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mlua/src/util.rs

670 lines
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Rust
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use std::{mem, ptr};
use std::sync::Arc;
use std::ffi::CStr;
use std::any::Any;
use std::os::raw::{c_char, c_int, c_void};
use std::panic::{catch_unwind, resume_unwind, UnwindSafe};
use ffi;
use error::{Error, Result};
// Checks that Lua has enough free stack space for future stack operations. On failure, this will
// clear the stack and panic.
pub unsafe fn check_stack(state: *mut ffi::lua_State, amount: c_int) {
lua_internal_assert!(
state,
ffi::lua_checkstack(state, amount) != 0,
"out of stack space"
);
}
// Similar to `check_stack`, but returns `Error::StackError` on failure. Useful for user controlled
// sizes, which should not cause a panic.
pub unsafe fn check_stack_err(state: *mut ffi::lua_State, amount: c_int) -> Result<()> {
if ffi::lua_checkstack(state, amount) == 0 {
Err(Error::StackError)
} else {
Ok(())
}
}
// Run an operation on a lua_State and check that the stack change is what is
// expected. If the stack change does not match, clears the stack and panics.
pub unsafe fn stack_guard<F, R>(state: *mut ffi::lua_State, change: c_int, op: F) -> R
where
F: FnOnce() -> R,
{
let expected = ffi::lua_gettop(state) + change;
lua_internal_assert!(
state,
expected >= 0,
"too many stack values would be popped"
);
let res = op();
let top = ffi::lua_gettop(state);
lua_internal_assert!(
state,
ffi::lua_gettop(state) == expected,
"expected stack to be {}, got {}",
expected,
top
);
res
}
// Run an operation on a lua_State and automatically clean up the stack before
// returning. Takes the lua_State, the expected stack size change, and an
// operation to run. If the operation results in success, then the stack is
// inspected to make sure the change in stack size matches the expected change
// and otherwise this is a logic error and will panic. If the operation results
// in an error, the stack is shrunk to the value before the call. If the
// operation results in an error and the stack is smaller than the value before
// the call, then this is unrecoverable and this will panic. If this function
// panics, it will clear the stack before panicking.
pub unsafe fn stack_err_guard<F, R>(state: *mut ffi::lua_State, change: c_int, op: F) -> Result<R>
where
F: FnOnce() -> Result<R>,
{
let expected = ffi::lua_gettop(state) + change;
lua_internal_assert!(
state,
expected >= 0,
"too many stack values would be popped"
);
let res = op();
let top = ffi::lua_gettop(state);
if res.is_ok() {
lua_internal_assert!(
state,
ffi::lua_gettop(state) == expected,
"expected stack to be {}, got {}",
expected,
top
);
} else {
lua_internal_assert!(
state,
top >= expected,
"{} too many stack values popped",
top - expected
);
if top > expected {
ffi::lua_settop(state, expected);
}
}
res
}
// Call a function that calls into the Lua API and may trigger a Lua error (longjmp) in a safe way.
// Wraps the inner function in a call to `lua_pcall`, so the inner function only has access to a
// limited lua stack. `nargs` and `nresults` are similar to the parameters of `lua_pcall`, but the
// given function return type is not the return value count, instead the inner function return
// values are assumed to match the `nresults` param. Internally uses 3 extra stack spaces, and does
// not call checkstack.
pub unsafe fn protect_lua_call<F, R>(
state: *mut ffi::lua_State,
nargs: c_int,
nresults: c_int,
f: F,
) -> Result<R>
where
F: FnOnce(*mut ffi::lua_State) -> R,
{
struct Params<F, R> {
function: F,
result: R,
nresults: c_int,
}
unsafe extern "C" fn do_call<F, R>(state: *mut ffi::lua_State) -> c_int
where
F: FnOnce(*mut ffi::lua_State) -> R,
{
let params = ffi::lua_touserdata(state, -1) as *mut Params<F, R>;
ffi::lua_pop(state, 1);
let function = mem::replace(&mut (*params).function, mem::uninitialized());
ptr::write(&mut (*params).result, function(state));
// params now has function uninitialied and result initialized
if (*params).nresults == ffi::LUA_MULTRET {
ffi::lua_gettop(state)
} else {
(*params).nresults
}
}
let stack_start = ffi::lua_gettop(state) - nargs;
ffi::lua_pushcfunction(state, error_traceback);
ffi::lua_pushcfunction(state, do_call::<F, R>);
ffi::lua_rotate(state, stack_start + 1, 2);
// We are about to do some really scary stuff with the Params structure, both because
// protect_lua_call is very hot, and becuase we would like to allow the function type to be
// FnOnce rather than FnMut. We are using Params here both to pass data to the callback and
// return data from the callback.
