Multi-Version Minecraft Support - Testing Protocol Compatibility

Server Version: 1.21
Compatible Clients: Only 1.21

Player with 1.20.4 client: ❌ Cannot connect
Player with 1.21.1 client: ❌ Cannot connect

Server Version: 1.21
ViaVersion Installed: ✅

Player with 1.20.4 client: ✅ Can connect
Player with 1.21 client: ✅ Can connect
Player with 1.21.1 client: ✅ Can connect

Example:
Server: 1.20.4
ViaVersion: Installed

Client 1.21 → ViaVersion translates → Server sees 1.20.4 client

# Download ViaVersion
wget https://github.com/ViaVersion/ViaVersion/releases/download/5.0.0/ViaVersion-5.0.0.jar

# Place in plugins folder
mv ViaVersion-5.0.0.jar plugins/

# Start server (config auto-generates)

Example:
Server: 1.21
ViaBackwards: Installed

Client 1.19 → ViaBackwards translates → Server sees 1.21 client

# ViaBackwards requires ViaVersion
# Download ViaBackwards
wget https://github.com/ViaVersion/ViaBackwards/releases/download/5.0.0/ViaBackwards-5.0.0.jar

mv ViaBackwards-5.0.0.jar plugins/

Example:
Server: 1.21
ViaRewind: Installed

Client 1.8 → ViaRewind translates → Server sees 1.21 client

# Download ViaRewind
wget https://github.com/ViaVersion/ViaRewind/releases/download/3.0.0/ViaRewind-3.0.0.jar

mv ViaRewind-3.0.0.jar plugins/

# Should ViaVersion check for updates?
checkforupdates: true

# Send supported versions info to clients
send-supported-versions: false

# Block protocols not explicitly handled
block-protocols: []

# Force specific version for everyone (usually empty)
force-json-transform: false

# Prevent version downgrade exploits
suppress-metadata-errors: false

# Debug mode (disable in production)
debug: false

# Minimize cool down for item pickup
minimize-cooldown: true

# Handle how team colors work across versions
team-colour-fix: true

# Serialize block entities in chunks
cache-values: false

# Ensure correct character width calculation
character-width-fix: false

# Suppress conversion warnings
suppress-conversion-warnings: false

# Fix fire animation on 1.12- clients
fix-fire-animation: true

# Make  shields work on 1.8 clients
shield-blocking: true

# Handle hologram conversion
hologram-patch: true

# Convert newer sounds to older equivalents
sound-conversion: true

1. Start server with ViaVersion suite
2. Connect with test client
3. Verify successful join

Expected:
- No connection errors
- Player spawns normally
- No console errors

1. Connect with various client versions
2. Walk, sprint, jump, swim, fly
3. Note any jank or rubber-banding

Expected:
- Smooth movement
- Correct sprint/jump mechanics
- No stuttering

Client 1.8:
- Sprint mechanics slightly different (client-side prediction)
- Swimming is walking underwater (pre-aquatic update)

Client 1.12:
- Elytra flight slightly different
- No swimming animations

1. Place variety of blocks (new and old)
2. Connect with various clients
3. Verify blocks appear (even if placeholder)

Test blocks:
- Deepslate (1.17+)
- Copper (1.17+)
- Amethyst (1.17+)
- Ancient debris (1.16+)
- Honey block (1.15+)

Client 1.16 seeing copper block (1.17):
- Appears as stone or another placeholder
- Collision box correct
- Can break block (drops as intended)

1. Connect with 1.8 client (old combat)
2. Connect with 1.9+ client (new combat)
3. Test PvP between clients

Expected:
- Both can damage each other
- Hit registration works
- Weapons deal appropriate damage

1. Give player items from various versions
2. Connect with older clients
3. Verify items appear (even if converted)

Test items:
- Netherite sword (1.16+)
- Trident (1.13+)
- Elytra (1.9+)
- Shield (1.9+)

Client 1.8 receiving netherite sword:
- Appears as diamond sword (or similar)
- Functions as weapon
- Durability works

1. Connect with various clients
2. Send chat messages
3. Execute commands
4. Check formatting

Expected:
- All versions can chat
- Colors/formatting work
- Commands execute
- JSON chat components display properly

# Avoid 1.16+ hex colors for older clients
Good: "&c&lWarning"  # Works on all versions
Bad: "&#FF5555Warning"  # Only works 1.16+

# Check client version before sending complex JSON
if (player.getProtocolVersion() >= 735) {  // 1.16+
    sendHexMessage()
} else {
    sendLegacyMessage()
}

1. Teleport player to y=-64 (below old bedrock)
2. Connect with 1.17- client
3. Verify behavior

Expected:
- Player can't see blocks below y=0
- Falls through "void" visually
- Server handles position correctly

