Added sortKeys option to MessagePackEncoder

Sources/MessagePack/Encoder/KeyedEncodingContainer.swift

@@ -15,6 +15,10 @@ extension _MessagePackEncoder {
             self.codingPath = codingPath
             self.userInfo = userInfo
         }
+
+        var sortKeys: Bool {
+            return userInfo[MessagePackEncoder.sortKeysKey] as? Bool ?? false
+        }
     }
 }
 
@@ -77,7 +81,12 @@ extension _MessagePackEncoder.KeyedContainer: _MessagePackEncodingContainer {
             fatalError()
         }
 
-        for (key, container) in self.storage {
+        var storageToEncode = Array(self.storage)
+        if sortKeys {
+            storageToEncode.sort { $0.key.stringValue < $1.key.stringValue }
+        }
+
+        for (key, container) in storageToEncode {
             let keyContainer = _MessagePackEncoder.SingleValueContainer(codingPath: self.codingPath, userInfo: self.userInfo)
             try! keyContainer.encode(key.stringValue)
             data.append(keyContainer.data)

Sources/MessagePack/Encoder/MessagePackEncoder.swift

@@ -23,6 +23,7 @@ final public class MessagePackEncoder {
     public func encode<T>(_ value: T) throws -> Data where T : Encodable {
         let encoder = _MessagePackEncoder()
         encoder.userInfo = self.userInfo
+        encoder.userInfo[MessagePackEncoder.sortKeysKey] = sortKeys
 
         switch value {
         case let data as Data:
@@ -35,6 +36,15 @@ final public class MessagePackEncoder {
 
         return encoder.data
     }
+
+    /**
+     An option used by the encoder whether to sort keys while encoding keyed containers to achieve a deterministic output
+     */
+    public var sortKeys: Bool = false
+
+    internal static var sortKeysKey: CodingUserInfoKey {
+        return CodingUserInfoKey(rawValue: "sortKeysKey")!
+    }
 }
 
 // MARK: - TopLevelEncoder

Tests/MessagePackTests/MessagePackEncodingTests.swift

@@ -6,6 +6,7 @@ class MessagePackEncodingTests: XCTestCase {
 
     override func setUp() {
         self.encoder = MessagePackEncoder()
+        self.encoder.sortKeys = true
     }
 
     func testEncodeNil() {
@@ -59,16 +60,43 @@ class MessagePackEncodingTests: XCTestCase {
     }
 
     func testEncodeFixedDictionary() {
-        let value = try! encoder.encode(["a": 1])
-        XCTAssertEqual(value, Data(bytes: [0x81, 0xA1, 0x61, 0x01]))
+        let value = try! encoder.encode(["a": 1, "b": 2])
+        XCTAssertEqual(value, Data(bytes: [0x82, 0xA1, 0x61, 0x01, 0xA1, 0x62, 0x02]))
     }
 
     func testEncodeVariableDictionary() {
         let letters = "abcdefghijklmnopqrstuvwxyz".unicodeScalars
         let dictionary = Dictionary(uniqueKeysWithValues: zip(letters.map { String($0) }, 1...26))
         let value = try! encoder.encode(dictionary)
-        XCTAssertEqual(value.count, 81)
-        XCTAssert(value.starts(with: [0xde] + [0x00, 0x1A]))
+        XCTAssertEqual(value, Data(bytes: [
+            0xDE, 0x0, 0x1A,
+            0xA1, 0x61, 0x1,
+            0xA1, 0x62, 0x2,
+            0xA1, 0x63, 0x3,
+            0xA1, 0x64, 0x4,
+            0xA1, 0x65, 0x5,
+            0xA1, 0x66, 0x6,
+            0xA1, 0x67, 0x7,
+            0xA1, 0x68, 0x8,
+            0xA1, 0x69, 0x9,
+            0xA1, 0x6A, 0xA,
+            0xA1, 0x6B, 0xB,
+            0xA1, 0x6C, 0xC,
+            0xA1, 0x6D, 0xD,
+            0xA1, 0x6E, 0xE,
+            0xA1, 0x6F, 0xF,
+            0xA1, 0x70, 0x10,
+            0xA1, 0x71, 0x11,
+            0xA1, 0x72, 0x12,
+            0xA1, 0x73, 0x13,
+            0xA1, 0x74, 0x14,
+            0xA1, 0x75, 0x15,
+            0xA1, 0x76, 0x16,
+            0xA1, 0x77, 0x17,
+            0xA1, 0x78, 0x18,
+            0xA1, 0x79, 0x19,
+            0xA1, 0x7A, 0x1A
+        ]))
     }
 
     func testEncodeData() {