Decode CFB stream names

SabreTools.Serialization/Deserializers/CFB.cs

@@ -244,7 +244,7 @@ namespace SabreTools.Serialization.Deserializers
             var obj = new DirectoryEntry();
 
             byte[] name = data.ReadBytes(64);
-            obj.Name = Encoding.Unicode.GetString(name);
+            obj.Name = Encoding.Unicode.GetString(name).DecodeStreamName();
             obj.NameLength = data.ReadUInt16LittleEndian();
             obj.ObjectType = (ObjectType)data.ReadByteValue();
             obj.ColorFlag = (ColorFlag)data.ReadByteValue();

SabreTools.Serialization/Extensions.CFB.cs

@@ -0,0 +1,99 @@
+using System.Text;
+
+namespace SabreTools.Serialization
+{
+    public static partial class Extensions
+    {
+        /// <summary>
+        /// Decode a MIME-encoded stream name stored as a byte array
+        /// </summary>
+        /// <param name="input">Byte array to decode</param>
+        /// <returns>Decoded string on success, null otherwise</returns>
+        /// <remarks>Adapted from LibMSI</remarks>
+        public static string? DecodeStreamName(this byte[]? input)
+        {
+            // Ignore invalid inputs
+            if (input == null)
+                return null;
+            else if (input.Length == 0)
+                return string.Empty;
+
+            int count = 0;
+            int p = 0; // inputBytes[0]
+
+            byte[] output = new byte[input.Length + 1];
+            int q = 0; // output[0]
+            while (p < input.Length && input[p] != 0)
+            {
+                byte ch = input[p];
+                if ((ch == 0xe3 && input[p + 1] >= 0xa0) || (ch == 0xe4 && input[p + 1] < 0xa0))
+                {
+                    // UTF-8 encoding of 0x3800..0x47ff. 
+                    output[q++] = (byte)Mime2Utf(input[p + 2] & 0x7f);
+                    output[q++] = (byte)Mime2Utf(input[p + 1] ^ 0xa0);
+                    p += 3;
+                    count += 2;
+                    continue;
+                }
+
+                if (ch == 0xe4 && input[p + 1] == 0xa0)
+                {
+                    // UTF-8 encoding of 0x4800..0x483f.
+                    output[q++] = (byte)Mime2Utf(input[p + 2] & 0x7f);
+                    p += 3;
+                    count++;
+                    continue;
+                }
+
+                output[q++] = input[p++];
+                if (ch >= 0xc1)
+                    output[q++] = input[p++];
+                if (ch >= 0xe0)
+                    output[q++] = input[p++];
+                if (ch >= 0xf0)
+                    output[q++] = input[p++];
+
+                count++;
+            }
+
+            output[q] = 0;
+            return Encoding.ASCII.GetString(output);
+        }
+
+        /// <summary>
+        /// Decode a MIME-encoded stream name stored as a string
+        /// </summary>
+        /// <param name="input">String to decode</param>
+        /// <returns>Decoded string on success, null otherwise</returns>
+        /// <remarks>Adapted from LibMSI</remarks>
+        public static string? DecodeStreamName(this string? input)
+        {
+            // Ignore invalid inputs
+            if (input == null)
+                return null;
+            else if (input.Length == 0)
+                return string.Empty;
+
+            byte[] inputBytes = Encoding.UTF8.GetBytes(input);
+            return inputBytes.DecodeStreamName();
+        }
+
+        /// <summary>
+        /// Decode a single MIME-encoded byte
+        /// </summary>
+        /// <param name="b">Byte to decode</param>
+        /// <returns>Decoded byte on success, `_` otherwise</returns>
+        /// <remarks>Adapted from LibMSI</remarks>
+        private static int Mime2Utf(int b)
+        {
+            return b switch
+            {
+                < 10 => b + '0',
+                < 10 + 26 => b - 10 + 'A',
+                < 10 + 26 + 26 => b - 10 - 26 + 'a',
+                10 + 26 + 26 => '.',
+                _ => '_'
+            };
+        }
+    }
+}