sdk: Implement decompiling Lua

Closes #48.

CHANGELOG.adoc

@@ -15,6 +15,7 @@
 - dtmm: match mods to Nexus and check for updates
 - dtmt: add utility to migrate mod projects
 - dtmm: reset dtkit-patch installations
+- sdk: implement decompiling Lua files
 
 === Fixed
 

Cargo.lock

@@ -964,6 +964,7 @@ dependencies = [
  "sdk",
  "serde",
  "serde_sjson",
+ "shlex",
  "string_template",
  "tempfile",
  "tokio",

crates/dtmt/Cargo.toml

@@ -33,6 +33,7 @@ path-slash = "0.2.1"
 async-recursion = "1.0.2"
 notify = "5.1.0"
 luajit2-sys = { path = "../../lib/luajit2-sys", version = "*" }
+shlex = "1.2.0"
 
 [dev-dependencies]
 tempfile = "3.3.0"

crates/dtmt/src/cmd/bundle/extract.rs

@@ -1,3 +1,4 @@
+use std::ffi::OsStr;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
@@ -7,7 +8,7 @@ use color_eyre::{Help, Report};
 use futures::future::try_join_all;
 use futures::StreamExt;
 use glob::Pattern;
-use sdk::{Bundle, BundleFile};
+use sdk::{Bundle, BundleFile, CmdLine};
 use tokio::fs;
 
 use crate::cmd::util::resolve_bundle_paths;
@@ -89,30 +90,78 @@ pub(crate) fn command_definition() -> Command {
             Arg::new("ljd")
                 .long("ljd")
                 .help(
-                    "Path to a custom ljd executable. If not set, \
-                        `ljd` will be called from PATH.",
+                    "A custom command line to execute ljd with. It is treated as follows:\n\
+                        * if the argument is a valid path to an existing file:\n\
+                        ** if the file is called 'main.py', it is assumed that 'python.exe' \
+                        exists in PATH to execute this with.\n\
+                        ** otherwise it is treated as an executable\n\
+                        * if it's a single word, it's treated as an executable in PATH\n\
+                        * otherwise it is treated as a command line template.\n\
+                        In any case, the application being run must accept ljd's flags '-c' and '-f'.",
                 )
                 .default_value("ljd"),
         )
-        .arg(
-            Arg::new("revorb")
-                .long("revorb")
-                .help(
-                    "Path to a custom revorb executable. If not set, \
-                        `revorb` will be called from PATH.",
-                )
-                .default_value("revorb"),
-        )
-        .arg(
-            Arg::new("ww2ogg")
-                .long("ww2ogg")
-                .help(
-                    "Path to a custom ww2ogg executable. If not set, \
-                        `ww2ogg` will be called from PATH.\nSee the documentation for how \
-                        to set up the script for this.",
-                )
-                .default_value("ww2ogg"),
-        )
+    // .arg(
+    //     Arg::new("revorb")
+    //         .long("revorb")
+    //         .help(
+    //             "Path to a custom revorb executable. If not set, \
+    //                 `revorb` will be called from PATH.",
+    //         )
+    //         .default_value("revorb"),
+    // )
+    // .arg(
+    //     Arg::new("ww2ogg")
+    //         .long("ww2ogg")
+    //         .help(
+    //             "Path to a custom ww2ogg executable. If not set, \
+    //                 `ww2ogg` will be called from PATH.\nSee the documentation for how \
+    //                 to set up the script for this.",
+    //         )
+    //         .default_value("ww2ogg"),
+    // )
+}
+
+#[tracing::instrument]
+async fn parse_command_line_template(tmpl: &String) -> Result<CmdLine> {
+    if tmpl.trim().is_empty() {
+        eyre::bail!("Command line template must not be empty");
+    }
+
+    let mut cmd = if matches!(fs::try_exists(tmpl).await, Ok(true)) {
+        let path = PathBuf::from(tmpl);
+        if path.file_name() == Some(OsStr::new("main.py")) {
+            let arg = path.display().to_string();
+            let mut cmd = CmdLine::new("python");
+            cmd.arg("-c").arg(shlex::quote(&arg).to_string());
+            cmd
+        } else {
+            CmdLine::new(path)
+        }
+    } else {
+        let Some(args) = shlex::split(tmpl) else {
+            eyre::bail!("Invalid shell syntax");
+        };
+
+        // We already checked that the template is not empty
+        let mut cmd = CmdLine::new(args[0].clone());
+        let mut it = args.iter();
+        // Skip the first one, that's the command name
+        it.next();
+
+        for arg in it {
+            cmd.arg(arg);
+        }
+
+        cmd
+    };
+
+    // Add ljd flags
+    cmd.arg("-c");
+
+    tracing::debug!("Parsed command line template: {:?}", cmd);
+
+    Ok(cmd)
 }
 
