Aether.java

package aether;

import aether.lexer.Lexer;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.file.Files;
import java.nio.file.Paths;

public class Aether {
 private static final Interpreter interpreter = new Interpreter();
 // Define your custom language extension here
 private static final String FILE_EXTENSION = ".aether";

 static void main(String[] args) throws IOException {
 if (args.length > 1) {
 System.out.println("Usage: java -jar target/java-project-aether-1.0-SNAPSHOT.jar [script" + FILE_EXTENSION + "]");
 System.exit(64);
 } else if (args.length == 1) {
 runFile(args[0]);
 } else {
 runPrompt();
 }
 }

 private static void runFile(String path) throws IOException {
 // Enforce the custom file extension constraint
 if (!path.endsWith(FILE_EXTENSION)) {
 System.err.println("Error: Invalid file format. Aether source files must end with '" + FILE_EXTENSION + "'.");
 System.exit(65); // EX_DATAERR: Input data was incorrect in some way
 }

 // 2. Define the base directory where your scripts are allowed
 var baseDir = Paths.get("scripts").toAbsolutePath().normalize();

 // 3. Resolve the requested path against the base directory
 var targetPath = baseDir.resolve(path).normalize();

 // 4. Vulnerability Check: Ensure the resolved path starts with the base directory
 if (!targetPath.startsWith(baseDir)) {
 throw new SecurityException("Access denied: File path outside of allowed directory.");
 }

 // 5. Proceed with execution
 var bytes = Files.readAllBytes(targetPath);
 run(new String(bytes));
 }

 private static void runPrompt() throws IOException {
 var input = new InputStreamReader(System.in);
 var reader = new BufferedReader(input);

 for (;;) {
 System.out.print("aether> ");
 var line = reader.readLine();
 if (line == null) break;
 run(line);
 }
 }

 private static void run(String source) {
 if (source.trim().isEmpty()) return;
 try {
 var lexer = new Lexer(source);
 var tokens = lexer.scanTokens();
 var parser = new Parser(tokens);
 var statements = parser.parse();

 if (statements == null || statements.contains(null)) {
 return;
 }

 interpreter.interpret(statements);
 } catch (Exception e) {
 System.err.println("Error: " + e.getMessage());
 }
 }
}