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InSim is a protocol which allows an external program to communicate with Live for Speed. It allows you to create a socket connection with the game and to send and receive packets of data. The InSim protocol describes how each of these packets is formatted, and any programming language which can create a network connection and send and receive strings of binary data can interface with it.

The official documentation is included in the file InSim.txt, found in the games docs folder. It consists of a C++ header file that contains the definition for each packet, as well as comments from Scawen as to how each should be used. The documentation here is intended as an ancillary to this file.


InSim supports both UDP and TCP connections. In UDP mode only a single connection can be made, however up to eight connections can be made to the game in TCP. Whether connected in TCP or UDP, it's possible to specify a separate UDP socket for receiving car position updates, such as IS_MCI and IS_NLP.

InSim example

How you go about creating an InSim connection is of course dependent on which programming language you are using, but here we make an attempt to document the process with some examples from the popular Python programming language. As mentioned above any language capable of making a socket connection can be used to interface with LFS, however the principle remain the same regardless.

Creating a connection

First of all we must establish a socket connection with the game, in this case in TCP.

# Import Python's socket module.
import socket

# Initialise the socket in TCP mode. 
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Connect to LFS.
sock.connect(('localhost', 29999))

Initialising InSim

After establishing the connection we must initialise the InSim system by sending the IS_ISI packet. Before we can do this however we must first intitailse InSim within LFS itself. To do this start the game and enter the chat command /insim 29999. The port number used can be any valid port, but 29999 generally tends to be the accepted default.

Here is the definition for the IS_ISI packet from InSim.txt.

struct IS_ISI // InSim Init - packet to initialise the InSim system
	byte	Size;		// 44
	byte	Type;		// ISP_ISI
	byte	ReqI;		// If non-zero LFS will send an IS_VER packet
	byte	Zero;		// 0

	word	UDPPort;	// Port for UDP replies from LFS (0 to 65535)
	word	Flags;		// Bit flags for options (see below)

	byte	Sp0;		// 0
	byte	Prefix;		// Special host message prefix character
	word	Interval;	// Time in ms between NLP or MCI (0 = none)

	char	Admin[16];	// Admin password (if set in LFS)
	char	IName[16];	// A short name for your program

Each InSim packet begins with a header, consisting of 4 bytes. The first byte is the size of the packet, followed by the packet type from the ISP_ enumeration, and then the ReqI (standing for Request Id). Whenever a request is made to LFS the value of the ReqI must be set to non-zero, whereby LFS will reply with the same value set in the ReqI of the requested packet. Finally the fourth byte varies depending on the type of packet in question, which in this case is blank.

As you can see the IS_ISI packet contains various options and flags that are used when initialising the InSim system. We must pack this data into a binary formatted string to send it to LFS.

# Import Python's struct module, which allows us to pack and unpack strings.
import struct

# Pack the IS_ISI data into a string.
isi = struct.pack('BBBBHHBcH16s16s', 
                  44,           # Size
                  1,            # Type
                  1,            # ReqI
                  0,            # Zero
                  0,            # UDPPort
                  0,            # Flags
                  0,            # Sp0
                  ' ',          # Prefix
                  0,            # Interval
                  'password',   # Admin
                  'MyProgram',) # IName

# Send the string to InSim

Receiving Data

After creating the connection and initialising InSim we must then setup the packet receive loop. As data in TCP mode is sent as a constant stream of data, multiple packets may arrive in a single receive call and some packets may arrive incomplete. This means we must store all incoming data in a buffer and then read each packet out when we are sure it is complete.

# We use a string as the buffer.
buffer = ''

while True:
    # Receive up to 1024 bytes of data.
    data = sock.recv(1024)

    # If no data is received the connection has closed.
    if data:
        # Append received data onto the buffer.
        buffer += data

        # Loop through each completed packet in the buffer. The first byte of
        # each packet is the packet size, so check that the length of the
        # buffer is at least the size of the first packet. 
        while len(buffer) > 0 and len(buffer) > ord(buffer[0]):
            # Copy the packet from the buffer.
            packet = buffer[:ord(buffer[0])]

            # Remove the packet from the buffer.
            buffer = buffer[ord(buffer[0]):]

            # The packet is now complete! :)
            # doSomethingWithPacket(packet)

# Release the socket.

Unpacking Packets

Once we have received the packet data as a binary formatted string, we then have to unpack this data into a format which is useful to us. In our previous example when we sent the IS_ISI initailisation packet, we set the ReqI to non-zero, meaning that LFS responded with an IS_VER version packet, however we didn't do anything with it. Firstly lets look at the definition for the IS_VER packet from InSim.txt.

struct IS_VER // VERsion
	byte	Size;			// 20
	byte	Type;			// ISP_VERSION
	byte	ReqI;			// ReqI as received in the request packet
	byte	Zero;

	char	Version[8];		// LFS version, e.g. 0.3G
	char	Product[6];		// Product : DEMO or S1
	word	InSimVer;		// InSim Version : increased when InSim packets change

Now lets look at how we would unpack that data in Python.

