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/* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ //! A library which uses JavaScript to safely manage the lifetimes of Rust data. //! //! ( //! [Repo](https://github.com/asajeffrey/josephine) | //! [CI](https://travis-ci.org/asajeffrey/josephine) //! ) //! //! This library allows Rust data to be attached to JavaScript objects: //! the lifetime of the Rust data is then the same as the JS object it is attached to. //! Since JS is garbage collected, it is safe to copy and discard references to //! JS managed data, and allows examples like doubly-linked lists which would //! otherwise require reference counting. Reference counting requires dynamic checks, //! for example getting mutable access to reference-counted data panics if the reference //! count is more than 1. //! //! The goals are: //! //! 1. Use JS to manage the lifetime of Rust data. //! 2. Allow references to JS managed data to be freely copied and discarded, relying on //! the garbage collector for safety. //! 3. Maintain Rust memory safety (for example no mutable aliasing), //! without requiring additional static analysis such as a lint. //! 4. Allow mutable and immutable access to Rust data via JS managed references, so //! we do not need to rely on interior mutability. //! 5. Provide a rooting API to ensure that JS managed data is not garbage collected //! while it is being used. //! //! To support safe access to JS managed data, the API uses a *JS context*, which //! is used as an access token to allow JS managed data to be accessed, allocated //! or deallocated. Mutable access to JS managed data requires mutable access to the //! JS context, which is how the API achieves memory safety even though JS managed //! references can be copied and discarded freely. //! //! JS managed memory is split into *compartments*, which are //! separately garbage collected, so the garbage collector can avoid //! scanning the entire heap. The API statically tracks compartments, to //! ensure that there are no direct references between compartments. //! //! The API is implemented as bindings to the SpiderMonkey JS engine, //! from which it borrows the garbage collector and the notions of compartment //! and JS context. The API allows calling into JavaScript //! from Rust, and calling back into Rust from JavaScript. These bindings are unsafe, //! and are intended for use by a trusted bindings generator. //! //! # JS-managed data //! //! Rust data can be given to JS to manage, and then accessed, //! using the JS context. The JS context is passed as a variable of type `JSContext<S>`, //! where the type parameter `S` is used to track the state of the context. //! The context comes with the permissions it grants, such as `CanAlloc` //! and `CanAccess`. These permissions are modelled as traits, for example //! a context in state `S` can allocate memory when `S: CanAlloc`. //! //! JS managed memory is split into compartments. Each JS context has a notion of //! the current compartment, which is part of the state. A JS context in compartment //! `C` has type `JSCompartment<S>` where `S: InCompartment<C>` and `C: Compartment`. //! A reference to JS managed data in compartment `C`, where the Rust data being //! managed by JS has type `T`, is given type `JSManaged<C, T>`. //! //! For example, we can give JS a Rust string to manage in compartment //! `C`: //! //! ```rust //! # use josephine::*; //! fn example<C, S>(cx: &mut JSContext<S>) where //! S: CanAlloc + InCompartment<C>, //! C: Compartment, //! { //! let x: JSManaged<C, String> = cx.manage(String::from("hello")); //! } //! ``` //! //! and then access it: //! //! ```rust //! # use josephine::*; //! fn example<C, S>(cx: &mut JSContext<S>, x: JSManaged<C, String>) where //! S: CanAccess, //! C: Compartment, //! { //! println!