fix: Compute correct relative Dockerfile file path

Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <PackageId>$(AssemblyName)</PackageId>
-    <Version>4.8.0</Version>
+    <Version>4.8.1</Version>
     <AssemblyVersion>$(Version)</AssemblyVersion>
     <FileVersion>$(Version)</FileVersion>
     <Product>Testcontainers</Product>

src/Testcontainers/Images/DockerfileArchive.cs

@@ -213,7 +213,15 @@ await AddAsync(absoluteFilePath, relativeFilePath, tarOutputStream)
               .ConfigureAwait(false);
           }
 
-          await AddAsync(_dockerfile.FullName, _dockerfile.Name, tarOutputStream)
+          var dockerfileDirectoryLength  = _dockerfileDirectory.FullName
+            .TrimEnd(Path.DirectorySeparatorChar).Length + 1;
+
+          var dockerfileRelativeFilePath = _dockerfile.FullName
+            .Substring(dockerfileDirectoryLength );
+
+          var dockerfileNormalizedRelativeFilePath = Unix.Instance.NormalizePath(dockerfileRelativeFilePath);
+
+          await AddAsync(_dockerfile.FullName, dockerfileNormalizedRelativeFilePath, tarOutputStream)
             .ConfigureAwait(false);
         }
       }

tests/Testcontainers.Tests/Unit/Images/ImageFromDockerfileTest.cs

@@ -78,6 +78,40 @@ public async Task DockerfileArchiveTar()
       Assert.Equal(expected, actual);
     }
 
+    [Fact]
+    public async Task IgnoredDockerfileIsCopiedToTarball()
+    {
+      // Given
+
+      // This test ensures Dockerfiles in subdirectories are copied to the right paths
+      // in the tarball, instead of ending up at the root directory:
+      // https://github.com/testcontainers/testcontainers-dotnet/issues/1557.
+      IImage image = new DockerImage("localhost/testcontainers", Guid.NewGuid().ToString("D"), string.Empty);
+
+      var actual = new SortedSet<string>();
+
+      var buildArguments = new ReadOnlyDictionary<string, string>(new Dictionary<string, string>());
+
+      var dockerfileArchive = new DockerfileArchive(null, "Assets/", "target/Dockerfile", image, buildArguments, NullLogger.Instance);
+
+      var dockerfileArchiveFilePath = await dockerfileArchive.Tar(TestContext.Current.CancellationToken)
+        .ConfigureAwait(true);
+
+      // When
+      using (var tarOut = new FileStream(dockerfileArchiveFilePath, FileMode.Open, FileAccess.Read))
+      {
+        using (var tarIn = TarArchive.CreateInputTarArchive(tarOut, Encoding.Default))
+        {
+          tarIn.ProgressMessageEvent += (_, entry, _) => actual.Add(entry.Name);
+          tarIn.ListContents();
+        }
+      }
+
+      // Then
+      Assert.Contains("target/Dockerfile", actual);
+      Assert.DoesNotContain("Dockerfile", actual);
+    }
+
     [Fact]
     public async Task ThrowsDockerfileDoesNotExist()
     {