如果你調(diào)用了Host.CreateDefaultBuilder方法，那么在該方法中，會通過UseContentRoot方法，將程序當前工作目錄（Directory.GetCurrentDirectory()）設置為項目根目錄。

public?static?IHostBuilder?CreateHostBuilder(string[]?args)?=>
????Host.CreateDefaultBuilder(args)
????????.ConfigureWebHostDefaults(webBuilder?=>
????????{
????????????webBuilder.UseStartup();
????????});

當然，你也可以通過UseWebRoot擴展方法將默認的路徑{Content Root}/wwwroot修改為自定義目錄（不過，你改它干啥捏？）

public?static?IHostBuilder?CreateHostBuilder(string[]?args)?=>
????Host.CreateDefaultBuilder(args)
????????.ConfigureWebHostDefaults(webBuilder?=>
????????{
????????????//?配置靜態(tài)資源的根目錄為?mywwwroot，?默認為?wwwroot
????????????webBuilder.UseWebRoot("mywwwroot");

????????????webBuilder.UseStartup();
????????});

為了方便，后面均使用 wwwroot 來表示W(wǎng)eb根目錄

首先，我們先在 wwwroot 文件夾下創(chuàng)建一個名為 config.json 的文件，內(nèi)容隨便填寫

注意，確保 wwwroot 下的文件的屬性為“如果較新則復制”或“始終復制”。

接著，我們通過UseStaticFiles擴展方法，來注冊靜態(tài)文件中間件StaticFileMiddleware：

public?void?Configure(IApplicationBuilder?app,?IWebHostEnvironment?env)
{
????app.UseStaticFiles();
}

現(xiàn)在，嘗試一下通過 http://localhost:5000/config.json 來獲取 wwwroot/config.json 的文件內(nèi)容吧

如果你的項目中啟用SwaggerUI，那么你會發(fā)現(xiàn)，即使你沒有手動通過調(diào)用UseStaticFiles()添加中間件，你也可以訪問 wwwroot 文件下的文件，這是因為 SwaggerUIMiddleware 中使用了 StaticFileMiddleware

提供Web根目錄之外的文件

上面我們已經(jīng)能夠提供 wwwroot 文件夾內(nèi)的靜態(tài)文件了，那如果我們的文件不在 wwwroot 文件夾內(nèi)，那如何提供呢？

很簡單，我們可以針對StaticFileMiddleware中間件進行一些額外的配置，了解一下配置項：

public?abstract?class?SharedOptionsBase
{
????//?用于自定義靜態(tài)文件的相對請求路徑
????public?PathString?RequestPath?{?get;?set;?}

????//?文件提供程序
????public?IFileProvider?FileProvider?{?get;?set;?}

????//?是否補全路徑末尾斜杠“/”，并重定向
????public?bool?RedirectToAppendTrailingSlash?{?get;?set;?}
}

public?class?StaticFileOptions?:?SharedOptionsBase
{
????//?ContentType提供程序
????public?IContentTypeProvider?ContentTypeProvider?{?get;?set;?}
????
????//?如果?ContentTypeProvider?無法識別文件類型，是否仍作為默認文件類型提供
????public?bool?ServeUnknownFileTypes?{?get;?set;?}
????
????//?當?ServeUnknownFileTypes?=?true?時，若出現(xiàn)無法識別的文件類型，則將該屬性的值作為此文件的類型
????//?當?ServeUnknownFileTypes?=?true?時，必須賦值該屬性，才會生效
????public?string?DefaultContentType?{?get;?set;?}
????
????//?當注冊了HTTP響應壓縮中間件時，是否對文件進行壓縮
????public?HttpsCompressionMode?HttpsCompression?{?get;?set;?}?=?HttpsCompressionMode.Compress;
????
????//?在HTTP響應的?Status?Code?和?Headers?設置完畢之后，Body?寫入之前進行調(diào)用
????//?用于添加或更改?Headers
????public?Action?OnPrepareResponse?{?get;?set;?}
}

假設我們現(xiàn)在有這樣一個文件目錄結構：

• wwwroot

  config.json

• files

  file.json

然后，除了用于提供 wwwroot 靜態(tài)文件的中間件外，我們還要注冊一個用于提供 files 靜態(tài)文件的中間件：

public?void?Configure(IApplicationBuilder?app,?IWebHostEnvironment?env)
{
????//?提供?wwwroot?靜態(tài)文件
????app.UseStaticFiles();

