chore: Remove isNull & readNull from ShapeSerializer

Sources/SmithyCBOR/Deserializer.swift

@@ -12,14 +12,14 @@ import struct Foundation.Date
 import class Smithy.Schema
 import protocol Smithy.SmithyDocument
 @_spi(SchemaBasedSerde)
+import struct SmithySerialization.DecodedNull
+@_spi(SchemaBasedSerde)
 import protocol SmithySerialization.DeserializableStruct
 @_spi(SchemaBasedSerde)
 import typealias SmithySerialization.ReadValueConsumer
 import struct SmithySerialization.SerializerError
 @_spi(SchemaBasedSerde)
 import protocol SmithySerialization.ShapeDeserializer
-@_spi(SchemaBasedSerde)
-import struct SmithySerialization.UnexpectedNullError
 
 @_spi(SchemaBasedSerde)
 public class Deserializer: ShapeDeserializer {
@@ -202,18 +202,6 @@ public class Deserializer: ShapeDeserializer {
         return value
     }
 
-    public func isNull() throws -> Bool {
-        try decoder.isNull()
-    }
-
-    public func readNull<T>(_ schema: Schema) throws -> T? {
-        let next = try decoder.popNext()
-        guard case .null = next else {
-            throw CBORDecoderError("member \(schema.id) expected .null but got \(next) instead")
-        }
-        return nil
-    }
-
     public func readStruct<T: DeserializableStruct>(_ schema: Schema, _ value: inout T) throws {
         guard depth < maxDepth else { throw CBORDecoderError("Maximum recursive depth exceeded during readStruct()") }
         depth += 1
@@ -250,7 +238,7 @@ public class Deserializer: ShapeDeserializer {
                     } else {
                         try skipValue()
                     }
-                } catch is UnexpectedNullError {
+                } catch is DecodedNull {
                     // skip null
                 }
                 guard decoder.hasNext() else {
@@ -274,7 +262,7 @@ public class Deserializer: ShapeDeserializer {
                     } else {
                         try skipValue()
                     }
-                } catch is UnexpectedNullError {
+                } catch is DecodedNull {
                     // skip null
                 }
             }
@@ -335,7 +323,7 @@ public class Deserializer: ShapeDeserializer {
                 do {
                     let nextElement = try consumer(self)
                     list.append(nextElement)
-                } catch is UnexpectedNullError {
+                } catch is DecodedNull {
                     // skip the null
                 }
                 guard decoder.hasNext() else {
@@ -349,7 +337,7 @@ public class Deserializer: ShapeDeserializer {
                 do {
                     let nextElement = try consumer(self)
                     list.append(nextElement)
-                } catch is UnexpectedNullError {
+                } catch is DecodedNull {
                     // skip the null
                 }
             }
@@ -382,7 +370,7 @@ public class Deserializer: ShapeDeserializer {
                 do {
                     let value = try consumer(self)
                     map[key] = value
-                } catch is UnexpectedNullError {
+                } catch is DecodedNull {
                     // skip the null
                 }
                 guard decoder.hasNext() else {
@@ -399,7 +387,7 @@ public class Deserializer: ShapeDeserializer {
                 do {
                     let value = try consumer(self)
                     map[key] = value
-                } catch is UnexpectedNullError {
+                } catch is DecodedNull {
                     // skip the null
                 }
             }
@@ -415,7 +403,7 @@ public class Deserializer: ShapeDeserializer {
     private func nullCheck() throws {
         if try decoder.isNull() {
             _ = try decoder.popNext()
-            throw UnexpectedNullError()
+            throw DecodedNull()
         }
     }
 }

Sources/SmithyEventStreams/Deserializers/EventContentDeserializer.swift

@@ -108,14 +108,6 @@ struct EventContentDeserializer: ShapeDeserializer {
         throw notImplemented
     }
 
-    func readNull<T>(_ schema: Schema) throws -> T? {
-        throw notImplemented
-    }
-
-    func isNull() throws -> Bool {
-        throw notImplemented
-    }
-
     var containerSize: Int { -1 }
 
     private var notImplemented: SerializerError { .init("Not implemented") }

Sources/SmithyEventStreams/Deserializers/EventHeaderDeserializer.swift

@@ -166,14 +166,6 @@ struct EventHeaderDeserializer: ShapeDeserializer {
         return value
     }
 
-    func readNull<T>(_ schema: Schema) throws -> T? {
-        throw notImplemented
-    }
-
-    func isNull() throws -> Bool {
-        throw notImplemented
-    }
-
     var containerSize: Int { -1 }
 
     private var notImplemented: SerializerError { .init("Not implemented") }

Sources/SmithyEventStreams/Deserializers/EventStreamDeserializer.swift

@@ -134,14 +134,6 @@ public struct EventStreamDeserializer: ShapeDeserializer {
         throw notImplemented
     }
 
-    public func readNull<T>(_ schema: Schema) throws -> T? {
-        throw notImplemented
-    }
-
-    public func isNull() throws -> Bool {
-        throw notImplemented
-    }
-
     public var containerSize: Int { -1 }
 
     private var notImplemented: SerializerError { .init("Not implemented") }

Sources/SmithyEventStreams/Deserializers/EventUnionDeserializer.swift

@@ -133,14 +133,6 @@ struct EventUnionDeserializer: ShapeDeserializer {
         throw notImplemented
     }
 
-    func readNull<T>(_ schema: Schema) throws -> T? {
-        throw notImplemented
-    }
-
-    func isNull() throws -> Bool {
-        throw notImplemented
-    }
-
     var containerSize: Int { -1 }
 
     private var notImplemented: SerializerError { .init("Not implemented") }

Sources/SmithyEventStreams/Deserializers/SDKUnknownDeserializer.swift

@@ -87,14 +87,6 @@ struct SDKUnknownDeserializer: ShapeDeserializer {
         throw notImplemented
     }
 
