Daikombat Server

Daikombat Server is the server code repository for a simple Doom-like online shooter game with a non-stop death-match mode. It is built using Maven, Netty, Spring, and Java 14. Client/desktop code is also publicly available on GitHub.

Prerequisites

• Java 14
• Maven 3.6.3

Architecture overview

The server opens a network connection and pushes in-game events as protobuf messages(find .proto schema in schema module). The client publishes game commands and then subscribes to server events by collecting them in an in-memory queue that is meant to be polled during game rendering. All communications (server-to-client and client-to-server) are totally non-blocking.

Core dev principles

• All configuration defaults should be prod-ready
• The code should be simple, so I can understand it at 2 AM after taking a two-month break
• Add as many tests as possible even if it looks non-practical at a moment(you will appreciate it later)
• All time related values(configs too) are stored in the millisecond format
• No AI

Known issues

• The server is not scalable
• The server is not fully authoritative
• Basic anti-cheat

Configuration

Game server can be configured using the following environment variables:

• GAME_SERVER_PORT TCP server port at which client connections are going to be accepted. For simplicity, UDP port is GAME_SERVER_PORT+1. Default - 7777.
• GAME_SERVER_BLACKLISTED_WORDS Blacklisted words. Affects chat messages and player names. Words should be separated by a comma (,) symbol. Case-insensitive. Example: ABC,XYZ,QWE. Not set by default.
• GAME_SERVER_BIG_UDP_WARNING Pushes a warning to logs if a big UDP datagram was sent over a network. Default - false.
• GAME_SERVER_GAMES_TO_CREATE Games to create. Default - 1.
• GAME_SERVER_MAX_PLAYERS_PER_GAME Maximum number of players to join a game. Default - 25. Total number of players on the server is GAME_SERVER_GAMES_TO_CREATE*GAME_SERVER_MAX_PLAYERS_PER_GAME.
• GAME_SERVER_MOVES_UPDATE_FREQUENCY_MLS Frequency(in milliseconds) at which server notifies players about other players' positioning on the map. Default - 25.
• GAME_SERVER_ACK_RESEND_FREQUENCY_MLS Frequency(in milliseconds) at which server resends UDP messages that require an ack but haven't received one. Default - 100.
• GAME_SERVER_MAX_IDLE_TIME_MLS Maximum idle time(in milliseconds) for a player. "Idle" - no network activity, which includes in-game events + ping responds. For example, if player connects to a game and doesn't move but responds to PING requests, then it's NOT considered idle. This check is mostly needed when a TCP connection was closed abruptly(no FIN). Default - 10_000.
• GAME_SERVER_MAX_VISIBILITY Maximum visibility on the map. Default - 14. Events outside of this radius won't be transmitted over the network to save traffic.
• GAME_SERVER_DEFAULT_SHOTGUN_DAMAGE Gunshot damage. Default - 20.
• GAME_SERVER_DEFAULT_RAILGUN_DAMAGE Railgun damage. Default - 75.
• GAME_SERVER_DEFAULT_PUNCH_DAMAGE Punch damage. Default - 50.
• GAME_SERVER_DEFAULT_ROCKET_DAMAGE Rocket damage. Default - 75.
• GAME_SERVER_DEFAULT_MINIGUN_DAMAGE Minigun damage. Default - 15.
• GAME_SERVER_DEFAULT_PLASMA_DAMAGE Plasma damage. Default - 15.
• GAME_SERVER_FAST_TCP Enables fast TCP configurations(used mostly for testing, not recommended to be set to false in prod). Default - true.
• GAME_SERVER_FRAGS_PER_GAME Frags to win a game. Default - 25.
• GAME_SERVER_SPAWN_IMMORTAL_MLS Time (in millisecond) players are immortal after spawn/respawn. Default - 2000
• GAME_SERVER_QUAD_DAMAGE_SPAWN_MLS Time (in millisecond) it takes to spawn a quad damage power-up orb. Default - 45_000.
• GAME_SERVER_QUAD_DAMAGE_LASTS_FOR_MLS Time (in millisecond) quad damage lasts for. Default - 15_000.
• GAME_SERVER_DEFENCE_SPAWN_MLS Time (in millisecond) it takes to spawn a defence power-up orb. Default - 35_000.
• GAME_SERVER_DEFENCE_LASTS_FOR_MLS Time (in millisecond) defence lasts for. Default - 10_000.
• GAME_SERVER_INVISIBILITY_SPAWN_MLS Time (in millisecond) it takes to spawn an invisibility power-up orb. Default - 30_000.
• GAME_SERVER_MAP_NAME Map name. Must be one of built-in maps ( see /server/main/resources/maps folder). Default - classic.
• GAME_SERVER_AMMO_SPAWN_MLS Time (in millisecond) it takes to spawn ammo. Default - 30_000.
• GAME_SERVER_HEALTH_SPAWN_MLS Time (in millisecond) it takes to spawn a health power-up orb. Default - 35_000.
• GAME_SERVER_INVISIBILITY_LASTS_FOR_MLS Time (in millisecond) invisibility lasts for. Default - 15_000.
• GAME_SERVER_POWER_UPS_ENABLED Turns power-ups on and off. Default - true.
• GAME_SERVER_TELEPORTS_ENABLED Turns teleports on and off. Default - true.
• GAME_SERVER_PLAYER_SPEED Base player speed. Changes depending on class. Default - 7.
• GAME_SERVER_PLAYER_STATS_TIMEOUT_MLS Time (in milliseconds) to store player's stats for connection recovery. Default - 120000.
• GAME_SERVER_PUNCH_DELAY_MLS Punch attack delay(in milliseconds). Default - 300
• GAME_SERVER_ROCKET_LAUNCHER_DELAY_MLS Rocket launcher delay(in milliseconds). Default - 1_500.
• GAME_SERVER_PLASMAGUN_DELAY_MLS Plasma gun delay(in milliseconds). Default - 155.
• GAME_SERVER_SHOTGUN_DELAY_MLS Shotgun attack delay(in milliseconds). Default - 450
• GAME_SERVER_RAILGUN_DELAY_MLS Railgun attack delay(in milliseconds). Default - 1_700
• GAME_SERVER_MINIGUN_DELAY_MLS Minigun attack delay(in milliseconds). Default - 155
• GAME_SERVER_SHOTGUN_MAX_AMMO Shotgun max ammo. Default - 20
• GAME_SERVER_RAILGUN_MAX_AMMO Railgun max ammo. Default - 15
• GAME_SERVER_MINIGUN_MAX_AMMO Minigun max ammo. Default - 100
• GAME_SERVER_PLASMAGUN_MAX_AMMO Plasmagun max ammo. Default - 50
• GAME_SERVER_ROCKET_LAUNCHER_MAX_AMMO Rocket launcher max ammo. Default - 10
• GAME_SERVER_BEAST_SPAWN_MLS Time (in millisecond) it takes to spawn a beast power-up orb. Default - 60_000.
• GAME_SERVER_BEAST_LASTS_FOR_MLS Time (in millisecond) defence lasts for. Default - 25_000.
• SENTRY_DSN Sentry DSN. Not specified by default.

