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jextract/jni: handle UnsafeRawBufferPointer params (#668)
* jextract/jni: handle UnsafeRawBufferPointer params This allows passing a Java byte array to an `UnsafeRawBufferPointer` accepting API in Swift. This conversion needs to copy a bunch but makes pretty much sense. This is in JNI mode specifically. In FFM mode we could do better by allocating and passing a MemorySegment but this is to unblock APIs in JNI mode specifically. * jextract/jni: handle UnsafeRawBufferPointer params This allows passing a Java byte array to an `UnsafeRawBufferPointer` accepting API in Swift. This conversion needs to copy a bunch but makes pretty much sense. This is in JNI mode specifically. In FFM mode we could do better by allocating and passing a MemorySegment but this is to unblock APIs in JNI mode specifically. * formatting * Update Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+NativeTranslation.swift
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7 files changed

Lines changed: 220 additions & 3 deletions

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‎Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/UnsafeRawBufferPointer.swift‎

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2026 Apple Inc. and the Swift.org project authors
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// Licensed under Apache License v2.0
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//
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// See LICENSE.txt for license information
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// See CONTRIBUTORS.txt for the list of Swift.org project authors
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//
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// SPDX-License-Identifier: Apache-2.0
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//
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//===----------------------------------------------------------------------===//
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import SwiftJava
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/// Sum all bytes in the buffer
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public func sumOfBytes(data: UnsafeRawBufferPointer) -> Int64 {
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var sum: Int64 = 0
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for byte in data {
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sum += Int64(byte)
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}
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return sum
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}
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/// Return the count of bytes in the buffer
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public func bufferCount(data: UnsafeRawBufferPointer) -> Int64 {
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Int64(data.count)
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}

‎Samples/SwiftJavaExtractJNISampleApp/src/test/java/com/example/swift/UnsafeRawBufferPointerTest.java‎

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2026 Apple Inc. and the Swift.org project authors
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// Licensed under Apache License v2.0
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//
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// See LICENSE.txt for license information
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// See CONTRIBUTORS.txt for the list of Swift.org project authors
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//
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// SPDX-License-Identifier: Apache-2.0
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//
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//===----------------------------------------------------------------------===//
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package com.example.swift;
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import org.junit.jupiter.api.Test;
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import static org.junit.jupiter.api.Assertions.*;
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public class UnsafeRawBufferPointerTest {
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@Test
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void sumOfBytes() {
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byte[] input = new byte[] { 1, 2, 3, 4, 5 };
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assertEquals(15, MySwiftLibrary.sumOfBytes(input));
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}
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@Test
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void sumOfBytes_empty() {
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byte[] input = new byte[] {};
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assertEquals(0, MySwiftLibrary.sumOfBytes(input));
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}
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@Test
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void bufferCount() {
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byte[] input = new byte[] { 10, 20, 30, 40 };
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assertEquals(4, MySwiftLibrary.bufferCount(input));
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}
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@Test
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void bufferCount_empty() {
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byte[] input = new byte[] {};
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assertEquals(0, MySwiftLibrary.bufferCount(input));
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}
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}

‎Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaTranslation.swift‎

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@@ -242,7 +242,7 @@ extension JNISwift2JavaGenerator {
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let javaName = javaIdentifiers.makeJavaMethodName(decl)
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// Swift -> Java
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var translatedFunctionSignature = try translate(
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var translatedFunctionSignature = try self.translate(
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functionSignature: decl.functionSignature,
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methodName: javaName,
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parentName: parentName,
@@ -509,6 +509,12 @@ extension JNISwift2JavaGenerator {
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case .foundationData, .essentialsData:
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break // Handled as wrapped struct
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case .unsafeRawBufferPointer, .unsafeMutableRawBufferPointer:
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return TranslatedParameter(
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parameter: JavaParameter(name: parameterName, type: .array(.byte)),
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conversion: .placeholder
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)
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case .foundationUUID, .essentialsUUID:
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return TranslatedParameter(
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parameter: JavaParameter(name: parameterName, type: .javaUtilUUID),

