How to escape the HTTP params in Swift - ios

Question

I'm trying to make a post to an HTTP server
By the way this is my code:
func sendPostToUrl(url:String, withParams params: [String: String?] ) {
var request = NSMutableURLRequest(URL: NSURL(string: url)!)
var session = NSURLSession.sharedSession()
request.HTTPMethod = "POST"
var err: NSError?
var bodyData = ""
for (key,value) in params{
if (value==nil){ continue }
let scapedKey = key.stringByAddingPercentEncodingWithAllowedCharacters(
.URLHostAllowedCharacterSet())!
let scapedValue = value!.stringByAddingPercentEncodingWithAllowedCharacters(
.URLHostAllowedCharacterSet())!
bodyData += "\(scapedKey)=\(scapedValue)&"
}
request.HTTPBody = bodyData.dataUsingEncoding
(NSUTF8StringEncoding, allowLossyConversion: true)
var task = session.dataTaskWithRequest(request,
completionHandler: {data, response, error -> Void in
println("Response: \(response)")
let dataString = NSString(data: data, encoding: NSUTF8StringEncoding)
println("Data: \(dataString)")
})
task.resume()
}
It works but is not perfect. If I call the function this way:
client.sendPostToUrl("http://novagecko.com/tests/test.php",
withParams: ["hello":"world","inject":"param1=value1&param2=value2"]);
The server detects 3 post fields (with keys hello,inject and param2) instead of 2.
How can I escape the key and values?
Is there something more I could do for improving the method?

Answer 1

If you can target iOS 8 (thanks #Rob), use NSURLComponents to escape your parameters instead:
import Foundation
func encodeParameters(#params: [String: String]) -> String {
var queryItems = map(params) { NSURLQueryItem(name:$0, value:$1)}
var components = NSURLComponents()
components.queryItems = queryItems
return components.percentEncodedQuery ?? ""
}
Now encodeParameters(params:["hello":"world","inject":"param1=value1&param2=value2"]) returns hello=world&inject=param1%3Dvalue1%26param2%3Dvalue2 as you would expect.
Otherwise, the best way to create the character set that will let you escape your values properly is this:
var safeCharacterSet = NSCharacterSet.URLQueryAllowedCharacterSet().mutableCopy()
safeCharacterSet.removeCharactersInString("&=")
and see #rintaro's answer to use filter/map properly to perform the encoding in a nice way.

Answer 2

It seems, NSCharacterSet doesn't have relevant set for that.
So, add this
extension NSCharacterSet {
class func URLUnreservedCharacterSet() -> NSCharacterSet {
return self(charactersInString: "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_.~")
}
}
Then
var bodyData = ""
var safeCharacterSet = NSCharacterSet.URLUnreservedCharacterSet()
for (key,value) in params{
if (value==nil){ continue }
let scapedKey = key.stringByAddingPercentEncodingWithAllowedCharacters(safeCharacterSet)!
let scapedValue = value!.stringByAddingPercentEncodingWithAllowedCharacters(safeCharacterSet)!
bodyData += "\(scapedKey)=\(scapedValue)&"
}
As following #Rob's advice in comment, here is a map and join example:
let params:[String:String?] = ["fubar":nil, "hello":"world", "inject":"param1=value1&param2=value2"]
let safeCharacterSet = NSCharacterSet.URLUnreservedCharacterSet()
let pairs = filter(params, {$1 != nil}).map { (key, value) -> String in
let _key = key.stringByAddingPercentEncodingWithAllowedCharacters(safeCharacterSet)!
let _val = value!.stringByAddingPercentEncodingWithAllowedCharacters(safeCharacterSet)!
return _key + "=" + _val
}
let bodyData = "&".join(pairs)
This is better because there is no trailing & in the result.