Some environment variables can be overridden for a specific game room. The format is <ROOM_ID>_<ENV_VAR_NAME>. For example 0_GAME_SERVER_DEFAULT_SHOTGUN_DAMAGE=99 overrides GAME_SERVER_DEFAULT_SHOTGUN_DAMAGE variable for game room 0. Here is the list of all room-specific configs:

• GAME_SERVER_ROOM_TITLE
• GAME_SERVER_ROOM_DESCRIPTION
• GAME_SERVER_DEFAULT_SHOTGUN_DAMAGE
• GAME_SERVER_DEFAULT_RAILGUN_DAMAGE
• GAME_SERVER_DEFAULT_MINIGUN_DAMAGE
• GAME_SERVER_DEFAULT_PLASMA_DAMAGE
• GAME_SERVER_DEFAULT_ROCKET_DAMAGE
• GAME_SERVER_DEFAULT_PUNCH_DAMAGE
• GAME_SERVER_PUNCH_DELAY_MLS
• GAME_SERVER_SHOTGUN_DELAY_MLS
• GAME_SERVER_RAILGUN_DELAY_MLS
• GAME_SERVER_ROCKET_LAUNCHER_DELAY_MLS
• GAME_SERVER_PLASMAGUN_DELAY_MLS
• GAME_SERVER_MINIGUN_DELAY_MLS
• GAME_SERVER_PLAYER_SPEED
• GAME_SERVER_MAX_VISIBILITY
• GAME_SERVER_SHOTGUN_MAX_AMMO
• GAME_SERVER_RAILGUN_MAX_AMMO
• GAME_SERVER_MINIGUN_MAX_AMMO
• GAME_SERVER_PLASMAGUN_MAX_AMMO
• GAME_SERVER_ROCKET_LAUNCHER_MAX_AMMO
• GAME_SERVER_MAP_NAME

Game client is also configurable through environments variables:

• CLIENT_MAX_SERVER_INACTIVE_MLS Maximum server inactivity time(in milliseconds). Default - 10_000.
• CLIENT_FAST_TCP Enables fast TCP configurations(used mostly for testing, not recommended to be set to false in prod). Default - true.
• CLIENT_UDP_GLITCHY_INBOUND_DROP_MESSAGE_PROBABILITY Probability to drop a UDP message while reading. Ranges from 0(0%) to 1(100%). Default - 0.
• CLIENT_UDP_GLITCHY_OUTBOUND_DROP_MESSAGE_PROBABILITY Probability to drop a UDP message while writing. Ranges from 0(0%) to 1(100%). Default - 0.

Note: all default (both client and server) configurations are production-ready.

Deployment and integration

Game client integration

All submodules, including network client, can be used as maven/gradle dependencies using jitpack.

Docker

Server image is deployed on every release to Github container registry. A sample docker-compose file can be found in the root folder.

Monitoring

Server monitoring

JVM metrics

Server JVM metrics can be monitored through JMX remotely. See docker-compose file. In the sample, JMX agent is running on port 9999 listening to incoming connections initiated by 127.0.0.1. If server is running in the cloud, then it's possible to port-forward JMX using the following command:

ssh -L 9999:127.0.0.1:9999 <user>@<remote_host>

Heap dumps

Apart from JMX metrics, the server is configured to drop a heap dump file on out-of-memory.

Micrometer

All command handlers publish Micrometer timer metrics through JMX. See "metrics" in Jconsole " MBeans" tab.

Sentry

All errors are automatically published to Sentry. See SENTRY_DSN env var.

Development

Handy Maven commands

Here are some commands that might be useful while coding.

Update all submodules' versions

mvn versions:set -DnewVersion=<version>

Run static code analysis

mvn spotbugs:check 

Update protobuf schema

rm .\schema\src\main\java\com\beverly\hills\money\gang\proto\* 
protoc --java_out=./schema/src/main/java/ .\schema\src\main\resources\server-common.proto
protoc --java_out=./schema/src/main/java/ .\schema\src\main\resources\server-response.proto
protoc --java_out=./schema/src/main/java/ .\schema\src\main\resources\server-command.proto