c# - Web API audit logging

Question

I need to audit log calls to my Web API, ideally I'd like to use an Attribute, something like:

    [HttpPost, Auditing]
    public dynamic MyAPICall()

The Attribute should be able to intercept the API call before and after execution in order to log the parameters and also, how long the API call took to run.

With MVC I could create an ActionFilterAttribute derivative and override OnActionExecuted and OnActionExecuting.

Is the equivalent possible in the Web API world?

Answer 1

Http message handler should be a good extensible point for such purposes. Be careful though, there can be some issues with concurrent request content reading. For instance, Model Binder may try to read request content while LoggingHandler is reading it and fail to deserialize a model. To prevent such issues just add Wait call to the LogRequestLoggingInfo method.

public class LoggingHandler : DelegatingHandler
{
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // Log the request information
        LogRequestLoggingInfo(request);

        // Execute the request
        return base.SendAsync(request, cancellationToken).ContinueWith(task =>
        {
            var response = task.Result;
            // Extract the response logging info then persist the information
            LogResponseLoggingInfo(response);
            return response;
        });
    }

    private void LogRequestLoggingInfo(HttpRequestMessage request)
    {
        if (request.Content != null)
        {
            request.Content.ReadAsByteArrayAsync()
                .ContinueWith(task =>
                    {
                        var result = Encoding.UTF8.GetString(task.Result);
                        // Log it somewhere
                    }).Wait(); // !!! Here is the fix !!!
        }
    }

    private void LogResponseLoggingInfo(HttpResponseMessage response)
    {
        if (response.Content != null)
        {
            response.Content.ReadAsByteArrayAsync()
                .ContinueWith(task =>
                {
                    var responseMsg = Encoding.UTF8.GetString(task.Result);
                    // Log it somewhere
                });
        }
    }
}

You can read more about it here.