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{{Navigation for Marauroa Top|Internals}}
<?plugin CreateToc with_toclink||=1 ?>
{{Navigation for Marauroa Developers}}


!!!UDP Packet Format
Last updated: 2003/08/26


Please note: This page explains the low level network communication. You won't need to bother with these implementation details if you want to use Marauroa to write a game. We document the network design anyway for contributors to Marauroa itself. And it is helpful for people porting Marauroa to other programming languages.
The Network design is based on Messages being transmitted using UDP Packets. There are two types of streams, one is Server to Client and another one that is Client to Server.


==Messages==
!!UDP Client to Server communication stream
Marauroa uses messages to communicate between client and server. The messages sent from the client to the server are prefixed with C2S and the ones sent from the server to the client use the prefix S2C.
Each message is self contained in a SINGLE UDP Packet. There is no mechanism for recovery of lost or repeated messages.


Each message is implemented in its own Java class in the package marauroa.common.net.message. You can lookup up the details about every message in the [http://stendhalgame.org/jenkins/job/marauroa_HEAD/javadoc/marauroa/common/net/message/package-summary.html javadoc]. If you want to port Marauroa to another programming language, you will need know how the message are serialized exactly. The easiest way to learn that is to look at the [http://arianne.cvs.sf.net/viewvc/arianne/marauroa/src/marauroa/common/net/message source code] of the readObject() and writeObject() methods.
Each UDP Packet is composed of:
*Protocol version ( 1 byte )
*Type of Message ( 1 byte )
*Client ID ( 4 bytes )
*Rest of Message ( up to 1494 bytes )


There are for different client states of the game: connected, logged in, in game, logged out. Depending on the state different messages are valid:
!!UDP Server to Client communication stream
Each message is contained in one or more UDP Packets, and the UDP Packet format is as follows: %%%1st UDP Packet is composed of:
*Total number of packets (1 byte)
*Position of this message (1 byte)
*Signature of the message (1 byte)
*Protocol version (1 byte)
*Type of Message (1 byte)
*Client ID (4 bytes)
*Rest of Message (up to 1491 bytes)
The following UDP Packets are composed of:
*Total number of packets (1 byte)
*Position of this message (1 byte)
*Signature of the message (1 byte)
*Rest of Message (up to 1497 bytes)
The idea is to send the serialized message inside several UDP Packets and then rebuild the full message on the Client. There is no kind of error recovery, or retransmission.


=== State connected ===
Messages are sent from the Server by simply serializing them. So the message itself contains the protocol version, the type of message and the Client id.


[[Image:messages-connected.png|thumb|Messages used to securely login.]]
Receiving the message is a bit more complex. First we need to determine that we are running a compatible version of the protocol. Once we have agreed that the protocol is compatible we read the type of message and we ask a ~MessageFactory ( "Java Design Patterns" ) to build an object of that type with the coresponding data. Once the message is build we simply store it in a queue of incoming messages waiting to be processed.


The login process is a bit complicated because of security requirements. Don't be scared, just follow it step by step.
<verbatim>
Thread Read
{
receive UDP


Onces the TCP connection is established the clients requests the RSA public key from the server using [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageC2SLoginRequestKey.java C2SLoginRequestKey]. The server checks the protocol version implicitly included in every message. If it is compatible, it replies with a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CLoginSendKey.java S2CLoginSendKey] including the RSA public key. It is composed of two bytes arrays: The first one contains the value of 'n', and the second the value of 'e'.
if(Packet[0]==PROTOCOL_VERSION)
{
push MessageFactory.getMessage(Packet[1])
}
}


The client now computes a nonce (a random number) and sends its hash as byte array to the server in a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageC2SLoginSendPromise.java C2SLoginPromise] message. The server remembers the client nonce and answers with its own nonce in a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CLoginSendNonce.java S2CLoginSendNonce].
Thread Write
{
send UDP
}
</verbatim>


Almost there: The client has now all the information it needs to actually send the [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageC2SLoginSendNonceNameAndPassword.java C2SLoginSendNonceNameAndPassword]: Its nonce, the username and the value rsaCrypt(xor(xor(client nonce, server nonce), password)). The first field is a bytes array containing the client nonce, the second one a string containing the username and the third one a byte array containing the encrypted password. On reception, the server checks that the hash he received at first is the hash of the nonce he just received. It then decodes the password field, and having the value of the client nonce and its nonce, it gets the value of the password.
!!!Message Types
Last updated: 2003/09/11


The [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CLoginNACK.java S2CLoginNACK] message is sent from the server to the client to tell the client that its login request was rejected because the username or password is wrong, the account was banned or the server is full. The included result object will tell which of the cases prevented the login.
To communicate, the Client and Server of Marauroa use a stream of UDP packets. The message system belongs to the marauroa.net package, so refer to code.


