Fix file path encoding edge cases in HTML export

DiscordChatExporter.Core/Exporting/ExportContext.cs

@@ -8,6 +8,7 @@
 using System.Threading.Tasks;
 using DiscordChatExporter.Core.Discord;
 using DiscordChatExporter.Core.Discord.Data;
+using DiscordChatExporter.Core.Utils;
 using DiscordChatExporter.Core.Utils.Extensions;
 
 namespace DiscordChatExporter.Core.Exporting;
@@ -118,7 +119,7 @@ public async ValueTask<string> ResolveAssetUrlAsync(
             var relativeFilePath = Path.GetRelativePath(Request.OutputDirPath, filePath);
 
             // Prefer the relative path so that the export package can be copied around without breaking references.
-            // However, if the assets directory lies outside of the export directory, use the absolute path instead.
+            // However, if the assets directory lies outside the export directory, use the absolute path instead.
             var shouldUseAbsoluteFilePath =
                 relativeFilePath.StartsWith(
                     ".." + Path.DirectorySeparatorChar,
@@ -133,14 +134,7 @@ public async ValueTask<string> ResolveAssetUrlAsync(
 
             // For HTML, the path needs to be properly formatted
             if (Request.Format is ExportFormat.HtmlDark or ExportFormat.HtmlLight)
-            {
-                // Format the path into a valid file URI
-                var href = new Uri(new Uri("file:///"), optimalFilePath).ToString();
-
-                // File schema does not support relative paths, so strip it if that's the case
-                // https://github.com/Tyrrrz/DiscordChatExporter/issues/1155
-                return shouldUseAbsoluteFilePath ? href : href[8..];
-            }
+                return Url.EncodeFilePath(optimalFilePath);
 
             return optimalFilePath;
         }

DiscordChatExporter.Core/Utils/Url.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Text;
+
+namespace DiscordChatExporter.Core.Utils;
+
+public static class Url
+{
+    public static string EncodeFilePath(string filePath)
+    {
+        var buffer = new StringBuilder();
+        var position = 0;
+
+        while (true)
+        {
+            if (position >= filePath.Length)
+                break;
+
+            var separatorIndex = filePath.IndexOfAny([':', '/', '\\'], position);
+            if (separatorIndex < 0)
+            {
+                buffer.Append(Uri.EscapeDataString(filePath[position..]));
+                break;
+            }
+
+            // Append the segment
+            buffer.Append(Uri.EscapeDataString(filePath[position..separatorIndex]));
+
+            // Append the separator
+            buffer.Append(
+                filePath[separatorIndex] switch
+                {
+                    // Normalize slashes
+                    '\\' => '/',
+                    var c => c,
+                }
+            );
+
+            position = separatorIndex + 1;
+        }
+
+        return buffer.ToString();
+    }
+}