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C# - ASP.NET Core 웹 응용 프로그램의 출력 가로채기

지난 글에서 다룬 ASP.NET 웹 응용 프로그램에 대한 가로채기 방식은,

C# - ASP.NET 웹 응용 프로그램의 출력 가로채기
; https://www.sysnet.pe.kr/2/0/12140

ASP.NET Core에서는 구조 자체가 바뀌기 때문에 적용할 수 없습니다. 단지, FilterStream 클래스는 거의 그대로 재사용할 수 있는데 대신 다음과 같이 WriteAsync를 하나 더 추가해야 합니다.

public override void Write(byte[] buffer, int offset, int count)
{
    _orginalStream.Write(buffer, offset, count);
}

public override async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
{
    await _orginalStream.WriteAsync(buffer, offset, count, cancellationToken);
}

마찬가지로 다음과 같은 식으로 구현하면 HTTP 출력의 chunk마다,

public override async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
{
    await _orginalStream.WriteAsync(buffer, offset, count, cancellationToken);

    byte[] buf = _encoding.GetBytes("TEST");
    await _orginalStream.WriteAsync(buf, 0, buf.Length, cancellationToken);
}

마지막에 "TEST" 문자열을 덧붙이게 됩니다. 또한, 이렇게 만든 Stream 타입을 기존 출력에 연결하려면 이것을 담당하는 middleware 타입을 하나 만들고,

public class HttpResponseFilter
{
    Microsoft.AspNetCore.Http.RequestDelegate _next;
    public HttpResponseFilter(Microsoft.AspNetCore.Http.RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(Microsoft.AspNetCore.Http.HttpContext context)
    {
        context.Response.Body = new FilterStream(context.Response.Body, Encoding.UTF8);
        await _next.Invoke(context);
    }
}

ASP.NET Core에 연결해 주면 됩니다. (또는 그냥 Middleware 없이 Use 확장 메서드를 이용해 단순 익명 함수로 연결해도 됩니다.)

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Error");
        // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
        app.UseHsts();
    }

    app.UseMiddleware<HttpResponseFilter>();

    app.UseHttpsRedirection();
    app.UseStaticFiles();

    app.UseRouting();

    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapRazorPages();
    });
}

이후 다음과 같은 식의 razor 페이지가 실행될 때마다,

@page
@model IndexModel
@{
    ViewData["Title"] = "Home page";
}

<div class="text-center">
    <h1 class="display-4">Welcome</h1>
    <p>Learn about <a href="https://docs.microsoft.com/aspnet/core">building Web apps with ASP.NET Core</a>.</p>
</div>

출력 결과는 "TEST" 문자열이 추가되는 방식으로 동작합니다.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Home page - WebApplication1</title>
    <link rel="stylesheet" href="/lib/bootstrap/dist/css/bootstrap.min.css" />
    <link rel="stylesheet" href="/css/site.css" />
</head>
<body>
    <header>
        <nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">
            <div class="container">
                <a class="navbar-brand" href="/">WebApplication1</a>
                <button class="navbar-toggler" type="button" data-toggle="collapse" data-target=".navbar-collapse" aria-controls="navbarSupportedContent"
                        aria-expanded="false" aria-label="Toggle navigation">
                    <span class="navbar-toggler-icon"></span>
                </button>
                <div class="navbar-collapse collapse d-sm-inline-flex flex-sm-row-reverse">
                    <ul class="navbar-nav flex-grow-1">
                        <li class="nav-item">
                            <a class="nav-link text-dark" href="/">Home</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link text-dark" href="/Privacy">Privacy</a>
                        </li>
                    </ul>
                </div>
            </div>
        </nav>
    </header>
    <div class="container">
        <main role="main" class="pb-3">
            
<div class="text-center">
    <h1 class="display-4">Welcome</h1>
    <p>Learn about <a href="https://docs.microsoft.com/aspnet/core">building Web apps with ASP.NET Core</a>.</p>
</div>

        </main>
    </div>

    <footer class="border-top footer text-muted">
        <div class="container">
            &copy; 2020 - WebApplication1 - <a href="/Privacy">Privacy</a>
        </div>
    </footer>

    <script src="/lib/jquery/dist/jquery.min.js"></script>
    <script src="/lib/bootstrap/dist/js/bootstrap.bundle.min.js"></script>
    <script src="/js/site.js?v=dLGP40S79Xnx6GqUthRF6NWvjvhQ1nOvdVSwaNcgG18"></script>

