Resolve and load fonts from filename first

Instead of loading font files into an NSData object via a .NET managed stream, load them by filename via the CGDataProvider directly (no need to marshal the file byte data).

This also mitigates the issue addressed in dotnet/runtime#61153 for the specific instance encountered by loading fonts this way.

src/Core/src/Fonts/EmbeddedFontLoader.iOS.cs

@@ -14,14 +14,25 @@ public partial class EmbeddedFontLoader
 		{
 			try
 			{
+				CGFont? cgFont;
+
 				if (font.ResourceStream == null)
-					throw new InvalidOperationException("ResourceStream was null.");
+				{
+					if (!System.IO.File.Exists(font.FontName))
+						throw new InvalidOperationException("ResourceStream was null.");
 
-				var data = NSData.FromStream(font.ResourceStream);
-				if (data == null)
-					throw new InvalidOperationException("Unable to load font stream data.");
-				var provider = new CGDataProvider(data);
-				var cgFont = CGFont.CreateFromProvider(provider);
+					var provider = new CGDataProvider(font.FontName);
+					cgFont = CGFont.CreateFromProvider(provider);
+				}
+				else
+				{
+					var data = NSData.FromStream(font.ResourceStream);
+					if (data == null)
+						throw new InvalidOperationException("Unable to load font stream data.");
+					var provider = new CGDataProvider(data);
+					cgFont = CGFont.CreateFromProvider(provider);
+				}
+
 				if (cgFont == null)
 					throw new InvalidOperationException("Unable to load font from the stream.");
 

src/Core/src/Fonts/FontRegistrar.cs

@@ -64,6 +64,18 @@ public void Register(string filename, string? alias)
 			return _fontLookupCache[font] = null;
 		}
 
+		string? LoadFileSystemFont(string cacheKey, string filename, string? alias)
+		{
+			var font = new EmbeddedFont { FontName = filename };
+
+			if (_fontLoader == null)
+				throw new InvalidOperationException("Font loader was not set on the font registrar.");
+
+			var result = _fontLoader.LoadFont(font);
+
+			return _fontLookupCache[cacheKey] = result;
+		}
+
 		string? LoadEmbeddedFont(string cacheKey, string filename, string? alias, Stream stream)
 		{
 			var font = new EmbeddedFont { FontName = filename, ResourceStream = stream };

src/Core/src/Fonts/FontRegistrar.iOS.cs

@@ -7,12 +7,15 @@ public partial class FontRegistrar : IFontRegistrar
 	{
 		string? LoadNativeAppFont(string font, string filename, string? alias)
 		{
-			using var stream = GetNativeFontStream(filename, alias);
+			var resolvedFilename = ResolveFileSystemFont(filename);
 
-			return LoadEmbeddedFont(font, filename, alias, stream);
+			if (!string.IsNullOrEmpty(resolvedFilename))
+				return LoadFileSystemFont(font, resolvedFilename, alias);
+
+			return LoadEmbeddedFont(font, filename, alias, GetNativeFontStream(filename, alias));
 		}
 
-		Stream GetNativeFontStream(string filename, string? alias)
+		string? ResolveFileSystemFont(string filename)
 		{
 			var mainBundlePath = Foundation.NSBundle.MainBundle.BundlePath;
 
@@ -23,22 +26,34 @@ Stream GetNativeFontStream(string filename, string? alias)
 
 			var fontBundlePath = Path.Combine(mainBundlePath, filename);
 			if (File.Exists(fontBundlePath))
-				return File.OpenRead(fontBundlePath);
+				return fontBundlePath;
 
 			fontBundlePath = Path.Combine(mainBundlePath, "Resources", filename);
 			if (File.Exists(fontBundlePath))
-				return File.OpenRead(fontBundlePath);
+				return fontBundlePath;
 
 			fontBundlePath = Path.Combine(mainBundlePath, "Fonts", filename);
 			if (File.Exists(fontBundlePath))
-				return File.OpenRead(fontBundlePath);
+				return fontBundlePath;
 
 			fontBundlePath = Path.Combine(mainBundlePath, "Resources", "Fonts", filename);
 			if (File.Exists(fontBundlePath))
-				return File.OpenRead(fontBundlePath);
+				return fontBundlePath;
 
 			// TODO: check other folders as well
 
+			return null;
+		}
+
+		Stream GetNativeFontStream(string filename, string? alias)
+		{
+			var resolvedFilename = ResolveFileSystemFont(filename);
+
+			if (!string.IsNullOrEmpty(resolvedFilename) && File.Exists(resolvedFilename))
+			{
+				return File.OpenRead(resolvedFilename);
+			}
+
 			throw new FileNotFoundException($"Native font with the name {filename} was not found.");
 		}
 	}