feat: add wasmtime

__wasm/wasmtime/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "wasmtime"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+anyhow = "1.0.58"
+wasmtime = "0.38.1"
+

__wasm/wasmtime/README.md

@@ -0,0 +1,12 @@
+
+
+wasmtime demo.wat
+
+wat2wasm demo.wat
+
+wasm2wat demo.wasm
+
+
+
+https://github.com/bytecodealliance/wasmtime/blob/main/docs/WASI-tutorial.md
+

__wasm/wasmtime/hello_world.wat

@@ -0,0 +1,27 @@
+(module
+    ;; Import the required fd_write WASI function which will write the given io vectors to stdout
+    ;; The function signature for fd_write is:
+    ;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written
+    (import "wasi_unstable" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32)))
+
+    (memory 1)
+    (export "memory" (memory 0))
+
+    ;; Write 'hello world\n' to memory at an offset of 8 bytes
+    ;; Note the trailing newline which is required for the text to appear
+    (data (i32.const 8) "hello world\n")
+
+    (func $main (export "_start")
+        ;; Creating a new io vector within linear memory
+        (i32.store (i32.const 0) (i32.const 8))  ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string
+        (i32.store (i32.const 4) (i32.const 12))  ;; iov.iov_len - The length of the 'hello world\n' string
+
+        (call $fd_write
+            (i32.const 1) ;; file_descriptor - 1 for stdout
+            (i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0
+            (i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one.
+            (i32.const 20) ;; nwritten - A place in memory to store the number of bytes written
+        )
+        drop ;; Discard the number of bytes written from the top of the stack
+    )
+)

__wasm/wasmtime/src/main.rs

@@ -0,0 +1,38 @@
+use anyhow::Result;
+use wasmtime::*;
+
+fn main() -> Result<()> {
+    // Modules can be compiled through either the text or binary format
+    let engine = Engine::default();
+    let wat = r#"
+        (module
+            (import "host" "hello" (func $host_hello (param i32)))
+
+            (func (export "hello")
+                i32.const 3
+                call $host_hello)
+        )
+    "#;
+    let module = Module::new(&engine, wat)?;
+
+    // Create a `Linker` which will be later used to instantiate this module.
+    // Host functionality is defined by name within the `Linker`.
+    let mut linker = Linker::new(&engine);
+    linker.func_wrap("host", "hello", |caller: Caller<'_, u32>, param: i32| {
+        println!("Got {} from WebAssembly", param);
+        println!("my host state is: {}", caller.data());
+    })?;
+
+    // All wasm objects operate within the context of a "store". Each
+    // `Store` has a type parameter to store host-specific data, which in
+    // this case we're using `4` for.
+    let mut store = Store::new(&engine, 4);
+    let instance = linker.instantiate(&mut store, &module)?;
+    let hello = instance.get_typed_func::<(), (), _>(&mut store, "hello")?;
+
+    // And finally we can call the wasm!
+    hello.call(&mut store, ())?;
+
+    Ok(())
+}
+