how to print pretty json string for data in swift

I would like to log payload into a pretty print format however, based on my following code. I still see \". how can I make the output like pretty json string format?

"{
    "string1":"string1",
    "string2":"string2",
    "val":42
    }"

extension Encodable {
    /// format the json data to string
    var jsonString: String? {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        encoder.outputFormatting = .prettyPrinted
        let jsonString = try! encoder.encode(self)
        return String(decoding: jsonString, as: UTF8.self)
    }
}
struct Foo: Codable {
    let string1: String
    let string2: String
    let val: Int
}
let foo = Foo(string1: "string1", string2: "string2", val: 42)
print(foo.jsonString)
//

// "{\"string1\":\"string1\",\"string2\":\"string2\",\"val\":42}"

You see \" because you are printing an Optional. When printing Optional, it shows you the string literal held by this optional container, which will be quoted in ", so the content is escaped as well, like when you write it in code.

Optional("{\n  \"string2\" : \"string2\",\n  \"val\" : 42,\n  \"string1\" : \"string1\"\n}")

If you replace the print statement with

print(foo.jsonString ?? "")

You will see the string content:

{
  "string2" : "string2",
  "string1" : "string1",
  "val" : 42
}

The confusion happens because you specified the wrong return type.

As you clearly return a non-optional string remove the question mark in the declaration line

var jsonString: String {

You get the same by force unwrapping jsonString in the print line

print(foo.jsonString!)

but changing the return type is the better choice.