AspNetCore.Docs/aspnetcore/fundamentals/static-files.md

title	author	description	monikerRange	ms.author	ms.custom	ms.date	no-loc	uid
Static files in ASP.NET Core	rick-anderson	Learn how to serve and secure static files and configure static file hosting middleware behaviors in an ASP.NET Core web app.	>= aspnetcore-2.1	riande	mvc	6/23/2020	Home Privacy Kestrel appsettings.json ASP.NET Core Identity cookie Cookie Blazor Identity Let's Encrypt Razor SignalR	fundamentals/static-files

Static files in ASP.NET Core

::: moniker range=">= aspnetcore-3.0"

By Rick Anderson and Kirk Larkin

Static files, such as HTML, CSS, images, and JavaScript, are assets an ASP.NET Core app serves directly to clients by default.

View or download sample code (how to download)

Serve static files

Static files are stored within the project's web root directory. The default directory is {content root}/wwwroot, but it can be changed with the xref:Microsoft.AspNetCore.Hosting.HostingAbstractionsWebHostBuilderExtensions.UseWebRoot%2A method. For more information, see Content root and Web root.

The xref:Microsoft.AspNetCore.WebHost.CreateDefaultBuilder%2A method sets the content root to the current directory:

[!code-csharp]

The preceding code was created with the web app template.

Static files are accessible via a path relative to the web root. For example, the Web Application project templates contain several folders within the wwwroot folder:

• wwwroot
  • css
  • js
  • lib

Consider creating the wwwroot/images folder and adding the wwwroot/images/MyImage.jpg file. The URI format to access a file in the images folder is https://<hostname>/images/<image_file_name>. For example, https://localhost:5001/images/MyImage.jpg

Serve files in web root

The default web app templates call the xref:Microsoft.AspNetCore.Builder.StaticFileExtensions.UseStaticFiles%2A method in Startup.Configure, which enables static files to be served:

[!code-csharp]

The parameterless UseStaticFiles method overload marks the files in web root as servable. The following markup references wwwroot/images/MyImage.jpg:

<img src="~/images/MyImage.jpg" class="img" alt="My image" />

In the preceding code, the tilde character ~/ points to the web root.

Serve files outside of web root

Consider a directory hierarchy in which the static files to be served reside outside of the web root:

• wwwroot
  • css
  • images
  • js
• MyStaticFiles
  • images
    • red-rose.jpg

A request can access the red-rose.jpg file by configuring the Static File Middleware as follows:

[!code-csharp]

In the preceding code, the MyStaticFiles directory hierarchy is exposed publicly via the StaticFiles URI segment. A request to https://<hostname>/StaticFiles/images/red-rose.jpg serves the red-rose.jpg file.

The following markup references MyStaticFiles/images/red-rose.jpg:

<img src="~/StaticFiles/images/red-rose.jpg" class="img" alt="A red rose" />

Set HTTP response headers

A xref:Microsoft.AspNetCore.Builder.StaticFileOptions object can be used to set HTTP response headers. In addition to configuring static file serving from the web root, the following code sets the Cache-Control header:

[!code-csharp]

Static files are publicly cacheable for 600 seconds:

Static file authorization

The ASP.NET Core templates call xref:Microsoft.AspNetCore.Builder.StaticFileExtensions.UseStaticFiles%2A before calling xref:Microsoft.AspNetCore.Builder.AuthorizationAppBuilderExtensions.UseAuthorization%2A. Most apps follow this pattern. When the Static File Middleware is called before the authorization middleware:

• No authorization checks are performed on the static files.
• Static files served by the Static File Middleware, such as those under wwwroot, are publicly accessible.

To serve static files based on authorization:

• Store them outside of wwwroot.
• Call UseStaticFiles, specifying a path, after calling UseAuthorization.
• Set the fallback authorization policy.

[!code-csharp]

[!code-csharp]

In the preceding code, the fallback authorization policy requires all users to be authenticated. Endpoints such as controllers, Razor Pages, etc that specify their own authorization requirements don't use the fallback authorization policy. For example, Razor Pages, controllers, or action methods with [AllowAnonymous] or [Authorize(PolicyName="MyPolicy")] use the applied authorization attribute rather than the fallback authorization policy.

xref:Microsoft.AspNetCore.Authorization.AuthorizationPolicyBuilder.RequireAuthenticatedUser%2A adds xref:Microsoft.AspNetCore.Authorization.Infrastructure.DenyAnonymousAuthorizationRequirement to the current instance, which enforces that the current user is authenticated.

