FineJSON

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More useful JSONEncoder, Decoder
omochi/FineJSON

FineJSON

FineJSON provides FineJSONEncoder and FineJSONDecoder which are more useful encoder of Codable. They alternates standard Foundation's JSONEncoder and JSONDecoder. This library helps practical requirements in real world which is weird sometime.

Index

Features

Working code of all example code in this section are in FeaturesTests.

Allowing unnecessary trailing commas

Decoder allows unnecessary trailing comma.

    struct A : Codable, Equatable {
        var a: Int
        var b: Int
    }

    func testAllowTrailingComma() throws {
        let json = """
[
  {
    "a": 1,
    "b": 2,
  },
]
"""
        let decoder = FineJSONDecoder()
        let x = try decoder.decode([A].self, from: json.data(using: .utf8)!)
        XCTAssertEqual(x, [A(a: 1, b: 2)])
    }

Allowing comments

Decoder allows comments in JSON.

    struct A : Codable, Equatable {
        var a: Int
        var b: Int
    }

    func testComment() throws {
        let json = """
[
  // entry 1
  {
    "a": 10,
    "b": 20
/*
    "a": 1,
    "b": 2,
*/
  }
]
"""
        let decoder = FineJSONDecoder()
        let x = try decoder.decode([A].self, from: json.data(using: .utf8)!)
        XCTAssertEqual(x, [A(a: 10, b: 20)])
    }

Line number information in parse error

Parser error tells location in JSON. line number, column number (in byte offset), byte offset.

    struct A : Codable, Equatable {
        var a: Int
        var b: Int
    }

    func testParseErrorLocation() throws {
        let json = """
[
  {
    "a": 1,
    "b": 2;
  }
]
"""
        let decoder = FineJSONDecoder()
        do {
            _ = try decoder.decode([A].self, from: json.data(using: .utf8)!)
            XCTFail()
        } catch {
            let message = "\(error)"
            // invalid character (";") at 4:11(28)
            XCTAssertTrue(message.contains("4:11(28)"))
        }
    }

File path also can be passed to decoder. It improves debugging experience.

    func testSourceLocationFilePath() throws {
        let json = """
{ invalid syntax }
"""
        do {
            let decoder = FineJSONDecoder()
            decoder.file = URL(fileURLWithPath: "resource/dir/info.json")
            _ = try decoder.decode(Int.self, from: json.data(using: .utf8)!)
            XCTFail("expect throw")
        } catch {
            let message = "\(error)"
            XCTAssertTrue(message.contains("resource/dir/info.json"))
        }
    }

Location information from decoder

You can get location information from Decoder.

    struct B : Decodable {
        var location: SourceLocation?
        var name: String
        enum CodingKeys : String, CodingKey { case name }
        init(from decoder: Decoder) throws {
            self.location = decoder.sourceLocation
            let c = try decoder.container(keyedBy: CodingKeys.self)
            self.name = try c.decode(String.self, forKey: .name)
        }
    }

    func testDecodeLocation() throws {
        let json = """
// comment
{
  "name": "b"
},
"""
        let decoder = FineJSONDecoder()
        let x = try decoder.decode(B.self, from: json.data(using: .utf8)!)
        XCTAssertEqual(x.location, SourceLocation(offset: 11, line: 2, columnInByte: 1))
        XCTAssertEqual(x.name, "b")
    }

See also auto location information decoding.

Keeping JSON key order

Encoder keeps JSON key order.

    struct A : Codable {
        var a: Int
        var b: String
        var c: Int?
        var d: String?
    }
    
    func testKeyOrder() throws {
        let a = A(a: 1, b: "b", c: 2, d: "d")
        let e = FineJSONEncoder()
        let json = String(data: try e.encode(a), encoding: .utf8)!
        let expected = """
{
  "a": 1,
  "b": "b",
  "c": 2,
  "d": "d"
}
"""
        XCTAssertEqual(json, expected)
    }

Foundation.JSONEncoder does not define key order. So you may get this.

{
  "d": "d",
  "b": "b",
  "c": 2,
  "a": 1
}

Control Optional.none encoding

You can specify Optional.none encoding.

Default is key absence which is same as Foundation.

    func testNoneKeyAbsence() throws {
        let a = A(a: 1, b: "b", c: nil, d: "d")
        let e = FineJSONEncoder()
        let json = String(data: try e.encode(a), encoding: .utf8)!
        let expected = """
{
  "a": 1,
  "b": "b",
  "d": "d"
}
"""
        XCTAssertEqual(json, expected)
    }

You can specify to emit explicit null for such key.

    func testNoneExplicitNull() throws {
        let a = A(a: 1, b: "b", c: nil, d: "d")
        let e = FineJSONEncoder()
        e.optionalEncodingStrategy = .explicitNull
        let json = String(data: try e.encode(a), encoding: .utf8)!
        let expected = """
{
  "a": 1,
  "b": "b",
  "c": null,
  "d": "d"
}
"""
        XCTAssertEqual(json, expected)
    }

Control indent width

You can specify indent width.

    func testIndent4() throws {
        let a = A(a: 1, b: "b", c: 2, d: "d")
        let e = FineJSONEncoder()
        e.jsonSerializeOptions = JSON.SerializeOptions(indentString: "    ")
        let json = String(data: try e.encode(a), encoding: .utf8)!
        let expected = """
{
    "a": 1,
    "b": "b",
    "c": 2,
    "d": "d"
}
"""
        XCTAssertEqual(json, expected)
    }

Oneline style is also supported.

    func testOnelineFormat() throws {
        let a = A(a: 1, b: "b", c: 2, d: "d")
        let e = FineJSONEncoder()
        e.jsonSerializeOptions = JSON.SerializeOptions(isPrettyPrint: false)
        let json = String(data: try e.encode(a), encoding: .utf8)!
        let expected = """
{"a":1,"b":"b","c":2,"d":"d"}
"""
        XCTAssertEqual(json, expected)
    }

And prettyprint is default.

