JSONSerialization: add WritingOptions.sortedKeys

Author: ianpartridge

Foundation/NSJSONSerialization.swift

@@ -31,6 +31,7 @@ extension JSONSerialization {
         public init(rawValue: UInt) { self.rawValue = rawValue }
 
         public static let prettyPrinted = WritingOptions(rawValue: 1 << 0)
+        public static let sortedKeys = WritingOptions(rawValue: 1 << 1)
     }
 }
 
@@ -116,6 +117,7 @@ open class JSONSerialization : NSObject {
 
         var writer = JSONWriter(
             pretty: opt.contains(.prettyPrinted),
+            sortedKeys: opt.contains(.sortedKeys),
             writer: { (str: String?) in
                 if let str = str {
                     jsonStr.append(str)
@@ -289,6 +291,7 @@ private struct JSONWriter {
     private let maxIntLength = String(describing: Int.max).characters.count
     var indent = 0
     let pretty: Bool
+    let sortedKeys: Bool
     let writer: (String?) -> Void
 
     private lazy var _numberformatter: CFNumberFormatter = {
@@ -299,8 +302,9 @@ private struct JSONWriter {
         return formatter
     }()
 
-    init(pretty: Bool = false, writer: @escaping (String?) -> Void) {
+    init(pretty: Bool = false, sortedKeys: Bool = false, writer: @escaping (String?) -> Void) {
         self.pretty = pretty
+        self.sortedKeys = sortedKeys
         self.writer = writer
     }
 
@@ -501,8 +505,19 @@ private struct JSONWriter {
         }
 
         var first = true
+
+        var keys = Array(dict.keys)
+        if sortedKeys {
+            try keys.sort(by: { a, b in
+                guard let a = a as? String,
+                      let b = b as? String else {
+                        throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: ["NSDebugDescription" : "NSDictionary key must be NSString"])
+                }
+                return a < b
+            })
+        }
 
-        for (key, value) in dict {
+        for key in keys {
             if first {
                 first = false
             } else if pretty {
@@ -518,7 +533,7 @@ private struct JSONWriter {
                 throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: ["NSDebugDescription" : "NSDictionary key must be NSString"])
             }
             pretty ? writer(": ") : writer(":")
-            try serializeJSON(value)
+            try serializeJSON(dict[key]!)
         }
         if pretty {
             writer("\n")

TestFoundation/TestNSJSONSerialization.swift

@@ -945,11 +945,12 @@ extension TestNSJSONSerialization {
             ("test_booleanJSONObject", test_booleanJSONObject),
             ("test_serialize_dictionaryWithDecimal", test_serialize_dictionaryWithDecimal),
             ("test_serializeDecimalNumberJSONObject", test_serializeDecimalNumberJSONObject),
+            ("test_serializeSortedKeys", test_serializeSortedKeys),
         ]
     }
 
-    func trySerialize(_ obj: Any) throws -> String {
-        let data = try JSONSerialization.data(withJSONObject: obj, options: [])
+    func trySerialize(_ obj: Any, options: JSONSerialization.WritingOptions = []) throws -> String {
+        let data = try JSONSerialization.data(withJSONObject: obj, options: options)
         guard let string = String(data: data, encoding: .utf8) else {
             XCTFail("Unable to create string")
             return ""
@@ -1334,6 +1335,19 @@ extension TestNSJSONSerialization {
         } catch {
             XCTFail("Failed during serialization")
         }
+    } 
+    
+    func test_serializeSortedKeys() {
+        var dict: [String: Any]
+
+        dict = ["z": 1, "y": 1, "x": 1, "w": 1, "v": 1, "u": 1, "t": 1, "s": 1, "r": 1, "q": 1, ]
+        XCTAssertEqual(try trySerialize(dict, options: .sortedKeys), "{\"q\":1,\"r\":1,\"s\":1,\"t\":1,\"u\":1,\"v\":1,\"w\":1,\"x\":1,\"y\":1,\"z\":1}")
+
+        dict = ["aaaa": 1, "aaa": 1, "aa": 1, "a": 1]
+        XCTAssertEqual(try trySerialize(dict, options: .sortedKeys), "{\"a\":1,\"aa\":1,\"aaa\":1,\"aaaa\":1}")
+
+        dict = ["c": ["c":1,"b":1,"a":1],"b":["c":1,"b":1,"a":1],"a":["c":1,"b":1,"a":1]]
+        XCTAssertEqual(try trySerialize(dict, options: .sortedKeys), "{\"a\":{\"a\":1,\"b\":1,\"c\":1},\"b\":{\"a\":1,\"b\":1,\"c\":1},\"c\":{\"a\":1,\"b\":1,\"c\":1}}")
     }
 
     fileprivate func createTestFile(_ path: String,_contents: Data) -> String? {