("{} world", x.borrow(cx)); //! } //! ``` //! //! # Lifetimes of JS-managed data //! //! Unfortunately, combining these two examples is not memory-safe, due to //! garbage collection: //! //! ```rust,ignore //! # use josephine::*; //! fn unsafe_example<C, S>(cx: &mut JSContext<S>) where //! S: CanAlloc + CanAccess + InCompartment<C>, //! C: Compartment, //! { //! let x: JSManaged<C, String> = cx.manage(String::from("hello")); //! // Imagine something triggers GC here //! println!("{} world", x.borrow(cx)); //! } //! ``` //! //! This example is not safe, as there is nothing keeping `x` alive in JS, //! so if garbage collection is triggered, then `x` will be reclaimed //! which will drop the Rust data, and so the call to `x.borrow(cx)` will be a use-after-free. //! //! This example is not memory-safe, and fortunately fails to typecheck: //! //! ```text //! error[E0502]: cannot borrow `*cx` as immutable because it is also borrowed as mutable //! --> src/lib.rs:10:35 //! | //! 8 | let x: JSManaged<C, String> = cx.manage(String::from("hello")); //! | -- mutable borrow occurs here //! 9 | // Imagine something triggers GC here //! 10 | println!("{} world", x.borrow(cx)); //! | ^^ immutable borrow occurs here //! 11 | } //! | - mutable borrow ends here //! ``` //! //! To see why this example fails to typecheck, we can introduce explicit lifetimes: //! //! ```rust,ignore //! # use josephine::*; //! fn unsafe_example<'a, C, S>(cx: &'a mut JSContext<S>) where //! S: CanAlloc + CanAccess + InCompartment<C>, //! C: Compartment, //! { //! // x has type JSManaged<'b, C, String> //! let x = cx.manage(String::from("hello")); //! // Imagine something triggers GC here //! // x_ref has type &'c String //! let x_ref = x.borrow(cx); //! println!("{} world", x_ref); //! } //! ``` //! //! We can now see why this fails to typecheck: since `cx` is borrowed mutably at type //! `&'b mut JSContext<S>`, then immutably at type `&'c mut JSContext<S>` these lifetimes //! cannot overlap, but the call to `x.borrow(cx)` requires them to overlap. These contradicting //! constraints cause the example to fail to compile. //! //! # Rooting //! //! To fix this example, we need to make sure that `x` lives long enough. One way to do this is //! to root `x`, so that it will not be garbage collected. //! //! ```rust //! # use josephine::*; //! fn example<C, S>(cx: &mut JSContext<S>) where //! S: CanAlloc + CanAccess + InCompartment<C>, //! C: Compartment, //! { //! // Declare a root which will be used to keep x alive during its lifetime //! let ref mut root = cx.new_root(); //! // Store a reference to x in the root //! let x = cx.manage(String::from("hello")).in_root(root); //! // This is what is keeping x alive ------^ //! // Imagine something triggers GC here //! // The root ensures that x survives GC, so is safe to use //! println!("{} world", x.borrow(cx)); //! } //! ``` //! //! To see why this example now typechecks, we again introduce explicit lifetimes: //! //! ```rust //! # use josephine::*; //! fn example<'a, C, S>(cx: &'a mut JSContext<S>) where //! S: CanAlloc + CanAccess + InCompartment<C>, //! C: Compartment, //! { //! // root has type JSRoot<'b, String> //! let ref mut root = cx.new_root(); //! // x has type JSManaged<'b, C, String> //! let x = { //! // x_unrooted has type JSManaged<'d, C, String> //! let x_unrooted = cx.manage(String::from("hello")); //! // By rooting it, its lifetime changes from 'd to 'b (the lifetime of the root) //! x_unrooted.in_root(root) //! }; //! // Imagine something triggers GC here //! // x_ref has type &'c String //! let x_ref = x.borrow(cx); //! println!