Wasmtime

https://docs.wasmtime.dev/
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Wasmtime is a standalone runtime for WebAssembly, WASI, and the Component Model that can be used as...
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### Concurrent Function Call Example Setup

Source: https://docs.wasmtime.dev/api/src/wasmtime/runtime/component/concurrent/func.rs.html

Example setup for using StoreContextMut::run_concurrent to obtain an Accessor for concurrent calls.

```rust
89    /// # use {
90    /// #   wasmtime::{
91    /// #     error::{Result},
92    /// #     component::{Component, Linker, ResourceTable},
93    /// #     Config, Engine, Store
94    /// #   },
95    /// # };
96    /// #
97    /// # struct Ctx { table: ResourceTable }
98    /// #
99    /// # async fn foo() -> Result<()> {
100    /// # let mut config = Config::new();
101    /// # let engine = Engine::new(&config)?;
102    /// # let mut store = Store::new(&engine, Ctx { table: ResourceTable::new() });
103    /// # let mut linker = Linker::new(&engine);
```

--------------------------------

### start method: error path and pipe setup

Source: https://docs.wasmtime.dev/api/src/wasmtime_wasi_tls/p3/host.rs.html

Handles the error case in the start method by returning a ready result with the error, and sets up pipes and channels for the TLS connection, spawning a task to combine results.

```rust
                let result = ResultProducer::ready(getter, Err(err));

                return Ok((
                    StreamReader::new(&mut store, cleartext)?,
                    FutureReader::new(&mut store, result)?,
                ));
            }
        }

        let (ciphertext_reader, ciphertext_writer) = pipe::pipe();
        let (ciphertext_result_tx, ciphertext_result_rx) = oneshot::channel();
        let (cleartext_result_tx, cleartext_result_rx) = oneshot::channel();
        let (recv_result_tx, recv_result_rx) = oneshot::channel();

        let connection = {
            let ctx = store.get();
            let connector = ctx.table.get_mut(&this)?;
            connector.recv = Some(ciphertext_reader);
            connector.connection.clone()
        };

        ciphertext.pipe(
            &mut store,
            AsyncWriteConsumer::new(ciphertext_writer, ciphertext_result_tx),
        )?;

        let cleartext = AsyncReadProducer::new(connection, cleartext_result_tx);
        store.spawn(FnTask(async move || {
            let ciphertext_result = match ciphertext_result_rx.await? {
                // Let the TLS implementation know the transport is closed.
                // Most likely, `shutdown` will be entirely synchronous and
                // complete immediately, but awaiting it anyway to adhere to
                // the AsyncWrite contract:
                Ok(mut inner) => inner.shutdown().await,
                Err(e) => Err(e),
            };
            let cleartext_result = cleartext_result_rx.await?.map(drop);
            let combined_result = cleartext_result
                .and(ciphertext_result)
                .map_err(|e| Error::from(e));
            _ = recv_result_tx.send(combined_result);
            Ok(())
        }))?;
        let result = ResultProducer::new(getter, recv_result_rx);

        Ok((
            StreamReader::new(&mut store, cleartext)?,
            FutureReader::new(&mut store, result)?,
        ))
    }
```

--------------------------------

### get example

Source: https://docs.wasmtime.dev/api/cranelift_codegen/type.FxHashMap.html

Returns a reference to the value corresponding to the key. The example inserts a key-value pair and asserts that get returns the correct value or None for missing keys.

```rust
use std::collections::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), None);
```

--------------------------------

### Test Setup for Run Command

Source: https://docs.wasmtime.dev/api/src/cranelift_reader/run_command.rs.html

Example of setting up a function signature for testing a run command.

```rust
#[test]
    fn run_a_command() {
        let mut signature = Signature::new(CallConv::Fast);
        signature.returns.push(AbiParam::new(types::I32));
```

--------------------------------

### Exported resources: setup with Engine, Component, Linker, Store

Source: https://docs.wasmtime.dev/api/src/wasmtime/runtime/component/bindgen_examples/mod.rs.html

Shows the beginning of an example that uses a world exporting a resource. It imports `Level` from the generated `exports::example::exported_resources::logging` module and includes the bindgen-generated code via `include_str!`. The example sets up an `Engine`, loads a component, creates a `Linker`, and creates a `Store` with `MyState`; the rest of the example is truncated in the source.

```rust
use wasmtime::{Result, Engine, Store};
use wasmtime::component::{bindgen, Component, Linker};
use self::exports::example::exported_resources::logging::Level;

#[doc = include_str!("./_6_exported_resources.rs")]

struct MyState;

fn main() -> Result<()> {
#   if true { return Ok(()) }
    let engine = Engine::default();
    let component = Component::from_file(&engine, "./your-component.wasm")?;

    let linker = Linker::new(&engine);
    // ... this small example has no imports so nothing is added here, but
    // if you had imports this is where they'd go.

    let mut store = Store::new(&engine, MyState);
```

