Merge PR #463: Improve support for Unix timestamps in ZIP archives

* Store ZipEntry.DateTime in dedicated backing field  
This allows reading values with a higher resolution than DOS time (2 second accuracy).

* Fix getting unix modification time in ZIP files
InfoZIP actually does respect a file's modification time, even if the access time and/or creation time are not set.

* Remove backing field for ZipEntry.DosTime, convert to and from ZipEntry.DateTime instead
This prevents the two values from becoming potentially inconsistent.

Author: bastianeicher

src/ICSharpCode.SharpZipLib/Zip/ZipEntry.cs

@@ -238,7 +238,7 @@ public ZipEntry(ZipEntry entry)
 			size = entry.size;
 			compressedSize = entry.compressedSize;
 			crc = entry.crc;
-			dosTime = entry.dosTime;
+			dateTime = entry.DateTime;
 			method = entry.method;
 			comment = entry.comment;
 			versionToExtract = entry.versionToExtract;
@@ -696,18 +696,54 @@ public long DosTime
 				}
 				else
 				{
-					return dosTime;
+					var year = (uint)DateTime.Year;
+					var month = (uint)DateTime.Month;
+					var day = (uint)DateTime.Day;
+					var hour = (uint)DateTime.Hour;
+					var minute = (uint)DateTime.Minute;
+					var second = (uint)DateTime.Second;
+
+					if (year < 1980)
+					{
+						year = 1980;
+						month = 1;
+						day = 1;
+						hour = 0;
+						minute = 0;
+						second = 0;
+					}
+					else if (year > 2107)
+					{
+						year = 2107;
+						month = 12;
+						day = 31;
+						hour = 23;
+						minute = 59;
+						second = 59;
+					}
+
+					return ((year - 1980) & 0x7f) << 25 |
+					       (month << 21) |
+					       (day << 16) |
+					       (hour << 11) |
+					       (minute << 5) |
+					       (second >> 1);
 				}
 			}
 
 			set
 			{
 				unchecked
 				{
-					dosTime = (uint)value;
+					var dosTime = (uint)value;
+					uint sec = Math.Min(59, 2 * (dosTime & 0x1f));
+					uint min = Math.Min(59, (dosTime >> 5) & 0x3f);
+					uint hrs = Math.Min(23, (dosTime >> 11) & 0x1f);
+					uint mon = Math.Max(1, Math.Min(12, ((uint)(value >> 21) & 0xf)));
+					uint year = ((dosTime >> 25) & 0x7f) + 1980;
+					int day = Math.Max(1, Math.Min(DateTime.DaysInMonth((int)year, (int)mon), (int)((value >> 16) & 0x1f)));
+					DateTime = new DateTime((int)year, (int)mon, day, (int)hrs, (int)min, (int)sec, DateTimeKind.Utc);
 				}
-
-				known |= Known.Time;
 			}
 		}
 
@@ -721,49 +757,13 @@ public DateTime DateTime
 		{
 			get
 			{
-				uint sec = Math.Min(59, 2 * (dosTime & 0x1f));
-				uint min = Math.Min(59, (dosTime >> 5) & 0x3f);
-				uint hrs = Math.Min(23, (dosTime >> 11) & 0x1f);
-				uint mon = Math.Max(1, Math.Min(12, ((dosTime >> 21) & 0xf)));
-				uint year = ((dosTime >> 25) & 0x7f) + 1980;
-				int day = Math.Max(1, Math.Min(DateTime.DaysInMonth((int)year, (int)mon), (int)((dosTime >> 16) & 0x1f)));
-				return new System.DateTime((int)year, (int)mon, day, (int)hrs, (int)min, (int)sec);
+				return dateTime;
 			}
 