("{} world", x_ref); //! } //! ``` //! //! The example typechecks because the //! constraints are that `'b` overlaps with `'c` and `'d`, and that //! `'c` and `'d` don't overlap. These constraints are satisfiable, so the //! example typechecks. //! //! # Mutating JS-managed data //! //! JS managed data can be accessed mutably as well as immutably. //! This is safe because mutably accessing JS manage data requires //! mutably borrowing the JS context, so there cannot be two simultaneous //! mutable accesses. //! //! ```rust //! # use josephine::*; //! fn example<C, S>(cx: &mut JSContext<S>, x: JSManaged<C, String>) where //! S: CanAccess, //! C: Compartment, //! { //! println!("{} world", x.borrow(cx)); //! *x.borrow_mut(cx) = String::from("hi"); //! println!("{} world", x.borrow(cx)); //! } //! ``` //! //! An attempt to mutably access JS managed data more than once simultaneously //! results in an error from the borrow-checker, for example: //! //! ```rust,ignore //! # use josephine::*; use std::mem; //! fn unsafe_example<C, S>(cx: &mut JSContext<S>, x: JSManaged<C, String>, y: JSManaged<C, String>) where //! S: CanAccess, //! C: Compartment, //! { //! mem::swap(x.borrow_mut(cx), y.borrow_mut(cx)); //! } //! ``` //! //! ```text //! error[E0499]: cannot borrow `*cx` as mutable more than once at a time //! --> src/lib.rs:8:46 //! | //! 8 | mem::swap(x.borrow_mut(cx), y.borrow_mut(cx)); //! | -- ^^ - first borrow ends here //! | | | //! | | second mutable borrow occurs here //! | first mutable borrow occurs here //! ``` //! //! # Snapshots //! //! Some cases of building JS managed data require rooting, but in some cases //! the rooting can be avoided, since the program does nothing to trigger //! garbage collection. In this case, we can snapshot the JS context after //! performing allocation. The snapshot supports accessing JS managed data, //! but does not support any calls that might trigger garbage collection. //! As a result, we know that any data which is live at the beginning of //! the snapshot is also live at the end. //! //! ```rust //! # use josephine::*; //! fn example<C, S>(cx: &mut JSContext<S>) where //! S: CanAlloc + CanAccess + InCompartment<C>, //! C: Compartment, //! { //! let (ref cx, x) = cx.snapshot_manage(String::from("hello")); //! // Since the context is snapshotted it can't trigger GC //! println!("{} world", x.borrow(cx)); //! } //! ``` //! //! A program which tries to use a function which might trigger GC will //! not typecheck, as the snapshotted JS context state does not support //! the appropriate traits. For example: //! //! ```rust,ignore //! # use josephine::*; //! fn unsafe_example<C, S>(cx: &mut JSContext<S>) where //! S: CanAlloc + CanAccess + InCompartment<C>, //! C: Compartment, //! { //! let (ref mut cx, x) = cx.snapshot_manage(String::from("hello")); //! cx.gc(); //! println!("{} world", x.borrow(cx)); //! } //! ``` //! //! In this program, the call to `cx.gc()` requires the state //! to support `CanAlloc<C>`, which is not allowed by the snapshotted state. //! //! ```text //! error[E0277]: the trait bound `josephine::Snapshotted<'_, S>: josephine::CanAlloc` is not satisfied //! --> src/lib.rs:9:8 //! | //! 9 | cx.gc(); //! | ^^ the trait `josephine::CanAlloc` is not implemented for `josephine::Snapshotted<'_, S>` //! ``` //! //! # Working with compartments //! //! To enter the compartment of a JS managed object, you can use `cx.enter_known_compartment(managed)`. //! This returns a context whose current compartment is that of the JS managed objecct. //! //! ```rust //! # use josephine::*; //! fn example<C, S>(cx: &mut JSContext<S>, x: JSManaged<C, String>) where //! S: CanAccess + CanAlloc, //! C: Compartment, //! { //! // We can't allocate data without entering the comartment. //! // Commenting out the next line gives an error //! // the trait `josephine::InCompartment<_>` is not implemented for `S`. //! let ref mut cx = cx.enter_known_compartment(x); //! let ref mut root = cx.new_root(); //! let y = cx.manage(String::from("world")).in_root(root); //! println!