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use crate::component::func::HostFunc;
use crate::component::instance::RuntimeImport;
use crate::component::matching::{InstanceType, TypeChecker};
use crate::component::types;
use crate::component::{
Component, ComponentNamedList, Instance, InstancePre, Lift, Lower, ResourceType, Val,
};
use crate::prelude::*;
use crate::{AsContextMut, Engine, Module, StoreContextMut};
use alloc::sync::Arc;
use core::future::Future;
use core::marker;
use core::pin::Pin;
use hashbrown::hash_map::HashMap;
use wasmtime_environ::component::{NameMap, NameMapIntern};
use wasmtime_environ::PrimaryMap;
/// A type used to instantiate [`Component`]s.
///
/// This type is used to both link components together as well as supply host
/// functionality to components. Values are defined in a [`Linker`] by their
/// import name and then components are instantiated with a [`Linker`] using the
/// names provided for name resolution of the component's imports.
///
/// # Names and Semver
///
/// Names defined in a [`Linker`] correspond to import names in the Component
/// Model. Names in the Component Model are allowed to be semver-qualified, for
/// example:
///
/// * `wasi:cli/stdout@0.2.0`
/// * `wasi:http/types@0.2.0-rc-2023-10-25`
/// * `my:custom/plugin@1.0.0-pre.2`
///
/// These version strings are taken into account when looking up names within a
/// [`Linker`]. You're allowed to define any number of versions within a
/// [`Linker`] still, for example you can define `a:b/c@0.2.0`, `a:b/c@0.2.1`,
/// and `a:b/c@0.3.0` all at the same time.
///
/// Specifically though when names are looked up within a linker, for example
/// during instantiation, semver-compatible names are automatically consulted.
/// This means that if you define `a:b/c@0.2.1` in a [`Linker`] but a component
/// imports `a:b/c@0.2.0` then that import will resolve to the `0.2.1` version.
///
/// This lookup behavior relies on hosts being well-behaved when using Semver,
/// specifically that interfaces once defined are never changed. This reflects
/// how Semver works at the Component Model layer, and it's assumed that if
/// versions are present then hosts are respecting this.
///
/// Note that this behavior goes the other direction, too. If a component
/// imports `a:b/c@0.2.1` and the host has provided `a:b/c@0.2.0` then that
/// will also resolve correctly. This is because if an API was defined at 0.2.0
/// and 0.2.1 then it must be the same API.
///
/// This behavior is intended to make it easier for hosts to upgrade WASI and
/// for guests to upgrade WASI. So long as the actual "meat" of the
/// functionality is defined then it should align correctly and components can
/// be instantiated.
pub struct Linker<T> {
engine: Engine,
strings: Strings,
map: NameMap<usize, Definition>,
path: Vec<usize>,
allow_shadowing: bool,
_marker: marker::PhantomData<fn() -> T>,
}
impl<T> Clone for Linker<T> {
fn clone(&self) -> Linker<T> {
Linker {
engine: self.engine.clone(),
strings: self.strings.clone(),
map: self.map.clone(),
path: self.path.clone(),
allow_shadowing: self.allow_shadowing,
_marker: self._marker,
}
}
}
#[derive(Clone, Default)]
pub struct Strings {
string2idx: HashMap<Arc<str>, usize>,
strings: Vec<Arc<str>>,
}
/// Structure representing an "instance" being defined within a linker.
///
/// Instances do not need to be actual [`Instance`]s and instead are defined by
/// a "bag of named items", so each [`LinkerInstance`] can further define items
/// internally.
pub struct LinkerInstance<'a, T> {
engine: &'a Engine,
path: &'a mut Vec<usize>,
path_len: usize,
strings: &'a mut Strings,
map: &'a mut NameMap<usize, Definition>,
allow_shadowing: bool,
_marker: marker::PhantomData<fn() -> T>,
}
#[derive(Clone)]
pub(crate) enum Definition {
Instance(NameMap<usize, Definition>),
Func(Arc<HostFunc>),
Module(Module),
Resource(ResourceType, Arc<crate::func::HostFunc>),
}
impl<T> Linker<T> {
/// Creates a new linker for the [`Engine`] specified with no items defined
/// within it.
