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Okay.

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In this lecture, we're going to expand our knowledge of client to server communication by using remote

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events and remote functions.

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A remote event is an instance in our game that allows the client to communicate to the server, or it

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allows the server to communicate to the client.

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A remote event can have a function called upon it, which is either a fire server or fire client, which

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triggers an event on either the client or the server.

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Any scripts in our game that are listening to those events get executed, and they can also be passed

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information from our client or from the server.

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So I'm going to create a new remote event inside of our replicated storage.

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That way both the client and the server can access it.

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And we're just going to add in here a new remote event.

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And I'm not going to change the name, I'm just going to leave it at Remote Event for now.

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And then I'm going to create a new server script in our server script service, and then a new local

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script inside of the starter player scripts.

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And to demonstrate this client to server communication, we're going to make a reference to our remote

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event by first getting the service that it's stored in, which is replicated storage.

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So I'm going to call this variable replicated Storage.

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And that's equal to game.

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And we're going to get the service replicated storage.

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And then we can copy this and do the exact same thing for our server script.

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And then inside of replicated storage we need to access that remote event.

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So I'll create a variable for it.

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I'll just call it event.

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And that's equal to replicated storage dot remote event.

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And again we can copy this and do the exact same thing on the server.

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And what I want to do on the client is I want to refer to my event, and I want to use a function called

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Fire Server.

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And what this function does is it allows us to trigger the event on the server, which is the on server

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event, and pass any additional information we would like to the server.

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So inside these two parentheses is where we can pass information such as strings, numbers, other instances

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and things like that.

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So for demonstration's sake I'm just going to pass a string that says hello.

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And then on the server script, what we're going to do is we're going to listen to that event.

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So we're going to refer to our remote event and then index it and get the on server event.

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So this event gets fired for our server scripts.

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And then we need to connect a function to this remote event.

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So we're going to connect and create a new lambda function or a function that has no identifier.

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And what gets passed to this function is first off it's going to tell us the player that fired this

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event, it's always going to be the first thing passed to this function.

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We're going to get a player instance.

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And this is the player who triggered the event.

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After the player, we can get all of the other information that gets passed to our function.

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So in this case we were expecting a string.

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So we can just call this parameter here example string.

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And then we can go ahead and print out the result inside of the console.

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And what I'm going to do is I'm going to print out the player's name.

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And then I'm also going to print out whatever they pass to the server.

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In this case that's our example string.

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So now when I go and run the game, we refer to the exact same event, and then we fire to the server

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to trigger the on server event and we pass the information of hello.

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So that means when this event gets triggered this function is going to execute.

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It's going to tell us the player that triggered this event.

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And then it's going to also pass whatever information the client passed to the server.

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In this case that is our string.

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So if we go ahead and play test our game, as you can see we get the name of our account printed out.

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And as you can see we also get the string of hello which we passed from the client to the server.

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Again, we can pass as much information as we'd like here.

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We can pass a bunch of numbers, and then here I'll just make this parameter variadic.

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And then we can just print out all of those variadic results into the console.

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So if I hit run.

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As you can see, we get one, two, three and four, and the only limitations with sending information

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through remote events are going to be tables that have mixed indexes.

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So for example, you can't pass a table to the server that has a mixture of keys and also has a mixture

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of indexes.

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Those won't work.

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And you also can't pass meta tables through remote events.

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So if you had a table with a meta table attached to it, and you try to send that to the client or the

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server, the table itself would be fine, but it would lose the meta table attached to it through that

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transfer from the client to the server or the server to the client.

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So that's just important to note.

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You can't pass meta tables through remote events, and you can't pass mixed tables through remote events.

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Now, another important thing you've got to be careful of is that the client can send whatever information

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they want to the server.

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So if you have any exploiters or hackers in your game, they can try to mess with your remote events

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and cause stuff that you don't want to happen.

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For example, if you ever had a tool in your game that dealt damage to other players and you made the

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mistake of passing the value of how much damage you're supposed to deal to the other player, well,

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if we fire this event and the server took, let's say that damage and then use that damage to apply

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it on another player that can be easily exploited.

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A hacker could fire this event and pass whatever number they'd like here, like a huge number to instantly

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kill the other player.

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So you always have to be mindful of the information that the client is passing to the server.

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You got to make sure that the information is correct, and you also got to make sure that they're not

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manipulating or being malicious with whatever information they're trying to send.

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And you should always script your code in a way where you don't have to pass how much damage to deal

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to another player through remote events that should instead be stored in some kind of property for the

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tool that the server can read without having to get that information from the client.

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Because, again, you never want to trust the information that is coming from the client.

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You always want to verify the information because you never know if it's an exploiter trying to mess

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with your game.

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Now let's go ahead and also demonstrate this working in the other direction.

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So if I would like the server to fire to a particular player, then what we could do is we could refer

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to our event and use a function called fire client, or we could use fire all clients.

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So fire client triggers an event for a particular player, while fire all clients triggers the event

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for every single player that's inside of your game.

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For this particular example, we're going to use fire all clients, and if you were to use the regular

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fire clients, you would have to specify the player that you would like the event to trigger for.

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But for fire all clients, we don't need to.

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And from here we can pass whatever information we would like to our clients.

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In some cases, you might not need to send any information, and in other cases you might want to send

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some information like strings or numbers or whatever the case may be.

