How to check the data in websocket? - html

Question

Am now using websocket in HTML5 to build my web app.
Because my previous work was based on TCP and I used CRC16 algorithm to wrap the content that will transfer to server side;
Construct message with CRC16 code below:
public static byte[] ConstructMessageWithCRC(string message)
{
//Message with a |
var messageToConstruct = message + "|";
//calculate CRC value
var crcCode = CRC16.CalculateCrc16(messageToConstruct);
var crcCodeShort = ushort.Parse(crcCode);
//CRC high value
var crcHigh = byte.Parse((crcCodeShort / 256).ToString());
//CRC low value
var crcLow = byte.Parse((crcCodeShort % 256).ToString());
var messageBytes = Encoding.Default.GetBytes(messageToConstruct);
var messageLength = messageBytes.Length;
var messageBytesWithCRC = new byte[messageLength + 2];
Array.Copy(messageBytes, 0, messageBytesWithCRC, 0, messageLength);
//append crc value to the message
messageBytesWithCRC[messageLength] = crcHigh;
messageBytesWithCRC[messageLength + 1] = crcLow;
return messageBytesWithCRC;
}
After server side received the data, it will calculate the content via CRC16 algorithm also to ensure that the data is correct.
Check CRC code below:
public static bool CheckMessageCRC(byte[] message, out string messageReceived)
{
//message length that received
var messageLength = message.Length;
//message received without crc value
var messageReceivedStrBytes = new byte[messageLength - 2];
Array.Copy(message, 0, messageReceivedStrBytes, 0, messageLength - 2);
//crc value received
var messageReceivedCrcBytes = new byte[2];
Array.Copy(message, messageLength - 2, messageReceivedCrcBytes, 0, 2);
//get the received message with correct decoding
var messageCalculatedString = Encoding.Default.GetString(messageReceivedStrBytes);
messageReceived = messageCalculatedString;
//get the received crc value
var currentCRC = byte.Parse(messageReceivedCrcBytes[0].ToString()) * 256 + byte.Parse(messageReceivedCrcBytes[1].ToString());
//crc value recalculate
var result = ushort.Parse(CRC16.CalculateCrc16(messageCalculatedString));
//comparison
if (currentCRC == result)
return true;
return false;
}
From above code, you can see what I did.
But in some articles that using websocket: Working with Websockets, it will use below code to handle the message directly:
//When the server is sending data to this socket, this method is called
ws.onmessage = function (evt) {
//Received data is a string; We parse it to a JSON object using jQuery
//http://api.jquery.com/jQuery.parseJSON/
var jsonObject = $.parseJSON(evt.data);
//Do something with the JSON object
};
//Creates an object that will be sent to the server
var myObject = {
Property: "Value",
AnotherProperty: "AnotherValue"
};
//We need to stringify it through JSON before sending it to the server
ws.send(JSON.stringify(myJsonObject));
It will directly send the data out without any check mechanism with the data. So if the data is intercepted by others and we won't know the data has been changed. Also, because of poor network, the data will arrival out of order, then below code won't work correctly, maybe we wanted data as ABC, but we got BCA:
var jsonObject = $.parseJSON(evt.data);
So for evt.data, just wonder how should we check the data transfer complete, data order correct, data content correct and so on.
I have googled a lot and didn't see any info regarding this, just want use this question to declare the right way to transfer data via websocket, thx.
EDIT:
My friend send me this: https://www.rfc-editor.org/rfc/rfc6455, in section 5.2
I think the protocol seems do this work already. Need more of your discusses on it. thx