Bughouse FEN Validator

A javascript/java library to validate Chess FEN strings. Bughouse is the name of a chess game played by 4 players on 2 boards, where pieces captured on one board can be given to players on the other board.
"bughouse" in the name was meant to indicate that this validator is not all encompassing and comprehensive as it only checks if position is playable as opposed to legal. I.e. it will only check for showstoppers e.g. it will invalidate a position with more than 1 king of a one color, but won't a position with more than 8 pawns of one color etc. At the same time, this validator does go beyound typical pure regex validation.

Utility

Written in both js and java, it can be used both on html/js front end and java back end of the same application.

Installation

js

place /resource/static/js/chess.js in js dir of your app. E.g. in Springboot in /resource/static/js

java

Run mvn clean install and add the following to your application pom, if you are using maven.

	<dependency>
		<groupId>org.bughouse.fen</groupId>
		<artifactId>bughouse-fen-validator</artifactId>
		<version>1.0</version>
	</dependency>

For gradle, it should be
compile 'org.bughouse.fen:bughouse-fen-validator:1.0' ,
although I haven't tried it myself.

Usage

html

add a reference to chess.js in your html file:

     <script src="js/chess.js"></script>

js

call validateFen() with your FEN string, and then depending on the value of valid property of the returned object, either do error handling (e.g. display the error using error property) or continue with happy path screnario.

        const err = validateFen(fen);  
        if (!err.valid) {
        	// error handling e.g.
            // alert(err.error);
            // return;
        } 

java

add the following in your application code e.g. before sending a FEN to a chess engine:

    ReturnCode returnCode = FenValidator.getInstance().validate(query.getFen());
    if (!returnCode.isValid()) {
    	// Error handling e.g.
	// throw new ResponseStatusException(HttpStatus.CONFLICT, returnCode.getDescription());
    }

    if using in a web service end point in SpringBoot, as in example above, add the following line to your application.properties file, so the error description does actually show up in the response:
    server.error.include-message=always

command line

   To check individual FENs in command prompt, replace the prepopulated FEN value in the line below in your pom.xml with yours and execute mvn exec:java

	<argument>KrkR4/8/8/8/8/8/8/8 w - - 0 1</argument>     

Credits

The bughouse FEN validator is reusing regex validation logic of chess.js, plus additing extra validation rules on top of it.
The java layer is implemented using Nashorn JavaScript engine for Java

License

GNU General Public License V3 except for chess.js which has its on license in the comments of the file header