Exercise: Math server

In this exercise you must program a simple Math TCP server. The server receives requests like "ADD 4.4 5.5" and send a response with the result ("9.9" in this case).

The structure of the server is very similar to the Echo TCP server. However, the service given by the Math server is slightly more advanced than the service given by the Echo server.

Protocol design

Before you start programming you must define a protocol: A set of rules explaining the structure of requests and responses.

I suggest a single-line request protocol:

• ADD 4.4 5.5
• SUB 6.2 2.1
• etc.

The response could be a simple number.

But you can chose another protocol if you want to, for example a multi-line protocol.

Error handling, etc.: Don't worry about this now ... it comes later in this exercise.

Server program

Make sure you can read and understand the Echo TCP server.

Make a copy of the Visual Studio Project holding the Echo TCP server (do not modify the original project).

With the Math TCP server you must rework the part of the server where it gives service to the client.

1. Read the request // like Echo
2. Split the request into parts
3. Find the operation (ADD, SUB, etc.)
   string.Split(separators) might be useful
4. Find the numbers
   Double.Parse(numberString) might be useful
5. Perform the operation on the numbers
6. Send the response back to the client. // like Echo

Client program

Make a simple client program (preferably Console Application in another Visual Studio solution) to try the Math TCP server.

The client program should be very similar to the Echo TCP client program.

Testing

Use your unit testing framework to test the Math TCP server.

Eventhough this is not exactly unit testing, the unit testing framework is still useful.

The test assumes that the server is running on a known host + port.

The test send a request to the server (very much like the client program) and make assertions about the response.

In the test you can make helper (not TestMethod) method like

• private static String GetResponse(String request) { ... }
  This method must connect to the server, send the request, and get the response.

Error handling: Bad request

The client may send a bad request, i.e. a request not according to the protocol.

Examples:

• add 4.4 5.5
• plop 4.4 5.5
• ADD 4.4 5a5
• DIVIDE 5 0 // division by zero

In any case the server must send back a proper response for example

• ERROR Illegal operation: plop
• ERROR Not a number

You will have to adapt the response part of your protocol AND add more lines to your server.

The response should have the following structure:

• MATH/1.0 200 OK
  9.9
• MATH/1.0 401 Illegal request: add
• MATH/1.0 402 Not a number: 5a5
• MATH/1.0 403 Division by zero

Trying and testing

• Try it from the client application.
• Test it: Add more lines to you test.

Does "Analyze Code Coverage" work? Why not?

Stop the server, Stop() method

Add a method Stop() to the server. The Stop() methods must stop the server.

stackoverflow.com How to gracefully close TcpListener/TcpClient connection?

The test must start and stop the server

Until now the test assumes that the test is running before the test starts

Now you must change so that the test is responsible for starting the server, running the tests, stopping the server.

The unit test annotations [ClassInitialize] and [ClassCleanUp] might be helpful, more information.

Stop the server using a special word

The server should stop running when it receives a special request like STOP, QUIT or ...

Theory: Discuss why this is generally not a good idea (but today we do it anyway, because it is easy ...)