Add a way for Swift code to access raw contents of a Typed Array (#151)

Author: yonihemi

IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift

@@ -424,8 +424,9 @@ try test("Closure Identifiers") {
 }
 #endif
 
-func checkArray<T>(_ array: [T]) throws where T: TypedArrayElement {
+func checkArray<T>(_ array: [T]) throws where T: TypedArrayElement & Equatable {
     try expectEqual(toString(JSTypedArray(array).jsValue().object!), jsStringify(array))
+    try checkArrayUnsafeBytes(array)
 }
 
 func toString<T: JSObject>(_ object: T) -> String {
@@ -436,14 +437,23 @@ func jsStringify(_ array: [Any]) -> String {
     array.map({ String(describing: $0) }).joined(separator: ",")
 }
 
+func checkArrayUnsafeBytes<T>(_ array: [T]) throws where T: TypedArrayElement & Equatable {
+    let copyOfArray: [T] = JSTypedArray(array).withUnsafeBytes { buffer in
+        Array(buffer)
+    }
+    try expectEqual(copyOfArray, array)
+}
+
 try test("TypedArray") {
     let numbers = [UInt8](0 ... 255)
     let typedArray = JSTypedArray(numbers)
     try expectEqual(typedArray[12], 12)
+    try expectEqual(numbers.count, typedArray.lengthInBytes)
 
     let numbersSet = Set(0 ... 255)
     let typedArrayFromSet = JSTypedArray(numbersSet)
     try expectEqual(typedArrayFromSet.jsObject.length, 256)
+    try expectEqual(typedArrayFromSet.lengthInBytes, 256 * MemoryLayout<Int>.size)
 
     try checkArray([0, .max, 127, 1] as [UInt8])
     try checkArray([0, 1, .max, .min, -1] as [Int8])

Runtime/src/index.ts

@@ -141,7 +141,7 @@ export class SwiftRuntime {
     private instance: WebAssembly.Instance | null;
     private heap: SwiftRuntimeHeap;
     private _closureHeap: SwiftClosureHeap | null;
-    private version: number = 703;
+    private version: number = 704;
 
     constructor() {
         this.instance = null;
@@ -224,7 +224,7 @@ export class SwiftRuntime {
             return this.heap.referenceHeap(ref);
         };
 
-        const writeString = (ptr: pointer, bytes: Uint8Array) => {
+        const writeBytes = (ptr: pointer, bytes: Uint8Array) => {
             const uint8Memory = new Uint8Array(memory().buffer);
             uint8Memory.set(bytes, ptr);
         };
@@ -445,7 +445,7 @@ export class SwiftRuntime {
 
             swjs_load_string: (ref: ref, buffer: pointer) => {
                 const bytes = this.heap.referenceHeap(ref);
-                writeString(buffer, bytes);
+                writeBytes(buffer, bytes);
             },
 
             swjs_call_function: (
@@ -582,6 +582,12 @@ export class SwiftRuntime {
                 return this.heap.retain(array.slice());
             },
 
+            swjs_load_typed_array: (ref: ref, buffer: pointer) => {
+                const typedArray = this.heap.referenceHeap(ref);
+                const bytes = new Uint8Array(typedArray.buffer);
+                writeBytes(buffer, bytes);
+            },
+
             swjs_release: (ref: ref) => {
                 this.heap.release(ref);
             },

Sources/JavaScriptKit/BasicObjects/JSTypedArray.swift

@@ -54,6 +54,38 @@ public class JSTypedArray<Element>: JSBridgedClass, ExpressibleByArrayLiteral wh
     public convenience init<S: Sequence>(_ sequence: S) where S.Element == Element {
         self.init(Array(sequence))
     }
+
+    /// Length (in bytes) of the typed array.
+    /// The value is established when a TypedArray is constructed and cannot be changed.
+    /// If the TypedArray is not specifying a `byteOffset` or a `length`, the `length` of the referenced `ArrayBuffer` will be returned.
+    public var lengthInBytes: Int {
+        Int(jsObject["byteLength"].number!)
+    }
+
+    /// Calls the given closure with a pointer to a copy of the underlying bytes of the
+    /// array's storage.
+    ///
+    /// - Note: The pointer passed as an argument to `body` is valid only for the
+    /// lifetime of the closure. Do not escape it from the closure for later
+    /// use.
+    ///
+    /// - Parameter body: A closure with an `UnsafeBufferPointer` parameter
+    ///   that points to the contiguous storage for the array.
+    ///    If `body` has a return value, that value is also
+    ///   used as the return value for the `withUnsafeBytes(_:)` method. The
+    ///   argument is valid only for the duration of the closure's execution.
+    /// - Returns: The return value, if any, of the `body` closure parameter.
+    public func withUnsafeBytes<R>(_ body: (UnsafeBufferPointer<Element>) throws -> R) rethrows -> R {
+        let bytesLength = lengthInBytes
+        let rawBuffer = malloc(bytesLength)!
+        defer { free(rawBuffer) }
+        _load_typed_array(jsObject.id, rawBuffer.assumingMemoryBound(to: UInt8.self))
+        let length = lengthInBytes /  MemoryLayout<Element>.size
+        let boundPtr = rawBuffer.bindMemory(to: Element.self, capacity: length)
+        let bufferPtr = UnsafeBufferPointer<Element>(start: boundPtr, count: length)
+        let result = try body(bufferPtr)
+        return result
+    }
 }
 
 // MARK: - Int and UInt support

Sources/JavaScriptKit/XcodeSupport.swift

@@ -82,6 +82,10 @@ import _CJavaScriptKit
         _: UnsafePointer<T>,
         _: Int32
     ) -> JavaScriptObjectRef { fatalError() }
+    func _load_typed_array(
+        _: JavaScriptObjectRef,
+        _: UnsafeMutablePointer<UInt8>!
+    ) { fatalError() }
     func _release(_: JavaScriptObjectRef) { fatalError() }
 
 #endif

Sources/_CJavaScriptKit/_CJavaScriptKit.c

@@ -36,7 +36,7 @@ void swjs_cleanup_host_function_call(void *argv_buffer) {
 /// this and `SwiftRuntime.version` in `./Runtime/src/index.ts`.
 __attribute__((export_name("swjs_library_version")))
 int swjs_library_version(void) {
-    return 703;
+    return 704;
 }
 
 int _library_features(void);

Sources/_CJavaScriptKit/include/_CJavaScriptKit.h

@@ -247,6 +247,14 @@ __attribute__((__import_module__("javascript_kit"),
 extern JavaScriptObjectRef _create_typed_array(const JavaScriptObjectRef constructor,
                                                const void *elements_ptr, const int length);
 
+/// Copies the byte contents of a typed array into a Swift side memory buffer.
+///
+/// @param ref A JavaScript typed array object.
+/// @param buffer A Swift side buffer into which to copy the bytes.
+__attribute__((__import_module__("javascript_kit"),
+               __import_name__("swjs_load_typed_array")))
+extern void _load_typed_array(const JavaScriptObjectRef ref, unsigned char *buffer);
+
 /// Decrements reference count of `ref` retained by `SwiftRuntimeHeap` in JavaScript side.
 ///
 /// @param ref The target JavaScript object.