//
// params starts out with function initialized and result uninitialized, nresults is Copy so we
// don't care about it.
let mut params = Params {
function: f,
result: mem::uninitialized(),
nresults,
};
ffi::lua_pushlightuserdata(state, &mut params as *mut Params<F, R> as *mut c_void);
let ret = ffi::lua_pcall(state, nargs + 1, nresults, stack_start + 1);
let result = mem::replace(&mut params.result, mem::uninitialized());
// params now has both function and result uninitialized, so we need to forget it so Drop isn't
// run.
mem::forget(params);
ffi::lua_remove(state, stack_start + 1);
if ret == ffi::LUA_OK {
Ok(result)
} else {
Err(pop_error(state, ret))
}
}
// Pops an error off of the stack and returns it. If the error is actually a WrappedPanic, clears
// the current lua stack and continues the panic. If the error on the top of the stack is actually
// a WrappedError, just returns it. Otherwise, interprets the error as the appropriate lua error.
// Uses 2 stack spaces, does not call lua_checkstack.
pub unsafe fn pop_error(state: *mut ffi::lua_State, err_code: c_int) -> Error {
lua_internal_assert!(
state,
err_code != ffi::LUA_OK && err_code != ffi::LUA_YIELD,
"pop_error called with non-error return code"
);
if let Some(err) = pop_wrapped_error(state) {
err
} else if is_wrapped_panic(state, -1) {
let panic = get_userdata::<WrappedPanic>(state, -1);
if let Some(p) = (*panic).0.take() {
ffi::lua_settop(state, 0);
resume_unwind(p);
} else {
lua_internal_panic!(state, "panic was resumed twice")
}
} else {
let err_string = gc_guard(state, || {
if let Some(s) = ffi::lua_tostring(state, -1).as_ref() {
CStr::from_ptr(s).to_string_lossy().into_owned()
} else {
"<unprintable error>".to_owned()
}
});
ffi::lua_pop(state, 1);
match err_code {
ffi::LUA_ERRRUN => Error::RuntimeError(err_string),
ffi::LUA_ERRSYNTAX => {
Error::SyntaxError {
// This seems terrible, but as far as I can tell, this is exactly what the
// stock Lua REPL does.
incomplete_input: err_string.ends_with("<eof>"),
message: err_string,
}
}
ffi::LUA_ERRERR => {
// The Lua manual documents this error wrongly: It is not raised when a message
// handler errors, but rather when some specific situations regarding stack
// overflow handling occurs. Since it is not very useful do differentiate
// between that and "ordinary" runtime errors, we handle them the same way.
Error::RuntimeError(err_string)
}
ffi::LUA_ERRMEM => {
// This should be impossible, as we set the lua allocator to one that aborts
// instead of failing.
lua_internal_abort!("impossible Lua allocation error, aborting!")
}
ffi::LUA_ERRGCMM => Error::GarbageCollectorError(err_string),
_ => lua_internal_panic!(state, "unrecognized lua error code"),
}
}
}
// Internally uses 4 stack spaces, does not call checkstack
pub unsafe fn push_string(state: *mut ffi::lua_State, s: &str) -> Result<()> {
protect_lua_call(state, 0, 1, |state| {
ffi::lua_pushlstring(state, s.as_ptr() as *const c_char, s.len());
})
}
// Internally uses 4 stack spaces, does not call checkstack
pub unsafe fn push_userdata<T>(state: *mut ffi::lua_State, t: T) -> Result<()> {
protect_lua_call(state, 0, 1, move |state| {
let ud = ffi::lua_newuserdata(state, mem::size_of::<T>()) as *mut T;
ptr::write(ud, t);
})
}
pub unsafe fn get_userdata<T>(state: *mut ffi::lua_State, index: c_int) -> *mut T {
let ud = ffi::lua_touserdata(state, index) as *mut T;
lua_internal_assert!(state, !ud.is_null(), "userdata pointer is null");
ud
}
// Pops the userdata off of the top of the stack and returns it to rust, invalidating the lua
// userdata.
pub unsafe fn take_userdata<T>(state: *mut ffi::lua_State) -> T {
// We set the metatable of userdata on __gc to a special table with no __gc method and with
// metamethods that trigger an error on access. We do this so that it will not be double
// dropped, and also so that it cannot be used or identified as any particular userdata type
// after the first call to __gc.
