Classic Protocol Extension
Classic Protocol Extension (CPE) is a project to augment the Minecraft Classic network protocol. Extensions are designed to keep custom clients and servers compatible to standard/vanilla clients and servers. Standard clients and extended clients can play on the same server at the same time. Extensions are also designed to be modular: clients and servers can choose to implement any subset of extensions, and only mutually-supported extensions will be used.
This specification has not yet been finalized, and is subject to change.
Last revision: 28 August 2013 |
Contents
Support
These custom servers plan to add support for CPE: fCraft, FemtoCraft, 800Craft, GGS
These custom clients plan to add support for CPE: Charged Miners, OpenClassic
Negotiation
Client behavior: Extended clients must use magic number of 0x42
for the padding byte of the Player Identification packet. After the client has sent its identification packet, it must await a response. If server responds with any packet other than ExtInfo, client must assume that the server does not support CPE. If the server responds with an ExtInfo packet, client must parse it and any ExtEntry packets that follow. Client must then compare its locally-supported set of extensions with the list of extensions provided by the server, and find an intersection of these sets. These are the mutually-supported extensions. Client must now send ExtInfo packet of its own, followed by a list of zero or more client-supported extensions. After sending the last of ExtEntry packets, client should activate all mutually-supported extensions and resume normal login procedure.
Server behavior: All standard/non-extended clients pad this packet with 0x00
, so extended servers can easily notice extended clients. All standard/non-extended servers will ignore the modified padding byte, preserving compatibility. When the server sees that padding byte is 0x42
, it must immediately reply with an ExtInfo packet, followed by zero or more ExtEntry packets, and await a response (ExtInfo packet) from the client. Client will respond with one ExtInfo and zero or more ExtEntry packets. Server must then compare its locally-supported set of extensions with the list of extensions provided by the client, and find an intersection of these sets. These are the mutually-supported extensions. After receiving the last of ExtEntry packets, server should activate all mutually-supported extensions and resume normal login procedure.
ExtInfo Packet
Packet ID Field Name Field Type Example Notes 0x10 (16)
AppName string MyServer
Client or server software name ExtensionCount short 1 Between 0 and 32767 Total Size: 67 bytes
ExtEntry Packet
Packet ID Field Name Field Type Example Notes 0x11 (17)
ExtName string MyExtension
Name of a supported extension Version int 1 Only extensions with identical version numbers should be considered compatible. Total Size: 69 bytes
Extensions
ClickDistance
- Used to extend or restrict the distance at which client may click blocks, controlled by the server. Click range is given in player-space units (32 units per block). In Minecraft Classic, the default range is 160.
- Motivation: This extension allows trusted players to have a wider or virtually-unlimited reach. It may simplify operation of certain bots. Restricting the reach may allow new games/mini-games.
- Client Behavior: Upon receiving a SetClickDistance packet, client should immediately apply the change. Distance should persist between worlds/maps.
- Server Behavior: Server should send SetClickDistance packet when the server connects, or whenever their permitted click distance changes. Server should allow for some margin-of-error (+/- 1 block) when enforcing click distance restrictions.
SetClickDistance packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x12 (18)
Distance short 160 Total Size: 3 bytes
CustomBlocks
- Used to add support for custom block types. Custom block IDs start at 50 (0x32). New block types will be added in batches, a few at a time. Both client and server declare which batch they support, and use the lower of the two versions. Claiming to supporting a batch implies fully implementing all the batches that came before it. If either server or client do not support this extension, only the standard 50 block types should be used.
- Motivation: Adding new visually distinct blocks, to enhance Classic players' experience.
- Client behavior: Client must expect a CustomBlockSupportLevel packet from a compatible server immediately after sending the last ExtEntry packet. It should then reply with its own CustomBlockSupportLevel packet, containing its actual support level. Client must then use the lower of the two levels in operation. Client must not send any block types that are not defined by the current support level. Client should expect Heartbeat packet only AFTER sending its CustomBlockSupportLevel packet.
- Server behavior: Server must send a CustomBlockSupportLevel packet to compatible clients immediately after receiving the last ExtEntry packet from the client. It should then wait to receive a CustomBlockSupportLevel packet from the client before sending the Handshake. Server must then use the lower of the two levels in operation. If this level is lower than the server's, it has to filter data sent to the client, to make sure that the client never receives any block types that it does not support. Each level will define what substitutions to use.
CustomBlockSupportLevel packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x13 (19)
SupportLevel byte 1 Total Size: 2
Blocks in support level 1
- Client must be able to receive/render all 16 custom blocks to claim support. Server must be able to receive/store all 16 custom blocks to claim support.
