Add FileDownloader service for Blazor apps

src/Components/Server/src/DependencyInjection/ComponentServiceCollectionExtensions.cs

@@ -67,6 +67,7 @@ public static IServerSideBlazorBuilder AddServerSideBlazor(this IServiceCollecti
         services.TryAddSingleton<ComponentParametersTypeCache>();
         services.TryAddSingleton<CircuitIdFactory>();
         services.TryAddScoped<IErrorBoundaryLogger, RemoteErrorBoundaryLogger>();
+        services.TryAddScoped<IFileDownloader, FileDownloader>();
 
         services.TryAddScoped(s => s.GetRequiredService<ICircuitAccessor>().Circuit);
         services.TryAddScoped<ICircuitAccessor, DefaultCircuitAccessor>();

src/Components/Server/src/Microsoft.AspNetCore.Components.Server.csproj

@@ -60,6 +60,7 @@
     <Compile Include="$(ComponentsSharedSourceRoot)src\ElementReferenceJsonConverter.cs" />
     <Compile Include="$(ComponentsSharedSourceRoot)src\ComponentParametersTypeCache.cs" />
     <Compile Include="$(ComponentsSharedSourceRoot)src\RootComponentTypeCache.cs" />
+    <Compile Include="$(ComponentsSharedSourceRoot)src\FileDownloader.cs" />
 
     <Compile Include="..\..\Shared\src\BrowserNavigationManagerInterop.cs" />
     <Compile Include="..\..\Shared\src\JsonSerializerOptionsProvider.cs" />

src/Components/Shared/src/FileDownloader.cs

@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.JSInterop;
+
+namespace Microsoft.AspNetCore.Components;
+
+/// <summary>
+/// Allows triggering a file download on the client from .NET.
+/// </summary>
+internal sealed class FileDownloader : IFileDownloader
+{
+    private readonly IJSRuntime _jsRuntime;
+    public FileDownloader(IJSRuntime JSRuntime)
+    {
+        _jsRuntime = JSRuntime;
+    }
+
+    /// <inheritdoc />
+    public Task SaveAs(string fileName, byte[] data)
+    {
+        var fileStream = new MemoryStream(data);
+
+        return SaveAs(fileName, fileStream);
+    }
+
+    /// <inheritdoc />
+    public async Task SaveAs(string fileName, Stream data)
+    {
+        if (string.IsNullOrWhiteSpace(fileName))
+        {
+            throw new ArgumentNullException(nameof(fileName));
+        }
+
+        using var streamRef = new DotNetStreamReference(stream: data);
+
+        await _jsRuntime.InvokeVoidAsync("Blazor._internal.downloadFile", streamRef, fileName);
+    }
+}

src/Components/Web.JS/src/FileDownloader.ts

@@ -0,0 +1,44 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+export async function downloadFile(data: any, fileName: string) {
+    // For Chromium browsers, show "Save As" dialog and then stream the data into the file without buffering it all in memory
+    if (typeof (window as any).showSaveFilePicker === 'function')
+    {
+        // Show the "Save As" dialog
+        let fileWriter;
+        try {
+            const fileHandle = await (window as any).showSaveFilePicker();
+            // Create a FileSystemWritableFileStream to write to.
+            fileWriter = await fileHandle.createWritable();
+        } catch {
+            // User pressed cancel, so abort the whole thing
+            return;
+        }
+
+        var dataStream = new ReadableStream(data);
+        const reader = dataStream.getReader();
+        while (true) {
+            const readResult = await reader.read();
+            if (readResult.done) {
+                break;
+            }
+            // Write the contents of the file to the stream.
+            await fileWriter.write(readResult.value);
+        }
+        // Close the file and write the contents to disk
+        await fileWriter.close();
+    }
+    else {
+        // The following option works for all browsers
+        const arrayBuffer = await data.arrayBuffer();
+        const blob = new Blob([arrayBuffer]);
+        const url = URL.createObjectURL(blob);
+        const anchorElement = document.createElement('a');
+        anchorElement.href = url;
+        anchorElement.download = fileName;
+        anchorElement.click();
+        anchorElement.remove();
+        URL.revokeObjectURL(url);
+    }
+}