Static assets under wwwroot are publicly accessible because the default Static File Middleware (app.UseStaticFiles();) is called before UseAuthentication. Static assets in the MyStaticFiles folder require authentication. The sample code demonstrates this.

An alternative approach to serve files based on authorization is to:

• Store them outside of wwwroot and any directory accessible to the Static File Middleware.
• Serve them via an action method to which authorization is applied and return a xref:Microsoft.AspNetCore.Mvc.FileResult object:

[!code-csharp]

Directory browsing

Directory browsing allows directory listing within specified directories.

Directory browsing is disabled by default for security reasons. For more information, see Security considerations for static files.

Enable directory browsing with:

• xref:Microsoft.Extensions.DependencyInjection.DirectoryBrowserServiceExtensions.AddDirectoryBrowser%2A in Startup.ConfigureServices.
• xref:Microsoft.AspNetCore.Builder.DirectoryBrowserExtensions.UseDirectoryBrowser%2A in Startup.Configure.

[!code-csharp]

The preceding code allows directory browsing of the wwwroot/images folder using the URL https://<hostname>/MyImages, with links to each file and folder:

Serve default documents

Setting a default page provides visitors a starting point on a site. To serve a default file from wwwroot without requiring the request URL to include the file's name, call the xref:Microsoft.AspNetCore.Builder.DefaultFilesExtensions.UseDefaultFiles%2A method:

[!code-csharp]

UseDefaultFiles must be called before UseStaticFiles to serve the default file. UseDefaultFiles is a URL rewriter that doesn't serve the file.

With UseDefaultFiles, requests to a folder in wwwroot search for:

• default.htm
• default.html
• index.htm
• index.html

The first file found from the list is served as though the request included the file's name. The browser URL continues to reflect the URI requested.

The following code changes the default file name to mydefault.html:

[!code-csharp]

The following code shows Startup.Configure with the preceding code:

[!code-csharp]

UseFileServer for default documents

xref:Microsoft.AspNetCore.Builder.FileServerExtensions.UseFileServer* combines the functionality of UseStaticFiles, UseDefaultFiles, and optionally UseDirectoryBrowser.

Call app.UseFileServer to enable the serving of static files and the default file. Directory browsing isn't enabled. The following code shows Startup.Configure with UseFileServer:

[!code-csharp]

The following code enables the serving of static files, the default file, and directory browsing:

app.UseFileServer(enableDirectoryBrowsing: true);

The following code shows Startup.Configure with the preceding code:

[!code-csharp]

Consider the following directory hierarchy:

• wwwroot
  • css
  • images
  • js
• MyStaticFiles
  • images
    • MyImage.jpg
  • default.html

The following code enables the serving of static files, the default file, and directory browsing of MyStaticFiles:

[!code-csharp]

xref:Microsoft.Extensions.DependencyInjection.DirectoryBrowserServiceExtensions.AddDirectoryBrowser%2A must be called when the EnableDirectoryBrowsing property value is true.

Using the file hierarchy and preceding code, URLs resolve as follows:

URI	Response
https://<hostname>/StaticFiles/images/MyImage.jpg	MyStaticFiles/images/MyImage.jpg
https://<hostname>/StaticFiles	MyStaticFiles/default.html

If no default-named file exists in the MyStaticFiles directory, https://<hostname>/StaticFiles returns the directory listing with clickable links:

xref:Microsoft.AspNetCore.Builder.DefaultFilesExtensions.UseDefaultFiles* and xref:Microsoft.AspNetCore.Builder.DirectoryBrowserExtensions.UseDirectoryBrowser* perform a client-side redirect from the target URI without a trailing / to the target URI with a trailing /. For example, from https://<hostname>/StaticFiles to https://<hostname>/StaticFiles/. Relative URLs within the StaticFiles directory are invalid without a trailing slash (/).

