HttpActionSelectorTracer.cs

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System.Diagnostics.Contracts;
using System.Linq;
using System.Web.Http.Controllers;
using System.Web.Http.Properties;
using System.Web.Http.Services;

namespace System.Web.Http.Tracing.Tracers
{
    /// <summary>
    /// Tracer for <see cref="IHttpActionSelector"/>.
    /// </summary>
    internal class HttpActionSelectorTracer : IHttpActionSelector, IDecorator<IHttpActionSelector>
    {
        private const string SelectActionMethodName = "SelectAction";

        private readonly IHttpActionSelector _innerSelector;
        private readonly ITraceWriter _traceWriter;

        public HttpActionSelectorTracer(IHttpActionSelector innerSelector, ITraceWriter traceWriter)
        {
            Contract.Assert(innerSelector != null);
            Contract.Assert(traceWriter != null);

            _innerSelector = innerSelector;
            _traceWriter = traceWriter;
        }

        public IHttpActionSelector Inner
        {
            get { return _innerSelector; }
        }

        public ILookup<string, HttpActionDescriptor> GetActionMapping(HttpControllerDescriptor controllerDescriptor)
        {
            return _innerSelector.GetActionMapping(controllerDescriptor);
        }

        HttpActionDescriptor IHttpActionSelector.SelectAction(HttpControllerContext controllerContext)
        {
            HttpActionDescriptor actionDescriptor = null;

            _traceWriter.TraceBeginEnd(
                    controllerContext.Request,
                    TraceCategories.ActionCategory,
                    TraceLevel.Info,
                    _innerSelector.GetType().Name,
                    SelectActionMethodName,
                    beginTrace: null,
                    execute: () => { actionDescriptor = _innerSelector.SelectAction(controllerContext); },
                    endTrace: (tr) =>
                    {
                        tr.Message = Error.Format(
                            SRResources.TraceActionSelectedMessage,
                            FormattingUtilities.ActionDescriptorToString(actionDescriptor));
                    },

                    errorTrace: null);

            // Intercept returned HttpActionDescriptor with a tracing version
            if (actionDescriptor != null && !(actionDescriptor is HttpActionDescriptorTracer))
            {
                return new HttpActionDescriptorTracer(controllerContext, actionDescriptor, _traceWriter);
            }

            return actionDescriptor;
        }
    }
}