDxicj4gIDxicj4gIDxmb250IHN0eWxlPSJjb2xvcjpncmVlbjtmb250LXdlaWdodDogYm9sZDsiPkludGVyZXN0IEZyZWUgRU1JPGJyPjxicj4xIFJzLiBEb3duIFBheW1lbnQ8L2ZvbnQ-ICA8YnI-ICA8YnI-ICA8YSBocmVmPSJodHRwOi8vY2Nwcm9tYWlsLmNvbTo4MTgxL3RyYWNrLmpzcD9pZD1UaUUtbldrcGhESUJuaHNUS2t0NENpclQzTHVvY09ZOVV2czJDb1lFbGo4YjZJWjl0TWp6SzNvRUpERkVHZnBnIiBzdHlsZT0iY29sb3I6IGJsdWU7IGJhY2tncm91bmQtY29sb3I6IHllbGxvdzsiPkdldCBZb3VyIEFwcG9pbnRtZW50IE5vdzwvYT4gIDxicj4gIDxicj4gPC9kaXY-PGJyLz48ZGl2IHN0eWxlPSJmb250LXNpemU6OXB4O3dpZHRoOjYwMHB4O21hcmdpbi1sZWZ0OiAxNTBweDsiPjxhIGhyZWY9Imh0dHA6Ly9jY3Byb21haWwuY29tOjgxODEvdHJhY2suanNwP2lkPVRpRS1uV2twaERJQm5oc1RLa3Q0Q2lyVDNMdW9jT1k5VXZzMkNvWUVsajhiNklaOXRNanpLM29FSkRGRUdmcGcmdT1hIj5DbGljayBIZXJlPC9hPiB0byB1bnN1YnNjcmliZSBmcm9tIHRoaXMgbmV3c2xldHRlci48YnIvPjwvZGl2Pg0K";
string result = System.Text.Encoding.Default.GetString(System.Convert.FromBase64String(input.Replace("-", "+").Replace("_", "/")));

我保留了您的替换内容，因为-和_对于BASE64是无效字符

Answer 2

您尝试解码的方式看起来像是您尝试解码base64 URL编码的字符串。

public byte[] Decode(string text) {
    var output = text;
    output = output.Replace('-', '+'); // 62nd char of encoding
    output = output.Replace('_', '/'); // 63rd char of encoding
    switch (output.Length % 4) { // Pad with trailing '='s
        case 0: break; // No pad chars in this case
        case 2: output += "=="; break; // Two pad chars
        case 3: output += "="; break;  // One pad char
        default: throw new FormatException("invalid format", text));
    }
    var converted = Convert.FromBase64String(output); // Standard base64 decoder
    return converted;
}

使用以上代码，您可以执行

string raw = "PGltZyBzcmM9Imh0dHA6Ly9jY3Byb21haWwuY29tOjgxODEvYWRtaW1wLmpzcD9pZD1UaUUtbldrcGhESUJuaHNUS2t0NENpclQzTHVvY09ZOVV2czJDb1lFbGo4YjZJWjl0TWp6SzNvRUpERkVHZnBnIiBib3JkZXI9IjAiIGhlaWdodD0iMCIgd2lkdGg9IjAiPjxkaXYgc3R5bGU9IndpZHRoOjYwMHB4OyAgZm9udC1mYW1pbHk6QXJpYWwsIEhlbHZldGljYSwgc2Fucy1zZXJpZjsgZm9udC1zaXplOiAxOHB4OyBsaW5lLWhlaWdodDoyMnB4OyB0ZXh0LWFsaWduOiBjZW50ZXI7Ij4gIDxmb250IHN0eWxlPSJmb250LXdlaWdodDogYm9sZDsgZm9udC1zaXplOiAyMHB4OyBjb2xvcjogcmVkOyI-IEdST1cgWU9VUiBPV04gSEFJUiBGT1IgSlVTVCAxIFJTLjwvZm9udD4gIDxicj4gIDxicj4gIDxmb250IHN0eWxlPSJjb2xvcjpncmVlbjtmb250LXdlaWdodDogYm9sZDsiPkludGVyZXN0IEZyZWUgRU1JPGJyPjxicj4xIFJzLiBEb3duIFBheW1lbnQ8L2ZvbnQ-ICA8YnI-ICA8YnI-ICA8YSBocmVmPSJodHRwOi8vY2Nwcm9tYWlsLmNvbTo4MTgxL3RyYWNrLmpzcD9pZD1UaUUtbldrcGhESUJuaHNUS2t0NENpclQzTHVvY09ZOVV2czJDb1lFbGo4YjZJWjl0TWp6SzNvRUpERkVHZnBnIiBzdHlsZT0iY29sb3I6IGJsdWU7IGJhY2tncm91bmQtY29sb3I6IHllbGxvdzsiPkdldCBZb3VyIEFwcG9pbnRtZW50IE5vdzwvYT4gIDxicj4gIDxicj4gPC9kaXY-PGJyLz48ZGl2IHN0eWxlPSJmb250LXNpemU6OXB4O3dpZHRoOjYwMHB4O21hcmdpbi1sZWZ0OiAxNTBweDsiPjxhIGhyZWY9Imh0dHA6Ly9jY3Byb21haWwuY29tOjgxODEvdHJhY2suanNwP2lkPVRpRS1uV2twaERJQm5oc1RLa3Q0Q2lyVDNMdW9jT1k5VXZzMkNvWUVsajhiNklaOXRNanpLM29FSkRGRUdmcGcmdT1hIj5DbGljayBIZXJlPC9hPiB0byB1bnN1YnNjcmliZSBmcm9tIHRoaXMgbmV3c2xldHRlci48YnIvPjwvZGl2Pg0K";
byte[] data = Decode(raw);
string body = Encoding.UTF8.GetString(data);

