一个简单的方法是使用(NS)String 方法
stringByRemovingPercentEncoding 用于此目的。
这是观察到的
decoding quoted-printables,
所以第一个解决方案主要是翻译答案
该线程到 Swift。
这个想法是用引号替换可打印的“=NN”编码
百分比编码“%NN”，然后使用现有方法去除
百分比编码。
续行单独处理。
此外，输入字符串中的百分比字符必须首先进行编码，
否则他们将被视为百分比中的主角
编码。
func decodeQuotedPrintable(message : String) -> String? {
return message
.stringByReplacingOccurrencesOfString("=\r\n", withString: "")
.stringByReplacingOccurrencesOfString("=\n", withString: "")
.stringByReplacingOccurrencesOfString("%", withString: "%25")
.stringByReplacingOccurrencesOfString("=", withString: "%")
.stringByRemovingPercentEncoding
}
对于无效输入，该函数返回一个可选字符串 nil。
无效输入可以是：
- 后面没有两个十六进制数字的“=”字符，
例如“=XX”。
- “=NN”序列未解码为有效的 UTF-8 序列，
例如“=E2=64”。
例子：
if let decoded = decodeQuotedPrintable("=C2=A31,000") {
print(decoded) // £1,000
}
if let decoded = decodeQuotedPrintable("=E2=80=9CHello =E2=80=A6 world!=E2=80=9D") {
print(decoded) // “Hello … world!”
}
更新 1： 上面的代码假设消息使用 UTF-8
用于引用非 ASCII 字符的编码，如您的大多数示例：C2 A3 是“£”的 UTF-8 编码，E2 80 A4 是 … 的 UTF-8 编码。
如果输入是"Rub=E9n"，则消息使用
Windows-1252 编码。
要正确解码，您必须替换
.stringByRemovingPercentEncoding
通过
.stringByReplacingPercentEscapesUsingEncoding(NSWindowsCP1252StringEncoding)
还有一些方法可以从“Content-Type”中检测编码
标头字段，比较例如https://stackoverflow.com/a/32051684/1187415.
更新 2：stringByReplacingPercentEscapesUsingEncoding
方法被标记为已弃用，因此上面的代码将始终生成
编译器警告。不幸的是，似乎没有替代方法
由 Apple 提供。
所以这里有一个新的、完全独立的解码方法，它
不会导致任何编译器警告。这次我写了
作为String 的扩展方法。解释 cmets 在
代码。
extension String {
/// Returns a new string made by removing in the `String` all "soft line
/// breaks" and replacing all quoted-printable escape sequences with the
/// matching characters as determined by a given encoding.
/// - parameter encoding: A string encoding. The default is UTF-8.
/// - returns: The decoded string, or `nil` for invalid input.
func decodeQuotedPrintable(encoding enc : NSStringEncoding = NSUTF8StringEncoding) -> String? {
// Handle soft line breaks, then replace quoted-printable escape sequences.
return self
.stringByReplacingOccurrencesOfString("=\r\n", withString: "")
.stringByReplacingOccurrencesOfString("=\n", withString: "")
.decodeQuotedPrintableSequences(enc)
}
/// Helper function doing the real work.
/// Decode all "=HH" sequences with respect to the given encoding.
private func decodeQuotedPrintableSequences(enc : NSStringEncoding) -> String? {
var result = ""
var position = startIndex
// Find the next "=" and copy characters preceding it to the result:
while let range = rangeOfString("=", range: position ..< endIndex) {
result.appendContentsOf(self[position ..< range.startIndex])
position = range.startIndex
// Decode one or more successive "=HH" sequences to a byte array:
let bytes = NSMutableData()
repeat {
let hexCode = self[position.advancedBy(1) ..< position.advancedBy(3, limit: endIndex)]
if hexCode.characters.count < 2 {
return nil // Incomplete hex code
}
guard var byte = UInt8(hexCode, radix: 16) else {
return nil // Invalid hex code
}
bytes.appendBytes(&byte, length: 1)
position = position.advancedBy(3)
} while position != endIndex && self[position] == "="
// Convert the byte array to a string, and append it to the result:
guard let dec = String(data: bytes, encoding: enc) else {
return nil // Decoded bytes not valid in the given encoding
}
result.appendContentsOf(dec)
}
// Copy remaining characters to the result:
result.appendContentsOf(self[position ..< endIndex])
return result
}
}
示例用法：
if let decoded = "=C2=A31,000".decodeQuotedPrintable() {
print(decoded) // £1,000
}
if let decoded = "=E2=80=9CHello =E2=80=A6 world!=E2=80=9D".decodeQuotedPrintable() {
print(decoded) // “Hello … world!”
}
if let decoded = "Rub=E9n".decodeQuotedPrintable(encoding: NSWindowsCP1252StringEncoding) {
print(decoded) // Rubén
}
Swift 4（及更高版本）更新：
extension String {
/// Returns a new string made by removing in the `String` all "soft line
/// breaks" and replacing all quoted-printable escape sequences with the
/// matching characters as determined by a given encoding.
/// - parameter encoding: A string encoding. The default is UTF-8.
/// - returns: The decoded string, or `nil` for invalid input.
func decodeQuotedPrintable(encoding enc : String.Encoding = .utf8) -> String? {
// Handle soft line breaks, then replace quoted-printable escape sequences.
return self
.replacingOccurrences(of: "=\r\n", with: "")
.replacingOccurrences(of: "=\n", with: "")
.decodeQuotedPrintableSequences(encoding: enc)
}
/// Helper function doing the real work.
/// Decode all "=HH" sequences with respect to the given encoding.
private func decodeQuotedPrintableSequences(encoding enc : String.Encoding) -> String? {
var result = ""
var position = startIndex
// Find the next "=" and copy characters preceding it to the result:
while let range = range(of: "=", range: position..<endIndex) {
result.append(contentsOf: self[position ..< range.lowerBound])
position = range.lowerBound
// Decode one or more successive "=HH" sequences to a byte array:
var bytes = Data()
repeat {
let hexCode = self[position...].dropFirst().prefix(2)
if hexCode.count < 2 {
return nil // Incomplete hex code
}
guard let byte = UInt8(hexCode, radix: 16) else {
return nil // Invalid hex code
}
bytes.append(byte)
position = index(position, offsetBy: 3)
} while position != endIndex && self[position] == "="
// Convert the byte array to a string, and append it to the result:
guard let dec = String(data: bytes, encoding: enc) else {
return nil // Decoded bytes not valid in the given encoding
}
result.append(contentsOf: dec)
}
// Copy remaining characters to the result:
result.append(contentsOf: self[position ..< endIndex])
return result
}
}
示例用法：
if let decoded = "=C2=A31,000".decodeQuotedPrintable() {
print(decoded) // £1,000
}
if let decoded = "=E2=80=9CHello =E2=80=A6 world!=E2=80=9D".decodeQuotedPrintable() {
print(decoded) // “Hello … world!”
}
if let decoded = "Rub=E9n".decodeQuotedPrintable(encoding: .windowsCP1252) {
print(decoded) // Rubén
}