Netty Packet Handling

[Ablaze]

I was reading through the IExtendedEntityProperties tutorial by coolAlias, and wanted to see the Gui Overlay bit. I reached the packet handling subsection(because properties are handled on server side and and the mana bar drawing thing on the client). There is said the following:

NOTE: 1.7.2 users, please see the section at the top of the post about updating to 1.7.2 - the following packet information is for 1.6.4!!!

 

So I scrolled up, and saw this link - http://www.minecraftforge.net/wiki/Netty_Packet_Handling . I was about to use that, but what worries me is that it is full of screams -

This is a poor example of using Netty. It can cause memory leaks. It doesn't separate handlers from codecs properly. It reimplements functionality existant in FML for months. If you are using this, consider switching to using FMLIndexedMessageToMessageCodec, or better yet, use the simpleimpl Message functionality.

 

DO NOT USE THIS IN NEW CODE OR CONVERSIONS

 

I have never used netty before, nor have I used  packet handlers. Can someone guide me?

 

coolAlias' tutorial - http://www.minecraftforum.net/topic/1952901-172164-eventhandler-and-iextendedentityproperties/

 

Regards, and I welcome myself back,

Ablaze

[Ablaze]

The point is not to use netty at all (or at least don't interact with it directly).

FML comes with a so-called "SimpleNetworkWrapper", you can see an example of it used here: https://github.com/diesieben07/Modjam-4/blob/master/src/main/java/mod/badores/BadOres.java#L150

 

I still don't quite get how this might help in the scenario I picture. This is the link I refer to -

http://www.minecraftforum.net/topic/1952901-172164-eventhandler-and-iextendedentityproperties/

 

Over there, check out post #2 (iExtendedEntityProperties) and check Step 3.3. That is where I stumbled upon.

[jabelar]

The point is that the extended properties is a feature intended to easily save and load extra information about entities (and in CoolAlias' example he uses it for players).  However, saving and loading refers to when you start and stop the game -- it doesn't actually handle syncing the client and the server.  I think you know this since you mention the issue that the client needs to know about it in order to draw the mana bar (in that example).

 

So you need a custom packet from server to client.  Unfortunately the packet handling method on the wiki, which many of us including CoolAlias used, turned out to have some memory leak issue.  Further, Forge has been fixing bugs in their simple network wrapper system, and it seems to be ready to use.  So we're just saying that (a) you need a custom packet system, and (b) gave you some links to examples of the recommended system.

 

It does seem painful at first to set up your first packet system -- you only want to send one int of data and need to have handlers and payload encoders and such.  However, it is worth taking the time to set it up once and then you can (usually) make use of it for many modding purposes thereafter.

[Ablaze]

Thanks a lot for the explanation jabelar

 

It does seem painful at first to set up your first packet system -- you only want to send one int of data and need to have handlers and payload encoders and such.  However, it is worth taking the time to set it up once and then you can (usually) make use of it for many modding purposes thereafter.

 

That isn't what bothers me, you see. The thing is I don't understand how to do it. Once I understand how to do it, I will do it no matter how much effort or how much typing it takes. I just want to understand how to do it. And that is what I'm unable to do.

 

EDIT:  Took a giant trip around the source of Forge and Minecraft and a bunch of other mods. All I want an explanation of is these three methods, and how to use them:

 

fromBytes()

toBytes()

onMessage()

 

Also, how would I use them in the context I provided?

[jabelar]

If you want a modern example (in addition to the one the diesieben07 already referenced) you can look at https://github.com/pahimar/Equivalent-Exchange-3/tree/master/src/main/java/com/pahimar/ee3/network

 

Those are really examples, rather than tutorials because they don't really explain all the concepts.  So you might want to check out my tutorial -- it is my own (not recommended exactly, but works fine) packet system but I wrote it as a tutorial so I explain the concepts.  The concepts are common to every Netty-based packet handling system, so maybe helpful.  Perhaps I put too much information there, but probably worth reading the subsection called "Steps Needed For A Packet Handling System".  Anyway, check it out at: http://jabelarminecraft.blogspot.com/p/packet-handling-for-minecraft-forge-172.html

 

 

[Ablaze]

toBytes encodes the message data into the stream provided (with the write*** methods).

fromBytes reads the message data from the stream (with the read*** methods). The stream will contain the same data you wrote in toBytes.

 

onMessage is called to actually perform the action of the message/packet.

 

If you want a modern example (in addition to the one the diesieben07 already referenced) you can look at https://github.com/pahimar/Equivalent-Exchange-3/tree/master/src/main/java/com/pahimar/ee3/network

 

Those are really examples, rather than tutorials because they don't really explain all the concepts.  So you might want to check out my tutorial -- it is my own (not recommended exactly, but works fine) packet system but I wrote it as a tutorial so I explain the concepts.  The concepts are common to every Netty-based packet handling system, so maybe helpful.  Perhaps I put too much information there, but probably worth reading the subsection called "Steps Needed For A Packet Handling System".  Anyway, check it out at: http://jabelarminecraft.blogspot.com/p/packet-handling-for-minecraft-forge-172.html

 

Okay how do I send a message?