1. Build structure at y=300 (above old limit)
2. Connect with 1.17- client
3. Fly up to y=300

Expected:
- Player can't see blocks above y=255
- Blocks invisible to client
- Server collision still works

# Build important structures within "safe" zones
Safe Y range (all clients): 0-255
Extended Y range (1.18+ only): -64-319

1. Spawn various mobs (old and new)
2. Connect with different clients
3. Verify mobs render

Test mobs:
- Warden (1.19+)
- Allay (1.19+)
- Frog (1.19+)
- Goat (1.17+)
- Axolotl (1.17+)

Client 1.16 seeing Warden:
- Appears as alternative mob (zombie, etc.)
- Hitbox correct
- Can be damaged
- AI works server-side

Player (1.20) → Proxy (ViaVersion) → Backend 1.21
Player (1.19) → Proxy (ViaVersion) → Backend 1.21
Player (1.21) → Proxy (ViaVersion) → Backend 1.21

Setup:
- Proxy: Velocity with ViaVersion
- Backend 1: Paper 1.21 (lobby)
- Backend 2: Paper 1.20.4 (survival)
- Backend 3: Paper 1.19 (creative)

Test clients:
- Client 1.21
- Client 1.20
- Client 1.19

1. Setup Velocity with modern forwarding
2. Install ViaVersion on proxy
3. Connect with various client versions
4. Verify UUIDs correct on backend

Expected:
- All clients get correct UUID
- Skins load properly
- No UUID conflicts

Client: 1.21 with ViaFabricPlus
Server: 1.8

ViaFabricPlus translates: Client sends 1.8 packets

Server versions to test:
- 1.21 (latest)
- 1.20.4
- 1.19
- 1.16.5 (popular modded version)
- 1.12.2 (popular modded version)
- 1.8.9 (PvP standard)
- Beta 1.7.3 (nostalgia)

Client: 1.21 with ViaFabricPlus

Expected: Can connect to all servers

# ViaVersion config.yml
minimize-cooldown: true

# Paper config (server-side)
# Reduce anti-cheat sensitivity for older clients

# Paper config
# Increase chunk send rate for older protocols

# ViaVersion config.yml

# Reduce cache size (if memory constrained)
cache-values: false  # Recompute instead of cache

# Disable features you don't need
character-width-fix: false  # Only needed for specific issues

# Minimize debug logging
debug: false

Objective: Verify all supported versions can connect

Setup:
- Server with ViaVersion suite
- Bot tool supporting multiple protocols

Test:
1. Connect bot with protocol 1.21
2. Verify connection success
3. Disconnect
4. Connect bot with protocol 1.20
5. Repeat for: 1.19, 1.18, 1.16.5, 1.12.2, 1.8.9

Expected:
- All versions connect successfully
- No errors in console

Objective: Multiple versions online simultaneously

Setup:
- Server with ViaVersion
- Multiple bot accounts

Test:
1. Connect 10 bots: 5x 1.21, 3x 1.20, 2x 1.19
2. All online simultaneously for 10 minutes
3. Monitor server performance

Expected:
- All bots stay connected
- TPS remains 19-20
- No protocol errors

Objective: Client updates don't break connection

Setup:
- Bot connected with version 1.20

Test:
1. Bot connects as 1.20 client
2. Bot disconnects
3. Bot connects as 1.21 client (same account)
4. Verify connection

Expected:
- Both versions connect successfully
- Account data persistent across versions

Server: 1.16.5 (modded)
SoulFire Configuration:
- Protocol Version: 1.16.5 (use dropdown/config)
- Bots: 5
- Join Delay: 2000-3000ms

Test:
1. Verify all 5 bots connect successfully
2. Bots remain online for 15 minutes
3. Check console for protocol errors

Expected:
- All bots connect to 1.16.5 server
- No "protocol mismatch" errors
- Server sees bots as 1.16.5 clients

Test Goal: Verify server supports all advertised versions

Server Setup:
- Paper 1.21 with ViaVersion + ViaBackwards + ViaRewind

Test Matrix:
- 5 bots on 1.21
- 5 bots on 1.20.4
- 5 bots on 1.19
- 5 bots on 1.16.5
- 5 bots on 1.12.2
- 5 bots on 1.8.9

Process:
1. Configure bot tool to cycle through versions
2. Connect all 30 bots (5 per version)
3. Run for 30 minutes
4. Monitor for disconnects or errors

Expected Results:
✅ All 30 bots remain connected
✅ Server TPS stable (18-20)
✅ No protocol errors
✅ /list shows 30 players

Interpretation:
- If all versions connect: ViaVersion working correctly
- If specific version fails: Missing ViaBackwards/ViaRewind or config issue
- If TPS drops: Performance tuning needed