From 98f3e905db7b9a8cda7950054ddc4fbeee8e74de Mon Sep 17 00:00:00 2001
From: Andrew Hershberger <andrew.hershberger@mapbox.com>
Date: Fri, 25 Feb 2022 11:49:56 -0600
Subject: [PATCH] Only unbox NSNumbers 0, 1 to Bool for objCType 'c'

* Previously, initializing JSONValue with NSNumber with value 0 or 1
  would produce JSONValue.boolean. This change updates the behavior to
  only interpret NSNumber as boolean if its objCType is 'c' and its
  value is 0 or 1.
---
 Sources/Turf/JSON.swift         | 38 +++++++++++++++++++++++++++++----
 Tests/TurfTests/JSONTests.swift | 12 +++++++++++
 2 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/Sources/Turf/JSON.swift b/Sources/Turf/JSON.swift
index 2f298d4c..5c9d1005 100644
--- a/Sources/Turf/JSON.swift
+++ b/Sources/Turf/JSON.swift
@@ -67,12 +67,42 @@ extension JSONValue: RawRepresentable {
     
     public init?(rawValue: Any) {
         // Like `JSONSerialization.jsonObject(with:options:)` with `JSONSerialization.ReadingOptions.fragmentsAllowed` specified.
-        if let bool = rawValue as? Bool {
-            self = .boolean(bool)
-        } else if let string = rawValue as? String {
+        if let string = rawValue as? String {
             self = .string(string)
         } else if let number = rawValue as? NSNumber {
-            self = .number(number.doubleValue)
+            /// When a Swift Bool or Objective-C BOOL is boxed with NSNumber, the value of the
+            /// resulting NSNumber's objCType property is 'c' (Int8 (aka CChar) in Swift, char in
+            /// Objective-C) and the value is 0 for false/NO and 1 for true/YES.
+            ///
+            /// Strictly speaking, an NSNumber with those characteristics can be created by boxing
+            /// other non-boolean values (e.g. boxing 0 or 1 using the `init(value: CChar)`
+            /// initializer). Moreover, NSNumber doesn't guarantee to preserve the type suggested
+            /// by the initializer that's used to create it.
+            ///
+            /// This means that when these values are encountered, it is ambiguous whether to
+            /// decode to JSONValue.number or JSONValue.boolean.
+            ///
+            /// In practice, choosing .boolean yields the desired result more often since it is more
+            /// common to work with Bool than it is Int8.
+            switch String(cString: number.objCType) {
+            case "c": // char
+                if number.int8Value == 0 {
+                    self = .boolean(false)
+                } else if number.int8Value == 1 {
+                    self = .boolean(true)
+                } else {
+                    self = .number(number.doubleValue)
+                }
+            default:
+                self = .number(number.doubleValue)
+            }
+        } else if let boolean = rawValue as? Bool {
+            /// This branch must happen after the `NSNumber` branch
+            /// to avoid converting `NSNumber` instances with values
+            /// 0 and 1 but of objCType != 'c' to `Bool` since `as? Bool`
+            /// can succeed when the NSNumber's value is 0 or 1 even
+            /// when its objCType is not 'c'.
+            self = .boolean(boolean)
         } else if let rawArray = rawValue as? JSONArray.RawValue,
                   let array = JSONArray(rawValue: rawArray) {
             self = .array(array)
diff --git a/Tests/TurfTests/JSONTests.swift b/Tests/TurfTests/JSONTests.swift
index de66c68a..e1dc4124 100644
--- a/Tests/TurfTests/JSONTests.swift
+++ b/Tests/TurfTests/JSONTests.swift
@@ -8,6 +8,10 @@ class JSONTests: XCTestCase {
         XCTAssertEqual(JSONValue(rawValue: 3.1415 as NSNumber), .number(3.1415))
         XCTAssertEqual(JSONValue(rawValue: false as NSNumber), .boolean(false))
         XCTAssertEqual(JSONValue(rawValue: true as NSNumber), .boolean(true))
+        XCTAssertEqual(JSONValue(rawValue: false), .boolean(false))
+        XCTAssertEqual(JSONValue(rawValue: true), .boolean(true))
+        XCTAssertEqual(JSONValue(rawValue: 0 as NSNumber), .number(0))
+        XCTAssertEqual(JSONValue(rawValue: 1 as NSNumber), .number(1))
         XCTAssertEqual(JSONValue(rawValue: ["Jason", 42, 3.1415, false, true, nil, [], [:]] as NSArray),
                        .array(["Jason", 42, 3.1415, false, true, nil, [], [:]]))
         XCTAssertEqual(JSONValue(rawValue: [
@@ -245,5 +249,13 @@ class JSONTests: XCTestCase {
         XCTAssertEqual(decodedValue?.rawValue as? NSDictionary, rawObject as NSDictionary)
         
         XCTAssertNoThrow(try JSONEncoder().encode(decodedValue))
+
+        // check decoding of 0/1 true/false to ensure unwanted conversions are avoided
+        let rawString = "[0, 1, true, false]"
+        // force-unwrap is safe since we control the input
+        let serializedArrayFromString = rawString.data(using: .utf8)!
+        XCTAssertNoThrow(decodedValue = try JSONDecoder().decode(JSONValue.self, from: serializedArrayFromString))
+        XCTAssertNotNil(decodedValue)
+        XCTAssertEqual(.array([.number(0), .number(1), .boolean(true), .boolean(false)]), decodedValue)
     }
 }