feat: store magic signature as a meaningful constant

src/cli/build.rs

@@ -8,6 +8,11 @@ use tokio::{
 use anyhow::Result;
 use mlua::Compiler as LuaCompiler;
 
+// The signature which separates indicates the presence of bytecode to execute
+// If a binary contains this magic signature as the last 8 bytes, that must mean
+//  it is a standalone binary
+pub const MAGIC: &[u8; 8] = b"cr3sc3nt";
+
 /**
     Compiles and embeds the bytecode of a requested lua file to form a standalone binary,
     then writes it to an output file, with the required permissions.
@@ -32,10 +37,6 @@ pub async fn build_standalone<T: AsRef<Path>>(
     let mut patched_bin = fs::read(env::current_exe()?).await?;
     let base_bin_offset = u64::try_from(patched_bin.len())?;
 
-    // The signature which separates indicates the presence of bytecode to execute
-    // If a binary contains this signature, that must mean it is a standalone binary
-    let signature: Vec<u8> = vec![0x4f, 0x3e, 0xf8, 0x41, 0xc3, 0x3a, 0x52, 0x16];
-
     // Compile luau input into bytecode
     let bytecode = LuaCompiler::new()
         .set_optimization_level(2)
@@ -45,18 +46,18 @@ pub async fn build_standalone<T: AsRef<Path>>(
 
     println!("  {bytecode_prefix} {script_path}");
 
-    patched_bin.append(&mut bytecode.clone());
+    patched_bin.extend(&bytecode);
 
-    let mut meta = base_bin_offset.to_ne_bytes().to_vec();
+    let mut meta = base_bin_offset.to_ne_bytes().to_vec(); // Start with the base bytecode offset
 
     // Include metadata in the META chunk, each field is 8 bytes
-    meta.append(&mut (bytecode.len() as u64).to_ne_bytes().to_vec()); // Size of bytecode, used to calculate end offset at runtime
-    meta.append(&mut 1_u64.to_ne_bytes().to_vec()); // Number of files, padded with null bytes - for future use
+    meta.extend((bytecode.len() as u64).to_ne_bytes()); // Size of bytecode, used to calculate end offset at runtime
+    meta.extend(1_u64.to_ne_bytes()); // Number of files, padded with null bytes - for future use
 
-    patched_bin.append(&mut meta);
+    patched_bin.extend(meta);
 
-    // Append the signature to the base binary
-    patched_bin.append(&mut signature.clone());
+    // Append the magic signature to the base binary
+    patched_bin.extend(MAGIC);
 
     // Write the compiled binary to file
     #[cfg(target_family = "unix")]

src/executor.rs

@@ -1,5 +1,6 @@
 use std::{env, ops::ControlFlow, process::ExitCode};
 
+use crate::cli::build::MAGIC;
 use lune::Lune;
 
 use anyhow::Result;
@@ -9,10 +10,7 @@ use tokio::fs::read as read_to_vec;
     Returns information about whether the execution environment is standalone
     or not, the standalone binary signature, and the contents of the binary.
 */
-pub async fn check_env() -> (bool, Vec<u8>, Vec<u8>) {
-    // Signature which is only present in standalone lune binaries
-    let signature: Vec<u8> = vec![0x4f, 0x3e, 0xf8, 0x41, 0xc3, 0x3a, 0x52, 0x16];
-
+pub async fn check_env() -> (bool, Vec<u8>) {
     // Read the current lune binary to memory
     let bin = if let Ok(contents) = read_to_vec(
         env::current_exe().expect("failed to get path to current running lune executable"),
@@ -24,20 +22,21 @@ pub async fn check_env() -> (bool, Vec<u8>, Vec<u8>) {
         Vec::new()
     };
 
-    let is_standalone = !bin.is_empty() && bin[bin.len() - signature.len()..bin.len()] == signature;
+    let is_standalone =
+        !bin.is_empty() && bin[bin.len() - MAGIC.len()..bin.len()] == MAGIC.to_vec();
 
-    (is_standalone, signature, bin)
+    (is_standalone, bin)
 }
 
 /**
     Discovers, loads and executes the bytecode contained in a standalone binary.
 */
-pub async fn run_standalone(signature: Vec<u8>, bin: Vec<u8>) -> Result<ExitCode> {
+pub async fn run_standalone(bin: Vec<u8>) -> Result<ExitCode> {
     let mut bytecode_offset = 0;
     let mut bytecode_size = 0;
 
     // standalone binary structure (reversed, 8 bytes per field)
-    // [0] => signature
+    // [0] => magic signature
     // ----------------
     // -- META Chunk --
     // [1] => file count
@@ -47,21 +46,21 @@ pub async fn run_standalone(signature: Vec<u8>, bin: Vec<u8>) -> Result<ExitCode
     // -- MISC Chunk --
     // [4..n] => bytecode (variable size)
     // ----------------
-    // NOTE: All integers are 8 byte unsigned 64 bit (u64's).
+    // NOTE: All integers are 8 byte, padded, unsigned & 64 bit (u64's).
 
     // The rchunks will have unequally sized sections in the beginning
     // but that doesn't matter to us because we don't need anything past the
     // middle chunks where the bytecode is stored
-    bin.rchunks(signature.len())
+    bin.rchunks(MAGIC.len())
         .enumerate()
         .try_for_each(|(idx, chunk)| {
             if bytecode_offset != 0 && bytecode_size != 0 {
                 return ControlFlow::Break(());
             }
 
-            if idx == 0 && chunk != signature {
+            if idx == 0 && chunk != MAGIC {
                 // Binary is guaranteed to be standalone, we've confirmed this before
-                unreachable!("expected proper signature for standalone binary")
+                unreachable!("expected proper magic signature for standalone binary")
             }
 
             if idx == 3 {
@@ -78,16 +77,19 @@ pub async fn run_standalone(signature: Vec<u8>, bin: Vec<u8>) -> Result<ExitCode
     // If we were able to retrieve the required metadata, we load
     // and execute the bytecode
 
+    // println!("offset: {}", bytecode_offset);
+    // println!("size: {}", bytecode_size);
+
     // Skip the first argument which is the path to current executable
     let args = env::args().skip(1).collect::<Vec<_>>();
+    let bytecode =
+        &bin[usize::try_from(bytecode_offset)?..usize::try_from(bytecode_offset + bytecode_size)?];
+
+    // println!("bytecode: {:?}", bytecode);
 
     let result = Lune::new()
         .with_args(args)
-        .run(
-            "STANDALONE",
-            &bin[usize::try_from(bytecode_offset)?
-                ..usize::try_from(bytecode_offset + bytecode_size)?],
-        )
+        .run("STANDALONE", bytecode)
         .await;
 
     Ok(match result {

src/main.rs

@@ -28,12 +28,12 @@ async fn main() -> ExitCode {
         .with_level(true)
         .init();
 
-    let (is_standalone, signature, bin) = executor::check_env().await;
+    let (is_standalone, bin) = executor::check_env().await;
 
     if is_standalone {
         // It's fine to unwrap here since we don't want to continue
         // if something fails
-        return executor::run_standalone(signature, bin).await.unwrap();
+        return executor::run_standalone(bin).await.unwrap();
     }
 
     match Cli::parse().run().await {