pub fn new(engine: &Engine) -> Linker<T> {
Linker {
engine: engine.clone(),
strings: Strings::default(),
map: NameMap::default(),
allow_shadowing: false,
path: Vec::new(),
_marker: marker::PhantomData,
}
}
/// Returns the [`Engine`] this is connected to.
pub fn engine(&self) -> &Engine {
&self.engine
}
/// Configures whether or not name-shadowing is allowed.
///
/// By default name shadowing is not allowed and it's an error to redefine
/// the same name within a linker.
pub fn allow_shadowing(&mut self, allow: bool) -> &mut Self {
self.allow_shadowing = allow;
self
}
/// Returns the "root instance" of this linker, used to define names into
/// the root namespace.
pub fn root(&mut self) -> LinkerInstance<'_, T> {
LinkerInstance {
engine: &self.engine,
path: &mut self.path,
path_len: 0,
strings: &mut self.strings,
map: &mut self.map,
allow_shadowing: self.allow_shadowing,
_marker: self._marker,
}
}
/// Returns a builder for the named instance specified.
///
/// # Errors
///
/// Returns an error if `name` is already defined within the linker.
pub fn instance(&mut self, name: &str) -> Result<LinkerInstance<'_, T>> {
self.root().into_instance(name)
}
fn typecheck<'a>(&'a self, component: &'a Component) -> Result<TypeChecker<'a>> {
let mut cx = TypeChecker {
types: component.types(),
strings: &self.strings,
imported_resources: Default::default(),
};
// Walk over the component's list of import names and use that to lookup
// the definition within this linker that it corresponds to. When found
// perform a typecheck against the component's expected type.
let env_component = component.env_component();
for (_idx, (name, ty)) in env_component.import_types.iter() {
let import = self.map.get(name, &self.strings);
cx.definition(ty, import)
.with_context(|| format!("component imports {desc} `{name}`, but a matching implementation was not found in the linker", desc = ty.desc()))?;
}
Ok(cx)
}
/// Returns the [`types::Component`] corresponding to `component` with resource
/// types imported by it replaced using imports present in [`Self`].
pub fn substituted_component_type(&self, component: &Component) -> Result<types::Component> {
let cx = self.typecheck(&component)?;
Ok(types::Component::from(
component.ty(),
&InstanceType {
types: cx.types,
resources: &cx.imported_resources,
},
))
}
/// Performs a "pre-instantiation" to resolve the imports of the
/// [`Component`] specified with the items defined within this linker.
///
/// This method will perform as much work as possible short of actually
/// instantiating an instance. Internally this will use the names defined
/// within this linker to satisfy the imports of the [`Component`] provided.
/// Additionally this will perform type-checks against the component's
/// imports against all items defined within this linker.
///
/// Note that unlike internally in components where subtyping at the
/// interface-types layer is supported this is not supported here. Items
/// defined in this linker must match the component's imports precisely.
///
/// # Errors
///
/// Returns an error if this linker doesn't define a name that the
/// `component` imports or if a name defined doesn't match the type of the
/// item imported by the `component` provided.
pub fn instantiate_pre(&self, component: &Component) -> Result<InstancePre<T>> {
self.typecheck(&component)?;
// Now that all imports are known to be defined and satisfied by this
// linker a list of "flat" import items (aka no instances) is created
// using the import map within the component created at
// component-compile-time.
let env_component = component.env_component();
let mut imports = PrimaryMap::with_capacity(env_component.imports.len());
for (idx, (import, names)) in env_component.imports.iter() {
let (root, _) = &env_component.import_types[*import];
// This is the flattening process where we go from a definition
// optionally through a list of exported names to get to the final
// item.
let mut cur = self.map.get(root, &self.strings).unwrap();
for name in names {
cur = match cur {
Definition::Instance(map) => map.get(&name, &self.strings).unwrap(),
_ => unreachable!(),
};
}
let import = match cur {
Definition::Module(m) => RuntimeImport::Module(m.clone()),
Definition::Func(f) => RuntimeImport::Func(f.clone()),
Definition::Resource(t, dtor) => RuntimeImport::Resource {
ty: *t,
_dtor: dtor.clone(),
dtor_funcref: component.resource_drop_func_ref(dtor),
},
// This is guaranteed by the compilation process that "leaf"
// runtime imports are never instances.
