Asp.Net Core 5中直接使用HttpContext时WebMarkupMin压缩异常

场景复现 #

在Asp.Net Core 5项目中使用WebMarkupMin库压缩cshtml文件，同时为了全局便捷使用HttpContext添加了HttpContextHelper工具类。配置完成后出现ArgumentNullException: Value cannot be null. (Parameter 'destination')异常，移除HttpContext相关配置后视图恢复正常显示。

相关代码 #

Startup.cs配置 #

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {

        services.AddWebMarkupMin(
                options =>
                {
                    options.AllowMinificationInDevelopmentEnvironment = true;
                    options.AllowCompressionInDevelopmentEnvironment = true;
                })
            .AddHtmlMinification(
                options =>
                {
                    options.MinificationSettings.RemoveRedundantAttributes = true;
                    options.MinificationSettings.RemoveHttpProtocolFromAttributes = true;
                    options.MinificationSettings.RemoveHttpsProtocolFromAttributes = true;
                    options.MinificationSettings.MinifyInlineJsCode = true;
                    options.MinificationSettings.RemoveHtmlComments = true;
                    options.CssMinifierFactory.CreateMinifier();
                    options.JsMinifierFactory.CreateMinifier();
                })
            .AddHttpCompression();

          services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
          services.AddHttpContextAccessor();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Error");
            app.UseHsts();
        }

        app.UseHttpsRedirection();
        app.UseStaticFiles();
        app.UseWebMarkupMin();
        HttpContextHelper.Configure(app.ApplicationServices.GetRequiredService<IHttpContextAccessor>());
    }
}

HttpContextHelper工具类 #

public class HttpContextHelper
{
    private static IHttpContextAccessor m_httpContextAccessor;

    public static HttpContext Current => m_httpContextAccessor.HttpContext;

    public static string AppBaseUrl => $"{Current.Request.Scheme}://{Current.Request.Host}{Current.Request.PathBase}";

    internal static void Configure(IHttpContextAccessor contextAccessor)
    {
        m_httpContextAccessor = contextAccessor;
    }
}

异常信息 #

ArgumentNullException: Value cannot be null. (Parameter 'destination')

System.IO.StreamHelpers.ValidateCopyToArgs(Stream source, Stream destination, int bufferSize)
System.IO.MemoryStream.CopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken)
System.IO.Stream.CopyToAsync(Stream destination)
WebMarkupMin.AspNetCore5.BodyWrapperStreamBase.InternalFinishAsync()
WebMarkupMin.AspNetCore5.BodyWrapperStreamWithResponseBodyFeature.FinishAsync()
WebMarkupMin.AspNetCore5.WebMarkupMinMiddleware.InvokeCore(HttpContext context, bool useMinification, bool useCompression)
WebMarkupMin.AspNetCore5.WebMarkupMinMiddleware.Invoke(HttpContext context)
Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

解决方案 #

1. 修复IHttpContextAccessor重复注册问题 #

services.AddHttpContextAccessor()内部已经完成了IHttpContextAccessor的单例注册，手动添加的services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>()属于重复注册，会导致上下文访问器实例冲突。删除手动注册代码，仅保留：

services.AddHttpContextAccessor();

2. 调整中间件初始化顺序 #

将HttpContextHelper.Configure的调用移至app.UseWebMarkupMin()之前，确保WebMarkupMin中间件执行时，HttpContextAccessor已经完成初始化：

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Error");
        app.UseHsts();
    }

    app.UseHttpsRedirection();
    app.UseStaticFiles();
    // 先初始化HttpContextHelper
    HttpContextHelper.Configure(app.ApplicationServices.GetRequiredService<IHttpContextAccessor>());
    // 再启用WebMarkupMin
    app.UseWebMarkupMin();
}

3. 为HttpContextHelper添加空值检查 #

在访问HttpContext相关属性时增加空值判断，避免在无上下文场景下抛出异常：

public class HttpContextHelper
{
    private static IHttpContextAccessor m_httpContextAccessor;

    public static HttpContext Current => m_httpContextAccessor?.HttpContext;

    public static string AppBaseUrl 
    { 
        get 
        {
            var context = Current;
            return context == null 
                ? string.Empty 
                : $"{context.Request.Scheme}://{context.Request.Host}{context.Request.PathBase}";
        }
    }

    internal static void Configure(IHttpContextAccessor contextAccessor)
    {
        m_httpContextAccessor = contextAccessor ?? throw new ArgumentNullException(nameof(contextAccessor));
    }
}

4. 移除WebMarkupMin冗余配置代码 #

HtmlMinification配置中的options.CssMinifierFactory.CreateMinifier()和options.JsMinifierFactory.CreateMinifier()属于冗余调用，会提前创建实例但未正确关联，可能导致流处理异常，直接删除这两行代码即可。

完成以上调整后，WebMarkupMin可正常处理响应流，同时HttpContextHelper也能全局正常使用HttpContext。

内容的提问来源于stack exchange，提问作者Mohamad Hasan Salmaaniyaan