Why is data bytes size different when serialized with JSONSerialization - json

Question

Why is data serialized using JSONSerialization differ from the data serialized with the extension below?
let uint8Array: [UInt8] = [123, 234, 255]
let data1 = uint8Array.data // 3bytes
let data2 = try! JSONSerialization.data(withJSONObject: uint8Array) // 13 bytes
extension Data {
var bytes: [UInt8] {
return [UInt8](self)
}
}
extension Array where Element == UInt8 {
var data: Data {
return Data(self)
}
}

Answer 1

JSON, and so the JSONSerialization will transform an object (here an array of Int), into Data according to some rules (like adding "[", "]", "," in our cases, in others input values and options, it can add if necessary ":", "{", "}", "\n"`, etc) and using the UTF8 (or kind of UTF16, but I'll skip this part for understanding, see this part in WikiPedia) encoding.
So in fact, for 123 value, it will be 1 into UTF8 encoding, then 2, then 3, so just for one number, it's 3 bytes.
So you see that for your 3 Int numbers, it will be 9 bytes, then, we need to add the "[", "]", and the two commas to separate them: ",", which makes 9 + 2 + 2 = 13 bytes.
To illustrates:
Let's add:
extension Data {
func hexRepresentation(separator: String) -> String {
map { String(format: "%02hhX", $0) }.joined(separator: separator)
}
func intRepresentation(separator: String) -> String {
map { String(format: "%d", $0) }.joined(separator: separator)
}
}
And use it to see what are the values inside data1 & data2:
print(data1.hexRepresentation(separator: "-"))
print(data1.intRepresentation(separator: "-"))
print(data2.hexRepresentation(separator: "-"))
print(data2.intRepresentation(separator: "-"))
$>7B-EA-FF
$>123-234-255
$>5B-31-32-33-2C-32-33-34-2C-32-35-35-5D
$>91-49-50-51-44-50-51-52-44-50-53-53-93
I let you chose as you prefers Int or hex raw value interpretations.
We see that using the first method, we get 3 bytes, with the initial values of your array.
But for the JSON one, we can split it as such:
$>91 -> [
$>49-50-51 -> 1, 2 & 3
$>44 -> ,
$>50-51-52 -> 2, 3, 4
$>44 -> ,
$>50-53-53 -> 2, 5, 5
$>93 -> ]
You can check on any UTF8 table (like https://www.utf8-chartable.de, etc), but 91 that for [, 49 it's for 1, etc.