????//?提供?files?靜態(tài)文件
????app.UseStaticFiles(new?StaticFileOptions
????{
????????FileProvider?=?new?PhysicalFileProvider(Path.Combine(env.ContentRootPath,?"files")),
????????//?指定文件的訪問路徑，允許與?FileProvider?中的文件夾不同名
????????//?如果不指定，則可通過?http://localhost:5000/file.json?獲取，
????????//?如果指定，則需要通過?http://localhost:5000/files/file.json?獲取
????????RequestPath?=?"/files",
????????OnPrepareResponse?=?ctx?=>
????????{
????????????//?配置前端緩存?600s（為了后續(xù)示例的良好運行，建議先不要配置該Header）
????????????ctx.Context.Response.Headers.Add(HeaderNames.CacheControl,?"public,max-age=600");
????????}
????});
}

建議將公開訪問的文件放置到 wwwroot 目錄下，而將需要授權訪問的文件放置到其他目錄下（在調(diào)用UseAuthorization之后調(diào)用UseStaticFiles并指定文件目錄）

提供目錄瀏覽

上面，我們可以通過Url訪問某一個文件的內(nèi)容，而通過UseDirectoryBrowser，注冊DirectoryBrowserMiddleware中間件，可以讓我們在瀏覽器中以目錄的形式來訪問文件列表。

另外，DirectoryBrowserMiddleware中間件的可配置項除了SharedOptionsBase中的之外，還有一個Formatter，用于自定義目錄視圖。

public?class?DirectoryBrowserOptions?:?SharedOptionsBase
{
????public?IDirectoryFormatter?Formatter?{?get;?set;?}
}

示例如下：

public?void?ConfigureServices(IServiceCollection?services)
{
????services.AddDirectoryBrowser();
}

public?void?Configure(IApplicationBuilder?app,?IWebHostEnvironment?env)
{
????//?通過?http://localhost:5000，即可訪問?wwwroot?目錄
????app.UseDirectoryBrowser();
????
????//?通過?http://localhost:5000/files，即可訪問?files?目錄
????app.UseDirectoryBrowser(new?DirectoryBrowserOptions
????{
????????//?如果指定了沒有在?UseStaticFiles?中提供的文件目錄，雖然可以瀏覽文件列表，但是無法訪問文件內(nèi)容
????????FileProvider?=?new?PhysicalFileProvider(Path.Combine(env.ContentRootPath,?"files")),
????????//?這里一定要和?StaticFileOptions?中的?RequestPath?一致，否則會無法訪問文件
????????RequestPath?=?"/files"
????});
}

提供默認頁

通過UseDefaultFiles，注冊DefaultFilesMiddleware中間件，允許在訪問靜態(tài)文件、但未提供文件名的情況下（即傳入的是一個目錄的路徑），提供默認頁的展示。

注意：UseDefaultFiles必須在UseStaticFiles之前進行調(diào)用。因為DefaultFilesMiddleware僅僅負責重寫Url，實際上默認頁文件，仍然是通過StaticFilesMiddleware來提供的。

默認情況下，該中間件會按照順序搜索文件目錄下的HTML頁面文件：

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

另外，DefaultFilesMiddleware中間件的可配置項除了SharedOptionsBase中的之外，還有一個DefaultFileNames，是個列表，用于自定義默認頁的文件名，里面的默認值就是上面提到的4個文件名。

public?class?DefaultFilesOptions?:?SharedOptionsBase
{
????public?IList<string>?DefaultFileNames?{?get;?set;?}
}

示例如下：

public?void?Configure(IApplicationBuilder?app,?IWebHostEnvironment?env)
{
????//?會去?wwwroot?尋找?default.htm?、default.html?、index.htm?或?index.html?文件作為默認頁
????app.UseDefaultFiles();

????//?設置?files?目錄的默認頁
????var?defaultFilesOptions?=?new?DefaultFilesOptions();
????defaultFilesOptions.DefaultFileNames.Clear();
????//?指定默認頁名稱
????defaultFilesOptions.DefaultFileNames.Add("index1.html");
????//?指定請求路徑
????defaultFilesOptions.RequestPath?=?"/files";
????//?指定默認頁所在的目錄
????defaultFilesOptions.FileProvider?=?new?PhysicalFileProvider(Path.Combine(env.ContentRootPath,?"files"));

????app.UseDefaultFiles(defaultFilesOptions);
}

UseFileServer

UseFileServer集成了UseStaticFiles、UseDefaultFiles和UseDirectoryBrowser的功能，用起來方便一些，也是我們項目中使用的首選擴展方法。

先看一下FileServerOptions：

public?class?FileServerOptions?:?SharedOptionsBase
{
????public?FileServerOptions()
????????:?base(new?SharedOptions())
????{
????????StaticFileOptions?=?new?StaticFileOptions(SharedOptions);
????????DirectoryBrowserOptions?=?new?DirectoryBrowserOptions(SharedOptions);
????????DefaultFilesOptions?=?new?DefaultFilesOptions(SharedOptions);
????????EnableDefaultFiles?=?true;
????}

