UrlTrigger.cs :  » Build-Systems » CruiseControl.NET » ThoughtWorks » CruiseControl » Core » Triggers » C# / CSharp Open Source

namespace ThoughtWorks.CruiseControl.Core.Triggers{
    using System;
    using Exortech.NetReflector;
    using ThoughtWorks.CruiseControl.Core.Util;
    using ThoughtWorks.CruiseControl.Remote;

    /// <summary>
    /// <para>
    /// The Url Trigger is used to trigger a CCNet build when the page at a particular url changes. The Url Trigger will poll the specified url according 
    /// to a configured polling interval to detect if the last modified date of the page has changed since the last integration.
    /// </para>
    /// <para>
    /// This trigger is especially useful in reducing the load on your source control system caused by the polling for modifications performed by an Interval
    /// Trigger. If your source control system supports trigger scripts (such as the use of commitinfo scripts in CVS), you can use create a trigger to touch
    /// the page that is being monitored by CCNet to start a new integration.
    /// </para>
    /// <para type="info">
    /// Like all triggers, the urlTrigger must be enclosed within a triggers element in the appropriate <link>Project Configuration Block</link>.
    /// </para>
    /// </summary>
    /// <title>URL Trigger</title>
    /// <version>1.0</version>
    /// <remarks>
    /// <para type="warning">
    /// There is currently a limitation in this trigger such that it will not persist the url's last modified date when the server restarts. This means
    /// that the trigger will always attempt to start a new integration when the first interval expires after the server starts up.
    /// </para>
    /// <para type="warning">
    /// The UrlTrigger will only work with pages that return a reliable LastModified date HTTP Header, such as static html pages or well-behaved dynamic
    /// pages. Using static html pages is the most reliable way to use this trigger.
    /// </para>
    /// <para>
    /// This trigger has been contributed by Steve Norman.
    /// </para>
    /// </remarks>
    /// <example>
    /// <code title="Minimalist example">
    /// &lt;urlTrigger url="http://server/page.html"  /&gt;
    /// </code>
    /// <code title="Full example">
    /// &lt;urlTrigger url="http://server/page.html" seconds="30" buildCondition="ForceBuild" /&gt;
    /// </code>
    /// </example>
    [ReflectorType("urlTrigger")]
  public class UrlTrigger : IntervalTrigger
  {
    private HttpWrapper httpRequest;
    private DateTime lastModified;
    private Uri uri;

        /// <summary>
        /// Initializes a new instance of the <see cref="UrlTrigger"/> class.
        /// </summary>
    public UrlTrigger() : this(new DateTimeProvider(), new HttpWrapper())
    {}

        /// <summary>
        /// Initializes a new instance of the <see cref="UrlTrigger"/> class.
        /// </summary>
        /// <param name="dtProvider">The dt provider.</param>
        /// <param name="httpWrapper">The HTTP wrapper.</param>
    public UrlTrigger(DateTimeProvider dtProvider, HttpWrapper httpWrapper) : base(dtProvider)
    {
      this.httpRequest = httpWrapper;
    }

        /// <summary>
        /// The url to poll for changes.
        /// </summary>
        /// <version>1.0</version>
        /// <default>n/a</default>
    [ReflectorProperty("url", Required=true)]
    public virtual string Url
    {
      get { return uri.ToString(); }
      set { uri = new Uri(value); }
    }

        /// <summary>
        /// Fires the trigger.
        /// </summary>
        /// <returns>
        /// A new <see cref="IntegrationResult"/> if the trigger has been fired; <c>null</c> otherwise.
        /// </returns>
    public override IntegrationRequest Fire()
    {
      IntegrationRequest request = base.Fire();
      if (request ==  null) return null;

      Log.Debug(string.Format("More than {0} seconds since last integration, checking url.", IntervalSeconds));
      if (HasUrlChanged())
      {
        return new IntegrationRequest(BuildCondition, Name, null);
      }
      
      IncrementNextBuildTime();
      return null;
    }

        /// <summary>
        /// Determines whether the URL has changed.
        /// </summary>
        /// <returns>
        /// <c>true</c> if the URL has changed; otherwise, <c>false</c>.
        /// </returns>
    private bool HasUrlChanged()
    {
      try
      {
        DateTime newModifiedTime = httpRequest.GetLastModifiedTimeFor(uri, lastModified);
        if (newModifiedTime > lastModified)
        {
          lastModified = newModifiedTime;
          return true;
        }
      }
      catch (Exception e)
      {
        Log.Error("Error accessing url: " + uri);
        Log.Error(e);
      }
      return false;
    }
  }
}