--------------------------------

### Example using wasm_bench_create, wasm_bench_compile, wasm_bench_instantiate, wasm_bench_execute, and wasm_bench_free

Source: https://docs.wasmtime.dev/api/wasmtime_bench_api/index.html

Rust example demonstrating the full benchmark lifecycle: creating a WasmBenchConfig with timer callbacks, parsing a Wasm module, and calling compile/instantiate/execute/free. Shows that 'compilation_{start,end}' timing functions are called on successful compile, 'instantiation_{start,end}' on successful instantiate, and 'execution_{start,end}' on successful execute. Error codes use OK constant and non-null assertions.

```rust
use std::ptr;
use wasmtime_bench_api::*;

let working_dir = std::env::current_dir().unwrap().display().to_string();
let stdout_path = "./stdout.log";
let stderr_path = "./stderr.log";

// Functions to start/end timers for compilation.
//
// The `compilation_timer` pointer configured in the `WasmBenchConfig` is
// passed through.
extern "C" fn compilation_start(timer: *mut u8) {
    // Start your compilation timer here.
}
extern "C" fn compilation_end(timer: *mut u8) {
    // End your compilation timer here.
}

// Similar for instantiation.
extern "C" fn instantiation_start(timer: *mut u8) {
    // Start your instantiation timer here.
}
extern "C" fn instantiation_end(timer: *mut u8) {
    // End your instantiation timer here.
}

// Similar for execution.
extern "C" fn execution_start(timer: *mut u8) {
    // Start your execution timer here.
}
extern "C" fn execution_end(timer: *mut u8) {
    // End your execution timer here.
}

let config = WasmBenchConfig {
    working_dir_ptr: working_dir.as_ptr(),
    working_dir_len: working_dir.len(),
    stdout_path_ptr: stdout_path.as_ptr(),
    stdout_path_len: stdout_path.len(),
    stderr_path_ptr: stderr_path.as_ptr(),
    stderr_path_len: stderr_path.len(),
    stdin_path_ptr: ptr::null(),
    stdin_path_len: 0,
    compilation_timer: ptr::null_mut(),
    compilation_start,
    compilation_end,
    instantiation_timer: ptr::null_mut(),
    instantiation_start,
    instantiation_end,
    execution_timer: ptr::null_mut(),
    execution_start,
    execution_end,
    execution_flags_ptr: ptr::null(),
    execution_flags_len: 0,
};

let mut bench_api = ptr::null_mut();
unsafe {
    let code = wasm_bench_create(config, &mut bench_api);
    assert_eq!(code, OK);
    assert!(!bench_api.is_null());
};

let wasm = wat::parse_bytes(br#"
    (module
        (func $bench_start (import "bench" "start"))
        (func $bench_end (import "bench" "end"))
        (func $start (export "_start")
            call $bench_start
            i32.const 1
            i32.const 2
            i32.add
            drop
            call $bench_end
        )
    )
"#).unwrap();

// This will call the `compilation_{start,end}` timing functions on success.
let code = unsafe { wasm_bench_compile(bench_api, wasm.as_ptr(), wasm.len()) };
assert_eq!(code, OK);

// This will call the `instantiation_{start,end}` timing functions on success.
let code = unsafe { wasm_bench_instantiate(bench_api) };
assert_eq!(code, OK);

// This will call the `execution_{start,end}` timing functions on success.
let code = unsafe { wasm_bench_execute(bench_api) };
assert_eq!(code, OK);

unsafe {
    wasm_bench_free(bench_api);
}

```

--------------------------------

### Basic Slab usage example

Source: https://docs.wasmtime.dev/api/wasmtime_internal_core/slab/index.html

Shows how to create a `Slab`, allocate values, access them via indexing and `get`/`get_mut`, deallocate an entry, and allocate a new one. Note that indexing panics on missing or deallocated entries, while `get` and `get_mut` provide fallible lookup.

```rust
use wasmtime_internal_core::slab::Slab;

let mut slab = Slab::new();

// Insert some values into the slab.
let rza = slab.alloc("Robert Fitzgerald Diggs")?;
let gza = slab.alloc("Gary Grice")?;
let bill = slab.alloc("Bill Gates")?;

// Allocated elements can be accessed infallibly via indexing (and missing and
// deallocated entries will panic).
assert_eq!(slab[rza], "Robert Fitzgerald Diggs");

// Alternatively, the `get` and `get_mut` methods provide fallible lookup.
if let Some(genius) = slab.get(gza) {
    println!("The gza gza genius: {}", genius);
}
if let Some(val) = slab.get_mut(bill) {
    *val = "Bill Gates doesn't belong in this set...";
}

// We can remove values from the slab.
slab.dealloc(bill);

// Allocate a new entry.
let bill = slab.alloc("Bill Murray")?;
```

--------------------------------

### Install QEMU user-mode emulation

Source: https://docs.wasmtime.dev/contributing-cross-compiling.html

Install qemu-user to enable running tests for cross-compiled binaries.

```bash
sudo apt install qemu-user
```