????public?StaticFileOptions?StaticFileOptions?{?get;?private?set;?}

????public?DirectoryBrowserOptions?DirectoryBrowserOptions?{?get;?private?set;?}

????public?DefaultFilesOptions?DefaultFilesOptions?{?get;?private?set;?}

????//?默認禁用目錄瀏覽
????public?bool?EnableDirectoryBrowsing?{?get;?set;?}

????//?默認啟用默認頁（在構造函數(shù)中初始化的）
????public?bool?EnableDefaultFiles?{?get;?set;?}
}

可以看到，FileServerOptions包含了StaticFileOptions、DirectoryBrowserOptions和DefaultFilesOptions三個選項，可以針對StaticFileMiddleware、DirectoryBrowserMiddleware和DefaultFilesMiddleware進行自定義配置。另外，其默認啟用了靜態(tài)文件和默認頁，禁用了目錄瀏覽。

下面舉個例子熟悉一下：

假設文件目錄：

• files

• images

  1.jpg

• file.json

• myindex.html

public?void?ConfigureServices(IServiceCollection?services)
{
????//?如果將?EnableDirectoryBrowsing?設為?true，記得注冊服務
????services.AddDirectoryBrowser();
}

public?void?Configure(IApplicationBuilder?app,?IWebHostEnvironment?env)
{???
????//?啟用?StaticFileMiddleware
????//?啟用?DefaultFilesMiddleware
????//?禁用?DirectoryBrowserMiddleware
????//?默認指向?wwwroot
????app.UseFileServer();
????
????//?針對?files?文件夾配置
????var?fileServerOptions?=?new?FileServerOptions
????{
????????FileProvider?=?new?PhysicalFileProvider(Path.Combine(env.ContentRootPath,?"files")),
????????RequestPath?=?"/files",
????????EnableDirectoryBrowsing?=?true
????};
????fileServerOptions.StaticFileOptions.OnPrepareResponse?=?ctx?=>
????{
????????//?配置緩存600s
????????ctx.Context.Response.Headers.Add(HeaderNames.CacheControl,?"public,max-age=600");
????};
????fileServerOptions.DefaultFilesOptions.DefaultFileNames.Clear();
????fileServerOptions.DefaultFilesOptions.DefaultFileNames.Add("myindex.html");
????app.UseFileServer(fileServerOptions);
}

當訪問 http://localhost:5000/files 時，由于在DefaultFilesOptions.DefaultFileNames中添加了文件名myindex.html，所以可以找到默認頁，此時會顯示默認頁的內(nèi)容。

假如我們沒有在DefaultFilesOptions.DefaultFileNames中添加文件名myindex.html，那么便找不到默認頁，但由于啟用了DirectoryBrowsing，所以此時會展示文件列表。

核心配置項

FileProvider

上面我們已經(jīng)見過PhysicalFileProvider了，它僅僅是眾多文件提供程序中的一種。所有的文件提供程序均實現(xiàn)了IFileProvider接口：

public?interface?IFileProvider
{
????//?獲取給定路徑的目錄信息，可枚舉該目錄中的所有文件
????IDirectoryContents?GetDirectoryContents(string?subpath);

????//?獲取給定路徑的文件信息
????IFileInfo?GetFileInfo(string?subpath);

????//?創(chuàng)建指定?filter?的?ChangeToken
????IChangeToken?Watch(string?filter);
}

public?interface?IDirectoryContents?:?IEnumerable<IFileInfo>,?IEnumerable
{
????bool?Exists?{?get;?}
}

public?interface?IFileInfo
{
????bool?Exists?{?get;?}

????bool?IsDirectory?{?get;?}?

????DateTimeOffset?LastModified?{?get;?}

????//?字節(jié)（bytes）長度
????//?如果是目錄或文件不存在，則是?-1
????long?Length?{?get;?}

????//?目錄或文件名，純文件名，不包括路徑
????string?Name?{?get;?}

????//?文件路徑，包含文件名
????//?如果文件無法直接訪問，則返回?null
????string?PhysicalPath?{?get;?}

????//?創(chuàng)建該文件只讀流
????Stream?CreateReadStream();
}

常用的文件提供程序有以下三種：

• PhysicalFileProvider
• ManifestEmbeddedFileProvider
• CompositeFileProvider

glob模式

在介紹這三種文件提供程序之前，先說一下glob模式，即通配符模式。兩個通配符分別是*和**。

• *：匹配當前目錄層級（不包含子目錄）下的任何內(nèi)容、任何文件名或任何文件擴展名，可以通過/、\和.進行分隔。
• **：匹配目錄多層級（包含子目錄）的任何內(nèi)容，用于遞歸匹配多層級目錄的多個文件。