Block name | Block ID | Fallback name | Fallback ID |
---|---|---|---|
CobblestoneSlab | 0x32 (50) | Slab | 0x2C (44) |
SpiderWeb | 0x33 (51) | Sapling | 0x06 (6) |
SmoothSandstone | 0x34 (52) | Sand | 0x0C (12) |
Snow | 0x35 (53) | Air | 0x00 (0) |
Fire | 0x36 (54) | Lava | 0x0A (10) |
LightPinkWool | 0x37 (55) | Pink | 0x21 (33) |
ForestGreenWool | 0x38 (56) | Green | 0x19 (25) |
BrownWool | 0x39 (57) | Dirt | 0x03 (3) |
DeepBlue | 0x3A (58) | Blue | 0x1d (29) |
Turquoise | 0x3B (59) | Cyan | 0x1c (28) |
Ice | 0x3C (60) | Glass | 0x14 (20) |
CeramicTile | 0x3D (61) | Iron | 0x2a (42) |
Magma | 0x3E (62) | Obsidian | 0x31 (49) |
Pillar | 0x3F (63) | White | 0x24 (36) |
Crate | 0x40 (64) | WoodenPlanks | 0x05 (5) |
StoneBrick | 0x41 (65) | Stone | 0x01 (1) |
HeldBlock
- Provides a way for the client to notify the server about the blocktype that it is currently holding, and for the server to change the currently-held block type.
- Motivation: This allows server to know which block player is holding, for example for drawing commands, without needing to wait for the player's click. it also allows for features like /Spectate to show what block a spectated player is holding.
- Client behavior: When this extension is mutually supported, client should use the Player ID field of the Position and Orientation packet (currently unused) to indicate which blocktype the client is currently holding. It should be ready to accept HoldThis packets to change the block that the player is holding. If
0
is given for BlockToHold, client should hide the hand/block from the screen, and should not be able to click blocks, until they switch to a different blocktype. If an unrecognized blocktype is given, no action is needed. - Server behavior: The server can use HoldThis packet to force the client to hold the desired block type. It should be done sparingly.
HoldThis packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x14 (20)
BlockToHold byte 49
Standard block type PreventChange byte 0 0 = Allow player to change blocktype 1 = Prevent player from changing blocktype
Total Size: 2 bytes
EmoteFix
- This extension indicates that the client can render emotes (ASCII control characters) in chat properly, without padding or suffixes that are required for vanilla client. This extension does not define any new packets.
- Motivation: To improve appearance of emotes in chat.
- Client behavior: Client should not emulate vanilla client's quirks.
- Server behavior: Server should not pad or suffix emotes in chat.
TextHotKey
- This extension allows the server to define "hotkeys" for certain commands.
- Motivation: To speed up and simplify access to commonly-used commands and command macros by providing server-defined client-side hotkeys.
- Client behavior: Client should not try to persist previously-defined hotkeys between sessions. When a defined hotkey is activated by the user, client should open up a text prompt and type in contents of the Action field. A newline character (
\n
) in the Action field indicates that whatever is currently typed-in should be sent to the server. If Action does not end with a newline, text prompt should be left open, for the user to complete. Client may provide a way for the user to see a list of currently-defined hotkeys, and a way to notify the user when a hotkey was activated. - Server behavior: The server should send a definition of each hotkey (SetTextHotKey packet) once per connection.
SetTextHotKey packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x15 (21)
Label string Copy
Readable name of the hotkey Action string /Copy
Text to type in KeyCode int 113
LWJGL keycode of the key KeyMods byte 0
Key modifier flags, may be combined: - 0 = None
- 1 = Ctrl
- 2 = Shift
- 4 = Alt
Total Size: 134 bytes
ExtPlayerList
- This extension augments the Spawn Player packet to provide more flexibility in naming of players and loading of skins, autocompletion, and player tab-list display.
- Motivation: Allows listing and autocompleting names of players on worlds/maps other than client's own, organizing player names into groups, and making the player tab-list easier to read.
Client Behavior
- When ExtAddPlayerName packet is received for an unrecognized PlayerID, a new entry must be added to the autocompletion list and player tab-list. When receiving ExtAddPlayerName packet for an already-listed PlayerID, client must update its ListName, GroupName, and GroupRank.
- Player names should be grouped by GroupName in the player tab-list. Players within a GroupName should be sorted by GroupRank (in ascending order). Players with the same GroupName and GroupRank should be sorted alphabetically by ListName. Color codes should be either drawn or stripped in ListName, GroupName, and InGameName. Lists should persist when client changes worlds/maps.
- When an ExtAddEntity packet is received, it should be treated as the Spawn Player packet. InGameName should be shown above the player's heads in-game. Skin should be loaded from minecraft.net using the given SkinName for a player name. Client should still be ready to treat Spawn Player packets normally. When client receives ExtAddEntity packet for an already-spawned player, their InGameName and SkinName should be updated.
- When a standard Despawn Player packet is received, player model should be removed from a world, but player name should stay on the autocompletion list and tab-list until ExtRemovePlayerName packet is received for the PlayerID.