Definition::Instance(_) => unreachable!(),
};
let i = imports.push(import);
assert_eq!(i, idx);
}
Ok(unsafe { InstancePre::new_unchecked(component.clone(), imports) })
}
/// Instantiates the [`Component`] provided into the `store` specified.
///
/// This function will use the items defined within this [`Linker`] to
/// satisfy the imports of the [`Component`] provided as necessary. For more
/// information about this see [`Linker::instantiate_pre`] as well.
///
/// # Errors
///
/// Returns an error if this [`Linker`] doesn't define an import that
/// `component` requires or if it is of the wrong type. Additionally this
/// can return an error if something goes wrong during instantiation such as
/// a runtime trap or a runtime limit being exceeded.
pub fn instantiate(
&self,
store: impl AsContextMut<Data = T>,
component: &Component,
) -> Result<Instance> {
assert!(
!store.as_context().async_support(),
"must use async instantiation when async support is enabled"
);
self.instantiate_pre(component)?.instantiate(store)
}
/// Instantiates the [`Component`] provided into the `store` specified.
///
/// This is exactly like [`Linker::instantiate`] except for async stores.
///
/// # Errors
///
/// Returns an error if this [`Linker`] doesn't define an import that
/// `component` requires or if it is of the wrong type. Additionally this
/// can return an error if something goes wrong during instantiation such as
/// a runtime trap or a runtime limit being exceeded.
#[cfg(feature = "async")]
pub async fn instantiate_async(
&self,
store: impl AsContextMut<Data = T>,
component: &Component,
) -> Result<Instance>
where
T: Send,
{
assert!(
store.as_context().async_support(),
"must use sync instantiation when async support is disabled"
);
self.instantiate_pre(component)?
.instantiate_async(store)
.await
}
/// Implement any imports of the given [`Component`] with a function which traps.
///
/// By default a [`Linker`] will error when unknown imports are encountered when instantiating a [`Component`].
/// This changes this behavior from an instant error to a trap that will happen if the import is called.
pub fn define_unknown_imports_as_traps(&mut self, component: &Component) -> Result<()> {
use wasmtime_environ::component::ComponentTypes;
use wasmtime_environ::component::TypeDef;
// Recursively stub out all imports of the component with a function that traps.
fn stub_item<T>(
linker: &mut LinkerInstance<T>,
item_name: &str,
item_def: &TypeDef,
parent_instance: Option<&str>,
types: &ComponentTypes,
) -> Result<()> {
// Skip if the item isn't an instance and has already been defined in the linker.
if !matches!(item_def, TypeDef::ComponentInstance(_)) && linker.get(item_name).is_some()
{
return Ok(());
}
match item_def {
TypeDef::ComponentFunc(_) => {
let fully_qualified_name = parent_instance
.map(|parent| format!("{parent}#{item_name}"))
.unwrap_or_else(|| item_name.to_owned());
linker.func_new(&item_name, move |_, _, _| {
bail!("unknown import: `{fully_qualified_name}` has not been defined")
})?;
}
TypeDef::ComponentInstance(i) => {
let instance = &types[*i];
let mut linker_instance = linker.instance(item_name)?;
for (export_name, export) in instance.exports.iter() {
stub_item(
&mut linker_instance,
export_name,
export,
Some(item_name),
types,
)?;
}
}
TypeDef::Resource(_) => {
let ty = crate::component::ResourceType::host::<()>();
linker.resource(item_name, ty, |_, _| Ok(()))?;
}
TypeDef::Component(_) | TypeDef::Module(_) => {
bail!("unable to define {} imports as traps", item_def.desc())
}
_ => {}
}
Ok(())
}
for (_, (import_name, import_type)) in &component.env_component().import_types {
stub_item(
&mut self.root(),
import_name,
import_type,
None,
component.types(),
)?;
}
Ok(())
}
}
impl<T> LinkerInstance<'_, T> {
fn as_mut(&mut self) -> LinkerInstance<'_, T> {
LinkerInstance {
engine: self.engine,
path: self.path,
path_len: self.path_len,
strings: self.strings,
map: self.map,
allow_shadowing: self.allow_shadowing,
_marker: self._marker,
}
}
/// Defines a new host-provided function into this [`Linker`].