--------------------------------

### WasiHttpView standalone server example

Source: https://docs.wasmtime.dev/api/wasmtime_wasi_http/p2/index.html

Standalone example that implements WasiHttpView, adds WASI HTTP interfaces to a Linker, pre-instantiates a component with ProxyPre, and serves HTTP/1.1 requests over a TCP listener. Requires a MyServer type with a ProxyPre field and a handle_request method; the example only shows the main setup and connection loop.

```rust
use wasmtime::bail;
use hyper::server::conn::http1;
use std::sync::Arc;
use tokio::net::TcpListener;
use wasmtime::component::{Component, Linker, ResourceTable};
use wasmtime::{Engine, Result, Store};
use wasmtime_wasi::{WasiCtx, WasiCtxView, WasiView};
use wasmtime_wasi_http::p2::bindings::ProxyPre;
use wasmtime_wasi_http::p2::bindings::http::types::Scheme;
use wasmtime_wasi_http::p2::body::HyperOutgoingBody;
use wasmtime_wasi_http::io::TokioIo;
use wasmtime_wasi_http::{WasiHttpCtx, WasiHttpView, WasiHttpCtxView};

#[tokio::main]
async fn main() -> Result<()> {
    let component = std::env::args().nth(1).unwrap();

    // Prepare the `Engine` for Wasmtime
    let engine = Engine::default();

    // Compile the component on the command line to machine code
    let component = Component::from_file(&engine, &component)?;

    // Prepare the `ProxyPre` which is a pre-instantiated version of the
    // component that we have. This will make per-request instantiation
    // much quicker.
    let mut linker = Linker::new(&engine);
    wasmtime_wasi::p2::add_to_linker_async(&mut linker)?;
    wasmtime_wasi_http::p2::add_only_http_to_linker_async(&mut linker)?;
    let pre = ProxyPre::new(linker.instantiate(&component)?)?;

    // Prepare our server state and start listening for connections.
    let server = Arc::new(MyServer { pre });
    let listener = TcpListener::bind("127.0.0.1:8000").await?;
    println!("Listening on {}", listener.local_addr()?);

    loop {
        // Accept a TCP connection and serve all of its requests in a separate
        // tokio task. Note that for now this only works with HTTP/1.1.
        let (client, addr) = listener.accept().await?;
        println!("serving new client from {addr}");

        let server = server.clone();
        tokio::task::spawn(async move {
            if let Err(e) = http1::Builder::new()
                .keep_alive(true)
                .serve_connection(
                    TokioIo::new(client),
                    hyper::service::service_fn(move |req| {
                        let server = server.clone();
                        async move { server.handle_request(req).await }
                    }),
                )
                .await
            {
                eprintln!("error serving client[{addr}]: {e:?}");
            }
        });
    }
}

struct MyServer {
    pre: ProxyPre<MyClientState>,
}
```

--------------------------------

### C multi-value example (multi.c)

Source: https://docs.wasmtime.dev/examples-multi-value.html

C example that instantiates the WebAssembly module and invokes its exported functions. Build with `cmake -B build -S examples`, `cmake --build build --target wasmtime-multi`, then `./build/wasmtime-multi`. Defines a `callback` and a `closure_callback` that set result values.

```c
/*
Example of instantiating of the WebAssembly module and invoking its exported
function.

You can build and run this example using cmake:

  cmake -B build -S examples
  cmake --build build --target wasmtime-multi
  ./build/wasmtime-multi

Also note that this example was taken from
https://github.com/WebAssembly/wasm-c-api/blob/master/example/multi.c
originally
*/

#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <wasm.h>
#include <wasmtime.h>

static void exit_with_error(const char *message, wasmtime_error_t *error,
                            wasm_trap_t *trap);

// A function to be called from Wasm code.
wasm_trap_t *callback(void *env, wasmtime_caller_t *caller,
                      const wasmtime_val_t *args, size_t nargs,
                      wasmtime_val_t *results, size_t nresults) {
  (void)env;
  (void)caller;
  (void)nargs;
  (void)nresults;

  printf("Calling back...\n");
  printf("> %" PRIu32 " %" PRIu64 "\n", args[0].of.i32, args[1].of.i64);
  printf("\n");

  results[0] = args[1];
  results[1] = args[0];
  return NULL;
}

// A function closure.
wasm_trap_t *closure_callback(void *env, wasmtime_caller_t *caller,
                              const wasmtime_val_t *args, size_t nargs,
                              wasmtime_val_t *results, size_t nresults) {
  (void)caller;
  (void)args;
  (void)nargs;
  (void)nresults;

  int i = *(int *)env;
  printf("Calling back closure...\n");
  printf("> %d\n", i);

  results[0].kind = WASMTIME_I32;
  results[0].of.i32 = (int32_t)i;
  return NULL;
}

int main() {
  // Initialize.
  printf("Initializing...\n");
  wasm_engine_t *engine = wasm_engine_new();
  wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL);
  wasmtime_context_t *context = wasmtime_store_context(store);
```

--------------------------------

### C Memory Interaction Setup

Source: https://docs.wasmtime.dev/examples-memory.html

Initial setup for a C program to instantiate a WebAssembly module and invoke exported functions, including helper functions for error checking.

```c
/*
Example of instantiating of the WebAssembly module and invoking its exported
function.

You can build and run this example using cmake:

  cmake -B build -S examples
  cmake --build build --target wasmtime-memory
  ./build/wasmtime-memory

Also note that this example was taken from
https://github.com/WebAssembly/wasm-c-api/blob/master/example/memory.c
originally
*/

#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <wasm.h>
#include <wasmtime.h>

static void exit_with_error(const char *message, wasmtime_error_t *error,
                            wasm_trap_t *trap);

void check(bool success) {
  if (!success) {
    printf("> Error, expected success\n");
    exit(1);
  }
}

void check_call(wasmtime_context_t *store, wasmtime_func_t *func,
                const wasmtime_val_t *args, size_t nargs, int32_t expected) {
  wasmtime_val_t results[1];
  wasm_trap_t *trap = NULL;
  wasmtime_error_t *error =
      wasmtime_func_call(store, func, args, nargs, results, 1, &trap);
  if (error != NULL || trap != NULL)
    exit_with_error("failed to call function", error, trap);
  if (results[0].of.i32 != expected) {
    printf("> Error on result\n");
    exit(1);
  }
}
```

