从ASP.NET [ScriptService]服务全局记录异常

Question

我正在使用[System.Web.Script.Services.ScriptService]标记来使用可从客户端javascript调用的Web服务.我需要的是一种全局记录这些方法中任何未处理的异常的方法.在客户端,我得到错误回调并可以从那里继续,但我需要一个服务器端catch来记录异常.

这个网址的人:http: //ayende.com/Blog/archive/2008/01/06/ASP.Net-Ajax-Error-Handling-and-WTF.aspx

表明这不可能做到.

那是准确的吗？我是否真的必须在整个系统中使用每一个web方法并尝试/捕获整个方法.

Answer 1

您可以使用HTTP模块捕获Web服务方法引发的异常消息,堆栈跟踪和异常类型.

首先是一些背景......

• 如果Web服务方法抛出异常,则HTTP响应的状态代码为500.

• 如果关闭自定义错误,则Web服务将以JSON的形式将异常消息和堆栈跟踪返回给客户端.例如:
  {"Message":"Exception message","StackTrace":" at WebApplication.HelloService.HelloWorld() in C:\Projects\Stackoverflow Examples\WebApplication\WebApplication\HelloService.asmx.cs:line 22","ExceptionType":"System.ApplicationException"}

• 当启用自定义错误时,Web服务会向客户端返回默认消息,并删除堆栈跟踪和异常类型:
  {"Message":"There was an error processing the request.","StackTrace":"","ExceptionType":""}

所以我们需要做的是为Web服务设置自定义错误并插入一个HTTP模块:

1. 检查请求是否适用于Web服务方法
2. 检查是否抛出异常 - 即返回状态代码500
3. 如果1)和2)为真,则获取将发送到客户端的原始JSON,并将其替换为默认的JSON

下面的代码是执行此操作的HTTP模块的示例:

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Web;

public class ErrorHandlerModule : IHttpModule {

  public void Init(HttpApplication context) {
    context.PostRequestHandlerExecute += OnPostRequestHandlerExecute;
    context.EndRequest += OnEndRequest;
  }

  static void OnPostRequestHandlerExecute(object sender, EventArgs e) {
    HttpApplication context = (HttpApplication) sender;
    // TODO: Update with the correct check for your application
    if (context.Request.Path.StartsWith("/HelloService.asmx") 
        && context.Response.StatusCode == 500) {
      context.Response.Filter = 
        new ErrorHandlerFilter(context.Response.Filter);
      context.EndRequest += OnEndRequest;
    }
  }

  static void OnEndRequest(object sender, EventArgs e) {
    HttpApplication context = (HttpApplication) sender;
    ErrorHandlerFilter errorHandlerFilter = 
      context.Response.Filter as ErrorHandlerFilter;
    if (errorHandlerFilter == null) {
      return;
    }

    string originalContent =
      Encoding.UTF8.GetString(
        errorHandlerFilter.OriginalBytesWritten.ToArray());

    // If customErrors are Off then originalContent will contain JSON with
    // the original exception message, stack trace and exception type.

    // TODO: log the exception
  }

  public void Dispose() { }
}

此模块使用以下过滤器覆盖发送到客户端的内容并存储原始字节(包含异常消息,堆栈跟踪和异常类型):

public class ErrorHandlerFilter : Stream {

  private readonly Stream _responseFilter;

  public List OriginalBytesWritten { get; private set; }

  private const string Content = 
    "{\"Message\":\"There was an error processing the request.\"" +
    ",\"StackTrace\":\"\",\"ExceptionType\":\"\"}";

  public ErrorHandlerFilter(Stream responseFilter) {
    _responseFilter = responseFilter;
    OriginalBytesWritten = new List();
  }

  public override void Flush() {
    byte[] bytes = Encoding.UTF8.GetBytes(Content);
    _responseFilter.Write(bytes, 0, bytes.Length);
    _responseFilter.Flush();
  }

  public override long Seek(long offset, SeekOrigin origin) {
    return _responseFilter.Seek(offset, origin);
  }

  public override void SetLength(long value) {
    _responseFilter.SetLength(value);
  }

  public override int Read(byte[] buffer, int offset, int count) {
    return _responseFilter.Read(buffer, offset, count);
  }

  public override void Write(byte[] buffer, int offset, int count) {
    for (int i = offset; i < offset + count; i++) {
      OriginalBytesWritten.Add(buffer[i]);
    }
  }

  public override bool CanRead {
    get { return _responseFilter.CanRead; }
  }

  public override bool CanSeek {
    get { return _responseFilter.CanSeek; }
  }

  public override bool CanWrite {
    get { return _responseFilter.CanWrite; }
  }

  public override long Length {
    get { return _responseFilter.Length; }
  }

  public override long Position {
    get { return _responseFilter.Position; }
    set { _responseFilter.Position = value; }
  }
}

此方法要求关闭Web服务的自定义错误.您可能希望为应用程序的其余部分保留自定义错误,因此Web服务应放在子目录中.只能使用覆盖父设置的web.config在该目录中关闭自定义错误.