每个Web请求的StructureMap注入

Question

I have an ASP.NET Web Api 2 REST service with several controllers. Each one of these controllers' constructor has got an ILogger argument which I have to inject with StructureMap. Is it possibile to instantiate an ILogger per request, in order to get client's specific informations - such as the IP address - and thus save the log file to a specific path?

This is the code I'm trying to run in the DefaultRegistry, but HttpContext is always null. Where am I wrong?

For<ILogger>()
    .Use(() => new TextFileLogger(
        HttpContext.Current.Request.UserHostAddress +
        DirectorySeparatorChar + "log.txt"));

Answer 1

I'm not an expert on StructureMap but I understand the problem. The problem you have is that you use runtime data to build up your object graph. And injecting runtime data is an anti-pattern .

The simple solution here is not to use the HttpContext directly in your composition root but to create a provider which you can use to determine the path in the FileLogger . In that case both the FileLogger as this new provider can become singleton, which is far easier to work with and understand.

A provider could be as simple as (c#6 syntax):

public class HttpLogfileProvider : ILogFileProvider
{
     public string PathToLogfile => 
        Path.Combine(HttpContext.Current.Request.UserHostAddress, "log.txt");
}

Your FileLogger can use this provider as follows:

public class FileLogger : ILogger
{
    private readonly ILogFileProvider logFileProvider;
    public FileLogger(ILogFileProvider logFileProvider)
    {
        this.logFileProvider = logFileProvider;
    }

    public void Log(string message)
    {
         using (var writer = new StreamWriter(this.currentLogFile))
         {
              writer.WriteLine(message);
         }
    }

    private string currentLogFile =>
         this.logFileProvider.PathToLogFile;
}

I'm not an structuremap user but I think the registration should be:

For<ILogFileProvider>.Use<HttpLogfileProvider>.Singleton;
For<ILogger>.Use<FileLogger>.Singleton;