Ability to decode from dec/hex string

Sources/Codable.swift

@@ -102,28 +102,42 @@ extension Array where Element: FixedWidthInteger {
 
 extension BigInt: Codable {
     public init(from decoder: Decoder) throws {
-        var container = try decoder.unkeyedContainer()
+        if let container = try? decoder.singleValueContainer(), let stringValue = try? container.decode(String.self) {
+            if stringValue.hasPrefix("0x") || stringValue.hasPrefix("0X") {
+                guard let bigUInt = BigUInt(stringValue.dropFirst(2), radix: 16) else {
+                    throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid hexadecimal BigInt string")
+                }
+                self.init(sign: .plus, magnitude: bigUInt)
+            } else {
+                guard let bigInt = BigInt(stringValue) else {
+                    throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid decimal BigInt string")
+                }
+                self = bigInt
+            }
+        } else {
+            var container = try decoder.unkeyedContainer()
 
-        // Decode sign
-        let sign: BigInt.Sign
-        switch try container.decode(String.self) {
-        case "+":
-            sign = .plus
-        case "-":
-            sign = .minus
-        default:
-            throw DecodingError.dataCorrupted(.init(codingPath: container.codingPath,
-                                                    debugDescription: "Invalid big integer sign"))
-        }
+                // Decode sign
+                let sign: BigInt.Sign
+                switch try container.decode(String.self) {
+                    case "+":
+                        sign = .plus
+                    case "-":
+                            sign = .minus
+                    default:
+                                throw DecodingError.dataCorrupted(.init(codingPath: container.codingPath,
+                                            debugDescription: "Invalid big integer sign"))
+                }
 
-        // Decode magnitude
-        let words = try [UInt](count: container.count?.advanced(by: -1)) { () -> UInt64? in
-            guard !container.isAtEnd else { return nil }
-            return try container.decode(UInt64.self)
-        }
-        let magnitude = BigUInt(words: words)
+            // Decode magnitude
+            let words = try [UInt](count: container.count?.advanced(by: -1)) { () -> UInt64? in
+                guard !container.isAtEnd else { return nil }
+                return try container.decode(UInt64.self)
+            }
+            let magnitude = BigUInt(words: words)
 
-        self.init(sign: sign, magnitude: magnitude)
+                self.init(sign: sign, magnitude: magnitude)
+        }
     }
 
     public func encode(to encoder: Encoder) throws {

Tests/BigIntTests/BigIntTests.swift

@@ -663,6 +663,44 @@ class BigIntTests: XCTestCase {
             XCTAssertEqual(context.debugDescription, "Invalid big integer sign")
         }
     }
+
+    func testDecodableString() {
+        func test(_ a: BigInt, _ v: String? = nil, file: StaticString = #file, line: UInt = #line) {
+            do {
+                let json = try JSONEncoder().encode(v ?? a.description)
+                let b = try JSONDecoder().decode(BigInt.self, from: json)
+                XCTAssertEqual(a, b, file: file, line: line)
+            } catch let error {
+                XCTFail("Error thrown: \(error.localizedDescription)", file: file, line: line)
+            }
+        }
+
+        test(1, "1")
+        test(1, "+1")
+        test(-1, "-1")
+        test(0, "+0")
+        test(0, "-0")
+        test(15, "0xf")
+        test(15, "0Xf")
+        test(15, "0x0f")
+        test(BigInt(1) << 64)
+        test(-BigInt(1) << 64)
+    } 
+
+    func testDecodableStringError() {
+        func test(_ v: String, _ m: String) {
+            XCTAssertThrowsError(try JSONDecoder().decode(BigInt.self, from: try! JSONEncoder().encode(v))) { error in
+                guard let error = error as? DecodingError else { XCTFail("Expected a decoding error"); return }
+                guard case .dataCorrupted(let context) = error else { XCTFail("Expected a dataCorrupted error"); return }
+                XCTAssertEqual(m, context.debugDescription)
+            }
+        }
+
+        test("124q", "Invalid decimal BigInt string")
+        test("-124q", "Invalid decimal BigInt string")
+        test("0xXYZ", "Invalid hexadecimal BigInt string")
+    }
+
 
     func testConversionToData() {
         func test(_ b: BigInt, _ d: Array<UInt8>, file: StaticString = #file, line: UInt = #line) {