OpenFESLHook

Hook for Windows games that use EA's FESL online services, such as Battlefield: Bad Company 2, that sends their online traffic (FESL, Theater and HTTP) to a relay server over a WebSocket, or straight to servers of your choice.

Table of Contents

• Supported games
• Legal notes
• Features
• Build Requirements
• Compiling
• Installing
• Configuration
• Usage
• File formats
• Credits

Supported games

The hook's redirection knows no game in particular: it serves every host below the FESL and Theater domains on the ports each game connects to, so a game needs only to load dinput8.dll from its folder and to look its servers up by those names. Battlefield Heroes also gets parts of its own: its website among the default hosts, the launcher and the dedicated-server parts.

Game	Releases	Tried
Battlefield: Bad Company 2	Windows client (Steam, Origin, EA app) and dedicated server	yes
Battlefield Heroes	Windows client and dedicated server (game versions 1.46 and 1.89)	yes

Battlefield Heroes versions 1.46.222034.0 and 1.89.239937.0 are the only ones tested; other versions are expected to work, but that is not guaranteed. A dedicated server of a version in which the hook does not find the code it patches does not start, and the log names what was missing.

Other FESL games for Windows that meet both conditions may work as they are, or with their hosts in Configuration.

Legal notes

• The project contains no original code or assets from any game.
• To use this project you need to have an original copy of the game, the project doesn't make piracy easier and doesn't break any of the DRM included in-game.
• The project is not affiliated with or endorsed by Electronic Arts or the makers of the games it serves.

Features

• Answers the game's look-ups of the FESL, Theater and HTTP hosts with a loopback address of each host's own, through gethostbyname and, for a game's embedded browser, getaddrinfo, and refuses the game's gethostbyname look-ups of other hosts
• Starts a listener on the port the game connects to, so that no game needs ports of its own in the configuration and a game and its dedicated server can run on one PC
• Completes the game's SSLv3 on its FESL connections with a key and certificate generated on your PC that the game's client accepts; no certificate or key ships with the hook
• Carries FESL, Theater and Theater's UDP datagrams to a relay server over one WebSocket per game process (openfesl.v1), naming the host of each connection, through Windows' own TLS, certificate store and proxy settings
• Forwards the game's HTTP requests to the relay server's host, adding the host the game asked for as X-OpenFESL-Host and the relay token the server hands out with its WebSocket as X-OpenFESL-Relay, and leaves redirects and cookies to the game
• Opens the pages a game shows in the system's browser, such as Battlefield Heroes' hero creator and funds page, on the relay server or the host's own server instead of the game's former website
• Reaches the relay server's host name over IPv4 first, so that the server learns each player's IPv4 address even where the name also has IPv6 addresses; a request that cannot get through over IPv4 is sent again over every address family, and IPv4 is given up once IPv6 got through where IPv4 did not
• Sends chosen hosts straight to other servers as the game's own packets, over plain TCP or re-encrypted with TLS 1.2 or later
• Changes none of a client's code, so the client works the same with every release of a game
• Starts a dedicated server whose own start-up code cannot run without a display (Battlefield Heroes) by patching that code in memory, only when the game is launched as a server
• Gives Battlefield Heroes' client, run as a dedicated server, the server parts it lacks: it lists the server's game in Theater, under the same identity after every restart, with the attributes the game's server browser and Play Now filter on, keeps the attributes that change with the players and the map current, accepts players on the server's port, takes them into the game, and pings them and drops the silent ones, so a player who leaves can come back
• Finds everything it changes in a game's code by signature, string and run-time type, including what moves between a game's releases, so one hook serves each release tried
• Starts Battlefield Heroes from a launcher window when the game is started without a session, as from the game's own shortcut: signs in at the relay server and starts the game, or a dedicated server to host
• Starts Battlefield Heroes from the Play links of the relay server's website, once the launcher's option registers them for the copy you choose
• Shows the launcher and the hook's dialogs in English or Polish, following the Windows display language
• Shows in the Discord client on the same PC what the player is doing, as the relay server describes it, under the game's own name and with a button to the relay server's website
• Optional log to a console and to a file, from the hook's start and each game connection down to every packet with its fields and every HTTP request with its headers, tagged and coloured by topic, with passwords, login keys, session tickets, game join keys and host secrets hidden

Build Requirements

• Visual Studio 2026

Libraries (installed by vcpkg):