--------------------------------

### Build and run WASI example with CMake

Source: https://docs.wasmtime.dev/examples-wasip1.html

Commands to build and run the WASI example using CMake.

```bash
cargo build --target wasm32-wasip1 -p example-wasi-wasm
cmake -B build -S examples
cmake --build build --target wasmtime-wasip1
./build/wasmtime-wasip1
```

--------------------------------

### Build and run WASI example with Cargo and CC

Source: https://docs.wasmtime.dev/examples-wasip1.html

Commands to compile the WASI example on Linux using cargo and the C compiler.

```bash
cargo build --target wasm32-wasip1 -p example-wasi-wasm
cargo build --release -p wasmtime-c-api
cc examples/wasip1/main.c \
    -I crates/c-api/include \
    target/release/libwasmtime.a \
    -lpthread -ldl -lm \
    -o wasip1
./wasip1
```

--------------------------------

### Build and Run Multithreaded Wasmtime Example

Source: https://docs.wasmtime.dev/examples-multithreaded-embedding.html

Commands to build and execute the multithreaded C++ example using CMake.

```bash
cmake -B build -S examples
cmake --build build --target wasmtime-threads-cpp
./build/wasmtime-threads-cpp
```

--------------------------------

### Standalone example: setting up WASI HTTP with ProxyPre

Source: https://docs.wasmtime.dev/api/src/wasmtime_wasi_http/p2/mod.rs.html

Shows how to implement `WasiHttpView`, add WASI HTTP interfaces to a linker, pre-instantiate a component with `ProxyPre`, and serve requests. Requires a component file path as a command-line argument.

```rust
use wasmtime::bail;
use hyper::server::conn::http1;
use std::sync::Arc;
use tokio::net::TcpListener;
use wasmtime::component::{Component, Linker, ResourceTable};
use wasmtime::{Engine, Result, Store};
use wasmtime_wasi::{WasiCtx, WasiCtxView, WasiView};
use wasmtime_wasi_http::p2::bindings::ProxyPre;
use wasmtime_wasi_http::p2::bindings::http::types::Scheme;
use wasmtime_wasi_http::p2::body::HyperOutgoingBody;
use wasmtime_wasi_http::io::TokioIo;
use wasmtime_wasi_http::{WasiHttpCtx, WasiHttpView, WasiHttpCtxView};

#[tokio::main]
async fn main() -> Result<()> {
    let component = std::env::args().nth(1).unwrap();

    // Prepare the `Engine` for Wasmtime
    let engine = Engine::default();

    // Compile the component on the command line to machine code
    let component = Component::from_file(&engine, &component)?;

    // Prepare the `ProxyPre` which is a pre-instantiated version of the
    // component that we have. This will make per-request instantiation
    // much quicker.
    let mut linker = Linker::new(&engine);
    wasmtime_wasi::p2::add_to_linker_async(&mut linker)?;
    wasmtime_wasi_http::p2::add_only_http_to_linker_async(&mut linker)?;
```

--------------------------------

### Example: Using StoreContextMut::run_concurrent to get an Accessor

Source: https://docs.wasmtime.dev/api/src/wasmtime/runtime/component/concurrent/func.rs.html?search=

This example shows the setup for using StoreContextMut::run_concurrent to obtain an Accessor for concurrent calls. It includes the necessary imports and a basic store setup with a resource table.

```rust
# use {
#   wasmtime::{
#     error::{Result},
#     component::{Component, Linker, ResourceTable},
#     Config, Engine, Store
#   },
# };
#
# struct Ctx { table: ResourceTable }
#
# async fn foo() -> Result<()> {
# let mut config = Config::new();
# let engine = Engine::new(&config)?;
# let mut store = Store::new(&engine, Ctx { table: ResourceTable::new() });
# let mut linker = Linker::new(&engine);
```