 #[tracing::instrument(skip_all)]
@@ -121,16 +170,19 @@ pub(crate) async fn run(mut ctx: sdk::Context, matches: &ArgMatches) -> Result<(
         let ljd_bin = matches
             .get_one::<String>("ljd")
             .expect("no default value for 'ljd' parameter");
-        let revorb_bin = matches
-            .get_one::<String>("revorb")
-            .expect("no default value for 'revorb' parameter");
-        let ww2ogg_bin = matches
-            .get_one::<String>("ww2ogg")
-            .expect("no default value for 'ww2ogg' parameter");
+        // let revorb_bin = matches
+        //     .get_one::<String>("revorb")
+        //     .expect("no default value for 'revorb' parameter");
+        // let ww2ogg_bin = matches
+        //     .get_one::<String>("ww2ogg")
+        //     .expect("no default value for 'ww2ogg' parameter");
 
-        ctx.ljd = Some(ljd_bin.clone());
-        ctx.revorb = Some(revorb_bin.clone());
-        ctx.ww2ogg = Some(ww2ogg_bin.clone());
+        ctx.ljd = parse_command_line_template(ljd_bin)
+            .await
+            .map(Option::Some)
+            .wrap_err("Failed to parse command line template for flag 'ljd'")?;
+        // ctx.revorb = Some(revorb_bin.clone());
+        // ctx.ww2ogg = Some(ww2ogg_bin.clone());
     }
 
     let includes = match matches.get_many::<Pattern>("include") {

lib/sdk/src/binary.rs

@@ -133,6 +133,23 @@ pub mod sync {
         make_skip!(skip_u8, read_u8, u8);
         make_skip!(skip_u32, read_u32, u32);
 
+        // Implementation based on https://en.wikipedia.com/wiki/LEB128
+        fn read_uleb128(&mut self) -> io::Result<u64> {
+            let mut result: u64 = 0;
+            let mut shift: u64 = 0;
+
+            loop {
+                let byte = ReadExt::read_u8(self)? as u64;
+                result |= (byte & 0x7f) << shift;
+
+                if byte < 0x80 {
+                    return Ok(result);
+                }
+
+                shift += 7;
+            }
+        }
+
         fn skip_padding(&mut self) -> io::Result<()> {
             let pos = self.stream_position()?;
             let padding_size = 16 - (pos % 16);

lib/sdk/src/context.rs

@@ -1,10 +1,59 @@
-use std::path::PathBuf;
+use std::process::Command;
+use std::{ffi::OsString, path::PathBuf};
 
 use crate::murmur::{Dictionary, HashGroup, IdString64, Murmur32, Murmur64};
 
+pub struct CmdLine {
+    cmd: OsString,
+    args: Vec<OsString>,
+}
+
+impl CmdLine {
+    pub fn new(cmd: impl Into<OsString>) -> Self {
+        Self {
+            cmd: cmd.into(),
+            args: vec![],
+        }
+    }
+
+    pub fn arg(&mut self, arg: impl Into<OsString>) -> &mut Self {
+        self.args.push(arg.into());
+        self
+    }
+}
+
+impl std::fmt::Debug for CmdLine {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CmdLine")
+            .field("cmd", &self.cmd)
+            .field("args", &self.args)
+            .finish()
+    }
+}
+
+impl std::fmt::Display for CmdLine {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "\"{}\"", self.cmd.to_string_lossy())?;
+
+        for arg in &self.args {
+            write!(f, " \"{}\"", arg.to_string_lossy())?;
+        }
+
+        Ok(())
+    }
+}
+
+impl From<&CmdLine> for Command {
+    fn from(value: &CmdLine) -> Self {
+        let mut cmd = Command::new(&value.cmd);
+        cmd.args(&value.args);
+        cmd
+    }
+}
+
 pub struct Context {
     pub lookup: Dictionary,
-    pub ljd: Option<String>,
+    pub ljd: Option<CmdLine>,
     pub revorb: Option<String>,
     pub ww2ogg: Option<String>,
     pub game_dir: Option<PathBuf>,

lib/sdk/src/filetype/lua.rs

@@ -1,24 +1,109 @@
+use std::env;
 use std::ffi::CStr;
 use std::ffi::CString;
 use std::io::Cursor;
+use std::io::Read;
 use std::io::Write;
+use std::process::Command;
 
 use color_eyre::eyre;
 use color_eyre::eyre::Context;
 use color_eyre::Result;
 use luajit2_sys as lua;
+use tokio::fs;
 
