From 13dc2b53526eb87cbb891e9756fe6db2970499e2 Mon Sep 17 00:00:00 2001
From: Alex Orlenko <zxteam@protonmail.com>
Date: Sat, 12 Jul 2025 13:08:33 +0100
Subject: [PATCH] Don't release Lua lock prematurely when when accessing
 `Buffer` bytes (Luau)

---
 src/buffer.rs     | 29 ++++++++++++++++++-----------
 src/conversion.rs |  2 +-
 src/serde/de.rs   |  5 ++++-
 3 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/src/buffer.rs b/src/buffer.rs
index 181e369..52beffe 100644
--- a/src/buffer.rs
+++ b/src/buffer.rs
@@ -1,6 +1,7 @@
 #[cfg(feature = "serde")]
 use serde::ser::{Serialize, Serializer};
 
+use crate::state::RawLua;
 use crate::types::ValueRef;
 
 /// A Luau buffer type.
@@ -16,12 +17,14 @@ pub struct Buffer(pub(crate) ValueRef);
 impl Buffer {
     /// Copies the buffer data into a new `Vec<u8>`.
     pub fn to_vec(&self) -> Vec<u8> {
-        unsafe { self.as_slice().to_vec() }
+        let lua = self.0.lua.lock();
+        self.as_slice(&lua).to_vec()
     }
 
     /// Returns the length of the buffer.
     pub fn len(&self) -> usize {
-        unsafe { self.as_slice().len() }
+        let lua = self.0.lua.lock();
+        self.as_slice(&lua).len()
     }
 
     /// Returns `true` if the buffer is empty.
@@ -34,7 +37,8 @@ impl Buffer {
     /// Offset is 0-based.
     #[track_caller]
     pub fn read_bytes<const N: usize>(&self, offset: usize) -> [u8; N] {
-        let data = unsafe { self.as_slice() };
+        let lua = self.0.lua.lock();
+        let data = self.as_slice(&lua);
         let mut bytes = [0u8; N];
         bytes.copy_from_slice(&data[offset..offset + N]);
         bytes
@@ -45,21 +49,23 @@ impl Buffer {
     /// Offset is 0-based.
     #[track_caller]
     pub fn write_bytes(&self, offset: usize, bytes: &[u8]) {
+        let lua = self.0.lua.lock();
         let data = unsafe {
-            let (buf, size) = self.as_raw_parts();
+            let (buf, size) = self.as_raw_parts(&lua);
             std::slice::from_raw_parts_mut(buf, size)
         };
         data[offset..offset + bytes.len()].copy_from_slice(bytes);
     }
 
-    pub(crate) unsafe fn as_slice(&self) -> &[u8] {
-        let (buf, size) = self.as_raw_parts();
-        std::slice::from_raw_parts(buf, size)
+    pub(crate) fn as_slice(&self, lua: &RawLua) -> &[u8] {
+        unsafe {
+            let (buf, size) = self.as_raw_parts(lua);
+            std::slice::from_raw_parts(buf, size)
+        }
     }
 
     #[cfg(feature = "luau")]
-    unsafe fn as_raw_parts(&self) -> (*mut u8, usize) {
-        let lua = self.0.lua.lock();
+    unsafe fn as_raw_parts(&self, lua: &RawLua) -> (*mut u8, usize) {
         let mut size = 0usize;
         let buf = ffi::lua_tobuffer(lua.ref_thread(), self.0.index, &mut size);
         mlua_assert!(!buf.is_null(), "invalid Luau buffer");
@@ -67,7 +73,7 @@ impl Buffer {
     }
 
     #[cfg(not(feature = "luau"))]
-    unsafe fn as_raw_parts(&self) -> (*mut u8, usize) {
+    unsafe fn as_raw_parts(&self, lua: &RawLua) -> (*mut u8, usize) {
         unreachable!()
     }
 }
@@ -75,7 +81,8 @@ impl Buffer {
 #[cfg(feature = "serde")]
 impl Serialize for Buffer {
     fn serialize<S: Serializer>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error> {
-        serializer.serialize_bytes(unsafe { self.as_slice() })
+        let lua = self.0.lua.lock();
+        serializer.serialize_bytes(self.as_slice(&lua))
     }
 }
 
diff --git a/src/conversion.rs b/src/conversion.rs
index b7dfa30..f1f6ddc 100644
--- a/src/conversion.rs
+++ b/src/conversion.rs
@@ -645,7 +645,7 @@ impl FromLua for BString {
         match value {
             Value::String(s) => Ok((*s.as_bytes()).into()),
             #[cfg(feature = "luau")]
-            Value::Buffer(buf) => unsafe { Ok(buf.as_slice().into()) },
+            Value::Buffer(buf) => Ok(buf.to_vec().into()),
             _ => Ok((*lua
                 .coerce_string(value)?
                 .ok_or_else(|| Error::FromLuaConversionError {
diff --git a/src/serde/de.rs b/src/serde/de.rs
index 69d9056..07abd30 100644
--- a/src/serde/de.rs
+++ b/src/serde/de.rs
@@ -165,7 +165,10 @@ impl<'de> serde::Deserializer<'de> for Deserializer {
                 serde_userdata(ud, |value| value.deserialize_any(visitor))
             }
             #[cfg(feature = "luau")]
-            Value::Buffer(buf) => visitor.visit_bytes(unsafe { buf.as_slice() }),
+            Value::Buffer(buf) => {
+                let lua = buf.0.lua.lock();
+                visitor.visit_bytes(buf.as_slice(&lua))
+            }
             Value::Function(_)
             | Value::Thread(_)
             | Value::UserData(_)