("Hello, {}.", y.borrow(cx)); //! } //! ``` //! //! Working with named compartmens is fine when there is a fixed number of them, but not when //! the number of compartments is unbounded. For example, the type `Vec<JSManaged<C, T>>` contains //! a vector of managed objects, all in the same compartment, but sometimes you need a vector of //! objects in different compartments. This is what *wildcards* are for (borrowed from //! [Java wildcards](https://docs.oracle.com/javase/tutorial/java/generics/wildcards.html) //! which solve a similar problem). //! //! The wildcard compartment is called `SOMEWHERE`, and `JSManaged<SOMEWHERE, T>` refers //! to JS managed data whose compartment is unknown. For example `Vec<JSManaged<SOMEWHERE, T>>` //! contains a vector of managed objects, which may all be in different compartments. //! //! To create a `JSManaged<SOMEWHERE, T>`, we use `managed.forget_compartment()`. //! //! ```rust //! # use josephine::*; //! fn example<C, S>(cx: &mut JSContext<S>) -> JSManaged<SOMEWHERE, String> where //! S: CanAlloc + InCompartment<C>, //! C: Compartment, //! { //! cx.manage(String::from("hello")).forget_compartment() //! } //! ``` //! //! To access data with a wildcard compartment, first enter the compartment //! using `cx.enter_unknown_compartment(managed)`. //! //! ```rust //! # use josephine::*; //! fn example<S>(cx: &mut JSContext<S>, x: JSManaged<SOMEWHERE, String>) where //! S: CanAccess, //! { //! // We can't access x without first entering its compartment. //! // Commenting out the next two lines gives an error //! // the trait `josephine::Compartment` is not implemented for `josephine::SOMEWHERE`. //! let ref mut cx = cx.enter_unknown_compartment(x); //! let x = cx.entered(); //! println!("Hello, {}.", x.borrow(cx)); //! } //! ``` //! //! Sometimes you need to check to see if some JS managed data is in the current compartment or not. //! This is done with `managed.in_compartment(cx)`, which returns an `Option<JSManaged<C, T>>` //! when the context's current compartment is `C`. The result is `Some(managed)` if `managed` was in //! compartment `C`, and `None` if it was in a different compartment. //! //! ```rust //! # use josephine::*; //! fn example<S, C>(cx: &mut JSContext<S>, x: JSManaged<SOMEWHERE, String>) where //! S: CanAccess + InCompartment<C>, //! C: Compartment, //! { //! if let Some(x) = x.in_compartment(cx) { //! println!("Hello, {}.", x.borrow(cx)); //! } //! } //! ``` //! //! # User-defined types //! //! There are more types to manage than just `String`! //! //! To be managed by `JSManageable`, a type should implement the following traits: //! //! * `JSTraceable`: values of the type can be *traced*, that is can tell the garbage //! collector which objects are reachable from them. //! * `JSLifetime`: values of the type have their lifetime managed by JS. //! * `JSCompartmental`: values of the type have their compartment managed by JS. //! * `JSInitializable`: this type knows how to initialize a JS object which is used //! to manage its lifetime. //! //! Each of these traits can be derived. The fields of a `JSTraceable` type should be //! `JSTraceable`, and similarly for `JSLifetime` and `JSCompartmental`. This requirement //! is *not* true for `JSInitializable`. //! //! A typical use is to define two types: the *native* type `NativeThing` //! and then the *managed* type `Thing<'a, C>` which is just a `JSManaged<'a, C, NativeThing>`. //! //! ```rust //! # #[macro_use] extern crate josephine; //! # use josephine::*; //! #[derive(JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! struct