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So in this case, I'm just going to send a string to the client and I'm just going to call it howdy.

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And then here on our local script, what we're going to do is we're going to refer to our event, and

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we're going to listen to the on client event and connect a Lambda function to this.

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And then we can get the string that the server is going to pass here.

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So I'll just call this example string.

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And then we can go ahead and print this out into the console.

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Now something you need to note is that since this server script is going to execute immediately when

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we fire this event to our clients, our player may not have loaded the game yet and have and has executed

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this script.

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So that means the server fires this event.

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But we aren't listening to it yet because this script hasn't been executed.

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So to account for that, I'm going to put a delay in here.

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We'll use task Dot wait and we're going to wait 10s before we fire to our player in this particular

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instance.

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So that gives us enough time to load into our game and then connect a function to the on client event

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and listen for when we get that string passed to us.

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So if we go and play test again.

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As you can see, we pass information to the server and then we should wait and we should get information

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passed back to the client.

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Any second now.

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And there we go.

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Our client printed out the string that was on the server, which was howdy.

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So this is how we can use remote events.

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Any time you would like to listen to a remote event on the client, we use the on client event.

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And any time we would like to pass information to the server from the client, we use the fire server

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function.

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And then here on the server, whenever we would like to listen to a remote event, we use the on server

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event.

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And then any time we would like to send information to players in our game, we can use the fire client

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or Fire all clients function.

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Okay, now let's go ahead and take a look at a remote function.

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A remote function is one we use when we would like to grab or receive information from the server.

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When we trigger or invoke a remote function, our script is going to yield until that remote function

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returns information back to us.

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This can be useful in many situations.

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For example, maybe you have a door in your game that needs a special passcode.

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For security reasons, you would not want to store that password on the client, but instead you would

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like to store that password on the server in order to verify that the password the client enters is

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correct.

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We can give the server the password through a remote function, and then the server can verify if that

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password is correct or not, and then it can return back to us information telling us if we got it right

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or not.

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There are many use cases for remote functions, however, one use case you would not want to use is

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having the server invoke a client and wait for that client to send information back to the server.

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This is an unreliable practice, because a player could leave the game right when the server tries to

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invoke the client, which would cause the server to be stuck in an infinite yield because the player

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left the game and won't send any information back to the server.

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So you'll want to use remote functions for clients invoking the server, but you do not want to use

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remote functions in the case of the server invoking a client.

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So we can go ahead and create a new remote function inside of replicated storage.

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So remote function, there we go.

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And then inside of my local script I deleted everything except for our service.

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And again we're going to create a variable called event.

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And this time we're going to refer to our remote function.

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So that's going to be equal to replicated storage dot remote function.

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And what we can do here is we can refer to this event.

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And we have to use a different function for this remote function.

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And this function is called invoke server.

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So this tells the server that we would like to execute the function attached to the on server invoke

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callback.

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And a callback is simply a function that's passed as an argument to another piece of code.

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In this case, you would store a function in a property inside of the remote function, and that function

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is expected to be executed or basically called back to execute whatever functionality we would like.

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In this case, that's retrieving information from the server.

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So we're going to use the invoke server function.

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And let's say we have a password we would like to pass like hello.

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Maybe that's the password.

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And then what we're going to do in our server script is again refer to that event and replicated storage.

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So our replicated storage remote function.

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And this time with our remote function.

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We have a property in there called on Server Invoke.

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And what we have to store on this property is a function that needs to be called.

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So we can auto fill in this property.

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And then we assign this property with a function.

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In this case we're going to create a lambda function here.

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And this lambda function is also going to be passed the player that invoked this remote function.

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And then we get passed any other additional information that the client has passed to us.

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In this case that is our password.

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And inside of here we can go ahead and store the correct password.

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And let's say the correct password is howdy.

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And then we can go ahead and check if the password the player passed to the server matches the correct

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password.

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So what we could do here is we could check if the password the player passed is equal to the correct

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password.

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If it is, then we can return true back to this player to let them know that hey, that was the correct

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password.

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Otherwise we could just return false telling them hey, the password was incorrect.

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So whatever we return from this function gets sent back to our player.

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So that means when we use the invoke server function, what this is going to return is whatever the

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server returns back to us.

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In this case we expect a boolean.

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So we could call this variable result.

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And that's equal to what gets returned from our invoke server function.

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And then we can go ahead and print that result out inside of the console.

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In this case, since our password does not match the word of howdy, we should get false printed here.

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So let's go ahead and see what happens.

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And as you can see, there we go.

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We get false printed into the console because our password was not correct.

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However, let's say we entered in the correct password, which is howdy.

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Then when we go and run our game.

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As you can see, we get true returned back to us, which is the server letting us know, hey, you got

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the password correct?

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Now.

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This remote function also has a property for the client which is on client invoke.

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But again, I don't recommend using this because there shouldn't be ever a circumstance where the server

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would need to invoke the client, and the client has to send information back to the server.

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That's just trouble waiting to happen.

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I don't recommend doing it because a I can't find a use case for ever needing to do that, and b you're

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going to run into problems when, let's say a player leaves your game.

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So don't use on client invoke and don't invoke clients from the server.

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There's no need to do that.

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The main purpose of your remote functions is to get information from the server.

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All righty.

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You should now have a basic idea of client to server communication, and how we can use remote events

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and remote functions in our scripts.

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I will see you in the next lecture.