[jabelar]

Okay, here's the concept.  A network sends a byte stream.  They break it up into "chunks" called packets.  At the networking layer the packets have various bytes that delimit them, but Netty take care of that.  What we care about is called the "payload" of the packet.  The payload is just a series of bytes.  We can put whatever we want into them.

 

The Netty system allows us to access this series of bytes through a type called ByteBuf (meaning byte buffer).  There are methods that help convert various data types like boolean, String, int, float into series of bytes.  So it becomes easy to put variable values into the byte buffer and to read them back.

 

What you put into the payload is entirely up to you.  The only important thing is you need to read back the values in the exact order you write them.  Since you may have packets that have different orders of variables in their payloads, most people use the first int value as a packet type identifier (also called the discriminator).

 

So the toBytes() and fromBytes() methods are just creating and reading back the sequence of values from the packet payload (which is a ByteBuf).

 

So let's say you have a variable on server side that represents the mana level of the player.  If you want the client to also be aware of that mana value, you want to send a packet.  To send a packet you need a packet system with a sendToAll() method (because you usually want all the client players to know the value of the mana of all the players) and you will pass a packet (I think usually an FMLProxyPacket or some other class that implements IPacket) to the sendToAll() method.  The packet you pass needs to have the payload you want, so in the packet class you need to create the payload.

 

To create the payload, you simply take the ByteBuf that represents the payload and write the values you want to send.  Again the first int is usually a packet type, so if you want packet type 1 to represent a mana packet you would writeInteger(1) to the ByteBuf.  Then, assuming the mana value is also an int, you would write it to the buffer: writeInteger(mana).  That's it for sending the packet -- you call sendToAll(new ManaPacket()) where the ManaPacket writes the packet type and mana value to the payload.

 

Then on the receiving side (all the clients that will receive the packet) you will get an event when a packet is received and you will handle the event by taking the payload of the packet (which again will be a ByteBuf) and read back the values in same order.  You will first readInteger() and check that the value is 1 (representing mana packet), and then readInteger() and take that value and assign it to mana.  This will sync the client, as the mana value there will now match the server that sent the packet.

 

That's pretty much the idea.  You're writing data to ByteBuf in the order of your choosing and putting those into payload of a packet.  You send the packet, and when it is received you handle the event by reading back the data in the same order.

 

Does that make sense?  The toBytes() and fromBytes() are just the methods for creating and processing the payloads in the packet.

[Ablaze]

Okay, here's the concept.  A network sends a byte stream.  They break it up into "chunks" called packets.  At the networking layer the packets have various bytes that delimit them, but Netty take care of that.  What we care about is called the "payload" of the packet.  The payload is just a series of bytes.  We can put whatever we want into them.

 

The Netty system allows us to access this series of bytes through a type called ByteBuf (meaning byte buffer).  There are methods that help convert various data types like boolean, String, int, float into series of bytes.  So it becomes easy to put variable values into the byte buffer and to read them back.

 

What you put into the payload is entirely up to you.  The only important thing is you need to read back the values in the exact order you write them.  Since you may have packets that have different orders of variables in their payloads, most people use the first int value as a packet type identifier (also called the discriminator).

 

So the toBytes() and fromBytes() methods are just creating and reading back the sequence of values from the packet payload (which is a ByteBuf).

 

So let's say you have a variable on server side that represents the mana level of the player.  If you want the client to also be aware of that mana value, you want to send a packet.  To send a packet you need a packet system with a sendToAll() method (because you usually want all the client players to know the value of the mana of all the players) and you will pass a packet (I think usually an FMLProxyPacket or some other class that implements IPacket) to the sendToAll() method.  The packet you pass needs to have the payload you want, so in the packet class you need to create the payload.

 

To create the payload, you simply take the ByteBuf that represents the payload and write the values you want to send.  Again the first int is usually a packet type, so if you want packet type 1 to represent a mana packet you would writeInteger(1) to the ByteBuf.  Then, assuming the mana value is also an int, you would write it to the buffer: writeInteger(mana).  That's it for sending the packet -- you call sendToAll(new ManaPacket()) where the ManaPacket writes the packet type and mana value to the payload.

 

Then on the receiving side (all the clients that will receive the packet) you will get an event when a packet is received and you will handle the event by taking the payload of the packet (which again will be a ByteBuf) and read back the values in same order.  You will first readInteger() and check that the value is 1 (representing mana packet), and then readInteger() and take that value and assign it to mana.  This will sync the client, as the mana value there will now match the server that sent the packet.

 

That's pretty much the idea.  You're writing data to ByteBuf in the order of your choosing and putting those into payload of a packet.  You send the packet, and when it is received you handle the event by reading back the data in the same order.

 

Does that make sense?  The toBytes() and fromBytes() are just the methods for creating and processing the payloads in the packet.

 

Are you a teacher or a professor or something? You explain very well! Thanks to your explanation I understood even though I'm only 13

 

Just one thing - your approach uses packets, while the one diesieben and pahimar show uses messages. Is there any difference?