///
/// This method is used to give host functions to wasm components. The
/// `func` provided will be callable from linked components with the type
/// signature dictated by `Params` and `Return`. The `Params` is a tuple of
/// types that will come from wasm and `Return` is a value coming from the
/// host going back to wasm.
///
/// Additionally the `func` takes a
/// [`StoreContextMut`](crate::StoreContextMut) as its first parameter.
///
/// Note that `func` must be an `Fn` and must also be `Send + Sync +
/// 'static`. Shared state within a func is typically accessed with the `T`
/// type parameter from [`Store<T>`](crate::Store) which is accessible
/// through the leading [`StoreContextMut<'_, T>`](crate::StoreContextMut)
/// argument which can be provided to the `func` given here.
//
// TODO: needs more words and examples
pub fn func_wrap<F, Params, Return>(&mut self, name: &str, func: F) -> Result<()>
where
F: Fn(StoreContextMut<T>, Params) -> Result<Return> + Send + Sync + 'static,
Params: ComponentNamedList + Lift + 'static,
Return: ComponentNamedList + Lower + 'static,
{
self.insert(name, Definition::Func(HostFunc::from_closure(func)))?;
Ok(())
}
/// Defines a new host-provided async function into this [`Linker`].
///
/// This is exactly like [`Self::func_wrap`] except it takes an async
/// host function.
#[cfg(feature = "async")]
pub fn func_wrap_async<Params, Return, F>(&mut self, name: &str, f: F) -> Result<()>
where
F: for<'a> Fn(
StoreContextMut<'a, T>,
Params,
) -> Box<dyn Future<Output = Result<Return>> + Send + 'a>
+ Send
+ Sync
+ 'static,
Params: ComponentNamedList + Lift + 'static,
Return: ComponentNamedList + Lower + 'static,
{
assert!(
self.engine.config().async_support,
"cannot use `func_wrap_async` without enabling async support in the config"
);
let ff = move |mut store: StoreContextMut<'_, T>, params: Params| -> Result<Return> {
let async_cx = store.as_context_mut().0.async_cx().expect("async cx");
let mut future = Pin::from(f(store.as_context_mut(), params));
unsafe { async_cx.block_on(future.as_mut()) }?
};
self.func_wrap(name, ff)
}
/// Define a new host-provided function using dynamically typed values.
///
/// The `name` provided is the name of the function to define and the
/// `func` provided is the host-defined closure to invoke when this
/// function is called.
///
/// This function is the "dynamic" version of defining a host function as
/// compared to [`LinkerInstance::func_wrap`]. With
/// [`LinkerInstance::func_wrap`] a function's type is statically known but
/// with this method the `func` argument's type isn't known ahead of time.
/// That means that `func` can be by imported component so long as it's
/// imported as a matching name.
///
/// Type information will be available at execution time, however. For
/// example when `func` is invoked the second argument, a `&[Val]` list,
/// contains [`Val`] entries that say what type they are. Additionally the
/// third argument, `&mut [Val]`, is the expected number of results. Note
/// that the expected types of the results cannot be learned during the
/// execution of `func`. Learning that would require runtime introspection
/// of a component.