If the username/password combination, however, is correct then the Server must send a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CLoginACK.java S2CLoginACK] message to tell the client that the message has been correctly processed. It contains information about the last login, so that the user is able to recognize unauthorized usage of his account. The client state is changed to "logged in" in this case.
We have Client to Server, aka C2S, and Server to Client, aka S2C, messages. Most messages have two versions of themselves: the C2S and S2C versions.
{{br}}


=== State logged in ===
Communication Model
<pre>
Client Server
------ ------
--onConnect:
Send C2S Login If C2S Login is correct
Send S2C Login ACK
else
Send S2C Login NACK
end if


[[Image:messages-loggedin.png|thumb|Selecting a character and transmitting world meta data.]]
Send S2C Character List


The logging in stuff was complicated. But luckily things are getting much easier now. After the login completed successfully the server sends a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CServerInfo.java S2CServerInfo] message. It tells the client about what kind of server is running, and details on how to contact the server administrator (e.g. their email address). The message is composed of a List of strings of the form "attribute=value". In addition this message also contains the list of defined RPClasses.
Send S2C Server Info


Directly afterwards a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CCharacterList.java S2CCharacterList] message is sent from the server to the client. It offers a choice of character to play with. This feature models the behavior of having several characters associated with a single account. Each character name must be unique at server level, and it is assigned when the character is created.
Send Choose Character If character is correct
Send Choose Character ACK
else
Send Choose Character NACK
Finish


Now the client picks one of the offered characters. Games that do not support multiple characters can pick the one that matches the account name. The choice is transmitted to the server using a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageC2SChooseCharacter.java C2SChooseCharacter] message. The name of the character must be one of the names listed in the character list.
--onTimer:
Send Perception ACK Send Perception


The server will check the selected character and reply for a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CChooseCharacterNACK.java S2CChooseCharacterNACK] if the choice was invalid. This implies that the client should send another C2SChooseCharacter message.
--on Game Start:
Send Map Hash Send Map


If the selection, however, was successful, a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CChooseCharacterACK.java ChooseCharacterACK] message is sent and the client state changed to "in game".
--onEvent:
{{br}}
Send Action Send Action ACK


=== State in game ===
--onExit:
Send Logout If Client can logout
Send Logout ACK
else
Send Logout NAC
</pre>


[[Image:messages-game.png|thumb|Messages sent while the game is active.]]
Let's discuss in detail each message type.


==== Regular Messages ====
!!Message C2S Login
The login Message is sent from the Client to the Server to request the right to access to the game. The message is composed of a username and password. The Username is a string that is already registered on Server as the name of a user account, and password is a string that is associated with that account. If the username/password combination is correct then Server must send a Login ACK Message to indicate to the Client that the message has been correctly processed. On the contrary, if the username/password is wrong the Server will send a Login NACK.


The [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CPerception.java S2CPerception] message is a message sent from the server to the client to notify the client about changes to the objects that exist near it. The message is based on the idea explained in the [[RolePlayingDesign#Perceptions|Delta Perception]] document.
!!Message S2C Login ACK
The LoginACK Message is sent from the Server to the Client to indicate that the login process has been completed correctly and that it can proceed to the next step. It has no params.


The message is composed of:
!!Message S2C Login NACK
* A type that can be DELTA or TOTAL
The LoginNACK Message is sent from the Server to the Client to tell the Client that its login message is incorrect because either the username or password is wrong or because Server has decided to reject the login request, e.g. if the Server is full or because the IP is banned.
* A string indicating the name of the zone the perception is related to.
* A time stamp value that will be just one unit bigger than the previous perception
* A List of RPObject that contains added object
* A List of RPObject that contains modified added object attributes
* A List of RPObject that contains modified deleted object attributes
* A List of RPObject that contains deleted object
* A RPObject that describes the things the rest of players don't see about OUR own object.


Read the Delta perception algorithm to understand what it is for.
The message is composed of: Message indicating the resolution.