PhysicalFileProvider

PhysicalFileProvider用于提供物理文件系統(tǒng)的訪問。該提供程序需要將文件路徑范圍限定在一個目錄及其子目錄中，不能訪問目錄外部的內(nèi)容。

當實例化該文件提供程序時，需要提供一個絕對的目錄路徑，作為文件目錄的root。

PhysicalFileProvider目錄或文件路徑不支持glob（通配符）模式。

ManifestEmbeddedFileProvider

ManifestEmbeddedFileProvider用于提供嵌入在程序集中的文件的訪問。

可能你對這個嵌入文件比較陌生，沒關系，請按照下面的步驟來：

以下是 .csproj 文件的示例：

<Project?Sdk="Microsoft.NET.Sdk.Web">
??<PropertyGroup>
????<TargetFramework>net5.0TargetFramework>
????<GenerateEmbeddedFilesManifest>trueGenerateEmbeddedFilesManifest>
??PropertyGroup>

??<ItemGroup>
????<PackageReference?Include="Microsoft.Extensions.FileProviders.Embedded"?Version="5.0.11"?/>
??ItemGroup>

??<ItemGroup>
????<EmbeddedResource?Include="files\**"?/>
??ItemGroup>
Project>

現(xiàn)在我們通過ManifestEmbeddedFileProvider來提供嵌入到程序集的 files 目錄下文件的訪問：

public?void?Configure(IApplicationBuilder?app,?IWebHostEnvironment?env)
{
?????var?fileServerOptions?=?new?FileServerOptions();
????fileServerOptions.StaticFileOptions.FileProvider?=?new?ManifestEmbeddedFileProvider(Assembly.GetExecutingAssembly(),?"/files");
????fileServerOptions.StaticFileOptions.RequestPath?=?"/files";

????app.UseFileServer(fileServerOptions);
}

現(xiàn)在，你可以通過 http://localhost:5000/files/file.json 來訪問文件了。

CompositeFileProvider

CompositeFileProvider用于將多種文件提供程序進行集成。

如：

public?void?Configure(IApplicationBuilder?app,?IWebHostEnvironment?env)
{
????var?fileServerOptions?=?new?FileServerOptions();
????var?fileProvider?=?new?CompositeFileProvider(
????????env.WebRootFileProvider,
????????new?ManifestEmbeddedFileProvider(Assembly.GetExecutingAssembly(),?"/files")
????);
????fileServerOptions.StaticFileOptions.FileProvider?=?fileProvider;
????fileServerOptions.StaticFileOptions.RequestPath?=?"/composite";

????app.UseFileServer(fileServerOptions);
}

現(xiàn)在，你可以通過 http://localhost:5000/composite/file.json 來訪問文件了。

ContentTypeProvider

Http請求頭中的Content-Type大家一定很熟悉，ContentTypeProvider就是用來提供文件擴展名和MIME類型映射關系的。

若我們沒有顯示指定ContentTypeProvider，則框架默認使用FileExtensionContentTypeProvider，其實現(xiàn)了接口IContentTypeProvider：

public?interface?IContentTypeProvider
{
????//?嘗試根據(jù)文件路徑，獲取對應的?MIME?類型
????bool?TryGetContentType(string?subpath,?out?string?contentType);
}

public?class?FileExtensionContentTypeProvider?:?IContentTypeProvider
{
????public?FileExtensionContentTypeProvider()
????????:?this(new?Dictionary<string,?string>(StringComparer.OrdinalIgnoreCase)
????????{
????????????//?...此處省略一萬字
????????}
????{
????}

????public?FileExtensionContentTypeProvider(IDictionary<string,?string>?mapping)
????{
????????Mappings?=?mapping;
????}

????public?IDictionary<string,?string>?Mappings?{?get;?private?set;?}

????public?bool?TryGetContentType(string?subpath,?out?string?contentType)
????{
????????string?extension?=?GetExtension(subpath);
????????if?(extension?==?null)
????????{
????????????contentType?=?null;
????????????return?false;
????????}
????????return?Mappings.TryGetValue(extension,?out?contentType);
????}

????private?static?string?GetExtension(string?path)
????{
????????//?沒有使用 Path.GetExtension()?的原因是：當路徑中存在無效字符時，其會拋出異常，而這里不應拋出異常。

????????if?(string.IsNullOrWhiteSpace(path))
????????{
????????????return?null;
????????}

????????int?index?=?path.LastIndexOf('.');
????????if?(index?0)
????????{
????????????return?null;
????????}

