CORS issue when adding log4net config

Question

Context:

I have a simple Web API project with a controller and an action. In the header of each request, I add an authorization token. Everything work as expected. I can request a token based on some credentials, and use it to make HTTP requests successfully.

Problem: When I add the following in the web.config:

<log4net>
<appender name="FileAppender" type="log4net.Appender.FileAppender">
  <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
  <file value="logfile.txt" />
  <appendToFile value="true" />
  <layout type="log4net.Layout.PatternLayout">
    <conversionPattern value="%date: %-5level – %message%newline" />
  </layout>
</appender>
<root>
  <level value="DEBUG" />
  <appender-ref ref="FileAppender" />
</root>
</log4net>

I get the following error:

XMLHttpRequest cannot load http://localhost:4042/token. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access. The response had HTTP status code 500.

If I remove the configuration for log4net everything works as expected.

Note: I do not have any setting in web.config that adds headers in a request.

Startup.cs is the only point in the project were I specify:

app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);

Question: How does the log4net configuration relate to preflight requests? (based on my limited knowledge about the ASP.NET framework I would say it is non-sense). Is there a subtlety that am I missing?

My guess is that the log4net config is causing an exception, which is resulting in a 500 response that does not have the CORS header. Find out what the exception is. — user1620220, May 16 '16 at 13:46
@stuartd, yes it's a copy-paste mistake. I have it in my code. Apologies for that. — Radu Cojocari, May 17 '16 at 05:58

score 1 · Accepted Answer · edited May 16 '16 at 13:38

1

I looked into the webconfig of my project and there is a part from a working web.config

   <configSections> 
         <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" /> 
       </configSections> 
       <log4net> 
         <appender name="FileAppender" type="log4net.Appender.FileAppender"> 
          ...
        </log4net>

Maybe you missed configSection?

edited May 16 '16 at 13:38

aniski

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answered May 16 '16 at 13:08

Thank you. Thant was the problem I had. – Radu Cojocari May 19 '16 at 15:32

score 0 · Answer 2 · answered May 16 '16 at 13:09

use an external setting file for avoiding the problem :

At startup, call:

XmlConfigurator.Configure();

In your Web.config, specify log4net.Config in appSettings:

<add key="log4net.Config" value="Log.config" />

In the Log.config file put your configuration :

<log4net>
<appender name="FileAppender" type="log4net.Appender.FileAppender">
  <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
  <file value="logfile.txt" />
  <appendToFile value="true" />
  <layout type="log4net.Layout.PatternLayout">
    <conversionPattern value="%date: %-5level – %message%newline" />
  </layout>
</appender>
<root>
  <level value="DEBUG" />
  <appender-ref ref="FileAppender" />
</root>
<log4net>

CORS issue when adding log4net config

2 Answers2