Support serializing/loading ReadWriteZipFile as base64 string.

OpenRA.Game/FileSystem/ZipFile.cs

@@ -120,6 +120,23 @@ namespace OpenRA.FileSystem
 					entry.ExtraData = null;
 			}
 
+			public ReadWriteZipFile(byte[] data)
+			{
+				using (var copy = new MemoryStream(data))
+				{
+					pkgStream.Capacity = (int)copy.Length;
+					copy.CopyTo(pkgStream);
+				}
+
+				pkgStream.Position = 0;
+				pkg = new ZipFile(pkgStream);
+				Name = null;
+
+				// Remove subfields that can break ZIP updating.
+				foreach (ZipEntry entry in pkg)
+					entry.ExtraData = null;
+			}
+
 			void Commit()
 			{
 				if (!string.IsNullOrEmpty(Name))
@@ -141,6 +158,16 @@ namespace OpenRA.FileSystem
 				pkg.CommitUpdate();
 				Commit();
 			}
+
+			public static ReadWriteZipFile FromBase64String(string data)
+			{
+				return new ReadWriteZipFile(Convert.FromBase64String(data));
+			}
+
+			public string ToBase64String()
+			{
+				return Convert.ToBase64String(pkgStream.ToArray());
+			}
 		}
 
 		sealed class ZipFolder : IReadOnlyPackage