Add ListEncodingStrategy and ListDecodingStrategy

Sources/XMLCoding/Decoder/XMLDecoder.swift

@@ -102,6 +102,19 @@ open class XMLDecoder {
         case convertFromString(positiveInfinity: String, negativeInfinity: String, nan: String)
     }
 
+    /// The strategy to use when decoding lists.
+    public enum ListDecodingStrategy {
+        /// Preserves the XML structure, an outer type will contain lists
+        /// grouped under the tag used for individual items. This is the default strategy.
+        case preserveStructure
+
+        /// Collapse the XML structure to avoid the outer type.
+        /// Useful when individual items will all be listed under one tag;
+        /// the outer type will only include one list under this tag and can be
+        /// omitted.
+        case collapseListUsingItemTag(String)
+    }
+
     /// The strategy to use in decoding dates. Defaults to `.secondsSince1970`.
     open var dateDecodingStrategy: DateDecodingStrategy = .secondsSince1970
 
@@ -111,6 +124,9 @@ open class XMLDecoder {
     /// The strategy to use in decoding non-conforming numbers. Defaults to `.throw`.
     open var nonConformingFloatDecodingStrategy: NonConformingFloatDecodingStrategy = .throw
 
+    /// The strategy to use in decoding lists. Defaults to `.preserveStructure`.
+    open var listDecodingStrategy: ListDecodingStrategy = .preserveStructure
+
     /// Contextual user-provided information for use during decoding.
     open var userInfo: [CodingUserInfoKey : Any] = [:]
 
@@ -119,6 +135,7 @@ open class XMLDecoder {
         let dateDecodingStrategy: DateDecodingStrategy
         let dataDecodingStrategy: DataDecodingStrategy
         let nonConformingFloatDecodingStrategy: NonConformingFloatDecodingStrategy
+        let listDecodingStrategy: ListDecodingStrategy
         let userInfo: [CodingUserInfoKey : Any]
     }
 
@@ -127,6 +144,7 @@ open class XMLDecoder {
         return _Options(dateDecodingStrategy: dateDecodingStrategy,
                         dataDecodingStrategy: dataDecodingStrategy,
                         nonConformingFloatDecodingStrategy: nonConformingFloatDecodingStrategy,
+                        listDecodingStrategy: listDecodingStrategy,
                         userInfo: userInfo)
     }
 
@@ -610,4 +628,3 @@ extension _XMLDecoder {
         return decoded
     }
 }
-

Sources/XMLCoding/Decoder/XMLUnkeyedDecodingContainer.swift

@@ -28,9 +28,21 @@ internal struct _XMLUnkeyedDecodingContainer : UnkeyedDecodingContainer {
     /// Initializes `self` by referencing the given decoder and container.
     internal init(referencing decoder: _XMLDecoder, wrapping container: [Any]) {
         self.decoder = decoder
-        self.container = container
         self.codingPath = decoder.codingPath
         self.currentIndex = 0
+
+        switch decoder.options.listDecodingStrategy {
+        case .preserveStructure:
+            self.container = container
+        case .collapseListUsingItemTag(let itemTag):
+            if container.count == 1,
+                let itemKeyMap = container[0] as? [AnyHashable: Any],
+                let list = itemKeyMap[itemTag] as? [Any] {
+                    self.container = list
+            } else {
+                self.container = []
+            }
+        }
     }
 
     // MARK: - UnkeyedDecodingContainer Methods
@@ -362,3 +374,4 @@ internal struct _XMLUnkeyedDecodingContainer : UnkeyedDecodingContainer {
         return _XMLDecoder(referencing: value, at: self.decoder.codingPath, options: self.decoder.options)
     }
 }
+

Sources/XMLCoding/Encoder/XMLEncoder.swift

@@ -174,6 +174,19 @@ open class XMLEncoder {
         case custom((Encoder) -> Bool)
     }
 
+    /// The strategy to use when encoding lists.
+    public enum ListEncodingStrategy {
+        /// Preserves the type structure. The CodingKey of the List will be used as
+        /// the tag for each individual item. This is the default strategy.
+        case preserveStructure
+
+        /// Places the individual items of a list within the specified tag and the
+        /// CodingKey of the List becomes a single outer tag containing all items.
+        /// Useful for when you want the XML to have this structure but you don't
+        /// want the type structure to contain this additional wrapping layer.
+        case expandListWithItemTag(String)
+    }
+
     /// The output format to produce. Defaults to `[]`.
     open var outputFormatting: OutputFormatting = []
 
@@ -195,6 +208,9 @@ open class XMLEncoder {
     /// The strategy to use in encoding strings. Defaults to `.deferredToString`.
     open var stringEncodingStrategy: StringEncodingStrategy = .deferredToString
 
+    /// The strategy to use in encoding lists. Defaults to `.preserveStructure`.
+    open var listEncodingStrategy: ListEncodingStrategy = .preserveStructure
+
     /// Contextual user-provided information for use during encoding.
     open var userInfo: [CodingUserInfoKey : Any] = [:]
 
