# GServer

**Note:** This README is a work in progress 🛠️

A rudimentary TCP/UDP game server mimicking the architecture of Graal Online's GServer from the 90s-00s.

## Projects

The repo is made up of the following projects:
* GServer.Server - the server to be connected to
* GServer.Client - the client that connects to the server
* GServer.Common - a class library used by both of the above projects. Contains shared code.

## Networking

Packets are sent between the client and server to enable communication. Specific packets can carry data specific purposes, referred to as messages. A message has an ID that defines its type/purpose, as well as data related to its purpose.

The first byte of a message is used to denote its type, but no standard format is shared between messages for the data belonging to each message.

For example: when authenticating, the following message is used:

- Message ID (1 byte)
- Username length (1 byte)
- Username (x bytes, according to the username length)
- Password length (1 byte)
- Password (x bytes, according to the password length)

`{message_id}{username_len}{username}{password_len}{password}`

(see *Messages* section for this message and others' ASN.1 definitions)

All possible client and server message IDs can be found in [GServer.Common/Networking/Enums/ClientPacketIn.cs](GServer.Common/Networking/Enums/ClientPacketIn.cs) (for packets processed by the client) or [GServer.Common/Networking/Enums/ServerPacketIn.cs](GServer.Common/Networking/Enums/ServerPacketIn.cs) (for messages processed by the server)

### Messages

The below lists [ASN.1](https://en.wikipedia.org/wiki/ASN.1) definitions for each message exactly as they are intended to be send and received by the game client and server. All C# message definitons can be found in [GServer.Common/Networking/Messages](GServer.Common/Networking/Messages)

**AuthMessage**

```asn.1
AuthMessage ::= SEQUENCE {
    messageId   INTEGER (0..255),
    usernameLen INTEGER (0..255),
    username    OCTET STRING (SIZE (0..usernameLen)),
    passwordLen INTEGER (0..255),
    password    OCTET STRING (SIZE (0..passwordLen))
}
```

**AuthResponseMessage**

```asn.1
AuthResponseMessage ::= SEQUENCE {
    messageId       INTEGER (0..255),
    isSuccessful    INTEGER (0..255),
    TODO implement CHOICE for conditional fields
}
```

**ListServerResponseMessage** (TODO)

```asn.1
ServerListingBlock ::= SEQUENCE {
    name        OCTET STRING (SIZE (50)),
    description OCTET STRING (SIZE (1000)),
    playercount INTEGER (0..65535),
    ip          OCTET STRING (SIZE (15)),
    port        INTEGER (0..65535),
    serverTier  INTEGER (0..255)
}

ServerListing ::= SEQUENCE {
    messageId           INTEGER (0..255),
    serverListingBlocks SEQUENCE OF ServerListingBlock
}
```