///
/// Return values, stored in the third argument of `&mut [Val]`, are
/// type-checked at runtime to ensure that they have the appropriate type.
/// A trap will be raised if they do not have the right type.
///
/// # Examples
///
/// ```
/// use wasmtime::{Store, Engine};
/// use wasmtime::component::{Component, Linker, Val};
///
/// # fn main() -> wasmtime::Result<()> {
/// let engine = Engine::default();
/// let component = Component::new(
/// &engine,
/// r#"
/// (component
/// (import "thunk" (func $thunk))
/// (import "is-even" (func $is-even (param "x" u32) (result bool)))
///
/// (core module $m
/// (import "" "thunk" (func $thunk))
/// (import "" "is-even" (func $is-even (param i32) (result i32)))
///
/// (func (export "run")
/// call $thunk
///
/// (call $is-even (i32.const 1))
/// if unreachable end
///
/// (call $is-even (i32.const 2))
/// i32.eqz
/// if unreachable end
/// )
/// )
/// (core func $thunk (canon lower (func $thunk)))
/// (core func $is-even (canon lower (func $is-even)))
/// (core instance $i (instantiate $m
/// (with "" (instance
/// (export "thunk" (func $thunk))
/// (export "is-even" (func $is-even))
/// ))
/// ))
///
/// (func (export "run") (canon lift (core func $i "run")))
/// )
/// "#,
/// )?;
///
/// let mut linker = Linker::<()>::new(&engine);
///
/// // Sample function that takes no arguments.
/// linker.root().func_new("thunk", |_store, params, results| {
/// assert!(params.is_empty());
/// assert!(results.is_empty());
/// println!("Look ma, host hands!");
/// Ok(())
/// })?;
///
/// // This function takes one argument and returns one result.
/// linker.root().func_new("is-even", |_store, params, results| {
/// assert_eq!(params.len(), 1);
/// let param = match params[0] {
/// Val::U32(n) => n,
/// _ => panic!("unexpected type"),
/// };
///
/// assert_eq!(results.len(), 1);
/// results[0] = Val::Bool(param % 2 == 0);
/// Ok(())
/// })?;
///
/// let mut store = Store::new(&engine, ());
/// let instance = linker.instantiate(&mut store, &component)?;
/// let run = instance.get_typed_func::<(), ()>(&mut store, "run")?;
/// run.call(&mut store, ())?;
/// # Ok(())
/// # }
/// ```
pub fn func_new(
&mut self,
name: &str,
func: impl Fn(StoreContextMut<'_, T>, &[Val], &mut [Val]) -> Result<()> + Send + Sync + 'static,
) -> Result<()> {
self.insert(name, Definition::Func(HostFunc::new_dynamic(func)))?;
Ok(())
}
/// Define a new host-provided async function using dynamic types.
///
/// This is exactly like [`Self::func_new`] except it takes an async
/// host function.
#[cfg(feature = "async")]
pub fn func_new_async<F>(&mut self, name: &str, f: F) -> Result<()>
where
F: for<'a> Fn(
StoreContextMut<'a, T>,
&'a [Val],
&'a mut [Val],
) -> Box<dyn Future<Output = Result<()>> + Send + 'a>
+ Send
+ Sync
+ 'static,
{
assert!(
self.engine.config().async_support,
"cannot use `func_new_async` without enabling async support in the config"
);
let ff = move |mut store: StoreContextMut<'_, T>, params: &[Val], results: &mut [Val]| {
let async_cx = store.as_context_mut().0.async_cx().expect("async cx");
let mut future = Pin::from(f(store.as_context_mut(), params, results));
unsafe { async_cx.block_on(future.as_mut()) }?
};
self.func_new(name, ff)
}
/// Defines a [`Module`] within this instance.
///
/// This can be used to provide a core wasm [`Module`] as an import to a
/// component. The [`Module`] provided is saved within the linker for the
/// specified `name` in this instance.
pub fn module(&mut self, name: &str, module: &Module) -> Result<()> {
self.insert(name, Definition::Module(module.clone()))?;
Ok(())
}
/// Defines a new resource of a given [`ResourceType`] in this linker.