    
</body>
</html>
TEST

결국 실제 가로채기를 담당하는 FilterStream 타입의 구현은 변함이 없지만, 한 가지 아쉬운 점이 있다면 "Response.Encoding" 타입을 ASP.NET Core의 Middleware 수준에서는 알 수 없다는 점입니다. 이로 인해 가로채기한 출력 결과물의 byte []를 어떤 유형의 디코딩 방식을 적용해야 하는지 알 수 없는 문제가 있습니다. (현실적으로 대개의 경우 Encoding.UTF8이겠지만!)

(첨부 파일은 이 글의 예제 코드를 포함합니다.)




참고로, ASP.NET Core의 Stream을 대체한 타입이 WriteAsync 메서드를 구현하지 않으면,

public override void Write(byte[] buffer, int offset, int count)
{
    _orginalStream.Write(buffer, offset, count);
}

//public override async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
//{
//    await _orginalStream.WriteAsync(buffer, offset, count, cancellationToken);
//}

Write 동기 메서드가 실행이 되긴 합니다. 하지만 _orginalStream.Write 시점에 다음과 같은 식의 예외가 발생하는 것을 볼 수 있습니다.

Exception thrown: 'System.InvalidOperationException' in Microsoft.AspNetCore.Server.IIS.dll
Exception thrown: 'System.InvalidOperationException' in System.Private.CoreLib.dll
Exception thrown: 'System.InvalidOperationException' in System.Private.CoreLib.dll
Exception thrown: 'System.InvalidOperationException' in System.Private.CoreLib.dll
Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware: Error: An exception was thrown attempting to display the error page.

System.InvalidOperationException: Synchronous operations are disallowed. Call WriteAsync or set AllowSynchronousIO to true instead.
   at Microsoft.AspNetCore.Server.IIS.Core.HttpResponseStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at Microsoft.AspNetCore.Server.IIS.Core.WrappingStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at WebApplication1.FilterStream.Write(Byte[] buffer, Int32 offset, Int32 count) in C:\WebApplication1\WebApplication1\FilterStream.cs:line 55
   at System.IO.Stream.<>c.<BeginWriteInternal>b__51_0(Object <p0>)
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.<>c.<.cctor>b__274_0(Object obj)
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.Extensions.RazorViews.BaseView.ExecuteAsync(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
Exception thrown: 'System.InvalidOperationException' in System.Private.CoreLib.dll
Exception thrown: 'System.InvalidOperationException' in System.Private.CoreLib.dll
Microsoft.AspNetCore.Server.IIS.Core.IISHttpServer: Error: Connection ID "18230571301796315140", Request ID "80000005-0002-fd00-b63f-84710c7967bb": An unhandled exception was thrown by the application.

System.InvalidOperationException: Synchronous operations are disallowed. Call WriteAsync or set AllowSynchronousIO to true instead.
   at Microsoft.AspNetCore.Server.IIS.Core.HttpResponseStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at Microsoft.AspNetCore.Server.IIS.Core.WrappingStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at WebApplication1.FilterStream.Write(Byte[] buffer, Int32 offset, Int32 count) in C:\WebApplication1\WebApplication1\FilterStream.cs:line 55
   at System.IO.Stream.<>c.<BeginWriteInternal>b__51_0(Object <p0>)
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.<>c.<.cctor>b__274_0(Object obj)
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.WebUtilities.HttpResponseStreamWriter.FlushInternalAsync(Boolean flushEncoder)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeResultAsync>g__Logged|21_0(ResourceInvoker invoker, IActionResult result)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeResultFilters>g__Awaited|27_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at WebApplication1.HttpResponseFilter.Invoke(HttpContext context) in C:\WebApplication1\WebApplication1\HttpResponseFilter.cs:line 20
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Server.IIS.Core.IISHttpContextOfT`1.ProcessRequestAsync()




[이 글에 대해서 여러분들과 의견을 공유하고 싶습니다. 틀리거나 미흡한 부분 또는 의문 사항이 있으시면 언제든 댓글 남겨주십시오.]





[최초 등록일: ]
[최종 수정일: 2/10/2020 ]

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by SeongTae Jeong, mailto:techsharer@outlook.com

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