????????return?path.Substring(index);
????}
}

在FileExtensionContentTypeProvider的無參構造函數(shù)中，默認添加了380種已知的文件擴展名和MIME類型的映射，存放在Mappings屬性中。你也可以添加自定義的映射，或移除不想要的映射。

核心中間件

StaticFileMiddleware

通過UseStaticFiles擴展方法，可以方便的注冊StaticFileMiddleware中間件：

public?static?class?StaticFileExtensions
{
????public?static?IApplicationBuilder?UseStaticFiles(this?IApplicationBuilder?app)
????{
????????return?app.UseMiddleware();
????}
????
????public?static?IApplicationBuilder?UseStaticFiles(this?IApplicationBuilder?app,?string?requestPath)
????{
????????return?app.UseStaticFiles(new?StaticFileOptions
????????{
????????????RequestPath?=?new?PathString(requestPath)
????????});
????}

????public?static?IApplicationBuilder?UseStaticFiles(this?IApplicationBuilder?app,?StaticFileOptions?options)
????{
????????return?app.UseMiddleware(Options.Create(options));
????}
}

緊接著查看StaticFileMiddleware的Invoke方法：

public?class?StaticFileMiddleware
{
????private?readonly?StaticFileOptions?_options;
????private?readonly?PathString?_matchUrl;
????private?readonly?RequestDelegate?_next;
????private?readonly?ILogger?_logger;
????private?readonly?IFileProvider?_fileProvider;
????private?readonly?IContentTypeProvider?_contentTypeProvider;

????public?StaticFileMiddleware(RequestDelegate?next,?IWebHostEnvironment?hostingEnv,?IOptions?options,?ILoggerFactory?loggerFactory)
????{
????????_next?=?next;
????????_options?=?options.Value;
????????//?若未指定?ContentTypeProvider，則默認使用?FileExtensionContentTypeProvider
????????_contentTypeProvider?=?_options.ContentTypeProvider????new?FileExtensionContentTypeProvider();
????????//?若未指定?FileProvider，則默認使用?hostingEnv.WebRootFileProvider
????????_fileProvider?=?_options.FileProvider????Helpers.ResolveFileProvider(hostingEnv);
????????_matchUrl?=?_options.RequestPath;
????????_logger?=?loggerFactory.CreateLogger();
????}

????public?Task?Invoke(HttpContext?context)
????{
????????//?若已匹配到?Endpoint，則跳過
????????if?(!ValidateNoEndpoint(context))
????????{
????????????_logger.EndpointMatched();
????????}
????????//?若HTTP請求方法不是?Get，也不是?Head，則跳過
????????else?if?(!ValidateMethod(context))
????????{
????????????_logger.RequestMethodNotSupported(context.Request.Method);
????????}
????????//?如果請求路徑不匹配，則跳過
????????else?if?(!ValidatePath(context,?_matchUrl,?out?var?subPath))
????????{
????????????_logger.PathMismatch(subPath);
????????}
????????//?如果?ContentType?不受支持，則跳過
????????else?if?(!LookupContentType(_contentTypeProvider,?_options,?subPath,?out?var?contentType))
????????{
????????????_logger.FileTypeNotSupported(subPath);
????????}
????????else
????????{
????????????//?嘗試提供靜態(tài)文件
????????????return?TryServeStaticFile(context,?contentType,?subPath);
????????}

????????return?_next(context);
????}

????private?static?bool?ValidateNoEndpoint(HttpContext?context)?=>?context.GetEndpoint()?==?null;

????private?static?bool?ValidateMethod(HttpContext?context)?=>?Helpers.IsGetOrHeadMethod(context.Request.Method);

????internal?static?bool?ValidatePath(HttpContext?context,?PathString?matchUrl,?out?PathString?subPath)?=>?Helpers.TryMatchPath(context,?matchUrl,?forDirectory:?false,?out?subPath);

????internal?static?bool?LookupContentType(IContentTypeProvider?contentTypeProvider,?StaticFileOptions?options,?PathString?subPath,?out?string?contentType)
????{
????????//?查看?Provider?中是否支持該?ContentType
????????if?(contentTypeProvider.TryGetContentType(subPath.Value,?out?contentType))
????????{
????????????return?true;
????????}

????????//?如果提供未知文件類型，則將其設置為默認?ContentType
????????if?(options.ServeUnknownFileTypes)
????????{
????????????contentType?=?options.DefaultContentType;
????????????return?true;
????????}

????????return?false;
????}

????private?Task?TryServeStaticFile(HttpContext?context,?string?contentType,?PathString?subPath)
????{
????????var?fileContext?=?new?StaticFileContext(context,?_options,?_logger,?_fileProvider,?contentType,?subPath);