Handling arbitrary digits number

JSON supports arbitrary digits originally. You can handle this by JSONNumber type.

    struct B : Codable {
        var x: JSONNumber
        var y: JSONNumber
    }

    func testArbitraryNumber() throws {
        let json1 = """
{
  "x": 1234567890.1234567890,
  "y": 0.01
}
"""
        let d = FineJSONDecoder()
        var b = try d.decode(B.self, from: json1.data(using: .utf8)!)
        
        var y = Decimal(string: b.y.value)!
        y += Decimal(string: "0.01")!
        b.y = JSONNumber(y.description)
        
        let e = FineJSONEncoder()        
        let json2 = String(data: try e.encode(b), encoding: .utf8)!
        
        let expected = """
{
  "x": 1234567890.1234567890,
  "y": 0.02
}
"""
        XCTAssertEqual(json2, expected)
    }

Foundation.JSONEncoder can not do this. So you may get this with Float.

{
  "x": 1234567936,
  "y": 0.019999999552965164
}

Weak typing primitive decoding

JSON number and string are each compatible during decoding.

    struct C : Codable {
        var id: Int
        var name: String
    }

    func testWeakTypingDecoding() throws {
        let json = """
{
  "id": "123",
  "name": 4869.57
}
"""
        let d = FineJSONDecoder()
        let c = try d.decode(C.self, from: json.data(using: .utf8)!)
        
        XCTAssertEqual(c.id, 123)
        XCTAssertEqual(c.name, "4869.57")
    }

You can customize this behavior by inject your object which conforms to CodablePrimitiveJSONDecoder.

Handling complex JSON structure directly

You can use JSON type to handle complex structure.

    struct F : Codable {
        var name: String
        var data: JSON
    }
    
    func testJSONTypeProperty() throws {
        let json = """
{
  "name": "john",
  "data": [
    "aaa",
    { "bbb": "ccc" }
  ]
}
"""
        let d = FineJSONDecoder()
        let f = try d.decode(F.self, from: json.data(using: .utf8)!)
      
        XCTAssertEqual(f.name, "john")
        XCTAssertEqual(f.data, JSON.array(JSONArray([
            .string("aaa"),
            .object(JSONObject([
                "bbb": .string("ccc")
                ]))
            ])))
    }

Customizing JSON key with keeping Codable methods auto synthesis

You can customize JSON key for property with Codable methods auto synthesis.

    struct G : Codable, JSONAnnotatable {
        static let keyAnnotations: JSONKeyAnnotations = [
            "id": JSONKeyAnnotation(jsonKey: "no"),
            "userName": JSONKeyAnnotation(jsonKey: "user_name")
        ]
        
        var id: Int
        var point: Int
        var userName: String
    }
    
    func testAnnotateJSONKey() throws {
        let json1 = """
{
  "no": 1,
  "point": 100,
  "user_name": "john"
}
"""
        let d = FineJSONDecoder()
        var g = try d.decode(G.self, from: json1.data(using: .utf8)!)
        
        XCTAssertEqual(g.id, 1)
        XCTAssertEqual(g.point, 100)
        XCTAssertEqual(g.userName, "john")
        
        g.point += 3
        
        let e = FineJSONEncoder()
        let json2 = String(data: try e.encode(g), encoding: .utf8)!
        
        let expect = """
{
  "no": 1,
  "point": 103,
  "user_name": "john"
}
"""
        XCTAssertEqual(json2, expect)
    }

Default value for absent key

You can specify default value for property which is used when JSON key is absent.

    struct H : Codable, JSONAnnotatable {
        static let keyAnnotations: JSONKeyAnnotations = [
            "language": JSONKeyAnnotation(defaultValue: JSON.string("Swift"))
        ]
        
        var name: String
        var language: String
    }
    
    func testDefaultValue() throws {
        let json = """
{
  "name": "john"
}
"""
        let d = FineJSONDecoder()
        let h = try d.decode(H.self, from: json.data(using: .utf8)!)
        
        XCTAssertEqual(h.name, "john")
        XCTAssertEqual(h.language, "Swift")
    }

Auto location information decoding

Location information decoding can be enabled from annotation.

    func testAutoLocationDecoding() throws {
        let json = """
// comment
{
  "name": "b"
},
"""
        let decoder = FineJSONDecoder()
        let x = try decoder.decode(C.self, from: json.data(using: .utf8)!)
        XCTAssertEqual(x.location, SourceLocation(offset: 11, line: 2, columnInByte: 1))
        XCTAssertEqual(x.name, "b")
        
        let encoder = FineJSONEncoder()
        let json2 = String(data: try encoder.encode(x), encoding: .utf8)!
        XCTAssertEqual(json2, """
{
  "name": "b"
}
""")
        
    }

Supported building environment

  • SwiftPM for mac, iOS.

  • Carthage for mac, iOS.

  • Manual xcworkspace for mac, iOS. This is my favorite. Detail is here

Cautions

Coding for URL, Date

This library serializes URL as not string but object in JSON. It differ from Foundation.JSONEncoder, .JSONDecoder. Bacause this library uses native coding definition for these types. Foundation coders serialize them as string by following their internal custom coding logics.

License

MIT.

Description

  • Swift Tools 5.0.0
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Dependencies

Last updated: Mon May 12 2025 12:59:00 GMT-0900 (Hawaii-Aleutian Daylight Time)