解码Base64字符串返回零

Question

我一直在尝试在我的应用程序中实现GMAIL API，该应用程序是使用Swift5和Xcode构建的。我已经成功地检索到来自用户的电子邮件，但我无法从编码字符串中获得实际的文本。每当我尝试将这个base64编码的数据转换为普通字符串时，它都返回NIL。

这是绳子

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_RW1haWw9c2lkcmFpYnJhaGltMDM0OUBnbWFpbC5jb20mY29udGludWU9aHR0cHM6Ly9teWFjY291bnQuZ29vZ2xlLmNvbS9hbGVydC9udC8xNTY3ODQ3ODEyMDAwP3JmbiUzRDEyNyUyNnJmbmMlM0QxJTI2ZWlkJTNELTE1NzQzMDEyNjk4Mjg2MTM3OTQlMjZldCUzRDElMjZhbmV4cCUzRGdpdmFiLWZhLS1tZHYyLWZhPg0KWW91IHJlY2VpdmVkIHRoaXMgZW1haWwgdG8gbGV0IHlvdSBrbm93IGFib3V0IGltcG9ydGFudCBjaGFuZ2VzIHRvIHlvdXINCkdvb2dsZSBBY2NvdW50IGFuZCBzZXJ2aWNlcy4NCsKpIDIwMTkgR29vZ2xlIExMQywgMTYwMCBBbXBoaXRoZWF0cmUgUGFya3dheSwgTW91bnRhaW4gVmlldywgQ0EgOTQwNDMsIFVTQQ0K

stackoverflow的一些答案建议向string添加填充，但这也不起作用。

extension String {

    func base64Encoded() -> String? {
        return data(using: .utf8)?.base64EncodedString()
    }

    func base64Decoded() -> String? {
        var st = self;
        print(st.count)
        let remainder = self.count % 4
        if remainder > 0 {
            st = self.padding(toLength: self.count + 4 - remainder,
                                          withPad: "=",
                                          startingAt: 0)
        }

        print(st.count)
        guard let d = Data(base64Encoded: st, options: .ignoreUnknownCharacters) else{
            return nil
        }
        return String(data: d, encoding: .utf8)
    }   
}

Answer 1

字符串包含下划线字符('_'u+005f低行）,该字符作为base-64无效.

Base-64有一些变体，所以你需要找到你的Gmail中使用的是哪一个。（维基百科基础-64。）

假设它使用base64url URL和文件名安全，您可能需要编写如下内容：

extension String {
    func urlSafeBase64Decoded() -> String? {
        var st = self
            .replacingOccurrences(of: "_", with: "/")
            .replacingOccurrences(of: "-", with: "+")
        let remainder = self.count % 4
        if remainder > 0 {
            st = self.padding(toLength: self.count + 4 - remainder,
                              withPad: "=",
                              startingAt: 0)
        }
        guard let d = Data(base64Encoded: st, options: .ignoreUnknownCharacters) else{
            return nil
        }
        return String(data: d, encoding: .utf8)
    }
}

let base64 = "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_RW1haWw9c2lkcmFpYnJhaGltMDM0OUBnbWFpbC5jb20mY29udGludWU9aHR0cHM6Ly9teWFjY291bnQuZ29vZ2xlLmNvbS9hbGVydC9udC8xNTY3ODQ3ODEyMDAwP3JmbiUzRDEyNyUyNnJmbmMlM0QxJTI2ZWlkJTNELTE1NzQzMDEyNjk4Mjg2MTM3OTQlMjZldCUzRDElMjZhbmV4cCUzRGdpdmFiLWZhLS1tZHYyLWZhPg0KWW91IHJlY2VpdmVkIHRoaXMgZW1haWwgdG8gbGV0IHlvdSBrbm93IGFib3V0IGltcG9ydGFudCBjaGFuZ2VzIHRvIHlvdXINCkdvb2dsZSBBY2NvdW50IGFuZCBzZXJ2aWNlcy4NCsKpIDIwMTkgR29vZ2xlIExMQywgMTYwMCBBbXBoaXRoZWF0cmUgUGFya3dheSwgTW91bnRhaW4gVmlldywgQ0EgOTQwNDMsIFVTQQ0K"

print(base64.urlSafeBase64Decoded() ?? "* decoding failed*")

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