• Boost.Asio, Boost.Beast, Boost.Log, Boost.PropertyTree, Boost.URL, Boost.Endian, Boost.Algorithm, Boost.JSON and Boost.Locale
• OpenSSL 3.6, built with SSLv3 and its weak suites
• MinHook
• GoogleTest (unit tests)
• gettext's msgfmt (build tool), which compiles the translation catalogues in src/locale that the build embeds in dinput8.dll

Compiling

See the shared build workflows cpp-checks.yml and cpp-dll.yml, which CI and the release build run, for more detailed steps

1. Integrate vcpkg with Visual Studio
2. Build the solution OpenFESLHook.slnx in Visual Studio (x86 Release for the hook); to build in another default relay server, pass -p:OpenFESLHookServerUrl=wss://relay.example.net to MSBuild
3. Run Release\OpenFESLHook.Tests.exe to run the unit tests

The hook is Release\dinput8.dll.

Installing

1. Copy dinput8.dll, either from the latest build in GitHub Releases or from Release if you compiled it yourself, next to the game's executable (for Battlefield: Bad Company 2, BFBC2Game.exe, or Frost.Game.Main_Win32_Final.exe for its dedicated server; for Battlefield Heroes, BFHeroes.exe, which is both the client and, with +dedicated, the server); the game loads it instead of the system's dinput8.dll, to which the hook passes the game's DirectInput calls
2. Put OpenFESLHook.ini, described in Configuration, next to it if you want to change any default

To uninstall, delete dinput8.dll and OpenFESLHook.ini, and %LOCALAPPDATA%\OpenFESLHook\bfheroes.ini if the Battlefield Heroes launcher remembered a choice; untick Remember me before the last start, or remove the generic credential OpenFESLHook/bfheroes/<account> in the Windows Credential Manager, to remove the remembered password. If the launcher's website-link option is ticked, untick it first, or delete the registry key HKCU\Software\Classes\openfesl-bfheroes; otherwise the website's Play links still start that copy of the game, now without the hook.

Configuration

OpenFESLHook.ini is optional and is read from the folder of dinput8.dll, saved as UTF-8 (with or without a byte order mark) or UTF-16; a file in neither is read in the system's code page. Lines starting with ; or # are comments, section and key names ignore case, spaces around = and quotes around a value are left out, and an empty value keeps its default. Switches take 1, true, yes or on, and 0, false, no or off.

A value the file gets wrong keeps its default, a line of [Hosts] or [Forward] it gets wrong is left out, and a section or key the hook does not read is reported. A section or key that appears twice, or a line that is neither a [section] nor key=value, keeps every default. The hook lists each problem in its log, or in a dialog when it starts with no log output open.

Key	Description	Allowed values	Default
Server.Url	The relay server's WebSocket address; HTTP requests go to the same host and port over http:// for ws:// and https:// for wss://	ws:// or wss:// address	wss://fesl.grzyb.app
Redirect.BlockUnknownHosts	Make the game's gethostbyname look-ups of hosts that [Hosts] does not name fail, other than the PC's own names, which dedicated servers look up for their addresses; getaddrinfo look-ups of them go to the system's resolver, which is how the hook looks its [Forward] servers up	Switch	1
Forward.VerifyCertificates	Require tls:// servers in [Forward] to show a certificate from an authority in the Windows certificate store	Switch	1
Discord.Enabled	Show the presence the relay server sends for the game in the Discord client on the same PC (see Discord)	Switch	1
Log.Console	Show the log in a console window, or in the game's own console if it has one; in a window the hook opens, Ctrl+C does nothing, but closing it ends the game	Switch	0
Log.File	Save the log to a file, which other programs can read while the game runs	Switch	0
Log.Path	The log file, absolute or relative to the folder of dinput8.dll; missing folders are created, and a file named here is appended to	Any path	OpenFESLHook_<date>_<time>.log, new for each start
Log.ConsoleColors	Colour the console's lines by topic and level, in a console the hook opens itself	Switch	1
Log.ConsoleLevel	The least serious lines the console shows	trace, debug, info, warning, error	info
Log.FileLevel	The least serious lines the file holds	trace, debug, info, warning, error	debug

[Server]
Url=ws://127.0.0.1:8000

[Log]
Console=yes
ConsoleLevel=debug

Each log line names its level and its topic: Hook (the start, the settings and the log), DNS (the game's look-ups and its connections to the hook), FESL, Theater, HTTP, Relay (the WebSocket to the relay server) and Discord (the connection to the Discord client). The console shows each topic in a colour of its own, warnings in yellow, errors in red and the text of debug and trace lines in gray. info follows the hook's start, its listeners, the relay server and each game connection; debug adds every packet with its fields, every HTTP request and the hook's decisions, such as the ports it listens on; trace adds the headers of HTTP requests and responses. Passwords, login keys, session tickets, game join keys and host secrets are hidden at every level.

