Add Folders to ZipArchive

src/SharpCompress/Archives/Zip/ZipArchive.cs

@@ -182,12 +182,18 @@ public void SaveTo(Stream stream)
         {
             using (var writer = new ZipWriter(stream, new ZipWriterOptions(options)))
             {
-                foreach (var entry in oldEntries.Concat(newEntries)
-                                                .Where(x => !x.IsDirectory))
+                foreach (var entry in oldEntries.Concat(newEntries))
                 {
-                    using (var entryStream = entry.OpenEntryStream())
+                    if (entry.IsDirectory)
                     {
+                       //TODO What do to here?
+                    }
+                    else
+                    {
+                      using (var entryStream = entry.OpenEntryStream())
+                      {
                         writer.Write(entry.Key, entryStream, entry.LastModifiedTime);
+                      }
                     }
                 }
             }
@@ -210,5 +216,11 @@ protected override IReader CreateReaderForSolidExtraction()
             stream.Position = 0;
             return ZipReader.Open(stream, ReaderOptions);
         }
+
+      public void AddDirectory(string combine)
+      {
+        combine +=  "/";
+       var entry = AddEntry(combine, new MemoryStream());
+      }
     }
 }

src/SharpCompress/Archives/Zip/ZipWritableArchiveEntry.cs

@@ -41,7 +41,19 @@ internal class ZipWritableArchiveEntry : ZipArchiveEntry, IWritableArchiveEntry
 
         public override bool IsEncrypted => false;
 
-        public override bool IsDirectory => false;
+        public override bool IsDirectory 
+        {
+          get
+          {
+            if (Key.EndsWith("/"))
+            {
+              return true;
+            }
+
+            //.NET Framework 4.5 : System.IO.Compression::CreateFromDirectory() probably writes backslashes to headers
+            return CompressedSize == 0 && Key.EndsWith("\\");
+          }
+        }
 
         public override bool IsSplit => false;
 

tests/SharpCompress.Test/Zip/AddFolderTest.cs

@@ -0,0 +1,24 @@
+namespace SharpCompress.Test.Zip
+{
+  using System.IO;
+
+  using SharpCompress.Archives;
+  using SharpCompress.Archives.Zip;
+  using SharpCompress.Common;
+  using SharpCompress.Writers.Zip;
+
+  using Xunit;
+
+  public class AddFolderTest
+  {
+    [Fact]
+    public void When_subject_should_expectation()
+    {
+      using (var zip = ZipArchive.Create())
+      {
+        zip.AddDirectory(Path.Combine("Hallo", "Welt"));
+        zip.SaveTo(@"D:\Hallo.zip", new ZipWriterOptions(CompressionType.Deflate) { ArchiveComment = "HalloWelt" });
+      }
+    }
+  }
+}

tests/SharpCompress.Test/Zip/ZipArchiveTests.cs

@@ -461,5 +461,23 @@ public void TestSharpCompressWithEmptyStream()
                 }
             }
         }
+
+        [Fact]
+        public void When_adding_empty_folder_should_only_contain_folders()
+        {
+          var stream = new MemoryStream();
+          string folderName = "EmptyFolder";
+          using (var zipArchive = ZipArchive.Create())
+          {
+            zipArchive.AddDirectory(folderName);
+            zipArchive.SaveTo(stream);
+          }
+
+          using (var zipArchive = ZipArchive.Open(stream))
+          {
+            Assert.True(zipArchive.Entries.SingleOrDefault(me => me.Key.Contains("folderName")) != null);
+            Assert.True(zipArchive.Entries.All(me => me.IsDirectory));
+          }
+        }
     }
 }