将 base64URL 解码为 base64 -- Swift

Question

我还没有找到正确的方法来快速将 base64URL 解码为 base64 格式。

根据base64url to base64hJQWHABDBjoPHorYF5xghQ(base64URL) 应该是hJQWHABDBjoPHorYF5xghQ==(base64)。这里可能会有更多差异。

stackoverflow 上没有解决方案。

Answer 1

“base64url”与标准的Base64编码有两方面的不同：

• 索引 62 和 63 使用不同的字符（- 和 _ + 和 /)
• 没有强制填充= 字符来使字符串长度 四的倍数。

（比较https://en.wikipedia.org/wiki/Base64#Variants_summary_table）。

这是一个可能的转换函数：

func base64urlToBase64(base64url: String) -> String {
    var base64 = base64url
        .replacingOccurrences(of: "-", with: "+")
        .replacingOccurrences(of: "_", with: "/")
    if base64.characters.count % 4 != 0 {
        base64.append(String(repeating: "=", count: 4 - base64.characters.count % 4))
    }
    return base64
}

例子：

let base64url = "hJQWHABDBjoPHorYF5xghQ"
let base64 = base64urlToBase64(base64url: base64url)
print(base64) // hJQWHABDBjoPHorYF5xghQ==

if let data = Data(base64Encoded: base64) {
    print(data as NSData) // <8494161c 0043063a 0f1e8ad8 179c6085>
}

为了完整起见，这将是相反的转换：

func base64ToBase64url(base64: String) -> String {
    let base64url = base64
        .replacingOccurrences(of: "+", with: "-")
        .replacingOccurrences(of: "/", with: "_")
        .replacingOccurrences(of: "=", with: "")
    return base64url
}

---

Swift 4 更新：

func base64urlToBase64(base64url: String) -> String {
    var base64 = base64url
        .replacingOccurrences(of: "-", with: "+")
        .replacingOccurrences(of: "_", with: "/")
    if base64.count % 4 != 0 {
        base64.append(String(repeating: "=", count: 4 - base64.count % 4))
    }
    return base64
}

Answer 2

这是 Martin 在 Swift 4 扩展中发布的内容的清理版本：

import Foundation

/// Extension for making base64 representations of `Data` safe for
/// transmitting via URL query parameters
extension Data {

    /// Instantiates data by decoding a base64url string into base64
    ///
    /// - Parameter string: A base64url encoded string
    init?(base64URLEncoded string: String) {
        self.init(base64Encoded: string.toggleBase64URLSafe(on: false))
    }

    /// Encodes the string into a base64url safe representation
    ///
    /// - Returns: A string that is base64 encoded but made safe for passing
    ///            in as a query parameter into a URL string
    func base64URLEncodedString() -> String {
        return self.base64EncodedString().toggleBase64URLSafe(on: true)
    }

}

extension String {

    /// Encodes or decodes into a base64url safe representation
    ///
    /// - Parameter on: Whether or not the string should be made safe for URL strings
    /// - Returns: if `on`, then a base64url string; if `off` then a base64 string
    func toggleBase64URLSafe(on: Bool) -> String {
        if on {
            // Make base64 string safe for passing into URL query params
            let base64url = self.replacingOccurrences(of: "/", with: "_")
                .replacingOccurrences(of: "+", with: "-")
                .replacingOccurrences(of: "=", with: "")
            return base64url
        } else {
            // Return to base64 encoding
            var base64 = self.replacingOccurrences(of: "_", with: "/")
                .replacingOccurrences(of: "-", with: "+")
            // Add any necessary padding with `=`
            if base64.count % 4 != 0 {
                base64.append(String(repeating: "=", count: 4 - base64.count % 4))
            }
            return base64
        }
    }

}