Hosts

Each line of [Hosts] sends a host, or with *. every host below a domain, to the hook: host=protocol, where the protocol is fesl (SSLv3 over TCP), theater (TCP, and UDP datagrams on the same port) or http. Names ignore case, and a host takes the line that names it most closely. A [Hosts] section replaces the default lines as a whole, unless none of its lines can be used:

Host	Protocol
*.fesl.ea.com	fesl
*.theater.ea.com	theater
easo.ea.com	http
*.battlefieldheroes.com	http

Each FESL game has hosts of its own below the FESL and Theater domains, such as bfbc2-pc.fesl.ea.com and bfbc2-pc-server.fesl.ea.com for Battlefield: Bad Company 2 and its dedicated server, so the defaults cover them all. Battlefield Heroes also reaches its website, below battlefieldheroes.com, for its account, its store and the pages it opens in the browser.

Forward

Each line of [Forward] sends the services of a host that [Hosts] redirects, or with *. those of every such host below a domain, straight to a server instead of the relay server: host=server, where the server is host[:port] or tcp://host[:port] (the game's packets as they are, FESL decrypted) or tls://host[:port] (the same inside TLS 1.2 or later, where the server's certificate has to come from an authority in the Windows certificate store and name the server, unless VerifyCertificates=0 lets any certificate through). Without a port, the server gets the port the game connected to. Theater's datagrams go to the same host and port over UDP, which is never encrypted. An http host sends its requests to http://host:port, or https://host:port for tls://, whether the game sends them itself or through WinHTTP, and the pages the game opens in the browser open at the same path there. A line whose server [Hosts] redirects as well is left out, since the hook looks the server up through the same redirect.

[Forward]
bfbc2-pc.fesl.ea.com=tls://emulator.example.net
*.theater.ea.com=emulator.example.net

Usage

1. Install the hook as described in Installing
2. Change the defaults you need (see Configuration)
3. Start the game or its dedicated server as usual

When the game starts, the hook:

1. Reads OpenFESLHook.ini and opens the log; when no log output is on, it shows the problems it found in a dialog
2. Answers each look-up of a host from [Hosts] with a loopback address of that host's own, and makes the game's gethostbyname look-ups of other hosts fail
3. When the game connects to such an address, starts the host's listener on the port the game asked for, if it is not running yet
4. Completes the SSLv3 handshake of each FESL connection with a certificate it generated that the game's client accepts
5. Opens a WebSocket to the relay server with the game's first FESL or Theater connection, carries every packet in it and closes it with the last connection; when the relay server goes away, the game's connections close and the game connects again
6. Passes the game's HTTP requests on, opens the pages it hands to the system's browser on the relay server, and passes its DirectInput calls to the system's dinput8.dll

Discord

With Discord.Enabled on, the hook asks the relay server for the game's presence on each WebSocket (Presence) and shows it in the Discord client running on the same PC: "Playing" with the game's name, what the player is doing, the elapsed time and the players of the server, as the relay server describes them, and a button, OpenFESL, that opens the relay server's website, at the host and port of Server.Url over https:// for wss:// and http:// for ws://, on the game's page when the server names one. The hook adds nothing about the game itself: a game whose FESL and Theater go to [Forward] servers opens no WebSocket and shows nothing, and a Battlefield Heroes dedicated server asks for no presence. The presence is cleared when the WebSocket closes. Without a Discord client the hook tries again with growing pauses, and Discord's own activity privacy settings decide who sees the presence.

Battlefield Heroes

Started without +sessionId, BFHeroes.exe opens the hook's launcher instead of closing:

1. Choose Play to join a game or Server to host one
2. To play, enter the account and password the relay server knows; a server asks for none, since it signs in with the relay server's shared server account. Remember me keeps the mode, the account entered to play, language, map and ranked choice in %LOCALAPPDATA%\OpenFESLHook\bfheroes.ini, and the password in the Windows Credential Manager of the current user, never in the file. Unticking Remember me, or a sign-in the relay server refuses with the remembered password, removes the password
3. Choose the game's language (System default follows Windows), and for a server a map from its maplist.con (or the server's own map list) and whether it is ranked
4. The launcher signs in at the relay server (Launcher sign-in), starts the game or the server with the session it was given and closes; a refused sign-in shows the server's reason. The game opens on its hero selection

The launcher's texts follow the Windows display language: Polish for Polish, English for every other language. Game language sets only the game's own language.

