Better Luau buffer type support.

- Add `Lua::create_buffer()` function
- Support serializing buffer type as a byte slice
- Support accessing copy of underlying bytes using `BString`

Author: khvzak

src/conversion.rs

@@ -679,19 +679,49 @@ impl<'lua> IntoLua<'lua> for BString {
 }
 
 impl<'lua> FromLua<'lua> for BString {
-    #[inline]
     fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<Self> {
         let ty = value.type_name();
-        Ok(BString::from(
-            lua.coerce_string(value)?
+        match value {
+            Value::String(s) => Ok(s.as_bytes().into()),
+            #[cfg(feature = "luau")]
+            Value::UserData(ud) if ud.1 == crate::types::SubtypeId::Buffer => unsafe {
+                let mut size = 0usize;
+                let buf = ffi::lua_tobuffer(ud.0.lua.ref_thread(), ud.0.index, &mut size);
+                mlua_assert!(!buf.is_null(), "invalid Luau buffer");
+                Ok(slice::from_raw_parts(buf as *const u8, size).into())
+            },
+            _ => Ok(lua
+                .coerce_string(value)?
                 .ok_or_else(|| Error::FromLuaConversionError {
                     from: ty,
                     to: "BString",
                     message: Some("expected string or number".to_string()),
                 })?
                 .as_bytes()
-                .to_vec(),
-        ))
+                .into()),
+        }
+    }
+
+    unsafe fn from_stack(idx: c_int, lua: &'lua Lua) -> Result<Self> {
+        let state = lua.state();
+        match ffi::lua_type(state, idx) {
+            ffi::LUA_TSTRING => {
+                let mut size = 0;
+                let data = ffi::lua_tolstring(state, idx, &mut size);
+                Ok(slice::from_raw_parts(data as *const u8, size).into())
+            }
+            #[cfg(feature = "luau")]
+            ffi::LUA_TBUFFER => {
+                let mut size = 0;
+                let buf = ffi::lua_tobuffer(state, idx, &mut size);
+                mlua_assert!(!buf.is_null(), "invalid Luau buffer");
+                Ok(slice::from_raw_parts(buf as *const u8, size).into())
+            }
+            _ => {
+                // Fallback to default
+                Self::from_lua(lua.stack_value(idx), lua)
+            }
+        }
     }
 }
 

src/lua.rs

@@ -1373,6 +1373,27 @@ impl Lua {
         }
     }
 
+    /// Create and return a Luau [buffer] object from a byte slice of data.
+    ///
+    /// Requires `feature = "luau"`
+    ///
+    /// [buffer]: https://luau-lang.org/library#buffer-library
+    #[cfg(feature = "luau")]
+    pub fn create_buffer(&self, buf: impl AsRef<[u8]>) -> Result<AnyUserData> {
+        let state = self.state();
+        unsafe {
+            if self.unlikely_memory_error() {
+                crate::util::push_buffer(self.ref_thread(), buf.as_ref(), false)?;
+                return Ok(AnyUserData(self.pop_ref_thread(), SubtypeId::Buffer));
+            }
+
+            let _sg = StackGuard::new(state);
+            check_stack(state, 4)?;
+            crate::util::push_buffer(state, buf.as_ref(), true)?;
+            Ok(AnyUserData(self.pop_ref(), SubtypeId::Buffer))
+        }
+    }
+
     /// Creates and returns a new empty table.
     pub fn create_table(&self) -> Result<Table> {
         self.create_table_with_capacity(0, 0)

src/serde/de.rs

@@ -148,6 +148,14 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
             Value::UserData(ud) if ud.is_serializable() => {
                 serde_userdata(ud, |value| value.deserialize_any(visitor))
             }
+            #[cfg(feature = "luau")]
+            Value::UserData(ud) if ud.1 == crate::types::SubtypeId::Buffer => unsafe {
+                let mut size = 0usize;
+                let buf = ffi::lua_tobuffer(ud.0.lua.ref_thread(), ud.0.index, &mut size);
+                mlua_assert!(!buf.is_null(), "invalid Luau buffer");
+                let buf = std::slice::from_raw_parts(buf as *const u8, size);
+                visitor.visit_bytes(buf)
+            },
             Value::Function(_)
             | Value::Thread(_)
             | Value::UserData(_)

src/userdata.rs

@@ -1340,6 +1340,19 @@ impl<'lua> Serialize for AnyUserData<'lua> {
         S: Serializer,
     {
         let lua = self.0.lua;
+
+        // Special case for Luau buffer type
+        #[cfg(feature = "luau")]
+        if self.1 == SubtypeId::Buffer {
+            let buf = unsafe {
+                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");
+                std::slice::from_raw_parts(buf as *const u8, size)
+            };
+            return serializer.serialize_bytes(buf);
+        }
+
         let data = unsafe {
             let _ = lua
                 .get_userdata_ref_type_id(&self.0)

src/util/mod.rs

@@ -253,6 +253,20 @@ pub unsafe fn push_string(state: *mut ffi::lua_State, s: &[u8], protect: bool) -
     }
 }
 
