Hash files in chunks

Sources/tart/OCI/Digest.swift

@@ -7,6 +7,8 @@ enum DigestError: Error {
 }
 
 class Digest {
+  static let fileReadChunkSize = 4 * 1024 * 1024
+
   var hash: SHA256 = SHA256()
 
   func update(_ data: Data) {
@@ -22,7 +24,16 @@ class Digest {
   }
 
   static func hash(_ url: URL) throws -> String {
-    hash(try Data(contentsOf: url))
+    let fh = try FileHandle(forReadingFrom: url)
+    defer { try? fh.close() }
+
+    let digest = Digest()
+
+    while let data = try fh.read(upToCount: fileReadChunkSize), !data.isEmpty {
+      digest.update(data)
+    }
+
+    return digest.finalize()
   }
 
   static func hash(_ url: URL, offset: UInt64, size: UInt64) throws -> String {

Tests/TartTests/DigestTests.swift

@@ -21,4 +21,13 @@ final class DigestTests: XCTestCase {
 
     XCTAssertEqual(Digest.hash(data), "sha256:d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592")
   }
+
+  func testFileHashingReadsMultipleChunks() throws {
+    let data = Data(repeating: 0xab, count: Digest.fileReadChunkSize + 1)
+    let url = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString)
+    try data.write(to: url)
+    defer { try? FileManager.default.removeItem(at: url) }
+
+    XCTAssertEqual(try Digest.hash(url), Digest.hash(data))
+  }
 }