reproducible builds working as expected

explicitly setting tar archive entry modified dates & gzip modified dates. 

https://buildpacks.io/docs/features/reproducibility/
buildpacks/lifecycle#823
buildpacks/lifecycle#108

src/Dotknet/Commands/PublishCommand.cs

@@ -41,8 +41,8 @@ public void Execute()
 
  using var tarArchive = TarArchive.Create();
  tarArchive.AddAllFromDirectory(_options.Output!, "dotknet-app");
-
  using var layer = new TarArchiveLayer(tarArchive);
- _logger.LogInformation("Layer Created: {Layer}", layer);
+
+ _logger.LogInformation("Output will create layer {Layer}", layer);
  }
 }

src/Dotknet/Extensions/IWritableArchiveExtensions.cs

@@ -2,15 +2,19 @@
 
 public static class IWritableArchiveExtensions
 {
- public static void AddAllFromDirectory(this IWritableArchive writableArchive, string filePath, string rootDir, string searchPattern = "*.*", SearchOption searchOption = SearchOption.AllDirectories)
+ // timestamp necessary for reproducability
+ public static void AddAllFromDirectory(this IWritableArchive writableArchive, string filePath, string rootDir, string searchPattern = "*.*", SearchOption searchOption = SearchOption.AllDirectories, DateTime? timestamp = null)
  {
+ if (!timestamp.HasValue) {
+ timestamp = new DateTime(1980, 01, 01, 00, 00, 01);
+ }
  using (writableArchive.PauseEntryRebuilding())
  {
  foreach (var path in Directory.EnumerateFiles(filePath, searchPattern, searchOption))
  {
  var fileInfo = new FileInfo(path);
- var key = rootDir + "/" + path.Substring(filePath.Length);
- writableArchive.AddEntry(key, fileInfo.OpenRead(), true, fileInfo.Length, fileInfo.LastWriteTime);
+ var key = rootDir + path.Substring(filePath.Length);
+ writableArchive.AddEntry(key, fileInfo.OpenRead(), true, fileInfo.Length, timestamp);
  }
  }
  }

src/Dotknet/Models/Layer.cs

@@ -1,10 +1,11 @@
+using System.IO.Compression;
 using Dotknet.Extensions;
 using SharpCompress.Archives.Tar;
 
 namespace Dotknet.Models;
 
 /// ref: https://github.com/google/go-containerregistry/blob/main/pkg/v1/layer.go
-public interface ILayer: IDisposable
+public interface ILayer : IDisposable
 {
  // Digest returns the Hash of the compressed layer.
  public Hash Digest();
@@ -28,19 +29,34 @@ public interface ILayer: IDisposable
 //todo: consider perf/caching
 public class TarArchiveLayer : ILayer
 {
- public TarArchiveLayer(TarArchive tarArchive)
+ // timestamp necessary for reproducibility
+ public TarArchiveLayer(TarArchive tarArchive, DateTime? modified = null)
  {
  _tarArchive = tarArchive;
+ if (!modified.HasValue)
+ {
+ modified = new DateTime(1980, 01, 01, 00, 00, 01, DateTimeKind.Utc);
+ }
+ _modified = modified;
  }
 
+ private DateTime EPOCH = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+
  private bool disposedValue;
  private readonly TarArchive _tarArchive;
+ private readonly DateTime? _modified;
 
  public Stream Compressed()
  {
- var memoryStream = new MemoryStream();
- _tarArchive.SaveTo(memoryStream, new SharpCompress.Writers.WriterOptions(SharpCompress.Common.CompressionType.GZip));
- return memoryStream;
+ using var originalStream = new MemoryStream();
+ _tarArchive.SaveTo(originalStream, new SharpCompress.Writers.WriterOptions(SharpCompress.Common.CompressionType.GZip));
+ var buffer = originalStream.ToArray();
+ var seconds = (int)(_modified! - EPOCH).Value.TotalSeconds;
+ buffer[4] = (byte)seconds;
+ buffer[5] = (byte)(seconds >> 8);
+ buffer[6] = (byte)(seconds >> 16);
+ buffer[7] = (byte)(seconds >> 24);
+ return new MemoryStream(buffer);
  }
 
  public Hash DiffId()
@@ -89,7 +105,8 @@ public void Dispose()
  GC.SuppressFinalize(this);
  }
 
- public override string ToString(){
+ public override string ToString()
+ {
  return $"Layer DiffId: {DiffId().Hex.Substring(0, 6)} Digest: {Digest().Hex.Substring(0, 6)}";
  }
 }

test/Dotknet.Test/Models/LayerTests.cs

@@ -0,0 +1,44 @@
+using System;
+using System.IO;
+using System.Linq;
+using Dotknet.Models;
+using FluentAssertions;
+using SharpCompress.Archives.Tar;
+using Xunit;
+
+namespace Dotknet.Test.Models;
+
+public class LayerTests
+{
+ [Fact]
+ public void LayerModifiedTests()
+ {
+ var archive = TarArchive.Create();
+ var timestamp = new DateTime(1990, 05, 13, 0, 0, 0);
+ using var text = GenerateStreamFromString("foo foo foo foo foo foo foo");
+ archive.AddEntry("bar", text, text.Length, timestamp);
+ archive.AddEntry("baz", text, text.Length, timestamp);
+ using var layer = new TarArchiveLayer(archive);
+ using var compressed = layer.Compressed();
+ compressed.Seek(0, SeekOrigin.Begin);
+ using var ms2 = new MemoryStream();
+ compressed.CopyTo(ms2);
+ ms2.Seek(0, SeekOrigin.Begin);
+ var bytes = ms2.ToArray();
+ var timestampBytes = bytes.Skip(4).Take(4).ToArray();
+ var seconds = BitConverter.ToUInt32(timestampBytes, 0);
+ var EPOCH = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+ var datetime = EPOCH.AddSeconds(seconds);
+ datetime.Should().Be(new DateTime(1980, 01, 01, 00, 00, 01, DateTimeKind.Utc));
+ }
+
+ public static Stream GenerateStreamFromString(string s)
+ {
+ var stream = new MemoryStream();
+ var writer = new StreamWriter(stream);
+ writer.Write(s);
+ writer.Flush();
+ stream.Position = 0;
+ return stream;
+ }
+}