‎Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+NativeTranslation.swift‎

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@@ -125,6 +125,16 @@ extension JNISwift2JavaGenerator {
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parameterName: parameterName
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)
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case .unsafeRawBufferPointer, .unsafeMutableRawBufferPointer:
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return NativeParameter(
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parameters: [
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JavaParameter(name: parameterName, type: .array(.byte))
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],
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conversion: .jniByteArrayToUnsafeRawBufferPointer(.placeholder, name: parameterName),
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indirectConversion: nil,
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conversionCheck: nil
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)
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case .foundationDate, .essentialsDate, .foundationData, .essentialsData:
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// Handled as wrapped struct
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break
@@ -1154,6 +1164,9 @@ extension JNISwift2JavaGenerator {
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/// `SwiftType(inner)`
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indirect case labelessInitializer(NativeSwiftConversionStep, swiftType: SwiftType)
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/// Converts a jbyteArray to UnsafeRawBufferPointer via GetByteArrayElements
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indirect case jniByteArrayToUnsafeRawBufferPointer(NativeSwiftConversionStep, name: String)
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/// Constructs a Swift tuple from individually-converted elements.
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/// E.g. `(label0: conv0, conv1)` for `(label0: Int, String)`
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indirect case tupleConstruct(elements: [(label: String?, conversion: NativeSwiftConversionStep)])
@@ -1713,6 +1726,21 @@ extension JNISwift2JavaGenerator {
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let inner = inner.render(&printer, placeholder)
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return "\(swiftType)(\(inner))"
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case .jniByteArrayToUnsafeRawBufferPointer(let inner, let name):
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let inner = inner.render(&printer, placeholder)
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let countVar = "\(name)$count"
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let ptrVar = "\(name)$ptr"
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let rbpVar = "\(name)$rbp"
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printer.print(
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"""
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let \(countVar) = Int(environment.interface.GetArrayLength(environment, \(inner)))
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let \(ptrVar) = environment.interface.GetByteArrayElements(environment, \(inner), nil)!
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defer { environment.interface.ReleaseByteArrayElements(environment, \(inner), \(ptrVar), jint(JNI_ABORT)) }
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let \(rbpVar) = UnsafeRawBufferPointer(start: \(ptrVar), count: \(countVar))
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"""
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)
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return rbpVar
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case .tupleConstruct(let elements):
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let parts = elements.enumerated().map { idx, element in
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let converted = element.conversion.render(&printer, "\(placeholder)_\(idx)")

‎Sources/JExtractSwiftLib/JavaTypes/JavaType+JDK.swift‎

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@@ -58,4 +58,5 @@ extension JavaType {
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static var javaUtilUUID: JavaType {
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.class(package: "java.util", name: "UUID")
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}
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}

‎Sources/SwiftJavaDocumentation/Documentation.docc/SupportedFeatures.md‎

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@@ -93,7 +93,8 @@ SwiftJava's `swift-java jextract` tool automates generating Java bindings from S
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| Operators: `+`, `-`, user defined | ❌ | ❌ |
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| Subscripts: `subscript()` | ✅ | ✅ |
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| Equatable | ❌ | ❌ |
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| Pointers: `UnsafeRawPointer`, UnsafeBufferPointer (?) | 🟡 | ❌ |
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| Pointers: `UnsafeRawPointer` | 🟡 | ❌ |
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| Pointers as parameters: `UnsafeRawBufferPointer` (as `byte[]`) | ❌ | ✅ |
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| Nested types: `struct Hello { struct World {} }` | ❌ | ✅ |
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| Inheritance: `class Caplin: Capybara` | ❌ | ❌ |
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| Non-escaping `Void` closures: `func callMe(maybe: () -> ())` | ✅ | ✅ |
@@ -461,4 +462,4 @@ public final class FishBox ... {
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```
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> NOTE: Currently no helpers are available to convert between unspecialized types to specialized ones, but this can be offered
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> as additional `box.as(FishBox.class)` conversion methods in the future.
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> as additional `box.as(FishBox.class)` conversion methods in the future.

