feat: schema based XML

Package.swift

@@ -33,6 +33,7 @@ let package = Package(
         .library(name: "SmithySerialization", targets: ["SmithySerialization"]),
         .library(name: "SmithyAWSJSON", targets: ["SmithyAWSJSON"]),
         .library(name: "SmithyRPCv2CBOR", targets: ["SmithyRPCv2CBOR"]),
+        .library(name: "SmithyRestXML", targets: ["SmithyRestXML"]),
         .library(name: "ClientRuntime", targets: ["ClientRuntime"]),
         .library(name: "SmithyRetriesAPI", targets: ["SmithyRetriesAPI"]),
         .library(name: "SmithyRetries", targets: ["SmithyRetries"]),
@@ -315,6 +316,17 @@ let package = Package(
                 "SmithyCBOR",
             ]
         ),
+        .target(
+            name: "SmithyRestXML",
+            dependencies: [
+                "ClientRuntime",
+                "Smithy",
+                "SmithyEventStreams",
+                "SmithySerialization",
+                "SmithyXML",
+                "SmithyTimestamps",
+            ]
+        ),
         .testTarget(
             name: "ClientRuntimeTests",
             dependencies: [

Sources/Smithy/TraitLibrary/AllSupportedTraits.swift

@@ -28,6 +28,13 @@ private let allSupportedTraitTypes: [ShapeID: any Trait.Type] = [
     ErrorTrait.id: ErrorTrait.self,
     EventHeaderTrait.id: EventHeaderTrait.self,
     EventPayloadTrait.id: EventPayloadTrait.self,
+    HttpHeaderTrait.id: HttpHeaderTrait.self,
+    HttpLabelTrait.id: HttpLabelTrait.self,
+    HttpPayloadTrait.id: HttpPayloadTrait.self,
+    HttpPrefixHeadersTrait.id: HttpPrefixHeadersTrait.self,
+    HttpQueryTrait.id: HttpQueryTrait.self,
+    HttpQueryParamsTrait.id: HttpQueryParamsTrait.self,
+    HttpResponseCodeTrait.id: HttpResponseCodeTrait.self,
     InputTrait.id: InputTrait.self,
     OutputTrait.id: OutputTrait.self,
     RequiredTrait.id: RequiredTrait.self,
@@ -36,6 +43,10 @@ private let allSupportedTraitTypes: [ShapeID: any Trait.Type] = [
     StreamingTrait.id: StreamingTrait.self,
     TimestampFormatTrait.id: TimestampFormatTrait.self,
     UnitTypeTrait.id: UnitTypeTrait.self, // UnitTypeTrait will only ever appear in Prelude.unitSchema
+    XmlAttributeTrait.id: XmlAttributeTrait.self,
+    XmlFlattenedTrait.id: XmlFlattenedTrait.self,
+    XmlNameTrait.id: XmlNameTrait.self,
+    XmlNamespaceTrait.id: XmlNamespaceTrait.self,
 
     // Synthetic traits
     TargetsUnitTrait.id: TargetsUnitTrait.self,

Sources/Smithy/TraitLibrary/HttpHeaderTrait.swift

@@ -0,0 +1,20 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct HttpHeaderTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "httpHeader") }
+    public let value: String
+    public var node: Node { .string(value) }
+
+    public init(node: Node) throws {
+        guard case .string(let value) = node else {
+            throw TraitError("httpHeader trait requires a string value")
+        }
+        self.value = value
+    }
+}

Sources/Smithy/TraitLibrary/HttpLabelTrait.swift

@@ -0,0 +1,13 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct HttpLabelTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "httpLabel") }
+    public var node: Node { [:] }
+    public init(node: Node) throws {}
+}

Sources/Smithy/TraitLibrary/HttpPayloadTrait.swift

@@ -0,0 +1,13 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct HttpPayloadTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "httpPayload") }
+    public var node: Node { [:] }
+    public init(node: Node) throws {}
+}

Sources/Smithy/TraitLibrary/HttpPrefixHeadersTrait.swift

@@ -0,0 +1,20 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct HttpPrefixHeadersTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "httpPrefixHeaders") }
+    public let value: String
+    public var node: Node { .string(value) }
+
+    public init(node: Node) throws {
+        guard case .string(let value) = node else {
+            throw TraitError("httpPrefixHeaders trait requires a string value")
+        }
+        self.value = value
+    }
+}