get_destructed_userdata_metatable(state);
ffi::lua_setmetatable(state, -2);
let ud = ffi::lua_touserdata(state, -1) as *mut T;
lua_internal_assert!(state, !ud.is_null(), "userdata pointer is null");
ffi::lua_pop(state, 1);
ptr::read(ud)
}
pub unsafe extern "C" fn userdata_destructor<T>(state: *mut ffi::lua_State) -> c_int {
callback_error(state, || {
take_userdata::<T>(state);
Ok(0)
})
}
// In the context of a lua callback, this will call the given function and if the given function
// returns an error, *or if the given function panics*, this will result in a call to lua_error (a
// longjmp). The error or panic is wrapped in such a way that when calling pop_error back on
// the rust side, it will resume the panic.
pub unsafe fn callback_error<R, F>(state: *mut ffi::lua_State, f: F) -> R
where
F: FnOnce() -> Result<R> + UnwindSafe,
{
match catch_unwind(f) {
Ok(Ok(r)) => r,
Ok(Err(err)) => {
ffi::luaL_checkstack(state, 2, ptr::null());
push_wrapped_error(state, err);
ffi::lua_error(state)
}
Err(p) => {
ffi::luaL_checkstack(state, 2, ptr::null());
push_wrapped_panic(state, p);
ffi::lua_error(state)
}
}
}
// Takes an error at the top of the stack, and if it is a WrappedError, converts it to an
// Error::CallbackError with a traceback, if it is some lua type, prints the error along with a
// traceback, and if it is a WrappedPanic, does not modify it.
pub unsafe extern "C" fn error_traceback(state: *mut ffi::lua_State) -> c_int {
ffi::luaL_checkstack(state, 2, ptr::null());
if let Some(error) = pop_wrapped_error(state) {
ffi::luaL_traceback(state, state, ptr::null(), 0);
let traceback = CStr::from_ptr(ffi::lua_tostring(state, -1))
.to_string_lossy()
.into_owned();
push_wrapped_error(
state,
Error::CallbackError {
traceback,
cause: Arc::new(error),
},
);
ffi::lua_remove(state, -2);
} else if !is_wrapped_panic(state, 1) {
let s = ffi::lua_tostring(state, 1);
let s = if s.is_null() {
cstr!("<unprintable Rust panic>")
} else {
s
};
ffi::luaL_traceback(state, state, s, 0);
ffi::lua_remove(state, -2);
}
1
}
// A variant of pcall that does not allow lua to catch panic errors from callback_error
pub unsafe extern "C" fn safe_pcall(state: *mut ffi::lua_State) -> c_int {
ffi::luaL_checkstack(state, 2, ptr::null());
let top = ffi::lua_gettop(state);
if top == 0 {
ffi::lua_pushstring(state, cstr!("not enough arguments to pcall"));
ffi::lua_error(state);
} else if ffi::lua_pcall(state, top - 1, ffi::LUA_MULTRET, 0) != ffi::LUA_OK {
if is_wrapped_panic(state, -1) {
ffi::lua_error(state);
}
ffi::lua_pushboolean(state, 0);
ffi::lua_insert(state, -2);
2
} else {
ffi::lua_pushboolean(state, 1);
ffi::lua_insert(state, 1);
ffi::lua_gettop(state)
}
}
// A variant of xpcall that does not allow lua to catch panic errors from callback_error
pub unsafe extern "C" fn safe_xpcall(state: *mut ffi::lua_State) -> c_int {
unsafe extern "C" fn xpcall_msgh(state: *mut ffi::lua_State) -> c_int {
ffi::luaL_checkstack(state, 2, ptr::null());
if is_wrapped_panic(state, -1) {
1
} else {
ffi::lua_pushvalue(state, ffi::lua_upvalueindex(1));
ffi::lua_insert(state, 1);
ffi::lua_call(state, ffi::lua_gettop(state) - 1, ffi::LUA_MULTRET);
ffi::lua_gettop(state)
}
}
ffi::luaL_checkstack(state, 2, ptr::null());
let top = ffi::lua_gettop(state);
if top < 2 {
ffi::lua_pushstring(state, cstr!("not enough arguments to xpcall"));
ffi::lua_error(state);
}
ffi::lua_pushvalue(state, 2);
ffi::lua_pushcclosure(state, xpcall_msgh, 1);
ffi::lua_copy(state, 1, 2);
ffi::lua_replace(state, 1);
let res = ffi::lua_pcall(state, ffi::lua_gettop(state) - 2, ffi::LUA_MULTRET, 1);
if res != ffi::LUA_OK {
if is_wrapped_panic(state, -1) {
ffi::lua_error(state);
}
ffi::lua_pushboolean(state, 0);
ffi::lua_insert(state, -2);
2
} else {
ffi::lua_pushboolean(state, 1);
ffi::lua_insert(state, 2);
ffi::lua_gettop(state) - 1
}
}
// Does not call checkstack, uses 1 stack space
pub unsafe fn main_state(state: *mut ffi::lua_State) -> *mut ffi::lua_State {
ffi::lua_rawgeti(state, ffi::LUA_REGISTRYINDEX, ffi::LUA_RIDX_MAINTHREAD);
let main_state = ffi::lua_tothread(state, -1);
ffi::lua_pop(state, 1);
main_state
}
// Pushes a WrappedError::Error to the top of the stack. Uses two stack spaces and does not call
// lua_checkstack.