--------------------------------

### Rust host example: instantiate and call wasm module

Source: https://docs.wasmtime.dev/examples-hello-world.html

Rust example that compiles the wasm module, creates a Store with host state, defines an imported function that prints the state and increments a counter, instantiates the module, and calls the exported 'run' function. Run with `cargo run --example hello`.

```rust
//! Small example of how to instantiate a wasm module that imports one function,
//! showing how you can fill in host functionality for a wasm module.

// You can execute this example with `cargo run --example hello`

use wasmtime::*;

struct MyState {
    name: String,
    count: usize,
}

fn main() -> Result<()> {
    // First the wasm module needs to be compiled. This is done with a global
    // "compilation environment" within an `Engine`. Note that engines can be
    // further configured through `Config` if desired instead of using the
    // default like this is here.
    println!("Compiling module...");
    let engine = Engine::default();
    let module = Module::from_file(&engine, "examples/hello.wat")?;

    // After a module is compiled we create a `Store` which will contain
    // instantiated modules and other items like host functions. A Store
    // contains an arbitrary piece of host information, and we use `MyState`
    // here.
    println!("Initializing...");
    let mut store = Store::new(
        &engine,
        MyState {
            name: "hello, world!".to_string(),
            count: 0,
        },
    );

    // Our wasm module we'll be instantiating requires one imported function.
    // the function takes no parameters and returns no results. We create a host
    // implementation of that function here, and the `caller` parameter here is
    // used to get access to our original `MyState` value.
    println!("Creating callback...");
    let hello_func = Func::wrap(&mut store, |mut caller: Caller<'_, MyState>| {
        println!("Calling back...");
        println!("> {}", caller.data().name);
        caller.data_mut().count += 1;
    });

    // Once we've got that all set up we can then move to the instantiation
    // phase, pairing together a compiled module as well as a set of imports.
    // Note that this is where the wasm `start` function, if any, would run.
    println!("Instantiating module...");
    let imports = [hello_func.into()];
    let instance = Instance::new(&mut store, &module, &imports)?;

    // Next we poke around a bit to extract the `run` function from the module.
    println!("Extracting export...");
    let run = instance.get_typed_func::<(), ()>(&mut store, "run")?;

    // And last but not least we can call it!
    println!("Calling export...");
    run.call(&mut store, ())?;

    println!("Done.");
    Ok(())
}
```

--------------------------------

### get example

Source: https://docs.wasmtime.dev/api/cranelift_codegen/type.FxHashSet.html?search=

Returns a reference to the value in the set if it exists. The example gets Some(&2) for 2 and None for 4.

```rust
use std::collections::HashSet;

let set = HashSet::from([1, 2, 3]);
assert_eq!(set.get(&2), Some(&2));
assert_eq!(set.get(&4), None);
```

--------------------------------

### Full example with main function

Source: https://docs.wasmtime.dev/api/src/wasmtime_wasi_io/lib.rs.html?search=

Complete example showing how to set up a linker and store with the wasi-io implementation. It creates an Engine, a Linker, and a Store with a MyState that implements IoView, then calls add_to_linker_async. The example is intended to be used in a main function that returns a Result.

```rust
use wasmtime::{Engine, Result, Store};
use wasmtime::component::{ResourceTable, Linker};
use wasmtime_wasi_io::IoView;

fn main() -> Result<()> {
    let engine = Engine::default();

    let mut linker = Linker::<MyState>::new(&engine);
    wasmtime_wasi_io::add_to_linker_async(&mut linker)?;
    // ... add any further functionality to `linker` if desired ...

    let mut store = Store::new(
        &engine,
        MyState {
            table: ResourceTable::new(),
        },
    );

    // ... use `linker` to instantiate within `store` ...

    Ok(())
}

struct MyState {
    table: ResourceTable,
}

impl IoView for MyState {
    fn table(&mut self) -> &mut ResourceTable { &mut self.table }
}
```

--------------------------------

### Install Wasmtime via cargo-binstall

Source: https://docs.wasmtime.dev/cli-install.html

Use cargo-binstall to automatically fetch and install the appropriate precompiled binary for your system.

```bash
cargo binstall wasmtime-cli
```

--------------------------------

### Hello World Component Bindings Example

Source: https://docs.wasmtime.dev/api/src/wasmtime/runtime/component/bindgen_examples/mod.rs.html?search=

Shows how to instantiate a component with generated bindings and call a greet export. Uses HasSelf to avoid a custom projection and passes state through the linker.

```rust
    let mut linker = Linker::new(&engine);
    HelloWorld::add_to_linker::<_, HasSelf<_>>(&mut linker, |state| state)?;

    // As with the core wasm API of Wasmtime instantiation occurs within a
    // `Store`. The bindings structure contains an `instantiate` method which
    // takes the store, component, and linker. This returns the `bindings`
    // structure which is an instance of `HelloWorld` and supports typed access
    // to the exports of the component.
    let mut store = Store::new(
        &engine,
        MyState {
            name: "me".to_string(),
        },
    );
    let bindings = HelloWorld::instantiate(&mut store, &component, &linker)?;

    // Here our `greet` function doesn't take any parameters for the component,
    // but in the Wasmtime embedding API the first argument is always a `Store`.
    bindings.call_greet(&mut store)?;
    Ok(())
}
```

--------------------------------

### Compile, record, and inject for fib example

Source: https://docs.wasmtime.dev/examples-profiling-perf.html

Compiles the Fibonacci example to wasm, records it with perf and jitdump, then injects the jit data. The output shows the program result and perf record statistics.

```bash
$ rustc --target wasm32-wasip1 fib.rs -O
$ perf record -k mono wasmtime --profile=jitdump fib.wasm
fib(42) = 267914296
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.147 MB perf.data (3435 samples) ]
$ perf inject --jit --input perf.data --output perf.jit.data
```