????????//?如果文件不存在，則跳過
????????if?(!fileContext.LookupFileInfo())
????????{
????????????_logger.FileNotFound(fileContext.SubPath);
????????}
????????else
????????{
????????????//?若文件存在，則提供該靜態(tài)文件
????????????return?fileContext.ServeStaticFile(context,?_next);
????????}

????????return?_next(context);
????}
}

DirectoryBrowserMiddleware

通過UseDirectoryBrowser擴展方法，可以方便的注冊DirectoryBrowserMiddleware中間件：

public?static?class?DirectoryBrowserExtensions
{
????public?static?IApplicationBuilder?UseDirectoryBrowser(this?IApplicationBuilder?app)
????{
????????return?app.UseMiddleware();
????}

????public?static?IApplicationBuilder?UseDirectoryBrowser(this?IApplicationBuilder?app,?string?requestPath)
????{
????????return?app.UseDirectoryBrowser(new?DirectoryBrowserOptions
????????{
????????????RequestPath?=?new?PathString(requestPath)
????????});
????}

????public?static?IApplicationBuilder?UseDirectoryBrowser(this?IApplicationBuilder?app,?DirectoryBrowserOptions?options)
????{
????????return?app.UseMiddleware(Options.Create(options));
????}
}

緊接著查看DirectoryBrowserMiddleware的Invoke方法：

public?class?DirectoryBrowserMiddleware
{
????private?readonly?DirectoryBrowserOptions?_options;
????private?readonly?PathString?_matchUrl;
????private?readonly?RequestDelegate?_next;
????private?readonly?IDirectoryFormatter?_formatter;
????private?readonly?IFileProvider?_fileProvider;

????public?DirectoryBrowserMiddleware(RequestDelegate?next,?IWebHostEnvironment?hostingEnv,?IOptions?options)
????????:?this(next,?hostingEnv,?HtmlEncoder.Default,?options)
????{
????}

????public?DirectoryBrowserMiddleware(RequestDelegate?next,?IWebHostEnvironment?hostingEnv,?HtmlEncoder?encoder,?IOptions?options)
????{
????????_next?=?next;
????????_options?=?options.Value;
????????//?若未指定?FileProvider，則默認使用?hostingEnv.WebRootFileProvider
????????_fileProvider?=?_options.FileProvider????Helpers.ResolveFileProvider(hostingEnv);
????????_formatter?=?_options.Formatter????new?HtmlDirectoryFormatter(encoder);
????????_matchUrl?=?_options.RequestPath;
????}

????public?Task?Invoke(HttpContext?context)
????{
????????//?若已匹配到?Endpoint，則跳過
????????//?若HTTP請求方法不是?Get，也不是?Head，則跳過
????????//?如果請求路徑不匹配，則跳過
????????//?若文件目錄不存在，則跳過
????????if?(context.GetEndpoint()?==?null
????????????&&?Helpers.IsGetOrHeadMethod(context.Request.Method)
????????????&&?Helpers.TryMatchPath(context,?_matchUrl,?forDirectory:?true,?subpath:?out?var?subpath)
????????????&&?TryGetDirectoryInfo(subpath,?out?var?contents))
????????{
????????????if?(_options.RedirectToAppendTrailingSlash?&&?!Helpers.PathEndsInSlash(context.Request.Path))
????????????{
????????????????Helpers.RedirectToPathWithSlash(context);
????????????????return?Task.CompletedTask;
????????????}

????????????//?生成文件瀏覽視圖
????????????return?_formatter.GenerateContentAsync(context,?contents);
????????}

????????return?_next(context);
????}

????private?bool?TryGetDirectoryInfo(PathString?subpath,?out?IDirectoryContents?contents)
????{
????????contents?=?_fileProvider.GetDirectoryContents(subpath.Value);
????????return?contents.Exists;
????}
}

DefaultFilesMiddleware

通過UseDefaultFiles擴展方法，可以方便的注冊DefaultFilesMiddleware中間件：

public?static?class?DefaultFilesExtensions
{
????public?static?IApplicationBuilder?UseDefaultFiles(this?IApplicationBuilder?app)
????{
????????return?app.UseMiddleware();
????}

????public?static?IApplicationBuilder?UseDefaultFiles(this?IApplicationBuilder?app,?string?requestPath)
????{
????????return?app.UseDefaultFiles(new?DefaultFilesOptions
????????{
????????????RequestPath?=?new?PathString(requestPath)
????????});
????}

????public?static?IApplicationBuilder?UseDefaultFiles(this?IApplicationBuilder?app,?DefaultFilesOptions?options)
????{
????????return?app.UseMiddleware(Options.Create(options));
????}
}

