130 lines
7.1 KiB
Markdown
130 lines
7.1 KiB
Markdown
# rlua -- High level bindings between Rust and Lua
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[](https://travis-ci.org/chucklefish/rlua)
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[API Documentation](https://docs.rs/rlua)
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[Examples](examples/examples.rs)
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This library is a high level interface between Rust and Lua. Its major goal is
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to expose as easy to use, practical, and flexible of an API between Rust and Lua
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as possible, while also being completely safe.
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There are other high level Lua bindings systems for rust, and this crate is an
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exploration of a different part of the design space. The other high level
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interface to Lua that I am aware of right now is
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[hlua](https://github.com/tomaka/hlua/) which you should definitely check out
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and use if it suits your needs. This crate has the following differences with
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hlua:
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* Handles to Lua values use the Lua registry, not the stack
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* Handles to Lua values are all internally mutable
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* Handles to Lua values have non-mutable borrows to the main Lua object, so
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there can be multiple handles or long lived handles
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* Targets Lua 5.3
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The key difference here is that rlua handles rust-side references to Lua values
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in a fundamentally different way than hlua, more similar to other Lua bindings
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systems like [Selene](https://github.com/jeremyong/Selene) for C++. Values like
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`rlua::Table` and `rlua::Function` that hold onto Lua values in the Rust stack,
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instead of pointing at values in the Lua stack, are placed into the registry
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with luaL_ref. In this way, it is possible to have an arbitrary number of
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handles to internal Lua values at any time, created and destroyed in arbitrary
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order. This approach IS slightly slower than the approach that hlua takes of
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only manipulating the Lua stack, but this, combined with internal mutability,
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allows for a much more flexible API.
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There are currently a few notable missing pieces of this API:
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* Complete panic / abort safety. This is a near term goal, but currently
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there are ways to cause panics / aborts with the API and with lua scripts.
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* Security limits on Lua code such as total instruction limits and control
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over which potentially dangerous libraries (e.g. io) are available to
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scripts.
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* Lua profiling support
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* "Context" or "Sandboxing" support. There should be the ability to set the
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`_ENV` upvalue of a loaded chunk to a table other than `_G`, so that you can
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have different environments for different loaded chunks.
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* More fleshed out Lua API, there is some missing nice to have functionality
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not exposed like storing values in the registry.
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* Benchmarks, and quantifying performance differences with what you would
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might write in C.
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Additionally, there are ways I would like to change this API, once support lands
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in rustc. For example:
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* Currently, variadics are handled entirely with tuples and traits implemented
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by macro for tuples up to size 12, it would be great if this was replaced
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with real variadic generics when this is available in rust.
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It is also worth it to list some non-goals for the project:
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* Be a perfect zero cost wrapper over the Lua C API
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* Allow the user to do absolutely everything that the Lua C API might allow
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## API stability
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This library is very much Work In Progress, so there is a some API churn.
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Currently, it follows a pre-1.0 semver, so all API changes should be accompanied
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by 0.x version bumps.
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## Safety and panics
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The goal of this library is complete safety, it should not be possible to cause
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undefined behavior whatsoever with the API, even in edge cases. There is,
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however, QUITE a lot of unsafe code in this crate, and I would call the current
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safety level of the crate "Work In Progress". Still, UB is considered the most
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serious kind of bug, so if you find the ability to cause UB with this API *at
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all*, please file a bug report.
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There are, however, currently a few known ways to cause *panics* and even
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*aborts* with this API. There is a near term goal to completely eliminate all
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ways to cause panics / aborts from scripts, so many of these can be considered
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bugs, but since they're known only file a bug repor if you notice any behavior
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that does not match what's described here.
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Panic / abort considerations when using this API:
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* The API should be panic safe currently, whenever a panic is generated the
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Lua stack is cleared and the `Lua` instance should continue to be usable.
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* Panic unwinds in Rust callbacks should currently be handled correctly, the
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unwind is caught and carried across the Lua API boundary, and Lua code
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cannot catch rust panics. This is done by overriding the normal Lua 'pcall'
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and 'xpcall' with custom versions that cannot catch rust panics being piped
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through the normal Lua error system.
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* There are a few panics marked "internal error" that should be impossible to
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trigger. If you encounter one of these this is a bug.
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* When the internal version of Lua is built using the `gcc` crate (the
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default), `LUA_USE_APICHECK` is enabled. Any abort caused by this internal
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Lua API checking should be considered a bug, particularly because without
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`LUA_USE_APICHECK` it would generally be unsafe.
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* The library internally calls lua_checkstack to ensure that there is
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sufficient stack space, and if the stack cannot be sufficiently grown this
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is a panic. There should not be a way to cause this using this API, and if
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you encounter this, it is a bug.
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* Previous to version 0.10, `rlua` had a complicated system to guard against
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LUA_ERRGCMM, and this system could cause aborts. This is no longer the case
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as of version 0.10, `rlua` now attempts to handle all errors that the Lua C
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API can generate, including functions that can cause memory errors (any
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function marked as 'v', 'e', or 'm' in the Lua C API docs). This is,
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however, extremely complicated and difficult to test, so if there is any
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indication when using this API that a Lua error (longjmp) is being triggered
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without being turned into an `rlua::Error`, *please please report this as a
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bug*.
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* The internal Lua allocator is set to use `realloc` from `libc`, but it is
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wrapped in such a way that OOM errors are guaranteed to abort. This is not
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such a big deal, as this matches the behavior of rust itself. This allows
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the internals of `rlua` to, in certain rare cases, call 'm' Lua C API
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functions with the garbage collector disabled and know that these cannot
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error. Though this is not a problem now, this will need to be changed in
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order to add allocation limits to Lua instances.
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* There are currently no recursion limits on callbacks. This could cause one
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of two problems, either the API will run out of stack space and cause a
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panic in Rust, or more likely it will cause an internal `LUA_USE_APICHECK`
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abort, from exceeding LUAI_MAXCCALLS. This may be a source of unsafety if
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`LUA_USE_APICHECK` is disabled, and is considered a bug.
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* There are currently no checks on argument sizes, and I think you may be able
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to cause an abort by providing a large enough `rlua::Variadic`. I believe
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this would be unsafe without `LUA_USE_APICHECK` and should be considered a
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bug.
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