!!Message S2C Character List
The ~CharacterList Message is sent from the Server to the Client to give the Client a choice of character to play with. This feature models the behavior of having several characters associated with a single account.


The client sends [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageC2SKeepAlive.java C2SKeepAlive] messages regularly. If there has been no keep alive message for some time, the server will timeout the client.
The message is composed of: A List of Character names


Each character name must be unique at Server level, and it is assigned when the character is created.


==== Static Content Transfer ====
!!Message S2C Server Info
The Server Info Message is send from the Server to the Client to tell the Client about what Server is running, and how to inform Server administrator of problems.


Perceptions are about dynamic content. But most games have some static data, too. Like maps, tilesets, sounds. The RPManager keeps track of situation in which the client might need some of this static data. A common case is the movement of the client from one zone to another.
The message is composed of: A List of strings of the type "attribute=value"
!!Message C2S Choose Character
The ~ChooseCharacter Message is sent from the Client to the Server to indicate what character the user wishes to play the game with.


If the RPManager detects such a situation, it will offer the new content to the client using a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CTransferREQ.java S2CTransferREQ] message. The message is composed of an array of [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/TransferContent.java TransferContent] objects containing the name of each resource, its timestamp (or checksum) and if the resource is cacheable or not.
The message is composed of: the name of the character


The clients replies with a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageC2STransferACK.java C2STransferACK] acknowledging the offer. The message is composed of an array of TransferContent objects containing all the name of each resource and a flag indicating ack or not. Note: The C2STransferACK message is always sent, even if all flags indicate that no transfer should take place.
The name of the character must be one of the names listed in the Character List Message or the Server will reply with a Choose Character NACK message. Once the character has been chosen and the acknoledge has been recieved the Client is ready to start the game.


If the clients has acknowledged the need for content to be transfer, the server sends a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CTransfer.java S2CTransfer]. The message contains a again an an array of TransferContent objects. This time, however, the actual data is included as well.
The Server will reply to this message with a Choose Character ACK or a Choose Character NACK message. The Client must have already logged in before receiving this message, if not the Server will send a Choose Character NACK.


==== Actions ====
Once a character is chosen, the only way to choose a new one is by logging out and logging in again.


Actions are commands sent from the client to the server using a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageC2SAction.java C2SAction] message. Example for commands are "move to the right", "look at that object", "attack that rat". It is up to the server to decide whether to execute the action or reject it.
!!Message S2C Choose Character ACK
{{br}}
The Choose Character ACK Message is sent from the Server to the Client to notify the Client that the character has been chosen. The message is composed of: the object.ID of the character


=== Logging Out ===
We need this value to track our own character.


[[Image:messages-logout.png|thumb|The client sends a logout request and the server accepts or denies it.]]
!!Message S2C Choose Character NACK
The Choose Character NACK Message is sent from the Server to the Client to notify the Client that the character has not been chosen. This also implies to the Client that it should send another ~ChooseCharacter Message.


If the player is in some kind of combat it is often desirable to prevent him from saving his live by logging out. Therefore the client sends a logout request to the server and the game server can decide whether to accept or reject it. Of course the user can close the client window or force a disconnect of his Internet connection. But in these cases he will simple stay in a game unattended until the timeout anyway.
It has no params.


The clients indicates that it wants to finish the session by sending a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageC2SLogout.java C2SLogout].
!!Message C2S Logout
The Logout Message is sent from the Client to the Server to indicate that it wants to finish the session. It has no params.


The server can reply with a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CLogoutNACK.java S2CLogoutNACK] to reject the logout request. Or it confirms the request with a [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/MessageS2CLogoutACK.java S2CLogoutACK]. In this case the client state is changed to logged out.
If the Client can logout the Server will send a Logout ACK Message and the Client can safely close the connection, but if the Server sends a Logout NACK Message, the Client should keep playing as disconnecting at that moment will leave its avatar in the game uncontrolled ( idle ).
{{br}}


== Transmitting Messages over TCP ==
!!Message S2C Logout ACK
The idea behind Arianne's network protocol is to use a single TCP stream between the server and the clients. Different kinds of in-game actions create different types of messages that are then interpreted at the opposite side in to meaningful data. TCP takes care of sorting the packets and retransmitting lost ones.
The Logout ACK Message is sent from the Server to the Client to notify the Client that the logout has been accepted.


