From 8b86545a079daf596d50d09f3f42ae5ecce2de4d Mon Sep 17 00:00:00 2001
From: Ben Boeckel <ben.boeckel@kitware.com>
Date: Tue, 7 Jul 2026 12:10:05 -0400
Subject: [PATCH] feat(oci): add OCIArchiveWriter for OCI Image Layout tar
 archives

---
 Sources/tart/OCI/OCIArchiveWriter.swift | 113 ++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 Sources/tart/OCI/OCIArchiveWriter.swift

diff --git a/Sources/tart/OCI/OCIArchiveWriter.swift b/Sources/tart/OCI/OCIArchiveWriter.swift
new file mode 100644
index 0000000..80021ba
--- /dev/null
+++ b/Sources/tart/OCI/OCIArchiveWriter.swift
@@ -0,0 +1,113 @@
+import Foundation
+
+class OCIArchiveWriter {
+  private let tmpDir: URL
+  private let blobsDir: URL
+  private var manifestDigest: String?
+  private var manifestSize: Int?
+  private var manifestReferences: [String] = []
+  private var manifestData: Data?
+
+  init() throws {
+    tmpDir = try Config().tartTmpDir.appendingPathComponent(UUID().uuidString)
+    blobsDir = tmpDir.appendingPathComponent("blobs/sha256")
+    try FileManager.default.createDirectory(at: blobsDir, withIntermediateDirectories: true)
+  }
+
+  deinit {
+    try? FileManager.default.removeItem(at: tmpDir)
+  }
+}
+
+extension OCIArchiveWriter: BlobStorage {
+  func pushBlob(fromData: Data, chunkSizeMb: Int, digest: String?) async throws -> String {
+    let resolvedDigest = digest ?? Digest.hash(fromData)
+    let hex = resolvedDigest.replacingOccurrences(of: "sha256:", with: "")
+    let blobPath = blobsDir.appendingPathComponent(hex)
+    try fromData.write(to: blobPath)
+    return resolvedDigest
+  }
+
+  func blobExists(_ digest: String) async throws -> Bool {
+    let hex = digest.replacingOccurrences(of: "sha256:", with: "")
+    let blobPath = blobsDir.appendingPathComponent(hex)
+    return FileManager.default.fileExists(atPath: blobPath.path)
+  }
+
+  func pushManifest(reference: String, manifest: OCIManifest) async throws -> String {
+    if let existingDigest = manifestDigest, let existingData = manifestData {
+      let newData = try manifest.toJSON()
+      if newData == existingData {
+        manifestReferences.append(reference)
+        return existingDigest
+      }
+    }
+
+    let data = try manifest.toJSON()
+    let digest = Digest.hash(data)
+    let hex = digest.replacingOccurrences(of: "sha256:", with: "")
+    let blobPath = blobsDir.appendingPathComponent(hex)
+    try data.write(to: blobPath)
+    manifestDigest = digest
+    manifestSize = data.count
+    manifestData = data
+    manifestReferences.append(reference)
+    return digest
+  }
+
+  func finalize(path: String, tag: String? = nil) throws {
+    guard let manifestDigest = manifestDigest, let manifestSize = manifestSize else {
+      throw RuntimeError.Generic("no manifest was pushed")
+    }
+
+    let ociLayoutData = try JSONSerialization.data(withJSONObject: ["imageLayoutVersion": "1.0.0"])
+    try ociLayoutData.write(to: tmpDir.appendingPathComponent("oci-layout"))
+
+    var manifests: [[String: Any]] = []
+
+    let baseDescriptor: [String: Any] = [
+      "mediaType": ociManifestMediaType,
+      "digest": manifestDigest,
+      "size": manifestSize,
+    ]
+
+    let refs = manifestReferences.isEmpty
+      ? (tag.map { [$0] } ?? ["latest"])
+      : manifestReferences
+
+    for ref in refs {
+      var entry = baseDescriptor
+      entry["annotations"] = [
+        "org.opencontainers.image.ref.name": ref
+      ]
+      manifests.append(entry)
+    }
+
+    let index: [String: Any] = [
+      "schemaVersion": 2,
+      "manifests": manifests
+    ]
+
+    let indexData = try JSONSerialization.data(withJSONObject: index, options: [.prettyPrinted, .sortedKeys])
+    try indexData.write(to: tmpDir.appendingPathComponent("index.json"))
+
+    let absolutePath = URL(fileURLWithPath: path).path
+
+    let process = Process()
+    process.executableURL = URL(fileURLWithPath: "/usr/bin/tar")
+    process.arguments = ["-cf", absolutePath, "-C", tmpDir.path, "."]
+
+    let pipe = Pipe()
+    process.standardError = pipe
+
+    try process.run()
+    process.waitUntilExit()
+
+    if process.terminationStatus != 0 {
+      let errorData = pipe.fileHandleForReading.readDataToEndOfFile()
+      throw RuntimeError.Generic(
+        "creating OCI archive failed: \(String(data: errorData, encoding: .utf8) ?? "unknown error")"
+      )
+    }
+  }
+}