c# - 使用 PhysicalFile 时如何正确捕获 FileNotFoundException

Question

我在 Controller 方法中有这段代码；

try
{
    return PhysicalFile("c:\temp\my-non-existing-file.txt", "text/plain");
}
catch (FileNotFoundException)
{
    return NotFound();
}

但是，在这种情况下 catch 子句没有运行，而是向浏览器返回一个 500 Internal Server Error。开发人员错误页面处于事件状态，它表明确实抛出了 FileNotFoundException，但调用堆栈显示它来自中间件。

System.IO.FileNotFoundException: Could not find file 'c:\temp\my-non-existing-file.txt'.
File name: 'c:\temp\my-non-existing-file.txt'
   at System.IO.FileInfo.get_Length()
   at Microsoft.AspNetCore.Mvc.Infrastructure.PhysicalFileResultExecutor.GetFileInfo(String path)
   at Microsoft.AspNetCore.Mvc.Infrastructure.PhysicalFileResultExecutor.ExecuteAsync(ActionContext context, PhysicalFileResult result)
   at Microsoft.AspNetCore.Mvc.PhysicalFileResult.ExecuteResultAsync(ActionContext context)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeResultAsync(IActionResult result)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeNextResultFilterAsync[TFilter,TFilterAsync]()
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Rethrow(ResultExecutedContext context)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeResultFilters()
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeNextResourceFilter()
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Rethrow(ResourceExecutedContext context)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeFilterPipelineAsync()
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeAsync()
   at Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.Builder.Extensions.MapWhenMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware.Invoke(HttpContext context)
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at MyApp.Authorization.AuthorizationExtensions.<>c__DisplayClass0_0.<<---->b__1>d.MoveNext() in ---:line 51
--- End of stack trace from previous location where exception was thrown ---
   at MyApp.Authorization.AuthorizationExtensions.<>c__DisplayClass0_0.<<--->b__1>d.MoveNext() in ---:line 51
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Cors.Infrastructure.CorsMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

有人可以解释如何正确处理这种情况并返回 404 Not Found 吗？

更新:添加了完整堆栈(带有一些名称清理)

Answer 1

正如@KirkLarkin 正确指出的那样，文件直到稍后才解析，当响应被假脱机时，这发生在您的操作已经退出之后。因此，您无法在此处捕获该异常。您可能可以使用自定义中间件或异常处理程序来做一些事情，但老实说，为什么不直接执行以下操作:

var filename = "c:\temp\my-non-existing-file.txt";
if (System.IO.File.Exists(filename))
{
    return PhysicalFile(filename, "text/plain");
}
else
{
    return NotFound();
}

主动检查条件总是比依赖捕获异常更好。过度依赖异常处理会降低您的应用性能。