src/Components/Web.JS/src/GlobalExports.ts

@@ -16,6 +16,7 @@ import { Platform, Pointer, System_String, System_Array, System_Object, System_B
 import { getNextChunk, receiveDotNetDataStream } from './StreamingInterop';
 import { RootComponentsFunctions } from './Rendering/JSRootComponents';
 import { attachWebRendererInterop } from './Rendering/WebRendererInteropMethods';
+import { downloadFile } from './FileDownloader';
 
 interface IBlazor {
   navigateTo: (uri: string, options: NavigationOptions) => void;
@@ -63,6 +64,7 @@ interface IBlazor {
     getJSDataStreamChunk?: (data: any, position: number, chunkSize: number) => Promise<Uint8Array>,
     receiveDotNetDataStream?: (streamId: number, data: any, bytesRead: number, errorMessage: string) => void,
     attachWebRendererInterop?: typeof attachWebRendererInterop,
+    downloadFile?: (data: any, fileName: string) => Promise<void>,
 
     // APIs invoked by hot reload
     applyHotReload?: (id: string, metadataDelta: string, ilDelta: string, pdbDelta: string | undefined) => void,
@@ -85,6 +87,7 @@ export const Blazor: IBlazor = {
     getJSDataStreamChunk: getNextChunk,
     receiveDotNetDataStream: receiveDotNetDataStream,
     attachWebRendererInterop,
+    downloadFile: downloadFile,
   },
 };
 

src/Components/Web/src/IFileDownloader.cs

@@ -0,0 +1,24 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.AspNetCore.Components;
+
+/// <summary>
+/// Facilitates triggering a file download on the client using data from .NET.
+/// </summary>
+public interface IFileDownloader
+{
+    /// <summary>
+    /// Takes in a byte[] representing file data and triggers the file download on the client.
+    /// </summary>
+    /// <param name="fileName">A <see cref="string"/> that represents the default name of the file that will be downloaded.</param>
+    /// <param name="data"> The <see cref="byte"/>[] data that will be downloaded by the client.</param>
+    Task SaveAs(string fileName, byte[] data);
+
+    /// <summary>
+    /// Takes in a <see cref="Stream"/> representing file data and triggers the file download on the client.
+    /// </summary>
+    /// <param name="fileName">A <see cref="string"/> that represents the default name of the file that will be downloaded.</param>
+    /// <param name="data"> The <see cref="Stream"/> data that will be downloaded by the client.</param>
+    Task SaveAs(string fileName, Stream data);
+}

src/Components/Web/src/PublicAPI.Unshipped.txt

@@ -13,3 +13,6 @@ Microsoft.AspNetCore.Components.Web.MouseEventArgs.MovementX.get -> double
 Microsoft.AspNetCore.Components.Web.MouseEventArgs.MovementX.set -> void
 Microsoft.AspNetCore.Components.Web.MouseEventArgs.MovementY.get -> double
 Microsoft.AspNetCore.Components.Web.MouseEventArgs.MovementY.set -> void
+Microsoft.AspNetCore.Components.IFileDownloader
+Microsoft.AspNetCore.Components.IFileDownloader.SaveAs(string! fileName, byte[]! data) -> System.Threading.Tasks.Task!
+Microsoft.AspNetCore.Components.IFileDownloader.SaveAs(string! fileName, System.IO.Stream! data) -> System.Threading.Tasks.Task!

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostBuilder.cs

@@ -265,6 +265,7 @@ internal void InitializeDefaultServices()
         Services.AddSingleton<INavigationInterception>(WebAssemblyNavigationInterception.Instance);
         Services.AddSingleton(new LazyAssemblyLoader(DefaultWebAssemblyJSRuntime.Instance));
         Services.AddSingleton<ComponentStatePersistenceManager>();
+        Services.AddSingleton<IFileDownloader, FileDownloader>();
         Services.AddSingleton<PersistentComponentState>(sp => sp.GetRequiredService<ComponentStatePersistenceManager>().State);
         Services.AddSingleton<IErrorBoundaryLogger, WebAssemblyErrorBoundaryLogger>();
         Services.AddLogging(builder =>

src/Components/WebAssembly/WebAssembly/src/Microsoft.AspNetCore.Components.WebAssembly.csproj

