Metal Slug Attack Server Reimplementation

The purpose of this software is to preserve and archive a working version of Metal Slug Attack's backend server to prevent it from being lost and forgotten, as well as to retain the ability to usably play Metal Slug Attack which serves primarily to validate the accuracy of the implementation.

On October 12, 2022, SNK CORPORATION announced that this game's end of service is at January 12, 2023, 16:00 JST. Since the game version update on October 12, 2022, the game can no longer produce any more revenue for its developer/publisher, SNK CORPORATION, as medals will no longer be available for purchase. Furthermore, after January 12, 2023, users will have no way of playing the game since, presumably, all the servers would be shut down and taken offline. Hence, this game is considered as abandonware. This project was humbly started to offer an archived implementation of the backend server so as to keep the game available and accessible to everyone.

Coming soon!

1. Install Git and Go if you do not have them installed already.

2. Clone this Git repository to your local workspace:

   git clone https://github.com/jamestiotio/msattack

   If you have already cloned an older version of the Git repository, you can simply run the following command from the root of the repository to get the latest version:

   git pull

3. Connect your phone or your emulator to send Internet traffic via your PC.

4. Redirect traffic by installing and using your favorite proxy daemon (mitmproxy, Fiddler Classic, Burp Suite, Wireshark, Charles Proxy, etc.) Ensure that the certificate of your selected proxy software is installed as a trusted system-level root CA certificate (which might require rooting on Android). Since Metal Slug Attack implements Certificate Pinning, you would also need to modify the APK/IPA respectively to disable Certificate Pinning and allow for HTTPS MITM (which might require jailbreaking on iOS). You can check this section to find a list of various tools that can be used to achieve this.

5. Once the proxy setup is done, you would need to obtain all of the required binary data. There are two main ways that you can achieve this:

   • If the original Metal Slug Attack servers are still up, you can do this by playing the game normally and intercepting all of the traffic between the Metal Slug Attack game and its server:

     mitmdump -k -w <saved-flow-dump-file> --set stream_large_bodies=1

     Then, you can download all of the required binary data by running the download_assets.py script from the root of this workspace:

     mitmdump --quiet -nr <saved-flow-dump-file> -s scripts/download_assets.py

     Ensure that nothing else on your machine is accessing the data directory (and any of its files/subdirectories) as the script would place all of the necessary files there. The script assumes that it is the only accessor of the data directory at the time it is being executed and any filesystem-related race conditions might mess up the final state.

     While it might be possible to save the raw binary content of most of the files directly into the saved flow dump file without enabling streaming and process them later, it is highly improbable for this method to succeed for the master table. This is because the backend server is transmitting Base64-encoded binary data via JSON. Even with a very fast Internet speed via wired Ethernet, it is almost impossible to transmit all of the master table's contents back to the game process within the specified timeout requirements (since the bottleneck is likely to be somewhere else). Once a request has timed out, the game will attempt to retry the request. If there are 5 consecutive failed attempts for a particular request, the game will throw the communication timeout error banner. Granted, this issue can be solved by increasing the timeout value in the game's APK/IPA or maybe even by physically/directly connecting to the Metal Slug Attack server, however ridiculous/impossible that sounds. Since both options require a lot of effort, it is much simpler/easier to just stream the responses first and re-request them later separately by using the requests Python library/package.

   • If the original Metal Slug Attack servers are not up anymore, you would need to source this binary data from elsewhere. I am not including them in this repository due to 2 main reasons: to prevent copyright strikes or DMCA takedowns as the copyright for those binary assets are still owned by SNK CORPORATION, as well as to keep the size of this repository small and lean. Technically, sharing these assets should be fine since they are provided for free by default when players download and install the game anyway, which has a free "entry fee", and that sharing these assets for free do not decrease the potential revenue/profit that SNK CORPORATION would be able to make from players, but it is better to be safe than sorry. I will keep a lookout on the possible ways to publicly serve this content without violating any copyright laws (feel free to inform me if you have any information about this by publicly raising an issue or privately emailing me).

6. By default, the server uses TLS (HTTPS). Hence, in order for the server to be able to function properly, you would need to generate a self-signed TLS certificate-key pair using openssl:

   cd tls
   openssl genrsa -out snkplaymore.info.key 4096
   openssl req -key snkplaymore.info.key -new -x509 -days 25202 -out snkplaymore.info.crt

   Alternatively, you can disable TLS by setting the USE_TLS flags in config.yml and proxy.py to false.

7. You can now run the proxy service needed for the private server. If you are using mitmproxy, a script for mitmproxy has been provided here. Simply execute the following command:

   mitmdump -s scripts/proxy.py -k --set ssl_insecure=true --set keep_host_header=true --set upstream_cert=false --set keepserving=true --quiet

8. Build the private server executable by executing this command from the terminal:

   make all

   Then, run the executable by either double-clicking it or calling it via the terminal:

   ./msattack

   If you are on Windows, the executable's filename would be msattack.exe.

9. Have fun and enjoy!

This error might be caused by your antivirus or/and firewall on a Windows machine. Ensure that your antivirus or/and firewall allow traffic to flow through the private server.

This error is derived from the server being unable to bind to a certain port. Ensure that there are no other processes using the same port numbers as the private server. If you are running on an operating system that restricts ports below 1024 to privileged users only (i.e., not Windows), choose a different port above 1024 for the private server and point the proxy server to that port.

• METAL SLUG, METAL SLUG ATTACK and all related trademarks are the property of SNK CORPORATION. This project is not affiliated, endorsed or supported in any way by SNK CORPORATION. The use of information and software provided through this project may be used at your own risk. The information and software available through this project are provided as-is without any warranty or guarantee. By using this project you agree that: (1) We take no liability under any circumstance or legal theory for any software, error, omissions, loss of data or damage of any kind related to your use or exposure to any information provided through this project; (2) All software are made "AS AVAILABLE" and "AS IS" without any warranty or guarantee. All express and implied warranties are disclaimed. Some states do not allow limitations of incidental or consequential damages or on how long an implied warranty lasts, so the above may not apply to you.

• This project is non-commercial. The source code is available for free (both gratis and libre) and always will be.

• This is a black-box re-implementation project which adopts the clean-room design approach. The code in this project was written by observing the game running, inspecting the data being transmitted between the game process and the backend server to figure out the expected behavior and specifications of the private API, and then manually recreating/developing the private server to satisfy said specifications. This should put this project in the clear, legally speaking. If someone at SNK disagrees, feel free to contact me.

• If you want to contribute to this repository, your contribution must be either your own original code or open-source code with a clear acknowledgement of its origin. No code that was acquired through decompiling, disassembling, or reverse engineering executable binaries or binary files will be accepted as such methods are prohibited by SNK CORPORATION's Terms of Service for METAL SLUG ATTACK.

• No assets from the original game are included in this repository.