///
/// This function is used to specify resources defined in the host.
///
/// The `name` argument is the name to define the resource within this
/// linker.
///
/// The `dtor` provided is a destructor that will get invoked when an owned
/// version of this resource is destroyed from the guest. Note that this
/// destructor is not called when a host-owned resource is destroyed as it's
/// assumed the host knows how to handle destroying its own resources.
///
/// The `dtor` closure is provided the store state as the first argument
/// along with the representation of the resource that was just destroyed.
///
/// [`Resource<U>`]: crate::component::Resource
///
/// # Errors
///
/// The provided `dtor` closure returns an error if something goes wrong
/// when a guest calls the `dtor` to drop a `Resource<T>` such as
/// a runtime trap or a runtime limit being exceeded.
pub fn resource(
&mut self,
name: &str,
ty: ResourceType,
dtor: impl Fn(StoreContextMut<'_, T>, u32) -> Result<()> + Send + Sync + 'static,
) -> Result<()> {
let dtor = Arc::new(crate::func::HostFunc::wrap_inner(
&self.engine,
move |mut cx: crate::Caller<'_, T>, (param,): (u32,)| dtor(cx.as_context_mut(), param),
));
self.insert(name, Definition::Resource(ty, dtor))?;
Ok(())
}
/// Identical to [`Self::resource`], except that it takes an async destructor.
#[cfg(feature = "async")]
pub fn resource_async<F>(&mut self, name: &str, ty: ResourceType, dtor: F) -> Result<()>
where
F: for<'a> Fn(
StoreContextMut<'a, T>,
u32,
) -> Box<dyn Future<Output = Result<()>> + Send + 'a>
+ Send
+ Sync
+ 'static,
{
assert!(
self.engine.config().async_support,
"cannot use `resource_async` without enabling async support in the config"
);
let dtor = Arc::new(crate::func::HostFunc::wrap_inner(
&self.engine,
move |mut cx: crate::Caller<'_, T>, (param,): (u32,)| {
let async_cx = cx.as_context_mut().0.async_cx().expect("async cx");
let mut future = Pin::from(dtor(cx.as_context_mut(), param));
match unsafe { async_cx.block_on(future.as_mut()) } {
Ok(Ok(())) => Ok(()),
Ok(Err(trap)) | Err(trap) => Err(trap),
}
},
));
self.insert(name, Definition::Resource(ty, dtor))?;
Ok(())
}
/// Defines a nested instance within this instance.
///
/// This can be used to describe arbitrarily nested levels of instances
/// within a linker to satisfy nested instance exports of components.
pub fn instance(&mut self, name: &str) -> Result<LinkerInstance<'_, T>> {
self.as_mut().into_instance(name)
}
/// Same as [`LinkerInstance::instance`] except with different lifetime
/// parameters.
pub fn into_instance(mut self, name: &str) -> Result<Self> {
let name = self.insert(name, Definition::Instance(NameMap::default()))?;
self.map = match self.map.raw_get_mut(&name) {
Some(Definition::Instance(map)) => map,
_ => unreachable!(),
};
self.path.truncate(self.path_len);
self.path.push(name);
self.path_len += 1;
Ok(self)
}
fn insert(&mut self, name: &str, item: Definition) -> Result<usize> {
self.map
.insert(name, self.strings, self.allow_shadowing, item)
}
fn get(&self, name: &str) -> Option<&Definition> {
self.map.get(name, self.strings)
}
}
impl NameMapIntern for Strings {
type Key = usize;
fn intern(&mut self, string: &str) -> usize {
if let Some(idx) = self.string2idx.get(string) {
return *idx;
}
let string: Arc<str> = string.into();
let idx = self.strings.len();
self.strings.push(string.clone());
self.string2idx.insert(string, idx);
idx
}
fn lookup(&self, string: &str) -> Option<usize> {
self.string2idx.get(string).cloned()
}
}