Added additional comment encoding tests

Author: edwardneal

src/libraries/Common/tests/System/IO/Compression/ZipTestHelper.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Text;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -499,5 +500,17 @@ public static IEnumerable<object[]> Latin1Comment_Data()
                 yield return e;
             }
         }
+
+        // Returns pairs encoded with Latin1, but decoded with UTF8.
+        // Returns: originalComment, expectedComment, transcoded expectedComment
+        public static IEnumerable<object[]> MismatchingEncodingComment_Data()
+        {
+            foreach (object[] e in Latin1Comment_Data())
+            {
+                byte[] expectedBytes = Encoding.Latin1.GetBytes(e[1] as string);
+                
+                yield return new object[] { e[0], e[1], Encoding.UTF8.GetString(expectedBytes) };
+            }
+        }
     }
 }

src/libraries/System.IO.Compression/tests/ZipArchive/zip_CreateTests.Comments.cs

@@ -41,30 +41,50 @@ public static void Create_Comment_Utf8EntryName_Latin1Encoding(string originalCo
 
         [Theory]
         [MemberData(nameof(Utf8Comment_Data))]
-        public static void Create_Comment_Utf8EntryName_Varying_Encodings(string originalComment, string expectedComment)
+        public static void Create_Comment_Utf8EntryName_Utf8Encoding_Prioritised(string originalComment, string expectedComment)
             // UTF8 encoding bit is set in the general-purpose bit flags. The verification encoding of Latin1 should be ignored
-            => Create_Comment_EntryName_Encoding_Internal(Utf8FileName, originalComment, expectedComment, Encoding.UTF8, Encoding.Latin1);
+            => Create_Comment_EntryName_Encoding_Internal(Utf8FileName, originalComment, expectedComment, expectedComment, Encoding.UTF8, Encoding.Latin1);
+
+        [Theory]
+        [MemberData(nameof(MismatchingEncodingComment_Data))]
+        public static void Create_Comment_AsciiEntryName_Utf8Decoding_Invalid(string originalComment, string expectedPreWriteComment, string expectedPostWriteComment)
+            // The UTF8 encoding bit in the general-purpose bit flags should not be set, filenames should be encoded with Latin1, and thus
+            // decoding with UTF8 should result in incorrect filenames. This is because the filenames and comments contain code points in the
+            // range 0xC0..0xFF (which Latin1 encodes in one byte, and UTF8 encodes in two bytes.)
+            => Create_Comment_EntryName_Encoding_Internal(AsciiFileName, originalComment, expectedPreWriteComment, expectedPostWriteComment, Encoding.Latin1, Encoding.UTF8);
+
+        [Theory]
+        [MemberData(nameof(MismatchingEncodingComment_Data))]
+        public static void Create_Comment_AsciiEntryName_DefaultDecoding_Utf8(string originalComment, string expectedPreWriteComment, string expectedPostWriteComment)
+            // Filenames should be encoded with Latin1, resulting in the UTF8 encoding bit in the general-purpose bit flags not being set.
+            // However, failing to specify an encoding (or specifying a null encoding) for the read should result in UTF8 being used anyway.
+            // This should result in incorrect filenames, since the filenames and comments contain code points in the range 0xC0..0xFF (which
+            // Latin1 encodes in one byte, and UTF8 encodes in two bytes.)
+            => Create_Comment_EntryName_Encoding_Internal(AsciiFileName, originalComment, expectedPreWriteComment, expectedPostWriteComment, Encoding.Latin1, null);
 
         private static void Create_Comment_EntryName_Encoding_Internal(string entryName, string originalComment, string expectedComment, Encoding encoding)
-            => Create_Comment_EntryName_Encoding_Internal(entryName, originalComment, expectedComment, encoding, encoding);
+            => Create_Comment_EntryName_Encoding_Internal(entryName, originalComment, expectedComment, expectedComment, encoding, encoding);
 
-        private static void Create_Comment_EntryName_Encoding_Internal(string entryName, string originalComment, string expectedComment, Encoding creationEncoding, Encoding verificationEencoding)
+        private static void Create_Comment_EntryName_Encoding_Internal(string entryName, string originalComment,
+            string expectedPreWriteComment, string expectedPostWriteComment,
+            Encoding creationEncoding, Encoding verificationEncoding)
         {
             using var ms = new MemoryStream();
 
             using (var zip = new ZipArchive(ms, ZipArchiveMode.Create, leaveOpen: true, creationEncoding))
             {
                 ZipArchiveEntry entry = zip.CreateEntry(entryName, CompressionLevel.NoCompression);
                 entry.Comment = originalComment;
-                Assert.Equal(expectedComment, entry.Comment);
+                // The expected pre-write and post-write comment can be different when testing encodings which vary between operations.
+                Assert.Equal(expectedPreWriteComment, entry.Comment);
             }
 
-            using (var zip = new ZipArchive(ms, ZipArchiveMode.Read, leaveOpen: false, verificationEencoding))
+            using (var zip = new ZipArchive(ms, ZipArchiveMode.Read, leaveOpen: false, verificationEncoding))
             {
                 foreach (ZipArchiveEntry entry in zip.Entries)
                 {
                     Assert.Equal(entryName, entry.Name);
-                    Assert.Equal(expectedComment, entry.Comment);
+                    Assert.Equal(expectedPostWriteComment, entry.Comment);
                 }
             }
         }