Pass file extensions to the browser backend in the file picker

samples/ControlCatalog/Pages/DialogsPage.xaml.cs

@@ -82,7 +82,13 @@ namespace ControlCatalog.Pages
                 return new List<FilePickerFileType>
                             {
                                 FilePickerFileTypes.All,
-                                FilePickerFileTypes.TextPlain
+                                FilePickerFileTypes.TextPlain,
+                                new("Binary Log")
+                                {
+                                    Patterns = new[] { "*.binlog", "*.buildlog" },
+                                    MimeTypes = new[] { "application/binlog", "application/buildlog" },
+                                    AppleUniformTypeIdentifiers = new []{ "public.data" }
+                                }
                             };
             }
 

src/Avalonia.Base/Platform/Storage/FilePickerFileType.cs

@@ -1,4 +1,6 @@
 using System.Collections.Generic;
+using System.IO;
+using System.Linq;
 
 namespace Avalonia.Platform.Storage;
 
@@ -21,7 +23,7 @@ public sealed class FilePickerFileType
     /// List of extensions in GLOB format. I.e. "*.png" or "*.*".
     /// </summary>
     /// <remarks>
-    /// Used on Windows and Linux systems.
+    /// Used on Windows, Linux and Browser platforms.
     /// </remarks>
     public IReadOnlyList<string>? Patterns { get; set; }
 
@@ -29,7 +31,7 @@ public sealed class FilePickerFileType
     /// List of extensions in MIME format.
     /// </summary>
     /// <remarks>
-    /// Used on Android, Browser and Linux systems.
+    /// Used on Android, Linux and Browser platforms.
     /// </remarks>
     public IReadOnlyList<string>? MimeTypes { get; set; }
 
@@ -41,4 +43,14 @@ public sealed class FilePickerFileType
     /// See https://developer.apple.com/documentation/uniformtypeidentifiers/system_declared_uniform_type_identifiers.
     /// </remarks>
     public IReadOnlyList<string>? AppleUniformTypeIdentifiers { get; set; }
+
+    internal IReadOnlyList<string>? TryGetExtensions()
+    {
+        // Converts random glob pattern to a simple extension name.
+        // GetExtension should be sufficient here.
+        // Only exception is "*.*proj" patterns that should be filtered as well.
+        return Patterns?.Select(Path.GetExtension)
+            .Where(e => !string.IsNullOrEmpty(e) && !e.Contains('*') && e.StartsWith("."))
+            .ToArray()!;
+    }
 }

src/Browser/Avalonia.Browser/Interop/StorageHelper.cs

@@ -54,5 +54,5 @@ internal static partial class StorageHelper
     public static partial JSObject[] ItemsArray(JSObject item);
 
     [JSImport("StorageProvider.createAcceptType", AvaloniaModule.StorageModuleName)]
-    public static partial JSObject CreateAcceptType(string description, string[] mimeTypes);
+    public static partial JSObject CreateAcceptType(string description, string[] mimeTypes, string[]? extensions);
 }

src/Browser/Avalonia.Browser/Storage/BrowserStorageProvider.cs

@@ -147,7 +147,7 @@ internal class BrowserStorageProvider : IStorageProvider
     {
         var types = input?
             .Where(t => t.MimeTypes?.Any() == true && t != FilePickerFileTypes.All)
-            .Select(t => StorageHelper.CreateAcceptType(t.Name, t.MimeTypes!.ToArray()))
+            .Select(t => StorageHelper.CreateAcceptType(t.Name, t.MimeTypes!.ToArray(), t.TryGetExtensions()?.ToArray()))
             .ToArray();
         if (types?.Length == 0)
         {

src/Browser/Avalonia.Browser/webapp/modules/storage/storageProvider.ts

@@ -62,9 +62,9 @@ export class StorageProvider {
         }
     }
 
-    public static createAcceptType(description: string, mimeTypes: string[]): FilePickerAcceptType {
+    public static createAcceptType(description: string, mimeTypes: string[], extensions: string[] | undefined): FilePickerAcceptType {
         const accept: Record<string, string[]> = {};
-        mimeTypes.forEach(a => { accept[a] = []; });
+        mimeTypes.forEach(a => { accept[a] = extensions ?? []; });
         return { description, accept };
     }
 }

src/iOS/Avalonia.iOS/Storage/IOSStorageProvider.cs

@@ -43,6 +43,10 @@ internal class IOSStorageProvider : IStorageProvider
                     {
                         return f.AppleUniformTypeIdentifiers.Select(id => UTType.CreateFromIdentifier(id));
                     }
+                    if (f.TryGetExtensions() is { } extensions && extensions.Any())
+                    {
+                        return extensions.Select(id => UTType.CreateFromExtension(id.TrimStart('.')));
+                    }
                     if (f.MimeTypes?.Any() == true)
                     {
                         return f.MimeTypes.Select(id => UTType.CreateFromMimeType(id));