Sources/Smithy/TraitLibrary/HttpQueryParamsTrait.swift

@@ -0,0 +1,13 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct HttpQueryParamsTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "httpQueryParams") }
+    public var node: Node { [:] }
+    public init(node: Node) throws {}
+}

Sources/Smithy/TraitLibrary/HttpQueryTrait.swift

@@ -0,0 +1,20 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct HttpQueryTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "httpQuery") }
+    public let value: String
+    public var node: Node { .string(value) }
+
+    public init(node: Node) throws {
+        guard case .string(let value) = node else {
+            throw TraitError("httpQuery trait requires a string value")
+        }
+        self.value = value
+    }
+}

Sources/Smithy/TraitLibrary/HttpResponseCodeTrait.swift

@@ -0,0 +1,13 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct HttpResponseCodeTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "httpResponseCode") }
+    public var node: Node { [:] }
+    public init(node: Node) throws {}
+}

Sources/Smithy/TraitLibrary/XmlAttributeTrait.swift

@@ -0,0 +1,13 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct XmlAttributeTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "xmlAttribute") }
+    public var node: Node { [:] }
+    public init(node: Node) throws {}
+}

Sources/Smithy/TraitLibrary/XmlFlattenedTrait.swift

@@ -0,0 +1,13 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct XmlFlattenedTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "xmlFlattened") }
+    public var node: Node { [:] }
+    public init(node: Node) throws {}
+}

Sources/Smithy/TraitLibrary/XmlNameTrait.swift

@@ -0,0 +1,20 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct XmlNameTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "xmlName") }
+    public let value: String
+    public var node: Node { .string(value) }
+
+    public init(node: Node) throws {
+        guard case .string(let value) = node else {
+            throw TraitError("xmlName trait requires a string value")
+        }
+        self.value = value
+    }
+}

Sources/Smithy/TraitLibrary/XmlNamespaceTrait.swift

@@ -0,0 +1,33 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@_spi(SchemaBasedSerde)
+public struct XmlNamespaceTrait: Trait {
+    public static var id: ShapeID { .init("smithy.api", "xmlNamespace") }
+    public let uri: String
+    public let prefix: String?
+    public var node: Node {
+        var dict: [String: Node] = ["uri": .string(uri)]
+        if let prefix { dict["prefix"] = .string(prefix) }
+        return .object(dict)
+    }
+
+    public init(node: Node) throws {
+        guard case .object(let dict) = node else {
+            throw TraitError("xmlNamespace trait requires an object value")
+        }
+        guard case .string(let uri) = dict["uri"] else {
+            throw TraitError("xmlNamespace trait requires a 'uri' string")
+        }
+        self.uri = uri
+        if case .string(let prefix) = dict["prefix"] {
+            self.prefix = prefix
+        } else {
+            self.prefix = nil
+        }
+    }
+}

Sources/SmithyCodegenCore/ModelTransformer/Model+InputOutput.swift

@@ -14,6 +14,8 @@ import struct Smithy.ShapeID
 import struct Smithy.TargetsUnitTrait
 @_spi(SchemaBasedSerde)
 import struct Smithy.TraitCollection
+import struct Smithy.XmlNamespaceTrait
+import struct Smithy.XmlNameTrait
 
 extension Model {
 
@@ -27,6 +29,11 @@ extension Model {
             .filter { $0.type == .operation }
             .compactMap { $0 as? OperationShape }
 
+        // Get service-level @xmlNamespace to propagate to synthetic input shapes (for RestXML root element)
+        let serviceXmlNamespace = shapes.values
+            .first { $0.type == .service }
+            .flatMap { try? $0.traits.getTrait(XmlNamespaceTrait.self) }
+
         // Make a copy of this model's shapes to modify
         var newShapes = shapes
 
