chore: import upstream snapshot with attribution

Sources/ContainerizationOCI/Content/LocalContent.swift

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization project authors.
+//
+// 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
+//
+//   https://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 ContainerizationError
+import Crypto
+import Foundation
+
+public final class LocalContent: Content {
+    public let path: URL
+    private let file: FileHandle
+
+    public init(path: URL) throws {
+        guard FileManager.default.fileExists(atPath: path.path) else {
+            throw ContainerizationError(.notFound, message: "content at path \(path.absolutePath())")
+        }
+
+        self.file = try FileHandle(forReadingFrom: path)
+        self.path = path
+    }
+
+    public func digest() throws -> SHA256.Digest {
+        let bufferSize = 64 * 1024  // 64 KB
+        var hasher = SHA256()
+
+        try self.file.seek(toOffset: 0)
+        while case let data = file.readData(ofLength: bufferSize), !data.isEmpty {
+            hasher.update(data: data)
+        }
+
+        let digest = hasher.finalize()
+
+        try self.file.seek(toOffset: 0)
+        return digest
+    }
+
+    public func data(offset: UInt64 = 0, length size: Int = 0) throws -> Data? {
+        try file.seek(toOffset: offset)
+        if size == 0 {
+            return try file.readToEnd()
+        }
+        return try file.read(upToCount: size)
+    }
+
+    public func data() throws -> Data {
+        try Data(contentsOf: self.path)
+    }
+
+    public func size() throws -> UInt64 {
+        let fileAttrs = try FileManager.default.attributesOfItem(atPath: self.path.absolutePath())
+        if let size = fileAttrs[FileAttributeKey.size] as? UInt64 {
+            return size
+        }
+        throw ContainerizationError(.internalError, message: "could not determine file size for \(path.absolutePath())")
+    }
+
+    public func decode<T>() throws -> T where T: Decodable {
+        let json = JSONDecoder()
+        let data = try Data(contentsOf: self.path)
+        return try json.decode(T.self, from: data)
+    }
+
+    deinit {
+        try? self.file.close()
+    }
+}