Messages

Demo messages are stored in sequential order as the engine records them. A message always starts with a tagged type followed by the current session tick, a slot index and the type-specific message data.

Overview

Name	Type	Size in bytes	Size in bits	Value
Type	MessageType	1	8	-
Tick1	int	4	32	-
SlotNE 2	byte	1	8	-
Data	MessageData	-	-	-
1 Old engines might not even include the message tick after the stop byte.

² The term slot here refers to the selected split-screen index. This byte is only used in engines which support split-screen mode.

C

typedef struct {
    message_type type;
    int tick;
    char slot;
    message_data_t* data;
} message_t;

C++

struct message_t {
    message_type type;
    int32_t tick;
    std::byte slot;
    message_data_t* data;
};

C#

class Message {
    public MessageType Type { get; set; }
    public int Tick { get; set; }
    public byte Slot { get; set; }
    public MessageData Data { get; set; }
}

JS

class Message {
  /** @type {MessageType} */
  type;
  /** @type {number} */
  tick;
  /** @type {number} */
  slot;
  /** @type {MessageData} */
  data;
}

TS

export class Message {
  public type?: MessageType;
  public tick?: number;
  public slot?: number;
  public data?: MessageData;
}

Go

type Message struct {
	Type MessageType
	Tick int32
	Slot int8
	Data MessageData
}

Rust

pub struct Message {
    pub r#type: MessageType,
    pub tick: i32,
    pub slot: i8,
    pub data: MessageData,
}

Zig

const Message = struct {
    type: message_type,
    tick: i32,
    slot: i8,
    data: message_data,
};

Types

Overview

Type	Value	Description
SignOn	1	-
Packet	2	-
SyncTick	3	-
ConsoleCmd	4	-
UserCmd	5	-
DataTables	6	-
Stop	7	-
CustomData	8	-
StringTables	9	8 for old engine.

C

enum message_type {
    MT_SIGN_ON = 1,
    MT_PACKET = 2,
    MT_SYNC_TICK = 3,
    MT_CONSOLE_CMD = 4,
    MT_USER_CMD = 5,
    MT_DATA_TABLES = 6,
    MT_STOP = 7,
    MT_CUSTOM_DATA = 8,
    MT_STRING_TABLES = 9,
};

C++

enum class message_type {
    SIGN_ON = 1,
    PACKET = 2,
    SYNC_TICK = 3,
    CONSOLE_CMD = 4,
    USER_CMD = 5,
    DATA_TABLES = 6,
    STOP = 7,
    CUSTOM_DATA = 8,
    STRING_TABLES = 9,
};

C#

enum MessageType : byte {
    SignOn = 1,
    Packet = 2,
    SyncTick = 3,
    ConsoleCmd = 4,
    UserCmd = 5,
    DataTables = 6,
    Stop = 7,
    CustomData = 8,
    StringTables = 9,
};

JS

const MessageType = {
  SignOn = 1,
  Packet = 2,
  SyncTick = 3,
  ConsoleCmd = 4,
  UserCmd = 5,
  DataTables = 6,
  Stop = 7,
  CustomData = 8,
  StringTables = 9,
}

TS

export enum MessageType {
  SignOn = 1,
  Packet = 2,
  SyncTick = 3,
  ConsoleCmd = 4,
  UserCmd = 5,
  DataTables = 6,
  Stop = 7,
  CustomData = 8,
  StringTables = 9,
}

Go

type MessageType byte

const (
	SignOn       MessageType = 1,
	Packet                   = 2,
	SyncTick                 = 3,
	ConsoleCmd               = 4,
	UserCmd                  = 5,
	DataTables               = 6,
	Stop                     = 7,
	CustomData               = 8,
	StringTables             = 9,
)

Rust

pub enum MessageType {
    SignOn = 1,
    Packet = 2,
    SyncTick = 3,
    ConsoleCmd = 4,
    UserCmd = 5,
    DataTables = 6,
    Stop = 7,
    CustomData = 8,
    StringTables = 9,
}

Zig

const MessageType = enum {
    sign_on = 1,
    packet = 2,
    sync_tick = 3,
    console_cmd = 4,
    user_cmd = 5,
    data_tables = 6,
    stop = 7,
    custom_data = 8,
    string_tables = 9,
};

Pseudocode Example

To keep this example simple the stop message might contain additional data which is not read here. We also ignore the fact that that reading past the buffer might be possible when parsing corrupted demos.

loop {
    let message_type = read_le_i8();

    if message_type == 0x07 {
        break;
    }

    let tick = read_le_i32();
    let slot = read_le_i8();

    read_message_data(message_type);
}