Swift playground for testing standard iOS URL encoding methods

url_encoding.playground

//: Playground - noun: a place where people can play

import UIKit

extension Dictionary where Key: ExpressibleByStringLiteral, Value: ExpressibleByStringLiteral {
    var queryItems: [URLQueryItem] {
        return map {
            return URLQueryItem(name: String(describing: $0), value: String(describing: $1))
        }
    }
    func encodedFormDataWithAllowedCharacters(_ characterSet: CharacterSet) -> String {
        return (map {
            let name = String(describing: $0).addingPercentEncoding(withAllowedCharacters: characterSet)!
            let value = String(describing: $1).addingPercentEncoding(withAllowedCharacters: characterSet)!
            return name + "=" + value
            } as [String]).joined(separator: "&")
    }
}

extension CharacterSet {
    func ASCIICharacters() -> String {
        guard hasMember(inPlane: 0) else {
            return ""
        }
        // ASCII characters are in plane 0 (BMP) in range 0...7f
        return Array(0...0x7f).filter() {
            return contains(UnicodeScalar($0))
            }.map() {
                return Character(UnicodeScalar($0))
            }.reduce("") {
                return $0 + "\($1)"
        }
    }
    static func customURLQueryAllowedCharacterSet() -> CharacterSet {
        return CharacterSet(charactersIn: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890.-*_")
    }
}

func testEncoding(
    queryDictionary: [String: String],
    correctlyEncodedValue: String) -> (iOS8: Bool, iOS7: Bool, custom: Bool) {
    // iOS8+ method
    
    var urlComponents = URLComponents()
    
    urlComponents.queryItems = queryDictionary.queryItems
    let ios8 = urlComponents.percentEncodedQuery! == correctlyEncodedValue
    
    // iOS7 method
    
    let ios7 = queryDictionary.encodedFormDataWithAllowedCharacters(
        CharacterSet.urlQueryAllowed) == correctlyEncodedValue
    
    // Custom method
    
    let custom = queryDictionary.encodedFormDataWithAllowedCharacters(
        CharacterSet.customURLQueryAllowedCharacterSet()) == correctlyEncodedValue
    return (iOS8: ios8, iOS7: ios7, custom: custom)
}

testEncoding(queryDictionary: ["name": "value+value"], correctlyEncodedValue: "name=value%2Bvalue")

testEncoding(queryDictionary: ["name": "~!@#$%^&*()__{}\":|+?><,.//;'qow"],
             correctlyEncodedValue: "name=%7E%21%40%23%24%25%5E%26*%28%29__%7B%7D%22%3A%7C%2B%3F%3E%3C%2C.%2F%2F%3B%27qow")

// Allowed characters

CharacterSet.urlQueryAllowed.ASCIICharacters()
CharacterSet.customURLQueryAllowedCharacterSet().ASCIICharacters()

updated to Swift 3