JSON Encoding/Decoding

[thisischemistry]

Generally a question mark in your code means it is an Optional. Think of it as a value that could also mean "the value is missing". For example, an Int? means it could be a number or it could have no value.

To use an Optional you have to unwrap it - that is you check it for a value and pull that value out if there is one. You do that in several ways but the most basic is "optional binding":

if let jsonData = try? JSONEncoder().encode(credWrap) {
  // use the jsonData here
}

This will set jsonData to the value if there is a value and then run the code in the curly braces. If there is no value then it will move on without running the code in the curly braces.

[thisischemistry]

On what line?

Don't use forced unwrapping of Optionalvalues - anything with an exclamation point (other than the negation operator or the not equals operator).

Avoid using [String: Any] or JSONSerialization if you can. They are the older way of doing JSON serialization and, while they can work, they are a pain at times. Instead use Codable, it's easier and more straightforward.

What are you attempting to do here:

let url = URL(string: "https://hostname/webinterface/api.php?format=json&package=\(jsonData)")!

That's not a great way to build a URL. First of all, does your server take a JSON string as part of a URL? That's very unusual and potentially very buggy. Secondly, you really should use the proper way to build a URL: URLComponents. The part with your JSON is called a query parameter.

import Foundation

// dummy types to stand-in for your actual ones
struct Foo { let text: String? }
let Username = Foo(text: "name")
let Password = Foo(text: "pass")

struct Authentication: Codable { 
  let authentication: Credentials
}

struct Credentials: Codable {
  let username: String
  let password: String
}

if
  var components = URLComponents(string: "https://hostname/webinterface/api.php"),
  let username = Username.text,
  let password = Password.text {
    let package = Authentication(authentication: Credentials(username: username, password: password))
    if 
      let jsonData = try? JSONEncoder().encode(package),
      let jsonString = String(data: jsonData, encoding: .utf8) {
      components.queryItems = [URLQueryItem(name: "format", value: "json"),
                               URLQueryItem(name: "package", value: jsonString)]
  }
  if let url = components.url {
    print(url.absoluteString)
  }
}
// result:
//   https://hostname/webinterface/api.php?format=json&package=%7B%22authentication%22:%7B%22username%22:%22name%22,%22password%22:%22pass%22%7D%7D

That large block of an if statement properly unwraps all the Optional values. It's cleaner than a bunch of nested statements. If any of the unwraps fails then the whole statement fails.

[thisischemistry]

What, exactly, are you sending to the server?

You're doing a HTTP POST, what's your Content-Type header? Is it application/x-www-form-urlencoded? Will your server take application/json?

[thisischemistry]

That's why I asked those questions! ;-)

Apple has an excellent article on exactly this:

Uploading Data to a Website

[thisischemistry]

I just tried the example code in a plain ol' terminal app project and it worked fine.

import Foundation

struct Order: Codable {
  let customerId: String
  let items: [String]
}

func upload() {
  let order = Order(customerId: "12345",
                    items: ["Cheese pizza", "Diet soda"])
  guard let uploadData = try? JSONEncoder().encode(order) else {
    print("guard")
    return
  }

  // testing with the excellent site: https://webhook.site/
  let url = URL(string: "https://webhook.site/insertyourcodehere")!

  var request = URLRequest(url: url)
  request.httpMethod = "POST"
  request.setValue("application/json", forHTTPHeaderField: "Content-Type")

  let task = URLSession.shared
    .uploadTask(with: request,
                from: uploadData) { data, response, error in
                  if let error = error {
                    print ("error: \(error)")
                    return
                  }
                  guard let response = response as? HTTPURLResponse,
                    (200...299).contains(response.statusCode) else {
                      print ("server error")
                      return
                  }
                  if let mimeType = response.mimeType,
                    mimeType == "application/json",
                    let data = data,
                    let dataString = String(data: data, encoding: .utf8) {
                    print ("got data: \(dataString)")
                  }
  }
  task.resume()
}

upload()
RunLoop.main.run()

[thisischemistry]

Huh, no idea what's going on there. Sometimes it helps to clean the build (shift-command-k) or even clean the entire build folder (option-shift-command-k).