NativeName { name: String } //! //! #[derive(Clone, Copy, Debug, Eq, PartialEq, JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! pub struct Name<'a, C> (JSManaged<'a, C, NativeName>); //! //! impl<'a, C:'a> Name<'a, C> { //! pub fn new<S>(cx: &'a mut JSContext<S>, name: &str) -> Name<'a, C> where //! S: CanAlloc + InCompartment<C>, //! C: Compartment, //! { //! Name(cx.manage(NativeName { name: String::from(name) })) //! } //! pub fn name<S>(self, cx: &'a JSContext<S>) -> &'a str where //! S: CanAccess, //! C: Compartment, //! { //! &*self.0.borrow(cx).name //! } //! } //! //! # fn main() { //! # let ref mut cx = JSContext::new().expect("Creating a JSContext failed"); //! # let ref mut cx = cx.create_compartment().global_manage(37); //! let ref mut root = cx.new_root(); //! let hello = Name::new(cx, "hello").in_root(root); //! assert_eq!(hello.name(cx), "hello"); //! # } //! ``` //! //! Sometimes the native type will itself contain references to JS-managed data, //! so will need to be parameterized on a lifetime and compartment. //! //! ```rust //! # #[macro_use] extern crate josephine; //! # use josephine::*; //! # #[derive(JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! # struct NativeName { name: String } //! # //! # #[derive(Clone, Copy, Debug, Eq, PartialEq, JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! # pub struct Name<'a, C> (JSManaged<'a, C, NativeName>); //! # //! # impl<'a, C> Name<'a, C> { //! # pub fn new<S>(cx: &'a mut JSContext<S>, name: &str) -> Name<'a, C> where //! # S: CanAlloc + InCompartment<C>, //! # C: Compartment, //! # { //! # Name(cx.manage(NativeName { name: String::from(name) })) //! # } //! # pub fn name<S>(self, cx: &'a JSContext<S>) -> &'a str where //! # S: CanAccess, //! # C: Compartment, //! # { //! # &*self.0.borrow(cx).name //! # } //! # } //! # //! #[derive(JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! struct NativeNames<'a, C> { names: Vec<Name<'a, C>> } //! //! #[derive(Clone, Copy, Debug, JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! pub struct Names<'a, C> (JSManaged<'a, C, NativeNames<'a, C>>); //! impl<'a, C:'a> Names<'a, C> { //! pub fn new<S>(cx: &'a mut JSContext<S>) -> Names<'a, C> where //! S: CanAlloc + InCompartment<C>, //! C: Compartment, //! { //! Names(cx.manage(NativeNames { names: vec![] })) //! } //! pub fn push_str<S>(self, cx: &'a mut JSContext<S>, name: &str) where //! S: CanAccess + CanAlloc + InCompartment<C>, //! C: Compartment, //! { //! let ref mut root = cx.new_root(); //! let name = Name::new(cx, name).in_root(root); //! self.0.borrow_mut(cx).names.push(name); //! } //! pub fn get<S>(self, cx: &'a JSContext<S>, index: usize) -> Option<Name<'a, C>> where //! S: CanAccess, //! C: Compartment, //! { //! self.0.borrow(cx).names.get(index).cloned() //! } //! } //! //! # fn main() { //! # let ref mut cx = JSContext::new().expect("Creating a JSContext failed"); //! # let ref mut cx = cx.create_compartment().global_manage(37); //! let ref mut root = cx.new_root(); //! let hello_world = Names::new(cx).in_root(root); //! hello_world.push_str(cx, "hello"); //! hello_world.push_str(cx, "world"); //! assert_eq!(hello_world.get(cx, 0).map(|name| name.name(cx)), Some("hello")); //! assert_eq!