Swift JSON Decodable \u0000

Question

Problem

I'm currently getting JSON from a server that I don't have access to. The JSON I sometimes get will put this character \ at the end of a String. As a result my decoding fails because this character just fails it.

I'm trying to debug this in Playground but I keep getting this error.

Expected hexadecimal code in braces after unicode escape

Here is some sample code to try out.

import UIKit
import Foundation

struct GroceryProduct: Codable {
    var name: String
}

let json = """
{
    "name": "Durian \u0000"
}
""".data(using: .utf8)!

let decoder = JSONDecoder()
let product = try decoder.decode(GroceryProduct.self, from: json)

print(product.name)

Question

How do you deal with \ from JSON? I have been looking at DataDecodingStrategy from the Apple documentation but I can't even test anything out because the Playground fails to even run.

Any direction or advice would be appreciated.

---

Update

Here is some more setup code to tryout in your Playground or a real app.

JSON test.json

{
    "name": "Durian \u0000"
}

Code

extension Bundle {
    func decode<T: Decodable>(_ type: T.Type, from file: String, dateDecodingStrategy: JSONDecoder.DateDecodingStrategy = .deferredToDate, keyDecodingStrategy: JSONDecoder.KeyDecodingStrategy = .useDefaultKeys) -> T {
        
        guard let url = self.url(forResource: file, withExtension: nil) else {
            fatalError("Failed to locate \(file) in bundle.")
        }

        guard let data = try? Data(contentsOf: url) else {
            fatalError("Failed to load \(file) from bundle.")
        }
                
        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy    = .deferredToDate
        decoder.keyDecodingStrategy     = .useDefaultKeys

        do {
            return try decoder.decode(T.self, from: data)
        } catch DecodingError.keyNotFound(let key, let context) {
            fatalError("Failed to decode \(file) from bundle due to missing key '\(key.stringValue)' not found – \(context.debugDescription)")
        } catch DecodingError.typeMismatch(_, let context) {
            fatalError("Failed to decode \(file) from bundle due to type mismatch – \(context.debugDescription)")
        } catch DecodingError.valueNotFound(let type, let context) {
            fatalError("Failed to decode \(file) from bundle due to missing \(type) value – \(context.debugDescription)")
        } catch DecodingError.dataCorrupted(_) {
            fatalError("Failed to decode \(file) from bundle because it appears to be invalid JSON")
        } catch {
            fatalError("Failed to decode \(file) from bundle: \(error.localizedDescription)")
        }
    }
}


struct GroceryProduct: Codable {
    var name: String
}

// Try running this and it won't work
let results = Bundle.main.decode(GroceryProduct.self, from: "test.json")


print(results.name)

Answer 1

You need to escape \ characters first - this can be done before decoding:

guard let data = try? Data(contentsOf: url) else {
    fatalError("Failed to load \(file) from bundle.")
}

let escaped = Data(String(data: data, encoding: .utf8)!.replacingOccurrences(of: "\0", with: "").utf8)
...
return try decoder.decode(T.self, from: escaped)

Note: force-unwrapping for simplicity only.

---

In Playground you can escape it with an additional \\ (to make it work):

let json = """
{
    "name": "Durian \\u0000"
}
""".data(using: .utf8)!

or replace it with \\0 (to make it fail - behave like during the decoding):

let json = """
{
    "name": "Durian \0"
}
""".data(using: .utf8)!