緊接著查看DefaultFilesMiddleware的Invoke方法：

public?class?DefaultFilesMiddleware
{
????private?readonly?DefaultFilesOptions?_options;
????private?readonly?PathString?_matchUrl;
????private?readonly?RequestDelegate?_next;
????private?readonly?IFileProvider?_fileProvider;

????public?DefaultFilesMiddleware(RequestDelegate?next,?IWebHostEnvironment?hostingEnv,?IOptions?options)
????{
????????_next?=?next;
????????_options?=?options.Value;
????????//?若未指定?FileProvider，則默認使用?hostingEnv.WebRootFileProvider
????????_fileProvider?=?_options.FileProvider????Helpers.ResolveFileProvider(hostingEnv);
????????_matchUrl?=?_options.RequestPath;
????}
????
????public?Task?Invoke(HttpContext?context)
????{
????????//?若已匹配到?Endpoint，則跳過
????????//?若HTTP請求方法不是?Get，也不是?Head，則跳過
????????//?如果請求路徑不匹配，則跳過
????????if?(context.GetEndpoint()?==?null
????????????&&?Helpers.IsGetOrHeadMethod(context.Request.Method)
????????????&&?Helpers.TryMatchPath(context,?_matchUrl,?forDirectory:?true,?subpath:?out?var?subpath))
????????{
????????????var?dirContents?=?_fileProvider.GetDirectoryContents(subpath.Value);
????????????if?(dirContents.Exists)
????????????{
????????????????for?(int?matchIndex?=?0;?matchIndex?????????????????{
????????????????????string?defaultFile?=?_options.DefaultFileNames[matchIndex];
????????????????????var?file?=?_fileProvider.GetFileInfo(subpath.Value?+?defaultFile);
????????????????????
????????????????????//?找到了默認頁
????????????????????if?(file.Exists)
????????????????????{
????????????????????????if?(_options.RedirectToAppendTrailingSlash?&&?!Helpers.PathEndsInSlash(context.Request.Path))
????????????????????????{
????????????????????????????Helpers.RedirectToPathWithSlash(context);
????????????????????????????return?Task.CompletedTask;
????????????????????????}
????????????????????????
????????????????????????//?重寫為默認頁的Url，后續(xù)通過?StaticFileMiddleware?提供該頁面
????????????????????????context.Request.Path?=?new?PathString(Helpers.GetPathValueWithSlash(context.Request.Path)?+?defaultFile);
????????????????????????break;
????????????????????}
????????????????}
????????????}
????????}

????????return?_next(context);
????}
}

FileServer

FileServer并不是某個具體的中間件，它的實現(xiàn)還是依賴了StaticFileMiddleware、DirectoryBrowserMiddleware和DefaultFilesMiddleware這3個中間件。不過，我們可以看一下UseFileServer里的邏輯：

public?static?class?FileServerExtensions
{
????public?static?IApplicationBuilder?UseFileServer(this?IApplicationBuilder?app)
????{
????????return?app.UseFileServer(new?FileServerOptions());
????}

????public?static?IApplicationBuilder?UseFileServer(this?IApplicationBuilder?app,?bool?enableDirectoryBrowsing)
????{
????????return?app.UseFileServer(new?FileServerOptions
????????{
????????????EnableDirectoryBrowsing?=?enableDirectoryBrowsing
????????});
????}

????public?static?IApplicationBuilder?UseFileServer(this?IApplicationBuilder?app,?string?requestPath)
????{
????????return?app.UseFileServer(new?FileServerOptions
????????{
????????????RequestPath?=?new?PathString(requestPath)
????????});
????}

????public?static?IApplicationBuilder?UseFileServer(this?IApplicationBuilder?app,?FileServerOptions?options)
????{
????????//?啟用默認頁
????????if?(options.EnableDefaultFiles)
????????{
????????????app.UseDefaultFiles(options.DefaultFilesOptions);
????????}

????????//?啟用目錄瀏覽
????????if?(options.EnableDirectoryBrowsing)
????????{
????????????app.UseDirectoryBrowser(options.DirectoryBrowserOptions);
????????}

