ASP.NET Core中UriFormatException被异常处理器捕获的解决咨询

问题背景 #

已为ASP.NET Core应用添加全局异常处理逻辑，但爬虫访问不存在的端点时，会触发未处理的UriFormatException（错误信息：Invalid URI: The hostname could not be parsed.），这类异常会污染遥测数据，需要修复或优雅屏蔽，同时忽略针对未定义端点的无效流量。

异常详情 #

记录的异常 #

Unhandled exception | UriString: https:///favicon.ico | Exception: System.UriFormatException: Invalid URI: The hostname could not be parsed.

堆栈跟踪 #

at System.Uri.CreateThis(String uri, Boolean dontEscape, UriKind uriKind, UriCreationOptions& creationOptions)
   at System.Uri..ctor(String uriString)
   at Microsoft.AspNet.OData.Routing.ODataPathRouteConstraint.Match(HttpContext httpContext, IRouter route, String routeKey, RouteValueDictionary values, RouteDirection routeDirection)
   at Microsoft.AspNetCore.Routing.RouteConstraintMatcher.Match(IDictionary`2 constraints, RouteValueDictionary routeValues, HttpContext httpContext, IRouter route, RouteDirection routeDirection, ILogger logger)
   at Microsoft.AspNetCore.Routing.RouteBase.RouteAsync(RouteContext context)
   at Microsoft.AspNetCore.Routing.RouteCollection.RouteAsync(RouteContext context)
   at Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)

现有异常处理器代码 #

app.UseExceptionHandler(exceptionHandlerApp =>
{
    exceptionHandlerApp.Run(async context =>
    {
        context.Response.StatusCode = StatusCodes.Status500InternalServerError;
        IExceptionHandlerPathFeature exceptionHandlerPathFeature = 
        context.Features.Get<IExceptionHandlerPathFeature>();

        string uriString = null;
        uriString = context.Request.GetEncodedUrl();
        
        Logger.EmitLog(
            "Unhandled exception",
            "UriString",
            uriString,
            "Exception",
            exceptionHandlerPathFeature?.Error);
    });
});

解决方案 #

1. 前置拦截无效请求 #

在路由中间件（包括OData路由）之前添加自定义中间件，提前拦截Host为空的无效请求，避免进入后续路由逻辑：

// 放在app.UseRouting()之前
app.Use(async (context, next) =>
{
    // 检查请求Host是否合法（比如爬虫构造的https:///favicon.ico这类无Host的URI）
    if (string.IsNullOrEmpty(context.Request.Host.Host))
    {
        context.Response.StatusCode = StatusCodes.Status400BadRequest;
        await context.Response.WriteAsync("Invalid request URI");
        return;
    }
    await next();
});

2. 在异常处理器中针对性忽略该异常 #

修改现有异常处理逻辑，识别并跳过来自OData路由约束的UriFormatException，避免记录到遥测数据：

app.UseExceptionHandler(exceptionHandlerApp =>
{
    exceptionHandlerApp.Run(async context =>
    {
        var exceptionFeature = context.Features.Get<IExceptionHandlerPathFeature>();
        var exception = exceptionFeature?.Error;

        // 过滤掉OData路由引发的UriFormatException
        if (exception is UriFormatException && 
            exception.StackTrace?.Contains("Microsoft.AspNet.OData.Routing.ODataPathRouteConstraint") == true)
        {
            context.Response.StatusCode = StatusCodes.Status400BadRequest;
            await context.Response.WriteAsync("Invalid request URI");
            return;
        }

        // 处理其他真正的未处理异常
        context.Response.StatusCode = StatusCodes.Status500InternalServerError;
        string uriString = context.Request.GetEncodedUrl();
        
        Logger.EmitLog(
            "Unhandled exception",
            "UriString",
            uriString,
            "Exception",
            exception);
    });
});

3. 配置全局404处理 #

为不存在的端点配置404响应，避免无效请求触发500异常：

// 放在路由中间件之后
app.UseStatusCodePages(async context =>
{
    var response = context.HttpContext.Response;
    if (response.StatusCode == StatusCodes.Status404NotFound)
    {
        await response.WriteAsync("Requested endpoint not found");
    }
});

4. 优化OData路由配置 #

如果应用使用OData，可以调整路由约束，避免对无效URI进行解析：

• 确保OData路由仅针对合法的API前缀（比如/odata）
• 在OData路由注册前添加路径检查，过滤非OData路径的请求

组合建议 #

优先使用前置拦截无效请求+全局404处理的组合，从源头减少无效请求进入后续逻辑；再用异常处理器作为兜底，确保漏网的UriFormatException不会污染遥测数据。

内容的提问来源于stack exchange，提问作者hpatel