# Import Python's struct module.
import struct

# Unpack the binary formatted packet data into the values we need.
size, type, reqi, zero, version, product, insimver = struct.unpack('BBBB8s6sH', packet)

# Check the InSim version.
if insimver != 4:
    print 'Invalid InSim version!'

Keep Alive

In order to keep the connection open LFS will send a "keep alive" packet every 30 or so seconds. This packet is an IS_TINY with a SubT (sub-type) of TINY_NONE. We must respond to this packet every time it is received in order to prevent the connection with InSim from timing-out.

# Some constants.

# Check the packet type.
if ord(packet[1]) == ISP_TINY:
    # Unpack the packet data.
    tiny = struct.unpack('BBBB', packet)
    # Check the SubT.
    if tiny[3] == TINY_NONE:
       # Send the keep alive packet back to LFS.

Further examples

You can see the full example of this code as well as others on the InSim examples page.

InSim Libraries

Of course as the old adage goes you shouldn't try to reinvent the wheel (unless you're trying to learn more about wheels) and there are several mature InSim libraries available for use in your own code.

InSim Libraries
Library Platform License web
LFSLib .NET Framework GPL project page
LFS_External .NET Framework Freeware lfsforum thread
JInSim Java Mozilla lfsforum thread
pyinsim Python LGPL lfsforum thread
CInSim C/C++ Freeware lfsforum thread
phplfs PHP5 Apache License V2.0 project page
PRISM PHP7 MIT lfsforum section
InSim.NET .NET Framework LGPL lfsforum thread Rust MIT GitHub, Documentation,, lfsforum thread
PIE PHP7 Freeware LFS Forum Section

InSim Reference

Here is an attempt to reference the complete InSim protocol.

Packet Reference
Packet Description Type
IS_ISI InSim initialisation Instruction
General Purpose
IS_TINY General purpose 4 byte packet Both
IS_SMALL General purpose 8 byte packet Both
Version request
IS_VER Version information Info
State Reporting and Requests
IS_STA Sent whenever the game state changes Info
IS_SFP Send to set various state options Instruction
Screen Mode
IS_MOD Send to change screen mode Instruction
Text Messages and Key Presses
IS_MSO System and user messages sent from LFS Info
IS_III User messages to host InSim Info
IS_MST Send LFS a message or command (64 characters) Instruction
IS_MSX Extended version of IS_MST (96 characters), not for commands Instruction
IS_MSL Send message to local game client Instruction
IS_MTC Send message to specific connection or player Instruction
IS_SCH Send single character or key press Instruction
Multiplayer Notification
IS_ISM Sent when starting or joining a host Info
IS_NCI Sent when host admin password is set, contains user IP and language data Info
Vote Notify
IS_VTN Notify of player vote (restart race, qualify etc..) Info
Race Tracking
IS_RST Race starting or restarting Info
IS_NCN New connection joining server Info
IS_SLC to report changes in car state (currently start or stop) Info
IS_CSC reports a connection's currently selected car Info
IS_CNL Connection left server Info
IS_CPR Player changed name Info
IS_NPL New player joining race, or leaving pits Info
IS_MAL Allowed Mods - Set/Clear allowed mods (by skinID) in the server Info
IS_PLP Player pits (gone to garage screen) Info
IS_PLL Player left race (gone to spectate) Info
IS_CRS Car reset (pressed space bar) Info
IS_JRR can be used to reset or start a car at a specified location Instruction
IS_LAP Lap time completed Info
IS_SPX Split time completed Info
IS_PIT Pit stop started (at pit box) Info
IS_PSF Pit stop finished Info
IS_PLA Player entered pit lane (to pit or serve penalty) Info
IS_CHH Camera view changed (chase view, custom view etc..) Info
IS_PEN Penalty given or cleated Info
IS_TOC Player taken over another car (driver swap) Info
IS_FLG Player shown flag (yellow or blue) Info
IS_PFL Player flags changed (auto-gears, auto-clutch etc..) Info
IS_FIN Player finished race (crossed finish line) Info
IS_RES Player result awarded, confirmed finish Info
IS_REO Reorder starting grid Both
IS_AXI Autocross layout loaded Info
IS_AXO Player hit autocross object Info
IS_OCO can be used to override specific or all start lights Instruction
IS_UCO sends info about InSim checkpoints and circles Info
Car Tracking
IS_NLP Players current node, lap and race position Info
IS_MCI More detailed version of IS_NLP, world-coordinates, speed, angle and heading Info
Camera Control
IS_SCC Set viewed car and select camera Instruction
IS_CPP Set full camera position Instruction
Replay Control
IS_RIP Load replay and move to specific destination Instruction
IS_SSH Take a screenshot Instruction
InSim Buttons
IS_BFN Delete a button or all buttons Instruction
IS_BTN Send a button to the screen Instruction
IS_BTC Sent when a button is clicked Info
IS_BTT Sent when text is entered Info