Question

Some scenarios to ponder. There is a legacy code which has following implementation Example1 and Example2. If we try to implement MSDN recommendation then the legacy code fails.

Here is a Legacy code example:

Example 1:

void Page_Load() {
  .... some code
  if(condition) {
     /// some condition
  } else {
     RedirectPage(url);
  }

  // another code block
  // some other conditions. 
}
 

Example 2:

a. File1.ascx
void Page_Load() {
  try {
    .. some code
    base.CheckPreference();
    RedirectPage(defaultPage);
  }
  catch(Exception ex) {
    ExceptionHandling.GetErrorMessage(ex);
  }
}
b. BaseClass.cs  // this is the base class 
void CheckPreference() {
  try {
     if(condition) {
        RedirectPage(url1);
     } else if(condition2) {
        RedirectPage(url2);
     } else {
        // update session
     }

  }
  catch(Exception ex) {
     ExceptionHandling.GetErrorMessage(ex);
     throw;
  }
}

void RedirectPage(string url) {
  Response.Redirect(url);
}

One possible way is to add a boolean field in the class e.g endExecution, set the field to true whenever RedirectPage is called.

We have to update RedirectPage code see code snippet below:

// Updated code - MSDN recommendation.
void RedirectPage(url) {
  Response.Redirect(url, false);
  this.Context.ApplicationInstance.CompleteRequest();
  endExecution = true;
}

Please suggest some other better ways to improve the legacy code implementation.

Answer 1

Probably the most unintuitive thing for folks issuing a redirect is that in our minds we’ve already returned from the method what we call Respond.Redirect (or whatever the equivilent is in your language/platform of the day. All we’ve done is call a method.

Bottom line is that you have to stop processing the request to avoid trying to commit to responses for the same request. That would throw an exception on just about any platform I’ve worked with.

ASP.NET MVC improved this with the ActionResponse so that you are returning from the method (and terminating the remainder of request processing) with code that looks like this:

return Redirect(url);

Bottom line is that you need to get in the habit of returning from your event right after you perform your redirect. Any deviation from that habit needs to be documented in the code why. This will help make the application perform the way you expect.

The approach that you’ve taken is perfectly reasonable.