Errors that appear in the WCF client app...

I was setting a new server to host my WCF app and I hit the wall with the following error messages. I spent 2 days in solving this problem. I guess, many people is wondering how to resolve these interesting errors.

• The server has rejected the client credentials.
• The socket connection was aborted. This could be caused by an error processing your message or a receive timeout being exceeded by the remote host, or an underlying network resource issue. Local socket timeout was '00:00:59.9687500'.
• The communication object, System.ServiceModel.ServiceHost, cannot be used for communication because it is in the Faulted state.

I have developed a WCF solution in WinForm which allows you to comment out certain settings in the server and client so that you can reproduce the above mentioned error message.

  https://github.com/lauhw/WcfWinForm

Please beware that if you are running the WCF server and client in the same computer, the above error might not appear until you run them in a separate computer.

In a nutshell:

1. Both server and client config file must have the same settings in the "Binding" record. This includes the "security mode".
2. The "identity" settings must be the same in both server and client config file.
3. In the live environment, make sure you remove the "MEX" endpoint unless you want anyone to be able to query the interface.
4. Don't forget to open the port in the firewall.

In case you are hitting the same error mentioned above, the fastest way to solve this problem is to run the test WCF solution (as mentioned above). Make sure that the test solution works. After that, compare the differences in app.config between the test solution and your solution.

Hope you don't have to spend 2 days to solve the configuration problem. ;)

Security check point

In Windows client, you can develop a static function call SecurityCheckPoint() that gets the user ID and password. This SecurityCheckPoint() method will be very useful whenever you want the user to re-authenticate before any process start OR you want to get the supervisor authentication.

Well, this can be useful for the web application as well but you need to implement it using JavaScript that show a modal dialog and AJAX calls for authentication.

Executing a process periodically in Windows

There are many types of application running in an enterprise. One of it is called the "nightly job" (i.e., the job that runs periodically) which is running on every night. On the other hand, some of the jobs is running hourly, weekly or monthly.

In our experience, the main issue in running a process periodically is that "schedule" itself. Consider this:

• The simplest schedule job - run the job every night.
• Run the job once for every hour, week, month or year.
• Run the job once for every hour, week, month or year between 10AM to 6PM.
• Run the job on every Monday, hourly between 10AM to 6PM.

This is complicated and requires lots of testing if you are creating your scheduler program. Instead, the better way is to utilized the Task Scheduler that comes with Windows. This is what you have paid for.

Below is the screen snapshot of where you can find the Task Scheduler.

Below are a few ways to execute a job/process periodically in Windows:

1. Develop a Windows Service - add a System.Threading.Timer class and execute the callback periodically. With Timer class, it is able to run the process repeated in the same interval. If you want to run the next callback in different timing, you will have to calculate the interval and call Change() which will be complicated (depends on your need). Another problem that might arise is how to include the dependencies (or DLL)? For example, you need to generate daily report in PDF format and email it to the bosses.
2. Develop a program (.EXE) and schedule it in the Windows Task Scheduler - this is simple and clear cut. With this option, it solves the scheduling problem. But, it does not solve the dependencies problem as mentioned above.
3. Develop a web page which execute the process in a different thread and schedule it in the Windows Task scheduler - another requirement for this option is that it requires a small program which will call the URL (using System.Net.HttpWebRequest class) and pass the URL as the command line parameter. This solves the scheduling complexity (which handles by the Windows Task Scheudler) and also the dependencies (where all the business processes/rules are stay in the ASP.NET website). Of course, if the business processes/rules were in the Windows Client EXE, you will have no choice but fall back to strategy #2 as mentioned above.