pub unsafe fn push_wrapped_error(state: *mut ffi::lua_State, err: Error) {
gc_guard(state, || {
let ud = ffi::lua_newuserdata(state, mem::size_of::<WrappedError>()) as *mut WrappedError;
ptr::write(ud, WrappedError(err))
});
get_error_metatable(state);
ffi::lua_setmetatable(state, -2);
}
// Pops a WrappedError off of the top of the stack, if it is a WrappedError. If it is not a
// WrappedError, returns None and does not pop anything. Uses 2 stack spaces and does not call
// lua_checkstack
pub unsafe fn pop_wrapped_error(state: *mut ffi::lua_State) -> Option<Error> {
if !is_wrapped_error(state, -1) {
None
} else {
let err = &*get_userdata::<WrappedError>(state, -1);
let err = err.0.clone();
ffi::lua_pop(state, 1);
Some(err)
}
}
// Runs the given function with the Lua garbage collector disabled. `rlua` assumes that all
// allocation failures are aborts, so when the garbage collector is disabled, 'm' functions that can
// cause either an allocation error or a a `__gc` metamethod error are prevented from causing errors
// at all. The given function should never panic or longjmp, because this could inadverntently
// disable the gc. This is useful when error handling must allocate, and `__gc` errors at that time
// would shadow more important errors, or be extremely difficult to handle safely.
pub unsafe fn gc_guard<R, F: FnOnce() -> R>(state: *mut ffi::lua_State, f: F) -> R {
if ffi::lua_gc(state, ffi::LUA_GCISRUNNING, 0) != 0 {
ffi::lua_gc(state, ffi::LUA_GCSTOP, 0);
let r = f();
ffi::lua_gc(state, ffi::LUA_GCRESTART, 0);
r
} else {
f()
}
}
struct WrappedError(pub Error);
struct WrappedPanic(pub Option<Box<Any + Send>>);
// Pushes a WrappedError::Panic to the top of the stack. Uses two stack spaces and does not call
// lua_checkstack.
unsafe fn push_wrapped_panic(state: *mut ffi::lua_State, panic: Box<Any + Send>) {
gc_guard(state, || {
let ud = ffi::lua_newuserdata(state, mem::size_of::<WrappedPanic>()) as *mut WrappedPanic;
ptr::write(ud, WrappedPanic(Some(panic)))
});
get_panic_metatable(state);
ffi::lua_setmetatable(state, -2);
}
// Checks if the value at the given index is a WrappedError, uses 2 stack spaces and does not call
// lua_checkstack.
unsafe fn is_wrapped_error(state: *mut ffi::lua_State, index: c_int) -> bool {
let userdata = ffi::lua_touserdata(state, index);
if userdata.is_null() {
return false;
}
if ffi::lua_getmetatable(state, index) == 0 {
return false;
}
get_error_metatable(state);
let res = ffi::lua_rawequal(state, -1, -2) != 0;
ffi::lua_pop(state, 2);
res
}
// Checks if the value at the given index is a WrappedPanic. Uses 2 stack spaces and does not call
// lua_checkstack.