FileExtensionContentTypeProvider

The xref:Microsoft.AspNetCore.StaticFiles.FileExtensionContentTypeProvider class contains a Mappings property that serves as a mapping of file extensions to MIME content types. In the following sample, several file extensions are mapped to known MIME types. The .rtf extension is replaced, and .mp4 is removed:

[!code-csharp]

The following code shows Startup.Configure with the preceding code:

[!code-csharp]

See MIME content types.

Non-standard content types

The Static File Middleware understands almost 400 known file content types. If the user requests a file with an unknown file type, the Static File Middleware passes the request to the next middleware in the pipeline. If no middleware handles the request, a 404 Not Found response is returned. If directory browsing is enabled, a link to the file is displayed in a directory listing.

The following code enables serving unknown types and renders the unknown file as an image:

[!code-csharp]

The following code shows Startup.Configure with the preceding code:

[!code-csharp]

With the preceding code, a request for a file with an unknown content type is returned as an image.

[!WARNING] Enabling xref:Microsoft.AspNetCore.Builder.StaticFileOptions.ServeUnknownFileTypes is a security risk. It's disabled by default, and its use is discouraged. FileExtensionContentTypeProvider provides a safer alternative to serving files with non-standard extensions.

Serve files from multiple locations

UseStaticFiles and UseFileServer default to the file provider pointing at wwwroot. Additional instances of UseStaticFiles and UseFileServer can be provided with other file providers to serve files from other locations. For more information, see this GitHub issue.

Security considerations for static files

[!WARNING] UseDirectoryBrowser and UseStaticFiles can leak secrets. Disabling directory browsing in production is highly recommended. Carefully review which directories are enabled via UseStaticFiles or UseDirectoryBrowser. The entire directory and its sub-directories become publicly accessible. Store files suitable for serving to the public in a dedicated directory, such as <content_root>/wwwroot. Separate these files from MVC views, Razor Pages, configuration files, etc.

• The URLs for content exposed with UseDirectoryBrowser and UseStaticFiles are subject to the case sensitivity and character restrictions of the underlying file system. For example, Windows is case insensitive, but macOS and Linux aren't.

• ASP.NET Core apps hosted in IIS use the ASP.NET Core Module to forward all requests to the app, including static file requests. The IIS static file handler isn't used and has no chance to handle requests.

• Complete the following steps in IIS Manager to remove the IIS static file handler at the server or website level:

  1. Navigate to the Modules feature.
  2. Select StaticFileModule in the list.
  3. Click Remove in the Actions sidebar.

[!WARNING] If the IIS static file handler is enabled and the ASP.NET Core Module is configured incorrectly, static files are served. This happens, for example, if the web.config file isn't deployed.

• Place code files, including .cs and .cshtml, outside of the app project's web root. A logical separation is therefore created between the app's client-side content and server-based code. This prevents server-side code from being leaked.

Additional resources

• Middleware
• Introduction to ASP.NET Core

::: moniker-end

::: moniker range="< aspnetcore-3.0"

By Rick Anderson and Scott Addie

Static files, such as HTML, CSS, images, and JavaScript, are assets an ASP.NET Core app serves directly to clients. Some configuration is required to enable serving of these files.

View or download sample code (how to download)

Serve static files

Static files are stored within the project's web root directory. The default directory is {content root}/wwwroot, but it can be changed via the xref:Microsoft.AspNetCore.Hosting.HostingAbstractionsWebHostBuilderExtensions.UseWebRoot%2A method. See Content root and Web root for more information.

The app's web host must be made aware of the content root directory.

The WebHost.CreateDefaultBuilder method sets the content root to the current directory:

[!code-csharp]

Static files are accessible via a path relative to the web root. For example, the Web Application project template contains several folders within the wwwroot folder:

• wwwroot
  • css
  • images
  • js

The URI format to access a file in the images subfolder is http://<server_address>/images/<image_file_name>. For example, http://localhost:9189/images/banner3.svg.

If targeting .NET Framework, add the Microsoft.AspNetCore.StaticFiles package to the project. If targeting .NET Core, the Microsoft.AspNetCore.App metapackage includes this package.

Configure the middleware, which enables the serving of static files.