+// Uses 3 stack spaces (when protect), does not call checkstack.
+#[cfg(feature = "luau")]
+#[inline(always)]
+pub unsafe fn push_buffer(state: *mut ffi::lua_State, b: &[u8], protect: bool) -> Result<()> {
+    let data = if protect {
+        protect_lua!(state, 0, 1, |state| ffi::lua_newbuffer(state, b.len()))?
+    } else {
+        ffi::lua_newbuffer(state, b.len())
+    };
+    let buf = slice::from_raw_parts_mut(data as *mut u8, b.len());
+    buf.copy_from_slice(b);
+    Ok(())
+}
+
 // Uses 3 stack spaces, does not call checkstack.
 #[inline]
 pub unsafe fn push_table(

tests/conversion.rs

@@ -2,6 +2,7 @@ use std::borrow::Cow;
 use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
 use std::ffi::{CStr, CString};
 
+use bstr::BString;
 use maplit::{btreemap, btreeset, hashmap, hashset};
 use mlua::{
     AnyUserData, Error, Function, IntoLua, Lua, RegistryKey, Result, Table, Thread, UserDataRef,
@@ -409,3 +410,46 @@ fn test_conv_array() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_bstring_from_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    let s = lua.create_string("hello, world")?;
+    let bstr = lua.unpack::<BString>(Value::String(s))?;
+    assert_eq!(bstr, "hello, world");
+
+    let bstr = lua.unpack::<BString>(Value::Integer(123))?;
+    assert_eq!(bstr, "123");
+
+    let bstr = lua.unpack::<BString>(Value::Number(-123.55))?;
+    assert_eq!(bstr, "-123.55");
+
+    // Test from stack
+    let f = lua.create_function(|_, bstr: BString| Ok(bstr))?;
+    let bstr = f.call::<_, BString>("hello, world")?;
+    assert_eq!(bstr, "hello, world");
+
+    let bstr = f.call::<_, BString>(-43.22)?;
+    assert_eq!(bstr, "-43.22");
+
+    Ok(())
+}
+
+#[cfg(feature = "luau")]
+#[test]
+fn test_bstring_from_lua_buffer() -> Result<()> {
+    let lua = Lua::new();
+
+    let b = lua.create_buffer("hello, world")?;
+    let bstr = lua.unpack::<BString>(Value::UserData(b))?;
+    assert_eq!(bstr, "hello, world");
+
+    // Test from stack
+    let f = lua.create_function(|_, bstr: BString| Ok(bstr))?;
+    let buf = lua.create_buffer("hello, world")?;
+    let bstr = f.call::<_, BString>(buf)?;
+    assert_eq!(bstr, "hello, world");
+
+    Ok(())
+}

tests/serde.rs

@@ -728,3 +728,30 @@ fn test_arbitrary_precision() {
         "{\n  [\"$serde_json::private::Number\"] = \"124.4\",\n}"
     );
 }
+
+#[cfg(feature = "luau")]
+#[test]
+fn test_buffer_serialize() {
+    let lua = Lua::new();
+
+    let buf = lua.create_buffer(&[1, 2, 3, 4]).unwrap();
+    let val = serde_value::to_value(&buf).unwrap();
+    assert_eq!(val, serde_value::Value::Bytes(vec![1, 2, 3, 4]));
+
+    // Try empty buffer
+    let buf = lua.create_buffer(&[]).unwrap();
+    let val = serde_value::to_value(&buf).unwrap();
+    assert_eq!(val, serde_value::Value::Bytes(vec![]));
+}
+
+#[cfg(feature = "luau")]
+#[test]
+fn test_buffer_from_value() {
+    let lua = Lua::new();
+
+    let buf = lua.create_buffer(&[1, 2, 3, 4]).unwrap();
+    let val = lua
+        .from_value::<serde_value::Value>(Value::UserData(buf))
+        .unwrap();
+    assert_eq!(val, serde_value::Value::Bytes(vec![1, 2, 3, 4]));
+}