(hello_world.get(cx, 1).map(|name| name.name(cx)), Some("world")); //! # } //! ``` //! //! # Calling between JS and Rust //! //! Josephine exposes an unsafe API to allow JS to call Rust and back again. //! This is just a thin wrapper round the SpiderMonkey API. //! See the [`ffi`](ffi/index.html) module for details. //! //! # Globals //! //! Each JS compartment has a special object called a *global*. //! The compartment can be created using `cx.create_compartment()`, //! and the global can be given native data to manage with `cx.global_manage(data)`. //! The global can be accessed with `cx.global()`. //! //! ```rust //! # #[macro_use] extern crate josephine; //! # use josephine::*; //! #[derive(JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! pub struct NativeMyGlobal { name: String } //! type MyGlobal<'a, C> = JSManaged<'a, C, NativeMyGlobal>; //! //! fn example<'a, S>(cx: &'a mut JSContext<S>) -> MyGlobal<'a, SOMEWHERE> where //! S: CanAccess + CanAlloc, //! { //! let cx = cx.create_compartment(); //! let name = String::from("Alice"); //! let cx = cx.global_manage(NativeMyGlobal { name: name }); //! cx.global().forget_compartment() //! } //! # fn main() {} //! ``` //! //! In some cases, the global contains some JS-managed data, which is why the initialization //! is split into two steps: creating the compartment, and //! providing the JS-managed data for the global, for example: //! //! ```rust //! # #[macro_use] extern crate josephine; //! # use josephine::*; //! #[derive(JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! pub struct NativeMyGlobal<'a, C> { name: JSManaged<'a, C, String> } //! type MyGlobal<'a, C> = JSManaged<'a, C, NativeMyGlobal<'a, C>>; //! //! fn example<'a, S>(cx: &'a mut JSContext<S>) -> MyGlobal<'a, SOMEWHERE> where //! S: CanAccess + CanAlloc, //! { //! let mut cx = cx.create_compartment(); //! let ref mut root = cx.new_root(); //! let name = cx.manage(String::from("Alice")).in_root(root); //! let ref cx = cx.global_manage(NativeMyGlobal { name: name }); //! cx.global().forget_compartment() //! } //! # fn main() {} //! ``` //! //! # Bootstrapping //! //! The JSContext is built using `JSContext::new`. //! //! ```rust //! # #[macro_use] extern crate josephine; //! # use josephine::*; //! #[derive(JSInitializable, JSTraceable, JSLifetime, JSCompartmental)] //! pub struct NativeMyGlobal { name: String } //! type MyGlobal<'a, C> = JSManaged<'a, C, NativeMyGlobal>; //! //! fn example<'a, S>(cx: &'a mut JSContext<S>) -> MyGlobal<'a, SOMEWHERE> where //! S: CanAccess + CanAlloc, //! { //! let cx = cx.create_compartment(); //! let name = String::from("Alice"); //! let cx = cx.global_manage(NativeMyGlobal { name: name }); //! cx.global().forget_compartment() //! } //! fn main() { //! let ref mut cx = JSContext::new().expect("Creating a JSContext failed"); //! example(cx); //! } //! ``` #![feature(associated_type_defaults)] #![feature(const_fn)] #![feature(const_ptr_null)] #![feature(generic_param_attrs)] #![feature(dropck_eyepatch)] #![feature(refcell_replace_swap)] extern crate mozjs; extern crate libc; #[macro_use] extern crate log; pub mod context; pub use context::JSContext; pub use context::CanAccess; pub use context::CanAlloc; pub use context::InCompartment; pub use context::Initialized; pub use context::IsInitialized; pub use context::IsInitializing; pub use context::IsSnapshot; pub mod compartment; pub use compartment::SOMEWHERE; pub use compartment::Compartment; pub use compartment::JSCompartmental; pub mod ffi; pub use ffi::JSInitializable; pub mod js { pub use mozjs::glue; pub use mozjs::jsval; pub use mozjs::rust; #[cfg(feature = "smup")] pub use mozjs::heap; #[cfg(not(feature = "smup"))] pub use mozjs::jsapi as heap; #[cfg(feature = "smup")] pub use mozjs::jsapi; #[cfg(not(feature = "smup"))] pub mod jsapi { pub use mozjs::*; pub use mozjs::jsapi::*; pub use mozjs::jsapi as JS; pub use mozjs::jsapi as js; } } pub mod managed; pub use managed::JSManaged; pub mod root; pub use root::JSRoot; pub use root::JSLifetime; pub mod string; pub use string::JSString; pub mod trace; pub use trace::JSTraceable; // Re-export the derive macros #[allow(unused_imports)] #[macro_use] extern crate josephine_derive; #[doc(hidden)] pub use josephine_derive::*;