@@ -206,6 +222,7 @@ open class XMLEncoder {
         let keyEncodingStrategy: KeyEncodingStrategy
         let attributeEncodingStrategy: AttributeEncodingStrategy
         let stringEncodingStrategy: StringEncodingStrategy
+        let listEncodingStrategy: ListEncodingStrategy
         let userInfo: [CodingUserInfoKey : Any]
     }
 
@@ -217,6 +234,7 @@ open class XMLEncoder {
                         keyEncodingStrategy: keyEncodingStrategy,
                         attributeEncodingStrategy: attributeEncodingStrategy,
                         stringEncodingStrategy: stringEncodingStrategy,
+                        listEncodingStrategy: listEncodingStrategy,
                         userInfo: userInfo)
     }
 
@@ -317,8 +335,18 @@ internal class _XMLEncoder: Encoder {
         // If an existing unkeyed container was already requested, return that one.
         let topContainer: NSMutableArray
         if self.canEncodeNewValue {
-            // We haven't yet pushed a container at this level; do so here.
-            topContainer = self.storage.pushUnkeyedContainer()
+            switch options.listEncodingStrategy {
+            case .preserveStructure:
+                // We haven't yet pushed a container at this level; do so here.
+                topContainer = self.storage.pushUnkeyedContainer()
+            case .expandListWithItemTag(let itemTag):
+                // create an outer keyed container, with a new array as
+                // its sole entry
+                let outerContainer = self.storage.pushKeyedContainer()
+                let array = NSMutableArray()
+                outerContainer[itemTag] = array
+                topContainer = array
+            }
         } else {
             guard let container = self.storage.containers.last as? NSMutableArray else {
                 preconditionFailure("Attempt to push new unkeyed encoding container when already previously encoded at this path.")

Tests/XMLCodingTests/XMLParsingTests.swift

@@ -1,6 +1,22 @@
 import XCTest
 @testable import XMLCoding
 
+let LIST_XML = """
+    <Response>
+        <Result />
+        <MetadataList>
+            <item>
+                <Id>id1</Id>
+            </item>
+            <item>
+                <Id>id2</Id>
+            </item>
+            <item>
+                <Id>id3</Id>
+            </item>
+        </MetadataList>
+    </Response>
+    """
 
 class XMLParsingTests: XCTestCase {
     struct Result: Codable {
@@ -19,6 +35,14 @@ class XMLParsingTests: XCTestCase {
         }
     }
 
+    struct MetadataList: Codable {
+        let items: [Metadata]
+
+        enum CodingKeys: String, CodingKey {
+            case items = "item"
+        }
+    }
+
     struct Response: Codable {
         let result: Result
         let metadata: Metadata
@@ -29,6 +53,26 @@ class XMLParsingTests: XCTestCase {
         }
     }
 
+    struct ResponseWithList: Codable {
+        let result: Result
+        let metadataList: MetadataList
+
+        enum CodingKeys: String, CodingKey {
+            case result = "Result"
+            case metadataList = "MetadataList"
+        }
+    }
+
+    struct ResponseWithCollapsedList: Codable {
+        let result: Result
+        let metadataList: [Metadata]
+
+        enum CodingKeys: String, CodingKey {
+            case result = "Result"
+            case metadataList = "MetadataList"
+        }
+    }
+
     func testEmptyElement() throws {
         let inputString = """
             <Response>
@@ -69,9 +113,48 @@ class XMLParsingTests: XCTestCase {
 
         XCTAssertEqual("message", response.result.message)
     }
+
+    func testListDecodingWithDefaultStrategy() throws {
+        guard let inputData = LIST_XML.data(using: .utf8) else {
+            return XCTFail()
+        }
+
+        let response = try XMLDecoder().decode(ResponseWithList.self, from: inputData)
+
+        XCTAssertEqual(3, response.metadataList.items.count)
+
+        // encode the output to make sure we get what we started with
+        let data = try XMLEncoder().encode(response, withRootKey: "Response")
+        let encodedString = String(data: data, encoding: .utf8) ?? ""
+
+        XCTAssertEqual(LIST_XML, encodedString)
+    }
+
+    func testListDecodingWithCollapseItemTagStrategy() throws {
+        guard let inputData = LIST_XML.data(using: .utf8) else {
+            return XCTFail()
+        }
+
+        let decoder = XMLDecoder()
+        decoder.listDecodingStrategy = .collapseListUsingItemTag("item")
+        let response = try decoder.decode(ResponseWithCollapsedList.self, from: inputData)
+
+        XCTAssertEqual(3, response.metadataList.count)
+
+        let encoder = XMLEncoder()
+        encoder.listEncodingStrategy = .expandListWithItemTag("item")
+
+        // encode the output to make sure we get what we started with
+        let data = try encoder.encode(response, withRootKey: "Response")
+        let encodedString = String(data: data, encoding: .utf8) ?? ""
+
+        XCTAssertEqual(LIST_XML, encodedString)
+    }
 
     static var allTests = [
         ("testEmptyElement", testEmptyElement),
         ("testEmptyElementNotEffectingPreviousElement", testEmptyElementNotEffectingPreviousElement),
+        ("testListDecodingWithDefaultStrategy", testListDecodingWithDefaultStrategy),
+        ("testListDecodingWithCollapseItemTagStrategy", testListDecodingWithCollapseItemTagStrategy)
     ]
 }