@@ -52,9 +59,24 @@ extension Model {
             // Add UsedAsInput and UsedAsOutput traits to the input/output structures
             // These traits allow us to identify inputs/outputs by trait, but allow us to
             // leave the Smithy input & output traits as set on the original model.
-            let newInput = newStruct(newID: newInputShapeID, newTraits: [UsedAsInputTrait()], original: inputShape)
+            // Also add XmlNameTrait with the original shape name so XML serialization uses
+            // the correct root element name (e.g. "SimpleScalarPropertiesRequest" not "SimpleScalarPropertiesInput").
+            var inputExtraTraits = TraitCollection()
+            inputExtraTraits.add(UsedAsInputTrait())
+            if !inputShape.hasTrait(XmlNameTrait.self) && inputShape.id != Prelude.unitSchema.id {
+                inputExtraTraits.add(try XmlNameTrait(node: .string(inputShape.id.name)))
+            }
+            if let ns = serviceXmlNamespace, !inputShape.hasTrait(XmlNamespaceTrait.self) {
+                inputExtraTraits.add(ns)
+            }
+            var outputExtraTraits = TraitCollection()
+            outputExtraTraits.add(UsedAsOutputTrait())
+            if !outputShape.hasTrait(XmlNameTrait.self) && outputShape.id != Prelude.unitSchema.id {
+                outputExtraTraits.add(try XmlNameTrait(node: .string(outputShape.id.name)))
+            }
+            let newInput = newStruct(newID: newInputShapeID, newTraits: inputExtraTraits, original: inputShape)
             let newInputShapeMembers = try renamedMembers(newID: newInputShapeID, original: inputShape)
-            let newOutput = newStruct(newID: newOutputShapeID, newTraits: [UsedAsOutputTrait()], original: outputShape)
+            let newOutput = newStruct(newID: newOutputShapeID, newTraits: outputExtraTraits, original: outputShape)
             let newOutputShapeMembers = try renamedMembers(newID: newOutputShapeID, original: outputShape)
 
             // Add the new input & output and their members to the new shape dictionary.

Sources/SmithyCodegenCore/Schemas/SchemasCodegen.swift

@@ -13,6 +13,7 @@ import struct Smithy.ShapeID
 import enum Smithy.ShapeType
 @_spi(SchemaBasedSerde)
 import func Smithy.traitType
+import struct Smithy.XmlNameTrait
 
 /// A generator for the `Schemas.swift`
 package struct SchemasCodegen {
@@ -139,7 +140,9 @@ package struct SchemasCodegen {
             // Get all the trait IDs that apply to this member & sort
             let memberTraitIDs = Set(memberShape.traits.traitDict.keys)
             let targetTraitIDs = Set(try memberShape.target.traits.traitDict.keys)
-            let allTraitIDs = Array(memberTraitIDs.union(targetTraitIDs)).smithySorted()
+            // @xmlName on the target renames the target shape, not the member; don't inherit.
+            let inheritableTargetTraitIDs = targetTraitIDs.filter { $0 != XmlNameTrait.id }
+            let allTraitIDs = Array(memberTraitIDs.union(inheritableTargetTraitIDs)).smithySorted()
 
             var pairs = [(ShapeID, Node)]()
             for traitID in allTraitIDs {

Sources/SmithyEventStreams/Deserializers/EventContentDeserializer.swift

@@ -32,11 +32,17 @@ struct EventContentDeserializer: ShapeDeserializer {
 
         // Deserialize the event payload, to the member marked with @eventPayload if it exists,
         // to the structure's members otherwise.
-        // Use a deserializer for the protocol in use, by making it from the codec.
-        let payloadDeserializer = try codec.makeDeserializer(data: message.payload)
         if let payloadMember = schema.members.first(where: { $0.hasTrait(EventPayloadTrait.self) }) {
-            try T.readConsumer(payloadMember, &value, payloadDeserializer)
+            // Skip codec for blob payloads — codec would parse as XML/JSON.
+            if (payloadMember.target ?? payloadMember).type == .blob {
+                let blobDeserializer = RawBlobDeserializer(data: message.payload)
+                try T.readConsumer(payloadMember, &value, blobDeserializer)
+            } else {
+                let payloadDeserializer = try codec.makeDeserializer(data: message.payload)
+                try T.readConsumer(payloadMember, &value, payloadDeserializer)
+            }
         } else {
+            let payloadDeserializer = try codec.makeDeserializer(data: message.payload)
             try payloadDeserializer.readStruct(schema, &value)
         }