[System.IO.Compression] Fixed handling of Zip archives with duplicate entries with same name.

.NET supports this, from MSDN: "If an entry with the specified path and name already exists in the archive, a second entry is created with the same path and name.".

Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=42219.

3 files changed, 29 insertions, 7 deletions

diff --git a/mcs/class/System.IO.Compression/SharpCompress/Archive/AbstractWritableArchive.cs b/mcs/class/System.IO.Compression/SharpCompress/Archive/AbstractWritableArchive.cs
index 96af8c4131d..f844e5cb471 100644
--- a/mcs/class/System.IO.Compression/SharpCompress/Archive/AbstractWritableArchive.cs
+++ b/mcs/class/System.IO.Compression/SharpCompress/Archive/AbstractWritableArchive.cs
@@ -82,10 +82,14 @@ namespace SharpCompress.Archive
             {
                 key = key.Substring(1);
             }
+            // .NET allows duplicate entries when saving and loading Zip files.
+            // The following lines are disabled from upstream SharpCompress to allow this.
+#if ZIP_ALLOW_DUPLICATE_KEYS
             if (DoesKeyMatchExisting(key))
             {
                 throw new ArchiveException("Cannot add entry with duplicate key: " + key);
             }
+#endif
             var entry = CreateEntry(key, source, size, modified, closeStream);
             newEntries.Add(entry);
             RebuildModifiedCollection();
@@ -101,7 +105,8 @@ namespace SharpCompress.Archive
                 {
                     p = p.Substring(1);
                 }
-                return string.Equals(p, key, StringComparison.OrdinalIgnoreCase);
+                if (string.Equals(p, key, StringComparison.OrdinalIgnoreCase))
+                    return true;
             }
             return false;
         }
diff --git a/mcs/class/System.IO.Compression/Test/System.IO.Compression/ZipTest.cs b/mcs/class/System.IO.Compression/Test/System.IO.Compression/ZipTest.cs
index 64b102c2d3d..99692163002 100644
--- a/mcs/class/System.IO.Compression/Test/System.IO.Compression/ZipTest.cs
+++ b/mcs/class/System.IO.Compression/Test/System.IO.Compression/ZipTest.cs
@@ -358,6 +358,23 @@ namespace MonoTests.System.IO.Compression
 		}
 
 		[Test]
+		public void ZipCreateDuplicateEntriesUpdateMode()
+		{
+			var stream = new MemoryStream();
+			using (var zipArchive = new ZipArchive(stream, ZipArchiveMode.Update, true))
+			{
+				var e2 = zipArchive.CreateEntry("BBB");
+				var e3 = zipArchive.CreateEntry("BBB");
+			}
+
+			stream.Position = 0;
+			using (var zipArchive = new ZipArchive(stream, ZipArchiveMode.Read))
+			{
+				Assert.AreEqual(2, zipArchive.Entries.Count);
+			}
+		}
+
+		[Test]
 		public void ZipWriteEntriesUpdateModeNonZeroPosition()
 		{
 			File.Copy("archive.zip", "test.zip", overwrite: true);
diff --git a/mcs/class/System.IO.Compression/ZipArchive.cs b/mcs/class/System.IO.Compression/ZipArchive.cs
index 4f0c7bb70b9..9dbf04cd339 100644
--- a/mcs/class/System.IO.Compression/ZipArchive.cs
+++ b/mcs/class/System.IO.Compression/ZipArchive.cs
@@ -39,7 +39,7 @@ namespace System.IO.Compression
 		internal readonly ZipArchiveMode mode;
 		internal Encoding entryNameEncoding;
 		internal bool disposed;
-		internal Dictionary<string, ZipArchiveEntry> entries; 
+		internal List<ZipArchiveEntry> entries; 
 		internal SharpCompress.Archive.Zip.ZipArchive zipFile;
 
 		public ZipArchive (Stream stream)
@@ -111,11 +111,11 @@ namespace System.IO.Compression
 					throw new InvalidDataException("The contents of the stream are not in the zip archive format.", e);
 				}
 
-				entries = new Dictionary<string, ZipArchiveEntry>();
+				entries = new List<ZipArchiveEntry>();
 				if (Mode != ZipArchiveMode.Create) {
 					foreach (var entry in zipFile.Entries) {
 						var zipEntry = new ZipArchiveEntry(this, entry);
-						entries[entry.Key] = zipEntry;
+						entries.Add(zipEntry);
 					}
 				}
 			}
@@ -140,7 +140,7 @@ namespace System.IO.Compression
 				if (entries == null)
 					return new ReadOnlyCollection<ZipArchiveEntry>(new List<ZipArchiveEntry>());
 
-				return new ReadOnlyCollection<ZipArchiveEntry>(entries.Values.ToList());
+				return new ReadOnlyCollection<ZipArchiveEntry>(entries);
 			}
 		}
 
@@ -188,7 +188,7 @@ namespace System.IO.Compression
 
 			var internalEntry = CreateEntryInternal(entryName);
 			var archiveEntry = new ZipArchiveEntry(this, internalEntry);
-			entries[entryName] = archiveEntry;
+			entries.Add(archiveEntry);
 
 			return archiveEntry;
 		}
@@ -210,7 +210,7 @@ namespace System.IO.Compression
 			if (zipFile == null)
 				throw new InvalidDataException("The zip archive is corrupt, and its entries cannot be retrieved.");
 
-			return entries.ContainsKey(entryName) ? entries[entryName] : null;
+			return entries.FirstOrDefault(e => e.FullName == entryName);
 		}
 
 		private void Save()