Expose Last Modified time on GZipStream. Add CRC and Size to GZipEntries on Archive

src/SharpCompress/Common/GZip/GZipEntry.cs

@@ -15,15 +15,15 @@ internal GZipEntry(GZipFilePart filePart)
 
         public override CompressionType CompressionType => CompressionType.GZip;
 
-        public override long Crc => 0;
+        public override long Crc => _filePart.Crc ?? 0;
 
         public override string Key => _filePart.FilePartName;
 
         public override string? LinkTarget => null;
 
         public override long CompressedSize => 0;
 
-        public override long Size => 0;
+        public override long Size => _filePart.UncompressedSize ?? 0;
 
         public override DateTime? LastModifiedTime => _filePart.DateModified;
 

src/SharpCompress/Common/GZip/GZipFilePart.cs

@@ -16,14 +16,23 @@ internal sealed class GZipFilePart : FilePart
         internal GZipFilePart(Stream stream, ArchiveEncoding archiveEncoding)
             : base(archiveEncoding)
         {
-            ReadAndValidateGzipHeader(stream);
-            EntryStartPosition = stream.Position;
             _stream = stream;
+            ReadAndValidateGzipHeader();
+            if (stream.CanSeek)
+            {
+                long position = stream.Position;
+                stream.Position = stream.Length - 8;
+                ReadTrailer();
+                stream.Position = position;
+            }
+            EntryStartPosition = stream.Position;
         }
 
         internal long EntryStartPosition { get; }
 
         internal DateTime? DateModified { get; private set; }
+        internal int? Crc { get; private set; }
+        internal int? UncompressedSize { get; private set; }
 
         internal override string FilePartName => _name!;
 
@@ -37,11 +46,21 @@ internal override Stream GetRawStream()
             return _stream;
         }
 
-        private void ReadAndValidateGzipHeader(Stream stream)
+        private void ReadTrailer()
+        {
+            // Read and potentially verify the GZIP trailer: CRC32 and  size mod 2^32
+            Span<byte> trailer = stackalloc byte[8];
+            int n = _stream.Read(trailer);
+
+            Crc = BinaryPrimitives.ReadInt32LittleEndian(trailer);
+            UncompressedSize = BinaryPrimitives.ReadInt32LittleEndian(trailer.Slice(4));
+        }
+
+        private void ReadAndValidateGzipHeader()
         {
             // read the header on the first read
             Span<byte> header = stackalloc byte[10];
-            int n = stream.Read(header);
+            int n = _stream.Read(header);
 
             // workitem 8501: handle edge case (decompress empty stream)
             if (n == 0)
@@ -64,28 +83,28 @@ private void ReadAndValidateGzipHeader(Stream stream)
             if ((header[3] & 0x04) == 0x04)
             {
                 // read and discard extra field
-                n = stream.Read(header.Slice(0, 2)); // 2-byte length field
+                n = _stream.Read(header.Slice(0, 2)); // 2-byte length field
 
                 short extraLength = (short)(header[0] + header[1] * 256);
                 byte[] extra = new byte[extraLength];
 
-                if (!stream.ReadFully(extra))
+                if (!_stream.ReadFully(extra))
                 {
                     throw new ZlibException("Unexpected end-of-file reading GZIP header.");
                 }
                 n = extraLength;
             }
             if ((header[3] & 0x08) == 0x08)
             {
-                _name = ReadZeroTerminatedString(stream);
+                _name = ReadZeroTerminatedString(_stream);
             }
             if ((header[3] & 0x10) == 0x010)
             {
-                ReadZeroTerminatedString(stream);
+                ReadZeroTerminatedString(_stream);
             }
             if ((header[3] & 0x02) == 0x02)
             {
-                stream.ReadByte(); // CRC16, ignore
+                _stream.ReadByte(); // CRC16, ignore
             }
         }
 

src/SharpCompress/Compressors/Deflate/GZipStream.cs

@@ -37,10 +37,9 @@ public class GZipStream : Stream
     {
         internal static readonly DateTime UNIX_EPOCH = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
 
-        public DateTime? LastModified { get; set; }
-
         private string? _comment;
         private string? _fileName;
+        private DateTime? _lastModified;
 
         internal ZlibBaseStream BaseStream;
         private bool _disposed;
@@ -274,6 +273,7 @@ public override int Read(byte[] buffer, int offset, int count)
                 _firstReadDone = true;
                 FileName = BaseStream._GzipFileName;
                 Comment = BaseStream._GzipComment;
+                LastModified = BaseStream._GzipMtime;
             }
             return n;
         }
@@ -358,6 +358,20 @@ public override void Write(byte[] buffer, int offset, int count)
             }
         }
 
+
+        public DateTime? LastModified
+        {
+            get => _lastModified;
+            set
+            {
+                if (_disposed)
+                {
+                    throw new ObjectDisposedException(nameof(GZipStream));
+                }
+                _lastModified = value;
+            }
+        }
+
         public string? FileName
         {
             get => _fileName;
@@ -398,8 +412,8 @@ private int EmitHeader()
             byte[]? filenameBytes = (FileName is null) ? null
                 : _encoding.GetBytes(FileName);
 
-            int cbLength = (commentBytes is null) ? 0 : commentBytes.Length + 1;
-            int fnLength = (filenameBytes is null) ? 0 : filenameBytes.Length + 1;
+            int cbLength = commentBytes?.Length + 1 ?? 0;
+            int fnLength = filenameBytes?.Length + 1 ?? 0;
 
             int bufferLength = 10 + cbLength + fnLength;
             var header = new byte[bufferLength];
@@ -425,7 +439,7 @@ private int EmitHeader()
             header[i++] = flag;
 
             // mtime
-            if (!LastModified.HasValue)
+            if (LastModified is null)
             {
                 LastModified = DateTime.Now;
             }

tests/SharpCompress.Test/GZip/GZipArchiveTests.cs

@@ -22,6 +22,13 @@ public void GZip_Archive_Generic()
             {
                 var entry = archive.Entries.First();
                 entry.WriteToFile(Path.Combine(SCRATCH_FILES_PATH, entry.Key));
+
+                long size = entry.Size;
+                var scratch = new FileInfo(Path.Combine(SCRATCH_FILES_PATH, "Tar.tar"));
+                var test = new FileInfo(Path.Combine(TEST_ARCHIVES_PATH, "Tar.tar"));
+
+                Assert.Equal(size, scratch.Length);
+                Assert.Equal(size, test.Length);
             }
             CompareArchivesByPath(Path.Combine(SCRATCH_FILES_PATH, "Tar.tar"),
                 Path.Combine(TEST_ARCHIVES_PATH, "Tar.tar"));
@@ -35,6 +42,13 @@ public void GZip_Archive()
             {
                 var entry = archive.Entries.First();
                 entry.WriteToFile(Path.Combine(SCRATCH_FILES_PATH, entry.Key));
+
+                long size = entry.Size;
+                var scratch = new FileInfo(Path.Combine(SCRATCH_FILES_PATH, "Tar.tar"));
+                var test = new FileInfo(Path.Combine(TEST_ARCHIVES_PATH, "Tar.tar"));
+
+                Assert.Equal(size, scratch.Length);
+                Assert.Equal(size, test.Length);
             }
             CompareArchivesByPath(Path.Combine(SCRATCH_FILES_PATH, "Tar.tar"),
                 Path.Combine(TEST_ARCHIVES_PATH, "Tar.tar"));