‎Tests/JExtractSwiftTests/ByteArrayTests.swift‎

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@@ -183,4 +183,111 @@ final class ByteArrayTests {
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expectedChunks: expectedSwiftChunks
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)
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}
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// ==== -----------------------------------------------------------------------
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// MARK: JNI mode tests
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@Test("Import: accept [UInt8] array (JNI)")
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func func_accept_array_uint8_jni() throws {
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let text = "public func acceptArray(array: [UInt8])"
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try assertOutput(
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input: text,
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.jni,
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.swift,
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detectChunkByInitialLines: 2,
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expectedChunks: [
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"""
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@_cdecl("Java_com_example_swift_SwiftModule__00024acceptArray___3B")
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public func Java_com_example_swift_SwiftModule__00024acceptArray___3B(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, array: jbyteArray?) {
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SwiftModule.acceptArray(array: [UInt8](fromJNI: array, in: environment))
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}
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"""
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]
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)
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try assertOutput(
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input: text,
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.jni,
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.java,
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detectChunkByInitialLines: 2,
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expectedChunks: [
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"""
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public static void acceptArray(@Unsigned byte[] array) {
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SwiftModule.$acceptArray(Objects.requireNonNull(array, "array must not be null"));
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}
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""",
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"private static native void $acceptArray(byte[] array);",
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]
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)
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}
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@Test("Import: return [UInt8] array (JNI)")
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func func_return_array_uint8_jni() throws {
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let text = "public func returnArray() -> [UInt8]"
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try assertOutput(
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input: text,
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.jni,
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.swift,
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detectChunkByInitialLines: 2,
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expectedChunks: [
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"""
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@_cdecl("Java_com_example_swift_SwiftModule__00024returnArray__")
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public func Java_com_example_swift_SwiftModule__00024returnArray__(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass) -> jbyteArray? {
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return SwiftModule.returnArray().getJNILocalRefValue(in: environment)
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}
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"""
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]
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)
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try assertOutput(
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input: text,
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.jni,
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.java,
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detectChunkByInitialLines: 2,
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expectedChunks: [
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"""
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@Unsigned
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public static byte[] returnArray() {
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return SwiftModule.$returnArray();
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}
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""",
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"private static native byte[] $returnArray();",
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]
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)
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}
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@Test("Import: accept UnsafeRawBufferPointer (JNI)")
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func func_accept_unsafeRawBufferPointer_jni() throws {
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let text = "public func receiveBuffer(data: UnsafeRawBufferPointer)"
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try assertOutput(
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input: text,
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.jni,
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.swift,
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detectChunkByInitialLines: 2,
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expectedChunks: [
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"""
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@_cdecl("Java_com_example_swift_SwiftModule__00024receiveBuffer___3B")
268+
public func Java_com_example_swift_SwiftModule__00024receiveBuffer___3B(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, data: jbyteArray?) {
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let data$count = Int(environment.interface.GetArrayLength(environment, data))
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let data$ptr = environment.interface.GetByteArrayElements(environment, data, nil)!
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defer { environment.interface.ReleaseByteArrayElements(environment, data, data$ptr, jint(JNI_ABORT)) }
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let data$rbp = UnsafeRawBufferPointer(start: data$ptr, count: data$count)
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SwiftModule.receiveBuffer(data: data$rbp)
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}
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"""
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]
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)
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try assertOutput(
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input: text,
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.jni,
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.java,
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detectChunkByInitialLines: 2,
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expectedChunks: [
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"""
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public static void receiveBuffer(byte[] data) {
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SwiftModule.$receiveBuffer(data);
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}
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""",
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"private static native void $receiveBuffer(byte[] data);",
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]
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)
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}
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}

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