-    func readNull<T>(_ schema: Schema) throws -> T? {
-        throw notImplemented
-    }
-
-    func isNull() throws -> Bool {
-        throw notImplemented
-    }
-
     var containerSize: Int { -1 }
 
     private var notImplemented: SerializerError { .init("Not implemented") }

Sources/SmithyJSON/Deserializer.swift

@@ -12,11 +12,12 @@ import class Foundation.NSNumber
 @_spi(SchemaBasedSerde)
 @_spi(SmithyDocumentImpl) import Smithy
 @_spi(SchemaBasedSerde)
+import struct SmithySerialization.DecodedNull
+@_spi(SchemaBasedSerde)
 import protocol SmithySerialization.DeserializableStruct
 import struct SmithySerialization.SerializerError
 @_spi(SchemaBasedSerde)
 import protocol SmithySerialization.ShapeDeserializer
-import struct SmithySerialization.UnexpectedNullError
 @_spi(SmithyTimestamps) import struct SmithyTimestamps.TimestampFormatter
 
 @_spi(SchemaBasedSerde)
@@ -81,7 +82,7 @@ public final class Deserializer: ShapeDeserializer {
         return try list.compactMap {
             do {
                 return try consumer(Deserializer(usesJSONNameTrait: usesJSONNameTrait, node: $0))
-            } catch is UnexpectedNullError {
+            } catch is DecodedNull {
                 // JSON deserializer "tolerates" nulls in non-sparse lists.
                 // This nil will be compacted out of the returned list.
                 return nil
@@ -95,7 +96,7 @@ public final class Deserializer: ShapeDeserializer {
         return try map.compactMapValues {
             do {
                 return try consumer(Deserializer(usesJSONNameTrait: usesJSONNameTrait, node: $0))
-            } catch is UnexpectedNullError {
+            } catch is DecodedNull {
                 // JSON deserializer "tolerates" nulls in non-sparse maps.
                 // This nil will be compacted out of the returned map.
                 return nil
@@ -247,15 +248,6 @@ public final class Deserializer: ShapeDeserializer {
         return date
     }
 
-    public func readNull<T>(_ schema: Schema) throws -> T? {
-        // no action required
-        return nil
-    }
-
-    public func isNull() throws -> Bool {
-        value == .null
-    }
-
     public var containerSize: Int {
         switch value {
         case .object(let object):
@@ -281,7 +273,7 @@ public final class Deserializer: ShapeDeserializer {
 
     private func nullCheck() throws {
         if case .null = self.value {
-            throw UnexpectedNullError()
+            throw DecodedNull()
         }
     }
 }

Sources/SmithySerialization/DecodedNull.swift

@@ -0,0 +1,16 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+/// An error indicating that a null was encountered when deserializing a value.
+///
+/// This error may be handled if null is expected, or thrown back to the caller
+/// if not.
+@_spi(SchemaBasedSerde)
+public struct DecodedNull: Error {
+
+    public init() {}
+}

Sources/SmithySerialization/Deserialization/ShapeDeserializer.swift

@@ -12,6 +12,10 @@ import enum Smithy.ByteStream
 import class Smithy.Schema
 import protocol Smithy.SmithyDocument
 
+/// The protocol for a shape deserializer, which converts encoded data into modeled types.
+///
+/// If `null` is encountered while reading to any supported type, the `DecodedNull` error should be thrown back to the caller.
+/// `DecodedNull` may be caught and handled when a null value is to be expected or (at least) tolerated.
 @_spi(SchemaBasedSerde)
 public protocol ShapeDeserializer {
     func readStruct<T: DeserializableStruct>(_ schema: Schema, _ value: inout T) throws
@@ -30,12 +34,10 @@ public protocol ShapeDeserializer {
     func readString(_ schema: Schema) throws -> String
     func readDocument(_ schema: Schema) throws -> any SmithyDocument
     func readTimestamp(_ schema: Schema) throws -> Date
-    func readNull<T>(_ schema: Schema) throws -> T?
     func readDataStream(_ schema: Schema) throws -> ByteStream
     func readEventStream<E: DeserializableStruct & Sendable>(
         _ schema: Schema
     ) throws -> AsyncThrowingStream<E, any Error>
-    func isNull() throws -> Bool
     var containerSize: Int { get }
 }
 
@@ -54,20 +56,20 @@ public extension ShapeDeserializer {
 
     func readSparseList<E>(_ schema: Schema, _ consumer: ReadValueConsumer<E>) throws -> [E?] {
         try readList(schema) { deserializer in
-            if try deserializer.isNull() {
-                return try deserializer.readNull(schema.resolveTarget.member)
-            } else {
+            do {
                 return try consumer(deserializer)
+            } catch is DecodedNull {
+                return nil
             }
         }
     }
 
     func readSparseMap<V>(_ schema: Schema, _ consumer: ReadValueConsumer<V>) throws -> [String: V?] {
         try readMap(schema) { deserializer in
-            if try deserializer.isNull() {
-                return try deserializer.readNull(schema.resolveTarget.value)
-            } else {
+            do {
                 return try consumer(deserializer)
+            } catch is DecodedNull {
+                return nil
             }
         }
     }

test-sdks/Package.swift

@@ -46,6 +46,7 @@ let package = Package(
                 .product(name: "Smithy", package: "smithy-swift"),
                 .product(name: "AwsCommonRuntimeKit", package: "aws-crt-swift"),
                 testSDKProduct("MaxRecursion"),
+                testSDKProduct("NullTolerance"),
             ]
         ),
         .testTarget(