Adds API for copying memory within ByteBuffer, and tests

swift/Sources/FlatBuffers/ByteBuffer.swift

@@ -217,6 +217,22 @@ public struct ByteBuffer {
     _writerSize = capacity
   }
 
+  /// Constructor that creates a Flatbuffer from unsafe memory region by copying
+  /// the underlying data to a new pointer
+  ///
+  /// - Parameters:
+  ///   - copyingMemoryBound: The unsafe memory region
+  ///   - capacity: The size of the given memory region
+  @inline(__always)
+  public init(
+    copyingMemoryBound memory: UnsafeMutableRawPointer,
+    capacity: Int)
+  {
+    _storage = Storage(count: capacity, alignment: alignment)
+    _storage.copy(from: memory, count: capacity)
+    _writerSize = _storage.capacity
+  }
+
   /// Creates a copy of the existing flatbuffer, by copying it to a different memory.
   /// - Parameters:
   ///   - memory: Current memory of the buffer

swift/Sources/FlatBuffers/FlatBufferBuilder.swift

@@ -98,7 +98,7 @@ public struct FlatBufferBuilder {
   public var sizedBuffer: ByteBuffer {
     assert(finished, "Data shouldn't be called before finish()")
     return ByteBuffer(
-      assumingMemoryBound: _bb.memory.advanced(by: _bb.reader),
+      copyingMemoryBound: _bb.memory.advanced(by: _bb.reader),
       capacity: Int(_bb.size))
   }
 

tests/swift/tests/Tests/FlatBuffers.Test.SwiftTests/ByteBufferTests.swift

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2024 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import XCTest
+@testable import FlatBuffers
+
+final class ByteBufferTests: XCTestCase {
+  func testCopyingMemory() {
+    let count = 100
+    let ptr = UnsafeMutableRawPointer.allocate(byteCount: count, alignment: 1)
+    let byteBuffer = ByteBuffer(copyingMemoryBound: ptr, capacity: count)
+    XCTAssertNotEqual(byteBuffer.memory, ptr)
+  }
+
+  func testSamePointer() {
+    let count = 100
+    let ptr = UnsafeMutableRawPointer.allocate(byteCount: count, alignment: 1)
+    let byteBuffer = ByteBuffer(assumingMemoryBound: ptr, capacity: count)
+    XCTAssertEqual(byteBuffer.memory, ptr)
+  }
+
+  func testSameDataPtr() {
+    let count = 100
+    let ptr = Data(repeating: 0, count: count)
+    let byteBuffer = ByteBuffer(data: ptr)
+    ptr.withUnsafeBytes { ptr in
+      XCTAssertEqual(byteBuffer.memory, ptr.baseAddress)
+    }
+  }
+
+  func testSameArrayPtr() {
+    let count = 100
+    let ptr: [UInt8] = Array(repeating: 0, count: count)
+    let byteBuffer = ByteBuffer(bytes: ptr)
+    ptr.withUnsafeBytes { ptr in
+      XCTAssertEqual(byteBuffer.memory, ptr.baseAddress)
+    }
+  }
+}