chore: import upstream snapshot with attribution

Sources/ContainerizationOCI/Content/Content.swift

@@ -0,0 +1,59 @@
+//===----------------------------------------------------------------------===//
+// 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 ContainerizationExtras
+import Crypto
+import Foundation
+import NIOCore
+
+/// Protocol for defining a single OCI content
+public protocol Content: Sendable {
+    /// URL to the content
+    var path: URL { get }
+
+    /// sha256 of content
+    func digest() throws -> SHA256.Digest
+
+    /// Size of content
+    func size() throws -> UInt64
+
+    /// Data representation of entire content
+    func data() throws -> Data
+
+    /// Data representation partial content
+    func data(offset: UInt64, length: Int) throws -> Data?
+
+    /// Decode the content into an object
+    func decode<T>() throws -> T where T: Decodable
+}
+
+/// Protocol defining methods to fetch and push OCI content
+public protocol ContentClient: Sendable {
+    func fetch<T: Codable>(name: String, descriptor: Descriptor) async throws -> T
+
+    func fetchBlob(name: String, descriptor: Descriptor, into file: URL, progress: ProgressHandler?) async throws -> (Int64, SHA256Digest)
+
+    func fetchData(name: String, descriptor: Descriptor) async throws -> Data
+
+    func push<T: Sendable & AsyncSequence>(
+        name: String,
+        ref: String,
+        descriptor: Descriptor,
+        streamGenerator: () throws -> T,
+        progress: ProgressHandler?
+    ) async throws where T.Element == ByteBuffer
+
+}