I receive an improperly formatted unicode in a String - ios

Question

I am working with a web API that gives me strings like the following:
"Eat pok\u00e9."
Xcode complains that
Expected Hexadecimal code in braces after unicode escape
My understanding is that it should be converted to pok\u{00e9}, but I do not know how to achieve this.
Can anybody point me in the right direction for me develop a way of converting these as there are many in this API?
Bonus:
I also need to remove \n from the strings.

Answer 1

You may want to give us more context regarding what the raw server payload looked like, and show us how you're displaying the string. Some ways of examining strings in the debugger (or if you're looking at raw JSON) will show you escape strings, but if you use the string in the app, you'll see the actual Unicode character.
I wonder if you're just looking at raw JSON.
For example, I passed the JSON, {"foo": "Eat pok\u00e9."} to the following code:
let jsonString = String(data: data, encoding: NSUTF8StringEncoding)!
print(jsonString)
let dictionary = try! NSJSONSerialization.JSONObjectWithData(data, options: []) as! [String: String]
print(dictionary["foo"]!)
And it output:
{"foo": "Eat pok\u00e9."}
Eat poké.
By the way, this standard JSON escape syntax should not be confused with Swift's string literal escape syntax, in which the hex sequence must be wrapped in braces:
print("Eat pok\u{00e9}.")
Swift uses a different escape syntax in their string literals, and it should not be confused with that employed by formats like JSON.

Answer 2

#Rob has an excellent solution for the server passing invalid Swift String literals.
If you need to convert "Eat pok\u00e9.\n" to Eat poké it can be done as follows with Swift 3 regex.
var input = "Eat pok\\u00e9.\n"
// removes newline
input = String(input.characters.map {
$0 == "\n" ? " " : $0
})
// regex helper function for sanity's sake
func regexGroup(for regex: String!, in text: String!) -> String {
do {
let regex = try RegularExpression(pattern: regex, options: [])
let nsString = NSString(string: text)
let results = regex.matches(in: text, options: [], range: NSMakeRange(0, nsString.length))
let group = nsString.substring(with: results[0].range)
return group
} catch let error as NSError {
print("invalid regex: \(error.localizedDescription)")
return ""
}
}
let unicodeHexStr = regexGroup(for:"0\\w*", in: input)
let unicodeHex = Int(unicodeHexStr, radix: 16)!
let char = Character(UnicodeScalar(unicodeHex)!)
let replaced = input.stringByReplacingOccurrencesOfString("\\u"+unicodeHexStr, withString: String(char))
// prints "Eat poké"
print(replaced)

Answer 3

\u{00e9} is a formatting that's specific to Swift String literals. When the code is compiled, this notation is parsed and converted into the actual Unicode Scalar it represents.
What you've received is a String that escapes Unicode scalars in a particlar way. Transform those escaped Unicode Scalars into the Unicode Scalars they represent, see this answer.