--------------------------------

### Instantiate and call a WebAssembly module with Wasmtime C API

Source: https://docs.wasmtime.dev/examples-hello-world.html

This example demonstrates the complete process of instantiating a WebAssembly module and invoking its exported function using the Wasmtime C API. It reads a .wat file, compiles it, creates a callback function, instantiates the module, and calls the 'run' export. The example includes error handling and cleanup. Build with cmake: cmake -B build -S examples, cmake --build build --target wasmtime-hello, ./build/wasmtime-hello.

```C
/*
Example of instantiating of the WebAssembly module and invoking its exported
function.

You can build and run this example using cmake:

  cmake -B build -S examples
  cmake --build build --target wasmtime-hello
  ./build/wasmtime-hello
*/

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <wasm.h>
#include <wasmtime.h>

static void exit_with_error(const char *message, wasmtime_error_t *error,
                            wasm_trap_t *trap);

static wasm_trap_t *hello_callback(void *env, wasmtime_caller_t *caller,
                                   const wasmtime_val_t *args, size_t nargs,
                                   wasmtime_val_t *results, size_t nresults) {
  (void)env;
  (void)caller;
  (void)args;
  (void)nargs;
  (void)results;
  (void)nresults;
  printf("Calling back...\n");
  printf("> Hello World!\n");
  return NULL;
}

int main() {
  int ret = 0;
  // Set up our compilation context. Note that we could also work with a
  // `wasm_config_t` here to configure what feature are enabled and various
  // compilation settings.
  printf("Initializing...\n");
  wasm_engine_t *engine = wasm_engine_new();
  assert(engine != NULL);

  // With an engine we can create a *store* which is a long-lived group of wasm
  // modules. Note that we allocate some custom data here to live in the store,
  // but here we skip that and specify NULL.
  wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL);
  assert(store != NULL);
  wasmtime_context_t *context = wasmtime_store_context(store);

  // Read our input file, which in this case is a wasm text file.
  FILE *file = fopen("examples/hello.wat", "r");
  assert(file != NULL);
  fseek(file, 0L, SEEK_END);
  size_t file_size = ftell(file);
  fseek(file, 0L, SEEK_SET);
  wasm_byte_vec_t wat;
  wasm_byte_vec_new_uninitialized(&wat, file_size);
  if (fread(wat.data, file_size, 1, file) != 1) {
    printf("> Error loading module!\n");
    return 1;
  }
  fclose(file);

  // Parse the wat into the binary wasm format
  wasm_byte_vec_t wasm;
  wasmtime_error_t *error = wasmtime_wat2wasm(wat.data, wat.size, &wasm);
  if (error != NULL)
    exit_with_error("failed to parse wat", error, NULL);
  wasm_byte_vec_delete(&wat);

  // Now that we've got our binary webassembly we can compile our module.
  printf("Compiling module...\n");
  wasmtime_module_t *module = NULL;
  error = wasmtime_module_new(engine, (uint8_t *)wasm.data, wasm.size, &module);
  wasm_byte_vec_delete(&wasm);
  if (error != NULL)
    exit_with_error("failed to compile module", error, NULL);

  // Next up we need to create the function that the wasm module imports. Here
  // we'll be hooking up a thunk function to the `hello_callback` native
  // function above. Note that we can assign custom data, but we just use NULL
  // for now).
  printf("Creating callback...\n");
  wasm_functype_t *hello_ty = wasm_functype_new_0_0();
  wasmtime_func_t hello;
  wasmtime_func_new(context, hello_ty, hello_callback, NULL, NULL, &hello);
  wasm_functype_delete(hello_ty);

  // With our callback function we can now instantiate the compiled module,
  // giving us an instance we can then execute exports from. Note that
  // instantiation can trap due to execution of the `start` function, so we need
  // to handle that here too.
  printf("Instantiating module...\n");
  wasm_trap_t *trap = NULL;
  wasmtime_instance_t instance;
  wasmtime_extern_t import;
  import.kind = WASMTIME_EXTERN_FUNC;
  import.of.func = hello;
  error = wasmtime_instance_new(context, module, &import, 1, &instance, &trap);
  if (error != NULL || trap != NULL)
    exit_with_error("failed to instantiate", error, trap);

  // Lookup our `run` export function
  printf("Extracting export...\n");
  wasmtime_extern_t run;
  bool ok = wasmtime_instance_export_get(context, &instance, "run", 3, &run);
  assert(ok);
  assert(run.kind == WASMTIME_EXTERN_FUNC);

  // And call it!
  printf("Calling export...\n");
  error = wasmtime_func_call(context, &run.of.func, NULL, 0, NULL, 0, &trap);
  if (error != NULL || trap != NULL)
    exit_with_error("failed to call function", error, trap);

  // Clean up after ourselves at this point
  printf("All finished!\n");
  ret = 0;

  wasmtime_module_delete(module);
  wasmtime_store_delete(store);
  wasm_engine_delete(engine);
  return ret;
}

static void exit_with_error(const char *message, wasmtime_error_t *error,
                            wasm_trap_t *trap) {
  fprintf(stderr, "error: %s\n", message);
  wasm_byte_vec_t error_message;
  if (error != NULL) {
    wasmtime_error_message(error, &error_message);
    wasmtime_error_delete(error);
  } else {
    wasm_trap_message(trap, &error_message);
    wasm_trap_delete(trap);
  }
  fprintf(stderr, "%.*s\n", (int)error_message.size, error_message.data);
  wasm_byte_vec_delete(&error_message);
  exit(1);
}

```

--------------------------------

### allow_unknown_exports example

Source: https://docs.wasmtime.dev/api/src/wasmtime/runtime/linker.rs.html?search=

