layer json decoding over bufferview

Author: glessard

Sources/FoundationEssentials/JSON/BufferViewCompatibility.swift

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+extension String {
+    static func _tryFromUTF8(_ input: BufferView<UInt8>) -> String? {
+        input.withUnsafePointer { pointer, capacity in
+            _tryFromUTF8(.init(start: pointer, count: capacity))
+        }
+    }
+}
+
+extension Data {
+    func withBufferView<ResultType>(
+        _ body: (BufferView<UInt8>) throws -> ResultType
+    ) rethrows -> ResultType {
+        try withUnsafeBytes {
+            // Data never passes an empty buffer with a `nil` `baseAddress`.
+            try body(BufferView(unsafeRawBufferPointer: $0)!)
+        }
+    }
+}
+
+extension BufferView {
+    internal subscript(region: JSONMap.Region) -> BufferView {
+        precondition(
+            region.startOffset >= 0 && region.startOffset < count && region.count >= 0
+                && region.count <= count && region.startOffset &+ region.count <= count
+        )
+        return self[unchecked: region]
+    }
+
+    internal subscript(unchecked region: JSONMap.Region) -> BufferView {
+        let address = startIndex._rawValue.advanced(by: region.startOffset)
+        return BufferView(baseAddress: address, count: region.count)
+    }
+}