Swift - Encoding and Decoding String for special characters

Question

Here is my problem : I'm currently developping an app including an instant chat (using FCM). Every thing works except when i try to send special characters like "é" or emojis. The push notification received contains the good string but when the discussion is saved on the server and then reloaded, I can't read them and get UTF8 text like "u00ea" for "ê". I don't really know a lot about encoding etc. but if you guys could help I would be very happy !

Here is the code i use to send a message :

    func sendMessage(_ completion: @escaping (_ response: String) -> ()) {

    DispatchQueue.global(qos: .userInitiated).async { () -> Void in
        let urlString = //Server adress
        let url = URL(string: urlString)

        var request = URLRequest(url: url!)
        let set = CharacterSet()
        request.httpMethod = "POST"
        let postString = "Message=" + /*String text to send*/
        request.httpBody = postString.data(using: String.Encoding.utf8)

    let task = URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in

        })
        task.resume()
    }
}

Thanks a lot !

PS : I'm new to asking to stackoverflow so don't hesitate to ask for more details

Edit as asked by Rob : I sent the message "test é è".
The other phone received "test é è" via push notification.
When one phone loads discussion from the server where its stored the answer from the server is.

    [{"content":"test u00e9 u00e8","sender":"103","timestamp":"1475491191"}]

Also I'm not coding the server, but the guy who is is also making an android app which works really fine with special characters.

Edit #2 : I also try this code

    var request = URLRequest(url: url!)
        let set = CharacterSet()
        request.httpMethod = "POST"
        let postString = "Message=" + self.message.addingPercentEncoding(withAllowedCharacters: set)!
        let bytesArray = UTF8Encoding.decode(postString)

        request.httpBody = Data(bytes: UnsafePointer<UInt8>(bytesArray), count: bytesArray.count)

It does not make any difference.

Thanks a lot for your help guys.

Answer 1

You want to use addingPercentEncoding to percent escape the string. But don't be tempted to use a character set like urlQueryAllowed, as that will let some key characters (notably & and +) pass unescaped.

As a nice example of how to do this properly, see Alamofire's ParameterEncoding escape routine. Here is a rendition implemented as an extension:

extension String {
    public func addingPercentEncodingForQueryParameter() -> String? {
        return addingPercentEncoding(withAllowedCharacters: .urlQueryValueAllowed)
    }
}

extension CharacterSet {
    static let urlQueryValueAllowed: CharacterSet = {
        let generalDelimitersToEncode = ":#[]@" // does not include "?" or "/" due to RFC 3986 - Section 3.4
        let subDelimitersToEncode = "!$&'()*+,;="

        var allowed = CharacterSet.urlQueryAllowed
        allowed.remove(charactersIn: generalDelimitersToEncode + subDelimitersToEncode)

        return allowed
    }()
}

Then you can do something like:

func send(message: String, _ completion: @escaping (_ response: String) -> ()) {
    let urlString = ...
    let url = URL(string: urlString)

    var request = URLRequest(url: url!)
    request.httpMethod = "POST"
    request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
    let postString = "Message=\(message.addingPercentEncodingForQueryParameter()!)"
    request.httpBody = postString.data(using: .utf8)

    let task = URLSession.shared.dataTask(with: request) { data, response, error in
        ...
    }
    task.resume()
}

Answer 2

Ok so I think I have it,

As suggested, it was due partially to the server implementation. Due to its security it filtered certain characters and that's why it wasn't working.

We have corrected the problem but it's still doesn't work when the discussion is from iOS to Android or Android to iOS.

Thanks a lot for your help !

Here is my final code :

var request = URLRequest(url: url!)
request.httpMethod = "POST"
let postString = "Message=" + (self.message.addingPercentEncoding(withAllowedCharacters: .urlHostAllowed))!
request.httpBody = postString.data(using: String.Encoding.utf8, allowLossyConversion: true)