 			set
 			{
-				var year = (uint)value.Year;
-				var month = (uint)value.Month;
-				var day = (uint)value.Day;
-				var hour = (uint)value.Hour;
-				var minute = (uint)value.Minute;
-				var second = (uint)value.Second;
-
-				if (year < 1980)
-				{
-					year = 1980;
-					month = 1;
-					day = 1;
-					hour = 0;
-					minute = 0;
-					second = 0;
-				}
-				else if (year > 2107)
-				{
-					year = 2107;
-					month = 12;
-					day = 31;
-					hour = 23;
-					minute = 59;
-					second = 59;
-				}
-
-				DosTime = ((year - 1980) & 0x7f) << 25 |
-					(month << 21) |
-					(day << 16) |
-					(hour << 11) |
-					(minute << 5) |
-					(second >> 1);
+				dateTime = value;
+				known |= Known.Time;
 			}
 		}
 
@@ -1088,14 +1088,14 @@ internal void ProcessExtraData(bool localHeader)
 				}
 			}
 
-			DateTime = GetDateTime(extraData);
+			DateTime = GetDateTime(extraData) ?? DateTime;
 			if (method == CompressionMethod.WinZipAES)
 			{
 				ProcessAESExtraData(extraData);
 			}
 		}
 
-		private DateTime GetDateTime(ZipExtraData extraData)
+		private DateTime? GetDateTime(ZipExtraData extraData)
 		{
 			// Check for NT timestamp
 			// NOTE: Disable by default to match behavior of InfoZIP
@@ -1107,22 +1107,10 @@ private DateTime GetDateTime(ZipExtraData extraData)
 
 			// Check for Unix timestamp
 			ExtendedUnixData unixData = extraData.GetData<ExtendedUnixData>();
-			if (unixData != null &&
-				// Only apply modification time, but require all other values to be present
-				// This is done to match InfoZIP's behaviour
-				((unixData.Include & ExtendedUnixData.Flags.ModificationTime) != 0) &&
-				((unixData.Include & ExtendedUnixData.Flags.AccessTime) != 0) &&
-				((unixData.Include & ExtendedUnixData.Flags.CreateTime) != 0))
+			if (unixData != null && unixData.Include.HasFlag(ExtendedUnixData.Flags.ModificationTime))
 				return unixData.ModificationTime;
 
-			// Fall back to DOS time
-			uint sec = Math.Min(59, 2 * (dosTime & 0x1f));
-			uint min = Math.Min(59, (dosTime >> 5) & 0x3f);
-			uint hrs = Math.Min(23, (dosTime >> 11) & 0x1f);
-			uint mon = Math.Max(1, Math.Min(12, ((dosTime >> 21) & 0xf)));
-			uint year = ((dosTime >> 25) & 0x7f) + 1980;
-			int day = Math.Max(1, Math.Min(DateTime.DaysInMonth((int)year, (int)mon), (int)((dosTime >> 16) & 0x1f)));
-			return new DateTime((int)year, (int)mon, day, (int)hrs, (int)min, (int)sec, DateTimeKind.Utc);
+			return null;
 		}
 
 		// For AES the method in the entry is 99, and the real compression method is in the extradata
@@ -1328,7 +1316,7 @@ public static string CleanName(string name)
 		private ulong compressedSize;
 		private ushort versionToExtract;                // Version required to extract (library handles <= 2.0)
 		private uint crc;
-		private uint dosTime;
+		private DateTime dateTime;
 
 		private CompressionMethod method = CompressionMethod.Deflated;
 		private byte[] extra;

test/ICSharpCode.SharpZipLib.Tests/Zip/ZipEntryHandling.cs

@@ -195,10 +195,12 @@ public void DateAndTime()
 
 			// Over the limit are set to max.
 			ze.DateTime = new DateTime(2108, 1, 1);
+			ze.DosTime = ze.DosTime;
 			Assert.AreEqual(new DateTime(2107, 12, 31, 23, 59, 58), ze.DateTime);
 
 			// Under the limit are set to min.
 			ze.DateTime = new DateTime(1906, 12, 4);
+			ze.DosTime = ze.DosTime;
 			Assert.AreEqual(new DateTime(1980, 1, 1, 0, 0, 0), ze.DateTime);
 		}