Defining a very simple application protocol

Let's assume we are going to implement a remote calculator, initially, with the following six arithmetic operations:

• Sum
• Subtraction
• Multiplication
• Division
• Power
• Square root

In this case, to simplify things, let's define the structure of our request. Of the six operations, five expect two operands, and only one (square root) expects a single operand. Let's define a standard structure:

• Request:
• operand1: number
• operand2: number
• operator: text

An example of a sum operation can be viewed in the following code snippet. In defining the protocol that will be used, we will transmit serialized Java objects. This notation is a textual notation (in this case, the JSON format); however, the communication will be done by sending and receiving serialized Java objects.

Operation 2 + 3 → Request:
{
    "operand1": 2,
    "operand2": 3,
    "operator": "+"
}

Now, as an answer, you might be thinking that just returning a number with the result of the operation is enough, right? However, let's consider some restrictions:

• The division cannot have the second operand with the value of 0
• The square root cannot have the first operand with a negative value
• We will not accept any operator other than those defined (+, -, *, /, ^, and sqrt)

Therefore, if we send data that violates some of these restrictions, our protocol needs to signal that the operation cannot be performed. Also, if we send a symbol other than the supported operators, we have to signal that the operation is not recognized.

So, our answer is as follows:

Response:

• status: text
• value: number

We will now see a table where our protocol handles valid and invalid requests.

{
  "op1": 2,
  "op2": 3,
  "oper": "+"
}

{
  "status":"Ok",
  "value": 5
}

{
  "op1": 3,
  "op2": 0,
  "oper": "/"
}

{
  "status":"Invalid",
  "value": null
}

{
  "op1": 5,
  "op2": 8,
  "oper": "**"
}

{
  "status":"Unsupported",
  "value": null
}

Once we understand this concept, we can translate it into a programming language. But first, we need to understand how to make this communication possible through sockets!