Each message has a general header:
It has no params.
* Size of message (4 bytes)


* Protocol version (1 byte)
!!Message S2C Logout NACK
* Type of message (1 byte)
The Logout NACK Message is sent from the Server to the Client to tell the Client that the logout has not been accepted, possibly because something related to the RP entity, for example, combat is in progress.
* Client ID (4 bytes)
* Timestamp (4 bytes)


This header is followed by message specific data. Have a look at the [https://sourceforge.net/p/arianne/marauroa/ci/master/tree/src/marauroa/common/net/message/ source code] of the methods readObject() and writeObject() of the message in question.
It has no params.


==Network Manager==
!!Message C2S Action
The Network Manager is our router that sends and receives messages to and from the network. The manager exposes the interfaces that allow:
The Action message is sent from the Client to the Server to notify the Server of the Clients desire to execute an action. The message is simply composed of a single action.
* Reading a message from the network
* Sending a message to the network
* Finalizing the manager


The read operation is a blocking type operation so we have two options, either polling (i.e. continually checking if data is there) or blocking (i.e. only processing when data is actually available, otherwise sleeping).
!!Message S2C Action ACK
The Action ACK is sent from the Server to the Client to identify that the action has been received in the Server. It doesn't acknowledge that the action has been accepted by the RP Manager, it just means that the action successfully arrived at the Server.


We choose blocking because we don't want to waste CPU time polling the network for messages, we just want to sleep until messages are available. Hence we create a Thread to read from the Network, let's call it NetworkManagerRead.
It has 1 param: action_id - is used to identify to which action you referred. In Marauroa you can command several actions per turn.


Writing messages to the network can be simply coded as a method of Network Manager, as write is an operation that is non blocking by nature.
!!Message S2C Perception
The Perception message is a message sent from the Server to the Client to notify the Client about changes to the objects that exist near it. The message is based on the idea explained in Delta perception document.


The NetworkManager opens a Socket from which it will receive all the messages from the network. It will also write all the outbound messages to the network from this same socket. Note: Both write and read use the same Socket.
The message is composed of:
*A type that can be DELTA or TOTAL
*A time stamp value that will be just one unit bigger than the previous perception
*A List of RPObject that contains added object
*A List of RPObject that contains modified added object attributes
*A List of RPObject that contains modified deleted object attributes
*A List of RPObject that contains deleted object
*A RPObject that describe the things the rest of players don't see about OUR own object.


To encapsulate all this we create both the Read and Write methods as inner classes of Network Manager.
Read the Delta perception algorithm to understand what it is for.


<pre>
!!Message C2S Perception ACK
The perception ACK message is sent from the Client to the Server. We use this message to inform the Server that the Client is still there and listening. It has no params.

!!Message C2S Map Hash
(TODO)

!!Message S2C Map
The Map message is a message sent from the Server to the Client to notify the Client about the content of the map where the game play will happen.

The message is composed of: An array of Byte containing all the raw data.

This message is totally game dependent.

!!!Network Manager
Last updated: 2003/09/26

The Network Manager is our router that sends and receives messages to and from the network. The manager exposes the interfaces that allow:
*Reading a message from the network
*Sending a message to the network
*Finalizing the manager
The read operation is a blocking type operation so we have two options, either Polling and Blocking. We choose Blocking because we don't want to waste CPU time Polling the network for messages, we just want to sleep until messages are available. Hence we create a Thread to read from the Network, let's call it Network Manager Read. To write messages to the network so we can safely code it simply as a method of Network Manager as write is an operation that is non blocking by nature.

The Network Manager opens a Socket from which it will receive all the messages from the network, and to where it will write all the messages to the network. Both write and read use the same Socket.

To encapsulate all this we create both the Read and Write methods as inner classes of Network Manager. The only difference between them being that Read extends the Thread class while Write is just a standard class.
<verbatim>
NetworkManager
NetworkManager
{
{
socket
socket
messages
messages
pendingToSendMessages


NetworkManagerRead isa Thread
NetworkManagerRead isa Thread
Line 216: Line 137:
}
}


NetworkManagerWrite
NetworkManagerWrite isa Thread
{
{
build UDP from message
get from pendingToSendMessages
serialize message
send socket
send socket
}
}
}
}
</verbatim>
</pre>
As you can see, messages are stored in a list when they are received, hence access to the list is synchronized.

