Advanced - File providers

In this article

• IWebHostEnvironment exposes the app's content root and web root as IFileProvider types.

• Static File Middleware uses File Providers to locate static files.

• Razor uses File Providers to locate pages and views.

• .NET Core tooling uses File Providers and glob patterns to specify which files should be published.

File Provider interfaces

• Obtain file information (IFileInfo).

• Obtain directory information (IDirectoryContents).

• Set up change notifications (using an IChangeToken).

• Exists

• IsDirectory

• Name

• Length (in bytes)

• LastModified date

File Provider implementations

Implementation	Description
Composite File Provider	Used to provide combined access to files and directories from one or more other providers.
Manifest Embedded File Provider	Used to access files embedded in assemblies.
Physical File Provider	Used to access the system's physical files.

Physical File Provider

var provider = new PhysicalFileProvider(applicationRoot);
var contents = provider.GetDirectoryContents(string.Empty);
var filePath = Path.Combine("wwwroot", "js", "site.js");
var fileInfo = provider.GetFileInfo(filePath);

• provider is an IFileProvider.

• contents is an IDirectoryContents.

• fileInfo is an IFileInfo.

var physicalProvider = _env.ContentRootFileProvider;

Manifest Embedded File Provider

• Add the Microsoft.Extensions.FileProviders.Embedded NuGet package to your project.

• Set the <GenerateEmbeddedFilesManifest> property to true. Specify the files to embed with <EmbeddedResource>:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <GenerateEmbeddedFilesManifest>true</GenerateEmbeddedFilesManifest>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.FileProviders.Embedded" Version="3.1.0" />
  </ItemGroup>

  <ItemGroup>
    <EmbeddedResource Include="Resource.txt" />
  </ItemGroup>

</Project>

var manifestEmbeddedProvider = 
    new ManifestEmbeddedFileProvider(typeof(Program).Assembly);

• Specify a relative file path.

• Scope files to a last modified date.

• Name the embedded resource containing the embedded file manifest.

Overload	Description
ManifestEmbeddedFileProvider(Assembly, String)	Accepts an optional root relative path parameter. Specify the root to scope calls to GetDirectoryContents to those resources under the provided path.
ManifestEmbeddedFileProvider(Assembly, String, DateTimeOffset)	Accepts an optional root relative path parameter and a lastModified date (DateTimeOffset) parameter. The lastModified date scopes the last modification date for the IFileInfo instances returned by the IFileProvider.
ManifestEmbeddedFileProvider(Assembly, String, String, DateTimeOffset)	Accepts an optional root relative path, lastModified date, and manifestName parameters. The manifestName represents the name of the embedded resource containing the manifest.

Composite File Provider

var physicalProvider = _env.ContentRootFileProvider;
var manifestEmbeddedProvider = 
    new ManifestEmbeddedFileProvider(typeof(Program).Assembly);
var compositeProvider = 
    new CompositeFileProvider(physicalProvider, manifestEmbeddedProvider);

services.AddSingleton<IFileProvider>(compositeProvider);

Watch for changes

• Accepts a file path string, which can use glob patterns to specify multiple files.

• Returns an IChangeToken.

• HasChanged: A property that can be inspected to determine if a change has occurred.

• RegisterChangeCallback: Called when changes are detected to the specified path string. Each change token only calls its associated callback in response to a single change. To enable constant monitoring, use a TaskCompletionSource<TResult> (shown below) or recreate IChangeToken instances in response to changes.

private static readonly string _fileFilter = Path.Combine("TextFiles", "*.txt");

public static void Main(string[] args)
{
    Console.WriteLine($"Monitoring for changes with filter '{_fileFilter}' (Ctrl + C to quit)...");

    while (true)
    {
        MainAsync().GetAwaiter().GetResult();
    }
}

private static async Task MainAsync()
{
    var fileProvider = new PhysicalFileProvider(Directory.GetCurrentDirectory());
    IChangeToken token = fileProvider.Watch(_fileFilter);
    var tcs = new TaskCompletionSource<object>();

    token.RegisterChangeCallback(state =>
        ((TaskCompletionSource<object>)state).TrySetResult(null), tcs);

    await tcs.Task.ConfigureAwait(false);

    Console.WriteLine("file changed");
}

Glob patterns

Pattern	Description
directory/file.txt	Matches a specific file in a specific ```directory```.
directory/*.txt	Matches all files with .txt extension in a specific ```directory```.
directory/*/appsettings.json	Matches all appsettings.json files in directories exactly one level below the directory folder.
directory/**/*.txt	Matches all files with a .txt extension found anywhere under the directory folder.

Ref: File Providers in ASP.NET Core