feat: add --dry flag

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://git.rustybever.be/Chewing_Bever/alex/src/branch/dev)
 
+### Added
+
+* `--dry` flag to inspect command that will be run
+
 ## [0.2.0](https://git.rustybever.be/Chewing_Bever/alex/src/tag/0.2.0)
 
 ### Added

Dockerfile

@@ -18,7 +18,7 @@ RUN cargo build && \
 
 # We use ${:-} instead of a default value because the argument is always passed
 # to the build, it'll just be blank most likely
-FROM eclipse-temurin:17-jre-alpine
+FROM eclipse-temurin:18-jre-alpine
 
 # Build arguments
 ARG MC_VERSION=1.19.4

src/main.rs

@@ -66,6 +66,11 @@ struct Cli {
     /// How frequently to perform a backup, in minutes; 0 to disable.
     #[arg(short = 't', long, default_value_t = 0, env = "ALEX_FREQUENCY")]
     frequency: u64,
+
+    /// Don't actually run the server, but simply output the server configuration that would have
+    /// been ran
+    #[arg(short, long, default_value_t = false)]
+    dry: bool,
 }
 
 fn backups_thread(counter: Arc<Mutex<server::ServerProcess>>, frequency: u64) {
@@ -85,7 +90,7 @@ fn main() -> io::Result<()> {
     let (_, mut signals) = signals::install_signal_handlers()?;
     let cli = Cli::parse();
 
-    let cmd = server::ServerCommand::new(cli.type_, &cli.server_version)
+    let mut cmd = server::ServerCommand::new(cli.type_, &cli.server_version)
         .java(&cli.java)
         .jar(cli.jar)
         .config(cli.config)
@@ -94,6 +99,14 @@ fn main() -> io::Result<()> {
         .xms(cli.xms)
         .xmx(cli.xmx)
         .max_backups(cli.max_backups);
+    cmd.canonicalize()?;
+
+    if cli.dry {
+        print!("{}", cmd);
+
+        return Ok(());
+    }
+
     let counter = Arc::new(Mutex::new(cmd.spawn()?));
 
     if cli.frequency > 0 {

src/server/command.rs

@@ -105,14 +105,19 @@ impl ServerCommand {
         Ok(())
     }
 
-    pub fn spawn(self) -> std::io::Result<ServerProcess> {
+    /// Canonicalize all paths to absolute paths. Without this command, all paths will be
+    /// interpreted relatively from the config directory.
+    pub fn canonicalize(&mut self) -> std::io::Result<()> {
         // To avoid any issues, we use absolute paths for everything when spawning the process
-        let jar = self.jar.canonicalize()?;
-        let config_dir = self.config_dir.canonicalize()?;
-        let world_dir = self.world_dir.canonicalize()?;
-        let backup_dir = self.backup_dir.canonicalize()?;
+        self.jar = self.jar.canonicalize()?;
+        self.config_dir = self.config_dir.canonicalize()?;
+        self.world_dir = self.world_dir.canonicalize()?;
+        self.backup_dir = self.backup_dir.canonicalize()?;
 
-        self.accept_eula()?;
+        Ok(())
+    }
+
+    fn create_cmd(&self) -> std::process::Command {
         let mut cmd = Command::new(&self.java);
 
         // Apply JVM optimisation flags
@@ -155,24 +160,56 @@ impl ServerCommand {
             ]);
         }
 
-        cmd.current_dir(&config_dir)
+        cmd.current_dir(&self.config_dir)
             .arg("-jar")
-            .arg(&jar)
+            .arg(&self.jar)
             .arg("--universe")
-            .arg(&world_dir)
+            .arg(&self.world_dir)
             .arg("--nogui")
             .stdin(Stdio::piped());
 
+        cmd
+    }
+
+    pub fn spawn(&mut self) -> std::io::Result<ServerProcess> {
+        let mut cmd = self.create_cmd();
+        self.accept_eula()?;
         let child = cmd.spawn()?;
 
         Ok(ServerProcess::new(
             self.type_,
-            self.version,
-            config_dir,
-            world_dir,
-            backup_dir,
+            self.version.clone(),
+            self.config_dir.clone(),
+            self.world_dir.clone(),
+            self.backup_dir.clone(),
             self.max_backups,
             child,
         ))
     }
 }
+
+impl fmt::Display for ServerCommand {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let cmd = self.create_cmd();
+
+        write!(f, "Command: {}\n", self.java)?;
+        write!(f, "Working dir: {}\n", self.config_dir.as_path().display())?;
+
+        // Print command env vars
+        write!(f, "Environment:\n")?;
+
+        for (key, val) in cmd.get_envs().filter(|(_, v)| v.is_some()) {
+            let val = val.unwrap();
+            write!(f, "  {}={}\n", key.to_string_lossy(), val.to_string_lossy())?;
+        }
+
+        // Print command arguments
+        write!(f, "Arguments:\n")?;
+
+        for arg in cmd.get_args() {
+            write!(f, "  {}\n", arg.to_string_lossy())?;
+        }
+
+        Ok(())
+    }
+}