+use crate::binary::sync::ReadExt;
 use crate::binary::sync::WriteExt;
 use crate::bundle::file::{BundleFileVariant, UserFile};
 use crate::{BundleFile, BundleFileType};
 
+const BITSQUID_LUAJIT_HEADER: u32 = 0x8253461B;
+
 #[tracing::instrument(skip_all, fields(buf_len = data.as_ref().len()))]
-pub(crate) async fn decompile<T>(_ctx: &crate::Context, data: T) -> Result<Vec<UserFile>>
+pub(crate) async fn decompile<T>(ctx: &crate::Context, data: T) -> Result<Vec<UserFile>>
 where
     T: AsRef<[u8]>,
 {
-    let mut _r = Cursor::new(data.as_ref());
-    todo!();
+    let data = data.as_ref();
+    let length = {
+        let mut r = Cursor::new(data);
+        r.read_u32()? as usize
+    };
+
+    // This skips the unknown bytes 5..12
+    let content = &data[12..];
+    eyre::ensure!(
+        content.len() == length,
+        "Content length doesn't match. Expected {}, got {}",
+        length,
+        content.len()
+    );
+
+    let name = {
+        let mut r = Cursor::new(content);
+
+        eyre::ensure!(
+            r.read_u32()? == BITSQUID_LUAJIT_HEADER,
+            "Invalid magic bytes"
+        );
+
+        // Skip additional header bytes
+        let _ = r.read_uleb128()?;
+        let length = r.read_uleb128()? as usize;
+
+        let mut buf = vec![0u8; length];
+        r.read_exact(&mut buf)?;
+        let mut s = String::from_utf8(buf)
+            .wrap_err_with(|| format!("Invalid byte sequence for LuaJIT bytecode name"))?;
+        // Remove the leading `@`
+        s.remove(0);
+        s
+    };
+
+    let mut temp = env::temp_dir();
+    // Using the actual file name and keeping it in case of an error makes debugging easier.
+    // But to avoid creating a bunch of folders, we flatten the name.
+    temp.push(name.replace('/', "_"));
+    temp.set_extension("luao");
+
+    tracing::debug!(
+        "Writing temporary LuaJIT bytecode file to '{}'",
+        temp.display()
+    );
+
+    fs::write(&temp, content)
+        .await
+        .wrap_err_with(|| format!("Failed to write LuaJIT bytecode to '{}'", temp.display()))?;
+
+    let mut cmd = ctx
+        .ljd
+        .as_ref()
+        .map(|c| c.into())
+        .unwrap_or_else(|| Command::new("ljd"));
+
+    cmd.arg("-f").arg(&temp);
+
+    tracing::debug!("Executing command: '{:?}'", cmd);
+
+    let output = cmd.output().wrap_err("Failed to run ljd")?;
+
+    if !output.stderr.is_empty() {
+        eyre::bail!(
+            "Decompilation failed: {}",
+            String::from_utf8_lossy(&output.stderr)
+        );
+    }
+
+    let content = output.stdout;
+
+    if let Err(err) = fs::remove_file(&temp)
+        .await
+        .wrap_err("Failed to remove temporary file")
+    {
+        tracing::warn!("{:?}", err);
+    }
+
+    Ok(vec![UserFile::with_name(content, name)])
 }
 
 #[tracing::instrument(skip_all)]

lib/sdk/src/lib.rs

@@ -8,4 +8,4 @@ pub use binary::{FromBinary, ToBinary};
 pub use bundle::database::BundleDatabase;
 pub use bundle::decompress;
 pub use bundle::{Bundle, BundleFile, BundleFileType, BundleFileVariant};
-pub use context::Context;
+pub use context::{CmdLine, Context};