While fixing the ValuesPreserved test:

• Fix TMAGIC = "ustar " into TMAGIC = "ustar". It was meant to denote that this value should include a trailing NULL char, but actually the constant were authored with a space not NULL, so the NULL were never written, and the meaning space were written as is. Functions which checked for this value failed because they expected a 5-char word and got 6-char.
• GetAsciiBytes might be requested to write more chars than there are in the string, make sure these are written as NULLs (would be correctly ignored when reading), unlike whatever trash might be there in the buffer).
• Update HeaderEquality test, it were setting magic to the well-known "ustar" value and expecting to see a diff. But the entry is set to "ustar" by default. This test used to pass because the default "ustar" had a trailing space which made it another string. Set to smth which is really different now.

Author: hypersw

ICSharpCode.SharpZipLib.Tests/Tar/TarTests.cs

@@ -283,7 +283,7 @@ public void HeaderEquality()
 			h2.LinkName = h1.LinkName;
 			Assert.IsTrue(h1.Equals(h2));
 
-			h1.Magic = "ustar";
+			h1.Magic = "other";
 			Assert.IsFalse(h1.Equals(h2));
 			h2.Magic = h1.Magic;
 			Assert.IsTrue(h1.Equals(h2));

ICSharpCode.SharpZipLib/Tar/TarHeader.cs

@@ -225,9 +225,9 @@ public class TarHeader : ICloneable
 		public const byte LF_GNU_VOLHDR = (byte)'V';
 
 		/// <summary>
-		/// The magic tag representing a POSIX tar archive.  (includes trailing NULL)
+		/// The magic tag representing a POSIX tar archive.  (would be written with a trailing NULL)
 		/// </summary>
-		public const string TMAGIC = "ustar ";
+		public const string TMAGIC = "ustar";
 
 		/// <summary>
 		/// The magic tag representing an old GNU tar archive where version is included in magic and overwrites it
@@ -899,9 +899,13 @@ public static int GetAsciiBytes(string toAdd, int nameOffset, byte[] buffer, int
 				throw new ArgumentNullException(nameof(buffer));
 			}
 
-			for (int i = 0; i < length && nameOffset + i < toAdd.Length; ++i) {
+			int i;
+			for (i = 0; i < length && nameOffset + i < toAdd.Length; ++i) {
 				buffer[bufferOffset + i] = (byte)toAdd[nameOffset + i];
 			}
+			// If length is beyond the toAdd string length (which is OK by the prev loop condition), eg if a field has fixed length and the string is shorter, make sure all of the extra chars are written as NULLs, so that the reader func would ignore them and get back the original string
+			for (; i < length; ++i)
+				buffer[bufferOffset + i] = 0;
 			return bufferOffset + length;
 		}