Example usage of allow_unknown_exports: creates a Linker, enables unknown exports, and links a module. The example is wrapped in a doc-test with hidden setup lines.

```rust
# use wasmtime::*;
# fn main() -> Result<()> {
# let engine = Engine::default();
# let module = Module::new(&engine, "(module)")?;
# let mut store = Store::new(&engine, ());
let mut linker = Linker::new(&engine);
linker.allow_unknown_exports(true);
linker.module(&mut store, "mod", &module)?;
# Ok(())
# }
```

--------------------------------

### Rust multi-value example (multi.rs)

Source: https://docs.wasmtime.dev/examples-multi-value.html

Rust example that compiles `examples/multi.wat`, creates a host callback returning two values, and calls the exported `g` and `round_trip_many` functions. Run with `cargo run --example multi`. Uses `Func::wrap` for the callback and `get_typed_func` for multi-value calls.

```rust
//! This is an example of working with multi-value modules and dealing with
//! multi-value functions.
//!
//! Note that the `Func::wrap*` interfaces cannot be used to return multiple
//! values just yet, so we need to use the more dynamic `Func::new` and
//! `Func::call` methods.

// You can execute this example with `cargo run --example multi`

use wasmtime::Result;

fn main() -> Result<()> {
    use wasmtime::*;

    println!("Initializing...");
    let engine = Engine::default();
    let mut store = Store::new(&engine, ());

    // Compile.
    println!("Compiling module...");
    let module = Module::from_file(&engine, "examples/multi.wat")?;

    // Create a host function which takes multiple parameters and returns
    // multiple results.
    println!("Creating callback...");
    let callback_func = Func::wrap(&mut store, |a: i32, b: i64| -> (i64, i32) {
        (b + 1, a + 1)
    });

    // Instantiate.
    println!("Instantiating module...");
    let instance = Instance::new(&mut store, &module, &[callback_func.into()])?;

    // Extract exports.
    println!("Extracting export...");
    let g = instance.get_typed_func::<(i32, i64), (i64, i32)>(&mut store, "g")?;

    // Call `$g`.
    println!("Calling export \"g\"...");
    let (a, b) = g.call(&mut store, (1, 3))?;

    println!("Printing result...");
    println!("> {a} {b}");

    assert_eq!(a, 4);
    assert_eq!(b, 2);

    // Call `$round_trip_many`.
    println!("Calling export \"round_trip_many\"...");
    let round_trip_many = instance
        .get_typed_func::<
        (i64, i64, i64, i64, i64, i64, i64, i64, i64, i64),
        (i64, i64, i64, i64, i64, i64, i64, i64, i64, i64),
        >
        (&mut store, "round_trip_many")?;
    let results = round_trip_many.call(&mut store, (0, 1, 2, 3, 4, 5, 6, 7, 8, 9))?;

    println!("Printing result...");
    println!("> {results:?}");
    assert_eq!(results, (0, 1, 2, 3, 4, 5, 6, 7, 8, 9));

    Ok(())
}
```

--------------------------------

### Main Execution Entry Point

Source: https://docs.wasmtime.dev/api/src/veri/veri.rs.html?search=

Initializes the environment, parses arguments with optional configuration file expansion, sets up the Rayon thread pool, and prepares the working directory.

```rust
fn main() -> Result<()> {
    env_logger::builder().format_target(false).init();

    // Expand any `--config` files into the argument list before parsing.
    // Configuration arguments are placed ahead of the arguments given on the
    // command line so that the command line takes precedence.
    // No configuration file is applied unless one is asked for: a run should
    // only ever have the filters and exclusions that are visible in its own
    // command line.
    let raw: Vec<String> = std::env::args().collect();
    let config_paths = collect_config_paths(&raw[1..]);
    let opts = if config_paths.is_empty() {
        Opts::parse()
    } else {
        let mut combined = vec![raw[0].clone()];
        for path in &config_paths {
            combined.extend(read_config_args(path)?);
        }
        combined.extend(raw[1..].iter().cloned());
        Opts::parse_from(combined)
    };

    // Setup thread pool.
    //
    // Recursively evaluating complex spec encodings (e.g., `clz`) can overflow
    // the default Rayon worker thread stack size, so default to a larger stack.
    const DEFAULT_STACK_SIZE: usize = 256 * 1024 * 1024;
    let stack_size = std::env::var("ISLE_VERI_STACK_SIZE")
        .ok()
        .and_then(|s| s.parse().ok())
        .unwrap_or(DEFAULT_STACK_SIZE);
    rayon::ThreadPoolBuilder::new()
        .num_threads(opts.num_threads)
        .stack_size(stack_size)
        .build_global()?;
    log::info!("num theads: {}", rayon::current_num_threads());

    // Resolve the working directory, defaulting to a fresh temporary directory
    // that lives for the duration of the run.
    let temp_dir = match &opts.work_dir {
        Some(_) => None,
        None => Some(tempfile::tempdir()?),
    };
    let work_dir: &std::path::Path = match (&opts.work_dir, &temp_dir) {
        (Some(dir), _) => dir,
        (None, Some(temp)) => temp.path(),
        (None, None) => unreachable!(),
    };

    // Read ISLE inputs.
    let inputs = opts.isle_input_files(work_dir)?;
    let mut runner = Runner::from_files(&inputs)?;

    // Scope expansion to a single root term, if requested. Otherwise the
    // default is to expand from every term that has rules.
    if let Some(root) = &opts.only_root {
        runner.set_root_term(root);
    }

    // Scope verification to a single named rule, if requested. This seeds
```