Now lets get back to the interface as exposed to other objects. The Write method is immediate, just call it with the message to send, making sure that you have correctly filled ~SourceAddress and ClientID, and it will be sent to the Client. It is important to notice that as the transport is based on UDP there are no guarantees that the message is correctly sent. This situation is in the protocol itself. The Read method is blocking, when you call the Read method it either returns a message from the queue or if the queue is empty the thread blocks until one arrives. That is the basic idea of the Network Manager; however, the manager gets a bit more complex as a result of the need to support Server to Client messages that are bigger than one UDP package, the manager just sends the stream of packets once, and doesn't confirm if any of the messages are received. Please refer to UDP Packet Format for more info about it.


!!! Game Manager
Last updated: 2003/09/26

The idea behind the Game Manager is to handle all the "business logic". This Manager decides how to reply to each individual message.

The logic is something like this:
<verbatim>
GameManager
{
NetworkManager read Message

switch(Message type)
{
case ...;
}
}
</verbatim>

So let's define the reply to each message. Before explaining how to process eahc message, let's clarify that the best way of modelling this system is using finite automates, (finite state machine) where, based on the input, we change the state we are currently in and produce an output.
<verbatim>
Process C2S Login ( STATE_BEGIN_LOGIN )
Precondition: The state MUST be NULL

Test if there is room for more players.
if there is no more room
{
reply S2C Login NACK( SERVER_FULL )
state = NULL
}

if check username, password in database is correct
{
create clientid
add PlayerEntry
notify database

reply S2C Login ACK

get characters list of the player
reply S2C CharacterList

state = STATE_LOGIN_COMPLETE
}
else
{
notify database

reply S2C Login NACK( LOGIN_INCORRECT )
state = NULL
}

Postcondition: The state MUST be NULL or STATE_LOGIN_COMPLETE
and a we have created a PlayerEntry for this player with an unique correct clientid.


Process C2S ChooseCharacter ( STATE_LOGIN_COMPLETE )
Precondition: The state MUST be STATE_LOGIN_COMPLETE

if character exists in database
{
add character to Player's PlayerEntry
add character to game
reply S2C Choose Character ACK

state = STATE_GAME_BEGIN
}
else
{
reply S2C Choose Character NACK
state = STATE_LOGIN_COMPLETE
}

Postcondition: The state MUST be STATE_GAME_BEGIN and the PlayerStructure
should be completely filled or if the character choise was wrong the state is STATE_LOGIN_COMPLETE


Process C2S Logout ( STATE_GAME_END )
Precondition: The state can be anything but STATE_LOGIN_BEGIN

if( rpEngine allows player to logout )
{
reply S2C Logout ACK
state = NULL

store character in database
remove character from game
delete PlayerEntry
}
else
{
reply S2C Logout NACK
}

Postcondition: Either the same as the input state or the state currently in

Process C2S Perception ACK
Precondition: The state must be STATE_LOGIN_BEGIN

notify that the player received the perception.

Postcondition: The state is STATE_LOGIN_BEGIN and Timestamp field in
PlayerContainer is updated.
</verbatim>

!!!Versioning and port numbering
Last updated: 2004/05/24


As you can see, messages are stored in a list when they are received. Hence access to the list must be synchronized.
A problem arises when we need to have two versions of Marauroa on the same machine. This happens for example when you run a release version and a development version on the same machine.


Now lets get back to the interface as exposed to other objects. The write method is immediate, just call it with the message to send, making sure that you have correctly filled SourceAddress and ClientID. The message will then be sent to the Client.
So to avoid port collisions we will use different ports for each release. The release version will run on the standard game port bu the development version will run on the (standard game port)*10


The read method is blocking, when you call the read method it either returns a message from the queue or if the queue is empty the thread blocks (sleeps) until one arrives.
For example:
release version of gladiators runs at 3214
development version runs at 32140


That is the basic idea of the Network Manager. Note that the manager just sends the stream of packets once and doesn't confirm if any of the messages are received. TCP takes care of that.
To allow different servers of Marauroa to run on the same machine running different games we will assign an unique port number to each game.


gladiators runs at 3214
mapacman runs at 3215


[[Category:Marauroa]]
Feel free to follow or disgregard these port rules if you wish. They may not apply to you.
{{#breadcrumbs: [[Marauroa]] | [[Navigation for Marauroa Developers|Internals]] | [[NetworkDesign|Network Design]] }}
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