Ticking Open Play links from the website with this copy registers the link scheme openfesl-bfheroes: for the current Windows user, under HKCU\Software\Classes\openfesl-bfheroes; the hook writes there only when you tick or untick the option. A Play link from the relay server's website, openfesl-bfheroes://launch?role=play&code=<code>, then starts this copy: the launcher opens, signs in with the link's one-time code at once and starts the game to play, on its main menu already signed in to the hero the relay server names (or on its hero selection when it names none), leaving what Remember me keeps as it was. A link to host a server, or one without a code, is refused, and a code that expired or was already used asks for a new link or the account and password. No text of a link reaches the game as its options, and a link never starts a server. One copy holds the links at a time: ticking the option in another copy moves them there, the launcher names the copy that holds them when it is another one that still exists, and unticking removes the registration only while it names this copy. Each game has a scheme of its own, so the hooks of other games never take these links over.

The launcher also starts the game with +webSiteHostName www.battlefieldheroes.com +battleFundsHostName www.battlefieldheroes.com +survey 0: without the first two the game opens none of its website's pages, such as the hero creator, and +survey 1 would open a survey page once the game quits. A game started by hand needs the same options for those pages.

A server, started this way or by hand with +dedicated 1, shows only its console. Once it has logged in, it lists its game in Theater under its name, sv.serverName, for sv.maxPlayers players, and accepts players on sv.serverPort; with sv.serverIP empty, it listens on every network interface. The server's data center is sv.prodDataCenter, or sv.stestDataCenter when the server was started with +plasmaEnvironment test, as the game's client decides it; an empty one keeps the game's default. The server is ranked only when started with +ranked, which the launcher passes when Ranked is ticked: the game reads the option as a switch, whatever its value, and without it the hook sets sv.ranked to 0 wherever ServerSettings.con or the console sets it. A build in which the hook does not find every part it needs runs on without that part, and the log names what was missing.

Theater gives the server's game an identity, a UGID and a secret, the first time it lists the game. The hook keeps both in OpenFESLHook_Identity_<port>.ini next to dinput8.dll, one file per sv.serverPort, and lists the game under the same identity after every restart, so the relay server's approval of the server still holds. The file holds the server's secret, so keep it private; copy it along when you move the server to another PC, and rename it when you change the server's port. Without the file, or with one the hook cannot read, Theater gives the game a new identity, which replaces the file.

The game's own server code sets the game's version and attributes from its settings, and the hook adds the attributes the game's server browser and Play Now filter on, which Theater lists with the prefix B-U-:

Attribute	Value
ranked, servertype, easyzone, community_name	sv.ranked, sv.serverType, sv.easyzone and sv.serverCommunity
data_center	The data center above
newbie_server	no
elo_rank, avg_axis_rank, avg_ally_rank	1000.0000, ServerGame.con's default Elo rank
server_state	empty, or has_players
percent_full	The players as a percentage of sv.maxPlayers
avail_slots_national, avail_slots_royal	yes while the army (team 1 national, team 2 royal) has a free seat of its half of sv.maxPlayers
army_balance	The hook's own reading of ServerGame.con's balance deltas: Balanced with even armies, Axis (national) or Allies (royal) for the army with 1 to 3 players more, MaxAxis or MaxAllies with 4 or more
map_name, map_gamemode	The map being played, in lower case, and its game mode, such as gpm_tdm

The attributes from server_state on are sent again when they change, at most every 5 seconds. Players join without the server's approval, since the client lacks the code that would answer their requests.

File formats

The hook and the relay server talk the WebSocket protocol openfesl.v1, which carries the game's packets in frames of a four-byte header; docs/relay-protocol.md describes it, the games' packet framing, the presence for Discord, the HTTP requests, browser pages and launcher sign-ins the hook sends to the server's host, and what a relay server has to do.

Credits

• GrzybDev

Thanks to:

• Aim4kill (for the research into the games' ProtoSSL client)

Special thanks to:

• EA DICE and Electronic Arts (for making Battlefield: Bad Company 2)
• Easy Studios and Electronic Arts (for making Battlefield Heroes)