- When ExtRemovePlayerName packet is received for a recognized PlayerID, they should be removed from autocompletion list and player tab-list. If ExtAddEntity packet was used to spawn a player with the same ID, it should be despawned (treated as Despawn Player packet). When ExtRemovePlayerName is received for an unrecognized PlayerID, no action should be taken.
Server Behavior
- When a new player connects, ExtAddPlayerName should be sent. GroupName and GroupRank can be used in any way, for example to group players by map/world or rank/class/faction. Server should re-send ExtAddPlayerName packet, using the identical PlayerName, when player's ListName, GroupName, or GroupRank change. Server may opt to use ExtAddEntity or standard SpawnPlayer packet. Server should reliably send an ExtRemovePlayerName when the player disconnects. Color codes are permitted in ListName, GroupName, and InGameName.
ExtAddPlayerName Packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x16 (22)
PlayerID byte 5
Between 0 and 127 PlayerName string Notch
Player name used for autocompletion ListName string &c[Op]Notch
GroupName string Staff
GroupRank byte 0
Rank of a player within the group. Total Size: 193 bytes
ExtAddEntity Packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x17 (23)
PlayerID byte 5
Between 0 and 127 InGameName string &cNotch
Player name to be shown in-game, hovering above player model. SkinName string Notch
Player name whose skin should be used by the client. Total Size: 258 bytes
ExtRemovePlayerName Packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x18 (24)
PlayerName string Notch
Matches PlayerName of the ExtAddPlayerName packet Total Size: 65 bytes
EnvColors
- This extension allows server to alter some of the colors used by the client in environment rendering.
- Motivation: To allow the server to give worlds/maps a unique feel: time-of-day, weather/climate, lighting effect, etc.
- Client behavior: Client must check for EnvSetColor packets right before Level Finalize packet, and apply these changes before the map is displayed. Client should be able to read this packet at other times, but it is not required to then apply the changes immediately. If an unrecognized or unsupported Variable field is given, no action is needed.
- Server behavior: Server should normally only use EnvSetColor packets right before the Level Finalize packet.
EnvSetColor Packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x19 (25)
Variable byte 1
Enumeration of environmental variables - 0 = sky color
- 1 = cloud color
- 2 = fog color
- 3 = ambient light (blocks in shadow) color
- 4 = diffuse light (sunlight) color
Red unsigned byte 0xF9
Green unsigned byte 0x3C
Blue unsigned byte 0x50
Total Size: 5 bytes
SelectionCuboid
- Motivation: To allow the server to highlight parts of a world (e.g. for zoning). To allow players to preview draw commands, such as cuboids.
- Client behavior:
- Server behavior:
MakeSelection packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x20 (26)
SelectionID byte 0
Numeric ID of the selection Label string SomeZone
Text label associated with the selection StartX short 1
X coordinate of the starting point StartY short 2
Y coordinate of the starting point StartZ short 3
Z coordinate of the starting point EndX short 5
X coordinate of the ending point EndY short 6
Y coordinate of the ending point EndZ short 7
Z coordinate of the ending point Red unsigned byte 0xF9
Green unsigned byte 0x3C
Blue unsigned byte 0x50
Opacity unsigned byte 0xFF
0x00 = fully transparent 0xFF = fully opaque
Total Size: 82 bytes
RemoveSelection packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x21 (27)
SelectionID byte 0
Total Size: 2 bytes
BlockPermissions
- This extension allows the server to instruct the player that certain block types are allowed/disallowed to be placed or deleted.
- Motivation: To prevent players from inadvertently placing or removing prohibited block types (e.g. water, lava, grass, admincrete), before it even reaches the server.
- Client behavior: Client should prevent placement of prohibited block types (by graying out or hiding blocks in block-selection screen, or any other effective means). Client should prevent player from deleting prohibited block types. Client must be ready to receive SetBlockPermission packet after map load (MapEnd packet). Permission changes should take effect as soon as packet is received. Admincrete (solid block) permissions set by SetBlockPermission must always override permission set by Handshake packet. If BlockType is set to 0, given permissions should affect ALL block types at once, overriding permissions set by any earlier packets. Permissions must persist between map changes. Client may optionally warn the player attempting to place/delete prohibited blocks via sound effect, visual effect, chat message, etc.
- Server behavior: Server may send SetBlockPermission packets any time after map load (MapEnd packet). Any block type may be specified, including custom blocks (if CustomBlocks is mutually supported). Server must not assume that client is compliant/obedient, and server must still verify each SetBlock packet coming from the client. What to do with non-complying clients (kick or warn) is up to you.
SetBlockPermission packet
- Server to Client
Packet ID Field Name Field Type Example Notes 0x22 (28)
BlockType byte 8
Block's numeric ID (anything between 1 and max defined block). AllowPlacement byte 0
0 = Prohibited 1 = Allowed
AllowDeletion int 0
0 = Prohibited 1 = Allowed
Total Size: 4 bytes
OnScreenMenu
- TODO