[譯]ASP.NET Core 2.0 本地文件操作 - sanshi－IT工程師數位筆記本

文章出處

問題

如何在ASP.NET Core 2.0中受限地訪問本地目錄和文件信息？

答案

新建一個空項目，修改Startup類，添加訪問本地文件所需的服務：

public void ConfigureServices(IServiceCollection services)
{
	services.AddSingleton<IFileProvider>(
		new PhysicalFileProvider(Directory.GetCurrentDirectory()));
}

創建一個中間件，讀取根目錄下的所有文件，輸出文件名：

public class HelloFileProviderMiddleware
{
	private readonly RequestDelegate _next;
	private readonly IFileProvider _fileProvider;

	public HelloFileProviderMiddleware(RequestDelegate next, IFileProvider fileProvider)
	{
		_next = next;
		_fileProvider = fileProvider;
	}

	public async Task Invoke(HttpContext context)
	{
		var output = new StringBuilder("");
		IDirectoryContents dir = _fileProvider.GetDirectoryContents("");
		foreach (IFileInfo item in dir)
		{
		    output.AppendLine(item.Name);
		}
		await context.Response.WriteAsync(output.ToString());
	}
}

public static class UseHelloFileProviderExtensions
{
	public static IApplicationBuilder UseHelloFileProvider(this IApplicationBuilder app)
	{
		return app.UseMiddleware<HelloFileProviderMiddleware>();
	}
}

運行，此時頁面效果：

當然，我們也可以通過IFileProvider接口讀取單個文件信息：

public class HelloFileProviderMiddleware
{
	private readonly RequestDelegate _next;
	private readonly IFileProvider _fileProvider;

	public HelloFileProviderMiddleware(RequestDelegate next, IFileProvider fileProvider)
	{
		_next = next;
		_fileProvider = fileProvider;
	}

	public async Task Invoke(HttpContext context)
	{
		IFileInfo file = _fileProvider.GetFileInfo("Startup.cs");
		using (var stream = file.CreateReadStream())
		{
		    using (var reader = new StreamReader(stream))
		    {
		        var output = await reader.ReadToEndAsync();
		        await context.Response.WriteAsync(output.ToString());
		    }
		}
	}
}

運行，此時頁面效果：

討論

ASP.NET Core 2.0提供了繼承自接口IFileProvider的PhysicalFileProvider類型，用于受限地訪問本地文件系統，它是對System.IO.File的一個封裝。

我們可以在Startup的Configure()方法內將IFileProvider配置為一個服務，然后通過構造函數注入添加到中間件或者控制器中。這樣可以在一個地方控制文件的訪問路徑（也就是應用程序啟動的時候）。

IFileProvider有兩個重要的方法：

1. GetDirectoryContents：返回IDirectoryContents接口。可用于遍歷某個目錄中的全部文件或目錄。

2. GetFileInfo：返回IFileInfo接口。通過其CreateReadSteam方法可以讀取文件內容。

====start by sanshi=========================

下面通過遞歸來遍歷根目錄下全部文件和目錄，修改中間件代碼：

public class HelloFileProviderMiddleware
{
	private readonly RequestDelegate _next;
	private readonly IFileProvider _fileProvider;

	public HelloFileProviderMiddleware(RequestDelegate next, IFileProvider fileProvider)
	{
		_next = next;
		_fileProvider = fileProvider;
	}

	public async Task Invoke(HttpContext context)
	{
		var output = new StringBuilder("");
		ResolveDirectory(output, "", "");

		await context.Response.WriteAsync(output.ToString());
	}

	private void ResolveDirectory(StringBuilder output, string path, string prefix)
	{
		IDirectoryContents dir = _fileProvider.GetDirectoryContents(path);
		foreach (IFileInfo item in dir)
		{
			if (item.IsDirectory)
			{
				output.AppendLine(prefix + "[" + item.Name + "]");

				ResolveDirectory(output, 
					item.PhysicalPath.Substring(Directory.GetCurrentDirectory().Length), 
					prefix + "    ");
			} else
			{
				output.AppendLine(prefix + item.Name);
			}
		}
	}
}

運行，此時頁面效果：