Serve files inside of web root

Invoke the xref:Microsoft.AspNetCore.Builder.StaticFileExtensions.UseStaticFiles%2A method within Startup.Configure:

[!code-csharp]

The parameterless UseStaticFiles method overload marks the files in web root as servable. The following markup references wwwroot/images/banner1.svg:

[!code-cshtml]

In the preceding code, the tilde character ~/ points to the web root.

Serve files outside of web root

Consider a directory hierarchy in which the static files to be served reside outside of the web root:

• wwwroot
  • css
  • images
  • js
• MyStaticFiles
  • images
    • banner1.svg

A request can access the banner1.svg file by configuring the Static File Middleware as follows:

[!code-csharp]

In the preceding code, the MyStaticFiles directory hierarchy is exposed publicly via the StaticFiles URI segment. A request to http://<server_address>/StaticFiles/images/banner1.svg serves the banner1.svg file.

The following markup references MyStaticFiles/images/banner1.svg:

[!code-cshtml]

Set HTTP response headers

A xref:Microsoft.AspNetCore.Builder.StaticFileOptions object can be used to set HTTP response headers. In addition to configuring static file serving from the web root, the following code sets the Cache-Control header:

[!code-csharp] [!INCLUDEabout the series]

The xref:Microsoft.AspNetCore.Http.HeaderDictionaryExtensions.Append%2A?displayProperty=nameWithType method exists in the Microsoft.AspNetCore.Http package.

The files have been made publicly cacheable for 10 minutes (600 seconds) in the Development environment:

Static file authorization

The Static File Middleware doesn't provide authorization checks. Any files served by it, including those under wwwroot, are publicly accessible. To serve files based on authorization:

• Store them outside of wwwroot and any directory accessible to the Static File Middleware.

• Serve them via an action method to which authorization is applied. Return a xref:Microsoft.AspNetCore.Mvc.FileResult object:

  [!code-csharp]

Enable directory browsing

Directory browsing allows users of your web app to see a directory listing and files within a specified directory. Directory browsing is disabled by default for security reasons (see Considerations). Enable directory browsing by invoking the xref:Microsoft.AspNetCore.Builder.DirectoryBrowserExtensions.UseDirectoryBrowser%2A method in Startup.Configure:

[!code-csharp]

Add required services by invoking the xref:Microsoft.Extensions.DependencyInjection.DirectoryBrowserServiceExtensions.AddDirectoryBrowser%2A method from Startup.ConfigureServices:

[!code-csharp]

The preceding code allows directory browsing of the wwwroot/images folder using the URL http://<server_address>/MyImages, with links to each file and folder:

See Considerations on the security risks when enabling browsing.

Note the two UseStaticFiles calls in the following example. The first call enables the serving of static files in the wwwroot folder. The second call enables directory browsing of the wwwroot/images folder using the URL http://<server_address>/MyImages:

[!code-csharp]

Serve a default document

Setting a default home page provides visitors a logical starting point when visiting your site. To serve a default page without the user fully qualifying the URI, call the xref:Microsoft.AspNetCore.Builder.DefaultFilesExtensions.UseDefaultFiles%2A method from Startup.Configure:

[!code-csharp]

[!IMPORTANT] UseDefaultFiles must be called before UseStaticFiles to serve the default file. UseDefaultFiles is a URL rewriter that doesn't actually serve the file. Enable Static File Middleware via UseStaticFiles to serve the file.

With UseDefaultFiles, requests to a folder search for:

• default.htm
• default.html
• index.htm
• index.html

The first file found from the list is served as though the request were the fully qualified URI. The browser URL continues to reflect the URI requested.

The following code changes the default file name to mydefault.html:

[!code-csharp]

UseFileServer

xref:Microsoft.AspNetCore.Builder.FileServerExtensions.UseFileServer* combines the functionality of UseStaticFiles, UseDefaultFiles, and optionally UseDirectoryBrowser.

