Improve Plist and JSON Encoder/Decoder resilience to errors thrown during coding

stdlib/public/SDK/Foundation/JSONEncoder.swift

@@ -664,31 +664,38 @@ extension _JSONEncoder {
 
     // This method is called "box_" instead of "box" to disambiguate it from the overloads. Because the return type here is different from all of the "box" overloads (and is more general), any "box" calls in here would call back into "box" recursively instead of calling the appropriate overload, which is not what we want.
     fileprivate func box_<T : Encodable>(_ value: T) throws -> NSObject? {
-        if T.self == Date.self || T.self == NSDate.self {
-            // Respect Date encoding strategy
-            return try self.box((value as! Date))
-        } else if T.self == Data.self || T.self == NSData.self {
-            // Respect Data encoding strategy
-            return try self.box((value as! Data))
-        } else if T.self == URL.self || T.self == NSURL.self {
-            // Encode URLs as single strings.
-            return self.box((value as! URL).absoluteString)
-        } else if T.self == Decimal.self || T.self == NSDecimalNumber.self {
-            // JSONSerialization can natively handle NSDecimalNumber.
-            return (value as! NSDecimalNumber)
-        }
-
-        // The value should request a container from the _JSONEncoder.
         let depth = self.storage.count
-        try value.encode(to: self)
+        do {
+            if T.self == Date.self || T.self == NSDate.self {
+                // Respect Date encoding strategy
+                return try self.box((value as! Date))
+            } else if T.self == Data.self || T.self == NSData.self {
+                // Respect Data encoding strategy
+                return try self.box((value as! Data))
+            } else if T.self == URL.self || T.self == NSURL.self {
+                // Encode URLs as single strings.
+                return self.box((value as! URL).absoluteString)
+            } else if T.self == Decimal.self || T.self == NSDecimalNumber.self {
+                // JSONSerialization can natively handle NSDecimalNumber.
+                return (value as! NSDecimalNumber)
+            }
 
-        // The top container should be a new container.
-        guard self.storage.count > depth else {
-            return nil
-        }
+            // The value should request a container from the _JSONEncoder.
+            try value.encode(to: self)
 
-        return self.storage.popContainer()
-    }
+            // The top container should be a new container.
+            guard self.storage.count > depth else {
+                return nil
+            }
+
+            return self.storage.popContainer()
+        } catch let error {
+            if self.storage.count > depth {
+                assert(self.storage.count == depth + 1, "Internal inconsistency: more than one container on encoder stack during error unwinding")
+                self.storage.popContainer()
+            }
+            throw error
+        }
 }
 
 // MARK: - _JSONReferencingEncoder
@@ -2011,9 +2018,9 @@ extension _JSONDecoder {
         switch self.options.dateDecodingStrategy {
         case .deferredToDate:
             self.storage.push(container: value)
-            let date = try Date(from: self)
-            self.storage.popContainer()
-            return date
+            defer { self.storage.popContainer() }
+
+            return try Date(from: self)
 
         case .secondsSince1970:
             let double = try self.unbox(value, as: Double.self)!
@@ -2045,9 +2052,9 @@ extension _JSONDecoder {
 
         case .custom(let closure):
             self.storage.push(container: value)
-            let date = try closure(self)
-            self.storage.popContainer()
-            return date
+            defer { self.storage.popContainer() }
+
+            return try closure(self)
         }
     }
 
@@ -2057,9 +2064,9 @@ extension _JSONDecoder {
         switch self.options.dataDecodingStrategy {
         case .deferredToData:
             self.storage.push(container: value)
-            let data = try Data(from: self)
-            self.storage.popContainer()
-            return data
+            defer { self.storage.popContainer() }
+
+            return try Data(from: self)
 
         case .base64:
             guard let string = value as? String else {
@@ -2074,9 +2081,9 @@ extension _JSONDecoder {
 
         case .custom(let closure):
             self.storage.push(container: value)
-            let data = try closure(self)
-            self.storage.popContainer()
-            return data
+            defer { self.storage.popContainer() }
+
+            return try closure(self)
         }
     }
 
@@ -2116,8 +2123,9 @@ extension _JSONDecoder {
             decoded = decimal as! T
         } else {
             self.storage.push(container: value)
+            defer { self.storage.popContainer() }
+
             decoded = try type.init(from: self)
-            self.storage.popContainer()
         }
 
         return decoded

stdlib/public/SDK/Foundation/PlistEncoder.swift

@@ -490,7 +490,15 @@ extension _PlistEncoder {
 
         // The value should request a container from the _PlistEncoder.
         let depth = self.storage.count
-        try value.encode(to: self)
+        do {
+            try value.encode(to: self)
+        } catch let error {
+            if self.storage.count > depth {
+                assert(self.storage.count == depth + 1, "Internal inconsistency: more than one container on encoder stack during error unwinding")
+                self.storage.popContainer()
+            }
+            throw error
+        }
 
         // The top container should be a new container.
         guard self.storage.count > depth else {
@@ -1764,8 +1772,9 @@ extension _PlistDecoder {
             decoded = data as! T
         } else {
             self.storage.push(container: value)
+            defer { self.storage.popContainer() }
+
             decoded = try type.init(from: self)
-            self.storage.popContainer()
         }
 
         return decoded