--------------------------------

### starts_with example

Source: https://docs.wasmtime.dev/api/cranelift_codegen/ir/instructions/struct.VariableArgs.html

Checks whether the slice starts with a given prefix. The example shows true for prefixes and the slice itself, and false for non-prefixes.

```rust
let v = [10, 40, 30];
assert!(v.starts_with(&[10]));
assert!(v.starts_with(&[10, 40]));
assert!(v.starts_with(&v));
assert!(!v.starts_with(&[50]));
assert!(!v.starts_with(&[10, 50]));

```

--------------------------------

### Install Wasmtime via Cargo

Source: https://docs.wasmtime.dev/cli-install.html

Compile and install the Wasmtime CLI from crates.io using Cargo.

```bash
cargo install wasmtime-cli
```

--------------------------------

### Install wasm32 targets

Source: https://docs.wasmtime.dev/contributing-testing.html

Install the required wasm32-wasip1 and wasm32-unknown-unknown targets using rustup to enable test compilation.

```bash
rustup target add wasm32-wasip1 wasm32-unknown-unknown
```

--------------------------------

### hello.cc: Compile, instantiate, and run a WebAssembly module with Wasmtime C++ API

Source: https://docs.wasmtime.dev/c-api/hello_8cc-example.html

This example reads a WebAssembly text file (examples/hello.wat), compiles it with Module::compile, creates a Store, defines a host function that prints "Calling back...", instantiates the module, extracts the exported "run" function, and calls it. It prints progress messages to stdout. Requires the wasmtime.hh header and a C++ compiler.

```cpp
#include <fstream>
#include <iostream>
#include <sstream>
#include <wasmtime.hh>
using namespace wasmtime;

std::string readFile(const char *name) {
  std::ifstream watFile;
  watFile.open(name);
  std::stringstream strStream;
  strStream << watFile.rdbuf();
  return strStream.str();
}

int main() {
  // First the wasm module needs to be compiled. This is done with a global
  // "compilation environment" within an `Engine`. Note that engines can be
  // further configured through `Config` if desired instead of using the
  // default like this is here.
  std::cout << "Compiling module\n";
  Engine engine;
  auto module =
      Module::compile(engine, readFile("examples/hello.wat")).unwrap();

  // After a module is compiled we create a `Store` which will contain
  // instantiated modules and other items like host functions. A Store
  // contains an arbitrary piece of host information, and we use `MyState`
  // here.
  std::cout << "Initializing...\n";
  Store store(engine);

  // Our wasm module we'll be instantiating requires one imported function.
  // the function takes no parameters and returns no results. We create a host
  // implementation of that function here.
  std::cout << "Creating callback...\n";
  Func host_func =
      Func::wrap(store, []() { std::cout << "Calling back...\n"; });

  // Once we've got that all set up we can then move to the instantiation
  // phase, pairing together a compiled module as well as a set of imports.
  // Note that this is where the wasm `start` function, if any, would run.
  std::cout << "Instantiating module...\n";
  auto instance = Instance::create(store, module, {host_func}).unwrap();

  // Next we poke around a bit to extract the `run` function from the module.
  std::cout << "Extracting export...\n";
  auto run = std::get<Func>(*instance.get(store, "run"));

  // And last but not least we can call it!
  std::cout << "Calling export...\n";
  run.call(store, {}).unwrap();
  std::cout << "Done\n";
}

```

--------------------------------

### ScalarBitSet::len example

Source: https://docs.wasmtime.dev/api/cranelift_bitset/scalar/struct.ScalarBitSet.html

Getting the number of elements in the set.

```rust
use cranelift_bitset::ScalarBitSet;

let mut bitset = ScalarBitSet::<u64>::new();

assert_eq!(bitset.len(), 0);

bitset.insert(24);
bitset.insert(13);
bitset.insert(36);

assert_eq!(bitset.len(), 3);
```

--------------------------------

### Get OperandKind from Location

Source: https://docs.wasmtime.dev/api/cranelift_assembler_x64_meta/dsl/format/enum.OperandKind.html

Example of retrieving the OperandKind from a Location.

```rust
let k: OperandKind = Location::imm32.kind();
```

--------------------------------

### HelloWorldPre::instantiate_async

Source: https://docs.wasmtime.dev/api/wasmtime/component/bindgen_examples/_0_hello_world/struct.HelloWorldPre.html?search=

Same as `Self::instantiate`, except with `async`.

```APIDOC
## HelloWorldPre::instantiate_async

### Description
Same as `Self::instantiate`, except with `async`.

### Method
`pub async fn instantiate_async(&self, store: impl AsContextMut<Data = _T>) -> Result<HelloWorld>`

### Parameters
- **store** (`impl AsContextMut<Data = _T>`) - Required - The store to instantiate the component into.

### Returns
- `Result<HelloWorld>` - The instantiated `HelloWorld` bindings, or an error if instantiation fails.
```
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