The following code enables the serving of static files and the default file. Directory browsing isn't enabled.

app.UseFileServer();

The following code builds upon the parameterless overload by enabling directory browsing:

app.UseFileServer(enableDirectoryBrowsing: true);

Consider the following directory hierarchy:

• wwwroot
  • css
  • images
  • js
• MyStaticFiles
  • images
    • banner1.svg
  • default.html

The following code enables static files, default files, and directory browsing of MyStaticFiles:

[!code-csharp]

AddDirectoryBrowser must be called when the EnableDirectoryBrowsing property value is true:

[!code-csharp]

Using the file hierarchy and preceding code, URLs resolve as follows:

URI	Response
http://<server_address>/StaticFiles/images/banner1.svg	MyStaticFiles/images/banner1.svg
http://<server_address>/StaticFiles	MyStaticFiles/default.html

If no default-named file exists in the MyStaticFiles directory, http://<server_address>/StaticFiles returns the directory listing with clickable links:

[!NOTE] xref:Microsoft.AspNetCore.Builder.DefaultFilesExtensions.UseDefaultFiles* and xref:Microsoft.AspNetCore.Builder.DirectoryBrowserExtensions.UseDirectoryBrowser* perform a client-side redirect from http://{SERVER ADDRESS}/StaticFiles (without a trailing slash) to http://{SERVER ADDRESS}/StaticFiles/ (with a trailing slash). Relative URLs within the StaticFiles directory are invalid without a trailing slash.

FileExtensionContentTypeProvider

The xref:Microsoft.AspNetCore.StaticFiles.FileExtensionContentTypeProvider class contains a Mappings property serving as a mapping of file extensions to MIME content types. In the following sample, several file extensions are registered to known MIME types. The .rtf extension is replaced, and .mp4 is removed.

[!code-csharp]

See MIME content types.

For information on using a custom xref:Microsoft.AspNetCore.StaticFiles.FileExtensionContentTypeProvider or to configure other xref:Microsoft.AspNetCore.Builder.StaticFileOptions in Blazor Server apps, see xref:blazor/fundamentals/static-files.

Non-standard content types

Static File Middleware understands almost 400 known file content types. If the user requests a file with an unknown file type, Static File Middleware passes the request to the next middleware in the pipeline. If no middleware handles the request, a 404 Not Found response is returned. If directory browsing is enabled, a link to the file is displayed in a directory listing.

The following code enables serving unknown types and renders the unknown file as an image:

[!code-csharp]

With the preceding code, a request for a file with an unknown content type is returned as an image.

[!WARNING] Enabling xref:Microsoft.AspNetCore.Builder.StaticFileOptions.ServeUnknownFileTypes is a security risk. It's disabled by default, and its use is discouraged. FileExtensionContentTypeProvider provides a safer alternative to serving files with non-standard extensions.

Serve files from multiple locations

UseStaticFiles and UseFileServer defaults to the file provider pointing at wwwroot. You can provide additional instances of UseStaticFiles and UseFileServer with other file providers to serve files from other locations. For more information, see this GitHub issue.

Considerations

[!WARNING] UseDirectoryBrowser and UseStaticFiles can leak secrets. Disabling directory browsing in production is highly recommended. Carefully review which directories are enabled via UseStaticFiles or UseDirectoryBrowser. The entire directory and its sub-directories become publicly accessible. Store files suitable for serving to the public in a dedicated directory, such as <content_root>/wwwroot. Separate these files from MVC views, Razor Pages (2.x only), configuration files, etc.

• The URLs for content exposed with UseDirectoryBrowser and UseStaticFiles are subject to the case sensitivity and character restrictions of the underlying file system. For example, Windows is case insensitive—macOS and Linux aren't.

• ASP.NET Core apps hosted in IIS use the ASP.NET Core Module to forward all requests to the app, including static file requests. The IIS static file handler isn't used. It has no chance to handle requests before they're handled by the module.

• Complete the following steps in IIS Manager to remove the IIS static file handler at the server or website level:

  1. Navigate to the Modules feature.
  2. Select StaticFileModule in the list.
  3. Click Remove in the Actions sidebar.

[!WARNING] If the IIS static file handler is enabled and the ASP.NET Core Module is configured incorrectly, static files are served. This happens, for example, if the web.config file isn't deployed.

• Place code files (including .cs and .cshtml) outside of the app project's web root. A logical separation is therefore created between the app's client-side content and server-based code. This prevents server-side code from being leaked.

Additional resources

• Middleware
• Introduction to ASP.NET Core

::: moniker-end