@@ -35,6 +35,7 @@
     <Compile Include="$(ComponentsSharedSourceRoot)src\ElementReferenceJsonConverter.cs" />
     <Compile Include="$(ComponentsSharedSourceRoot)src\ComponentParametersTypeCache.cs" />
     <Compile Include="$(ComponentsSharedSourceRoot)src\RootComponentTypeCache.cs" />
+    <Compile Include="$(ComponentsSharedSourceRoot)src\FileDownloader.cs" />
     <Compile Include="$(SharedSourceRoot)Components\WebAssemblyComponentSerializationSettings.cs" Link="Prerendering/WebAssemblyComponentSerializationSettings.cs" />
     <Compile Include="$(SharedSourceRoot)Components\WebAssemblyComponentMarker.cs" Link="Prerendering/WebAssemblyComponentMarker.cs" />
     <Compile Include="$(SharedSourceRoot)Components\ComponentParameter.cs" Link="Prerendering/ComponentParameter.cs" />

src/Components/WebView/WebView/src/ComponentsWebViewServiceCollectionExtensions.cs

@@ -27,6 +27,7 @@ public static IServiceCollection AddBlazorWebView(this IServiceCollection servic
         services.TryAddScoped<INavigationInterception, WebViewNavigationInterception>();
         services.TryAddScoped<NavigationManager, WebViewNavigationManager>();
         services.TryAddScoped<IErrorBoundaryLogger, WebViewErrorBoundaryLogger>();
+        services.TryAddScoped<IFileDownloader, FileDownloader>();
         return services;
     }
 }

src/Components/WebView/WebView/src/Microsoft.AspNetCore.Components.WebView.csproj

@@ -25,6 +25,7 @@
     <Compile Include="$(ComponentsSharedSourceRoot)src\TransmitDataStreamToJS.cs" LinkBase="Shared" />
     <Compile Include="$(ComponentsSharedSourceRoot)src\ElementReferenceJsonConverter.cs" LinkBase="Shared" />
     <Compile Include="$(ComponentsSharedSourceRoot)src\JsonSerializerOptionsProvider.cs" LinkBase="Shared" />
+    <Compile Include="$(ComponentsSharedSourceRoot)src\FileDownloader.cs" LinkBase="Shared" />
     <Compile Include="$(SharedSourceRoot)LinkerFlags.cs" LinkBase="Shared" />
     <Compile Include="$(SharedSourceRoot)StaticWebAssets\**\*.cs" LinkBase="Shared" />
     <Compile Include="$(ComponentsSharedSourceRoot)src\ArrayBuilder.cs" LinkBase="Shared" />

src/Components/test/testassets/BasicTestApp/FileDownloaderComponent.razor

@@ -0,0 +1,36 @@
+@using Microsoft.AspNetCore.Components
+
+@inject IFileDownloader FileDownload
+
+<h1>File configuration</h1>
+File name:
+<br />
+
+<input type="text" @bind-value="@fileName" />
+<br />
+
+<h1>File download</h1>
+
+<button @onclick="SaveFile"> Save </button>
+
+@code {
+    private string fileName = "file.txt";
+
+    private Stream GetFileStream()
+    {
+        var data = new byte[100 * 1024];
+        for (var i = 0; i < data.Length; i++)
+        {
+            data[i] = (byte)(i % 256);
+        }
+        var fileStream = new MemoryStream(data);
+
+        return fileStream;
+    }
+
+    private async Task SaveFile()
+    {
+        var data = GetFileStream();
+        await FileDownload.SaveAs(fileName, data);
+    }
+}

src/Components/test/testassets/BasicTestApp/Index.razor

@@ -103,6 +103,7 @@
         <option value="BasicTestApp.VirtualizationDataChanges">Virtualization data changes</option>
         <option value="BasicTestApp.VirtualizationTable">Virtualization HTML table</option>
         <option value="BasicTestApp.HotReload.RenderOnHotReload">Render on hot reload</option>
+        <option value="BasicTestApp.FileDownloaderComponent">Save file download</option>
     </select>
 
     <span id="runtime-info"><code><tt>@System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription</tt></code></span>