????????return?app.UseStaticFiles(options.StaticFileOptions);
????}
}

FileProvider in IWebHostingEnvironment

在接口IHostingEnvironment中，包含ContentRootFileProvider和WebRootFileProvider兩個文件提供程序。下面我們就看一下他們是如何被初始化的。

internal?class?GenericWebHostBuilder?:?IWebHostBuilder,?ISupportsStartup,?ISupportsUseDefaultServiceProvider
{
????private?WebHostBuilderContext?GetWebHostBuilderContext(HostBuilderContext?context)
????{
????????if?(!context.Properties.TryGetValue(typeof(WebHostBuilderContext),?out?var?contextVal))
????????{
????????????var?options?=?new?WebHostOptions(context.Configuration,?Assembly.GetEntryAssembly()?.GetName().Name);
????????????var?webHostBuilderContext?=?new?WebHostBuilderContext
????????????{
????????????????Configuration?=?context.Configuration,
????????????????HostingEnvironment?=?new?HostingEnvironment(),
????????????};
????????????
????????????//?重點在這里，看這個?Initialize?方法
????????????webHostBuilderContext.HostingEnvironment.Initialize(context.HostingEnvironment.ContentRootPath,?options);
????????????context.Properties[typeof(WebHostBuilderContext)]?=?webHostBuilderContext;
????????????context.Properties[typeof(WebHostOptions)]?=?options;
????????????return?webHostBuilderContext;
????????}

????????var?webHostContext?=?(WebHostBuilderContext)contextVal;
????????webHostContext.Configuration?=?context.Configuration;
????????return?webHostContext;
????}
}

internal?static?class?HostingEnvironmentExtensions
{
????internal?static?void?Initialize(this?IWebHostEnvironment?hostingEnvironment,?string?contentRootPath,?WebHostOptions?options)
????{
????????hostingEnvironment.ApplicationName?=?options.ApplicationName;
????????hostingEnvironment.ContentRootPath?=?contentRootPath;
????????//?初始化?ContentRootFileProvider
????????hostingEnvironment.ContentRootFileProvider?=?new?PhysicalFileProvider(hostingEnvironment.ContentRootPath);

????????var?webRoot?=?options.WebRoot;
????????if?(webRoot?==?null)
????????{
????????????//?如果?/wwwroot?目錄存在，則設置為Web根目錄
????????????var?wwwroot?=?Path.Combine(hostingEnvironment.ContentRootPath,?"wwwroot");
????????????if?(Directory.Exists(wwwroot))
????????????{
????????????????hostingEnvironment.WebRootPath?=?wwwroot;
????????????}
????????}
????????else
????????{
????????????hostingEnvironment.WebRootPath?=?Path.Combine(hostingEnvironment.ContentRootPath,?webRoot);
????????}

????????if?(!string.IsNullOrEmpty(hostingEnvironment.WebRootPath))
????????{
????????????hostingEnvironment.WebRootPath?=?Path.GetFullPath(hostingEnvironment.WebRootPath);
????????????if?(!Directory.Exists(hostingEnvironment.WebRootPath))
????????????{
????????????????Directory.CreateDirectory(hostingEnvironment.WebRootPath);
????????????}
????????????
????????????//?初始化?WebRootFileProvider
????????????hostingEnvironment.WebRootFileProvider?=?new?PhysicalFileProvider(hostingEnvironment.WebRootPath);
????????}
????????else
????????{
????????????hostingEnvironment.WebRootFileProvider?=?new?NullFileProvider();
????????}

????????hostingEnvironment.EnvironmentName?=
????????????options.Environment???
????????????hostingEnvironment.EnvironmentName;
????}
}

注意

• 使用UseDirectoryBrowser和UseStaticFiles提供文件瀏覽和訪問時，URL 受大小寫和基礎文件系統(tǒng)字符的限制。例如，Windows 不區(qū)分大小寫，但 macOS 和 Linux 區(qū)分大小寫。
• 如果使用 IIS 托管應用，那么 IIS 自帶的靜態(tài)文件處理器是不工作的，均是使用 ASP.NET Core Module 進行處理的，包括靜態(tài)文件處理。

小結

• 使用UseFileServer擴展方法提供文件瀏覽和訪問，其集成了UseStaticFiles、UseDirectoryBrowser和UseDefaultFiles三個中間件的功能。
• UseStaticFiles：注冊StaticFilesMiddleware，提供文件訪問
• UseDirectoryBrowser：注冊DirectoryBrowserMiddleware，提供文件目錄瀏覽
• UseDefaultFiles：注冊DefaultFilesMiddleware，當Url未指定訪問的文件名時，提供默認頁。
• 文件提供程序均實現(xiàn)了接口IFileProvider，常用的文件提供程序有以下三種：
• PhysicalFileProvider：提供物理文件系統(tǒng)的訪問
• ManifestEmbeddedFileProvider：提供嵌入在程序集中的文件的訪問
• CompositeFileProvider：用于將多種文件提供程序進行集成。
• 可通過IWebHostingEnvironment獲取ContentRootFileProvider（默認目錄為項目根目錄）和WebRootFileProvider（默認目錄為Web根目錄）。