产生html输出

<img src="http://ccpromail.com:8181/admimp.jsp?id=TiE-nWkphDIBnhsTKkt4CirT3LuocOY9Uvs2CoYElj8b6IZ9tMjzK3oEJDFEGfpg" border="0" height="0" width="0"><div style="width:600px;  font-family:Arial, Helvetica, sans-serif; font-size: 18px; line-height:22px; text-align: center;">  <font style="font-weight: bold; font-size: 20px; color: red;"> GROW YOUR OWN HAIR FOR JUST 1 RS.</font>  <br>  <br>  <font style="color:green;font-weight: bold;">Interest Free EMI<br><br>1 Rs. Down Payment</font>  <br>  <br>  <a href="http://ccpromail.com:8181/track.jsp?id=TiE-nWkphDIBnhsTKkt4CirT3LuocOY9Uvs2CoYElj8b6IZ9tMjzK3oEJDFEGfpg" style="color: blue; background-color: yellow;">Get Your Appointment Now</a>  <br>  <br> </div><br/><div style="font-size:9px;width:600px;margin-left: 150px;"><a href="http://ccpromail.com:8181/track.jsp?id=TiE-nWkphDIBnhsTKkt4CirT3LuocOY9Uvs2CoYElj8b6IZ9tMjzK3oEJDFEGfpg&u=a">Click Here</a> to unsubscribe from this newsletter.<br/></div>

URL应用

当在HTTP环境中使用相当长的标识信息时，Base64编码会很有帮助。 例如，用于Java对象的数据库持久性框架可能使用Base64编码将相对较大的唯一ID（通常为128位UUID）编码为字符串，以用作HTTP形式或HTTP GET URL中的HTTP参数。 同样，许多应用程序需要以一种方便地包含在URL中（包括隐藏的Web表单字段中）的方式对二进制数据进行编码，而Base64是一种以紧凑方式呈现它们的便捷编码。

在URL中使用标准Base64要求将'+'，'/'和'='字符编码为特殊的百分比编码的十六进制序列（'+'成为'％2B'，'/'成为'％2F'而'='成为'％3D'），这会使字符串不必要地变长。

因此，存在针对URL变体的经过修改的Base64，其中标准Base64的'+'和'/'字符分别由'-'和'_'代替，因此不再需要使用URL编码器/解码器，并且不再使用影响编码值的长度，使相同的编码形式完整地保留在关系数据库，Web表单和对象标识符中。 一些变体允许或要求省略填充'='符号，以避免它们与字段分隔符混淆，或者要求对任何此类填充进行百分比编码。 一些库（例如org.bouncycastle.util.encoders.UrlBase64Encoder）会将'='编码为'。'。

参考Base64：来自Wikipedia

Answer 3

您在代码中犯了错误：您再次需要替换raw codebody

codedbody = raw.Replace("_", "/");

应该：

codedbody = codedbody.Replace("_", "/");