unsafe fn is_wrapped_panic(state: *mut ffi::lua_State, index: c_int) -> bool {
let userdata = ffi::lua_touserdata(state, index);
if userdata.is_null() {
return false;
}
if ffi::lua_getmetatable(state, index) == 0 {
return false;
}
get_panic_metatable(state);
let res = ffi::lua_rawequal(state, -1, -2) != 0;
ffi::lua_pop(state, 2);
res
}
unsafe fn get_error_metatable(state: *mut ffi::lua_State) -> c_int {
static ERROR_METATABLE_REGISTRY_KEY: u8 = 0;
unsafe extern "C" fn error_tostring(state: *mut ffi::lua_State) -> c_int {
ffi::luaL_checkstack(state, 2, ptr::null());
callback_error(state, || {
if is_wrapped_error(state, -1) {
let error = get_userdata::<WrappedError>(state, -1);
let error_str = (*error).0.to_string();
gc_guard(state, || {
ffi::lua_pushlstring(
state,
error_str.as_ptr() as *const c_char,
error_str.len(),
)
});
ffi::lua_remove(state, -2);
Ok(1)
} else {
panic!("userdata mismatch in Error metamethod");
}
})
}
ffi::lua_pushlightuserdata(
state,
&ERROR_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
);
let t = ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);
if t != ffi::LUA_TTABLE {
ffi::lua_pop(state, 1);
ffi::luaL_checkstack(state, 8, ptr::null());
gc_guard(state, || {
ffi::lua_newtable(state);
ffi::lua_pushlightuserdata(
state,
&ERROR_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
);
ffi::lua_pushvalue(state, -2);
ffi::lua_pushstring(state, cstr!("__gc"));
ffi::lua_pushcfunction(state, userdata_destructor::<WrappedError>);
ffi::lua_rawset(state, -3);
ffi::lua_pushstring(state, cstr!("__tostring"));
ffi::lua_pushcfunction(state, error_tostring);
ffi::lua_rawset(state, -3);
ffi::lua_pushstring(state, cstr!("__metatable"));
ffi::lua_pushboolean(state, 0);
ffi::lua_rawset(state, -3);
ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
})
}
ffi::LUA_TTABLE
}
unsafe fn get_panic_metatable(state: *mut ffi::lua_State) -> c_int {
static PANIC_METATABLE_REGISTRY_KEY: u8 = 0;
ffi::lua_pushlightuserdata(
state,
&PANIC_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
);
let t = ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);
if t != ffi::LUA_TTABLE {
ffi::lua_pop(state, 1);
ffi::luaL_checkstack(state, 8, ptr::null());
gc_guard(state, || {
ffi::lua_newtable(state);
ffi::lua_pushlightuserdata(
state,
&PANIC_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
);
ffi::lua_pushvalue(state, -2);
ffi::lua_pushstring(state, cstr!("__gc"));
ffi::lua_pushcfunction(state, userdata_destructor::<WrappedPanic>);
ffi::lua_rawset(state, -3);
ffi::lua_pushstring(state, cstr!("__metatable"));
ffi::lua_pushboolean(state, 0);
ffi::lua_rawset(state, -3);
ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
});
}
ffi::LUA_TTABLE
}
unsafe fn get_destructed_userdata_metatable(state: *mut ffi::lua_State) -> c_int {
static DESTRUCTED_USERDATA_METATABLE: u8 = 0;
unsafe extern "C" fn destructed_error(state: *mut ffi::lua_State) -> c_int {
ffi::luaL_checkstack(state, 2, ptr::null());
push_wrapped_error(state, Error::CallbackDestructed);
ffi::lua_error(state)
}
ffi::lua_pushlightuserdata(
state,
&DESTRUCTED_USERDATA_METATABLE as *const u8 as *mut c_void,
);
let t = ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);
if t != ffi::LUA_TTABLE {
ffi::lua_pop(state, 1);
ffi::luaL_checkstack(state, 8, ptr::null());
gc_guard(state, || {
ffi::lua_newtable(state);
ffi::lua_pushlightuserdata(
state,
&DESTRUCTED_USERDATA_METATABLE as *const u8 as *mut c_void,
);
ffi::lua_pushvalue(state, -2);
for &method in &[
cstr!("__add"),
cstr!("__sub"),
cstr!("__mul"),
cstr!("__div"),
cstr!("__mod"),
cstr!("__pow"),
cstr!("__unm"),
cstr!("__idiv"),
cstr!("__band"),
cstr!("__bor"),
cstr!("__bxor"),
cstr!("__bnot"),
cstr!("__shl"),
cstr!("__shr"),
cstr!("__concat"),
cstr!("__len"),
cstr!("__eq"),
cstr!("__lt"),
cstr!("__le"),
cstr!("__index"),
cstr!("__newindex"),
cstr!("__call"),
cstr!("__tostring"),
cstr!("__pairs"),
cstr!("__ipairs"),
] {
ffi::lua_pushstring(state, method);
ffi::lua_pushcfunction(state, destructed_error);
ffi::lua_rawset(state, -3);
}
ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
});
}
ffi::LUA_TTABLE
}
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