fix(zip): indicate that store/desc. entries cant be extracted

Author: piksel

src/ICSharpCode.SharpZipLib/Zip/ZipEntryExtensions.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace ICSharpCode.SharpZipLib.Zip
+{
+	/// <summary>
+	/// General ZipEntry helper extensions
+	/// </summary>
+	public static class ZipEntryExtensions
+	{
+		/// <summary>
+		/// Efficiently check if a <see cref="GeneralBitFlags">flag</see> is set without enum un-/boxing
+		/// </summary>
+		/// <param name="entry"></param>
+		/// <param name="flag"></param>
+		/// <returns>Returns whether the flag was set</returns>
+		public static bool HasFlag(this ZipEntry entry, GeneralBitFlags flag)
+			=> (entry.Flags & (int) flag) != 0;
+
+		/// <summary>
+		/// Efficiently set a <see cref="GeneralBitFlags">flag</see> without enum un-/boxing
+		/// </summary>
+		/// <param name="entry"></param>
+		/// <param name="flag"></param>
+		/// <param name="enabled">Whether the passed flag should be set (1) or cleared (0)</param>
+		public static void SetFlag(this ZipEntry entry, GeneralBitFlags flag, bool enabled = true)
+			=> entry.Flags = enabled 
+				? entry.Flags | (int) flag 
+				: entry.Flags & ~(int) flag;
+	}
+}

src/ICSharpCode.SharpZipLib/Zip/ZipInputStream.cs

@@ -126,14 +126,15 @@ public string Password
 		/// <remarks>
 		/// The entry can only be decompressed if the library supports the zip features required to extract it.
 		/// See the <see cref="ZipEntry.Version">ZipEntry Version</see> property for more details.
+		///
+		/// Since <see cref="ZipInputStream"/> uses the local headers for extraction, entries with no compression combined with the
+		/// <see cref="GeneralBitFlags.Descriptor"/> flag set, cannot be extracted as the end of the entry data cannot be deduced.
 		/// </remarks>
-		public bool CanDecompressEntry
-		{
-			get
-			{
-				return (entry != null) && IsEntryCompressionMethodSupported(entry) && entry.CanDecompress;
-			}
-		}
+		public bool CanDecompressEntry 
+			=> entry != null
+			&& IsEntryCompressionMethodSupported(entry)
+			&& entry.CanDecompress
+			&& (!entry.HasFlag(GeneralBitFlags.Descriptor) || entry.CompressionMethod != CompressionMethod.Stored);
 
 		/// <summary>
 		/// Is the compression method for the specified entry supported?
@@ -142,7 +143,7 @@ public bool CanDecompressEntry
 		/// Uses entry.CompressionMethodForHeader so that entries of type WinZipAES will be rejected. 
 		/// </remarks>
 		/// <param name="entry">the entry to check.</param>
-		/// <returns>true if the compression methiod is supported, false if not.</returns>
+		/// <returns>true if the compression method is supported, false if not.</returns>
 		private static bool IsEntryCompressionMethodSupported(ZipEntry entry)
 		{
 			var entryCompressionMethod = entry.CompressionMethodForHeader;