feat:(examples): Add metering example

Cargo.toml

@@ -255,3 +255,8 @@ required-features = ["cranelift"]
 name = "hello-world"
 path = "examples/hello_world.rs"
 required-features = ["cranelift"]
+
+[[example]]
+name = "metering"
+path = "examples/metering.rs"
+required-features = ["cranelift"]

examples/metering.rs

@@ -0,0 +1,97 @@
+//! Wasmer will let you easily run Wasm module in a Rust host.
+//!
+//! This example illustrates the basics of using Wasmer through a "Hello World"-like project:
+//!
+//!   1. How to load a Wasm modules as bytes
+//!   2. How to compile the module
+//!   3. How to create an instance of the module
+//!
+//! You can run the example directly by executing in Wasmer root:
+//!
+//! ```shell
+//! cargo run --example metering --release --features "cranelift"
+//! ```
+//!
+//! Ready?
+
+use std::sync::Arc;
+use wasmer::{imports, wat2wasm, Instance, Module, Store};
+use wasmer_compiler_cranelift::Cranelift;
+use wasmer_engine_jit::JIT;
+use wasmer_middlewares::Metering;
+use wasmer::CompilerConfig;
+use wasmer::wasmparser::Operator;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // Let's declare the Wasm module.
+    //
+    // We are using the text representation of the module here but you can also load `.wasm`
+    // files using the `include_bytes!` macro.
+    let wasm_bytes = wat2wasm(
+        br#"
+(module
+  (type $add_one_t (func (param i32) (result i32)))
+  (func $add_one_f (type $add_one_t) (param $value i32) (result i32)
+    local.get $value
+    i32.const 1
+    i32.add)
+  (export "add_one" (func $add_one_f)))
+"#,
+    )?;
+
+    // Create a Store.
+    // Note that we don't need to specify the engine/compiler if we want to use
+    // the default provided by Wasmer.
+    // You can use `Store::default()` for that.
+    let metering = Metering::new(5, |operator| -> u64 {
+        match operator {
+            Operator::LocalGet { .. }
+            | Operator::I32Add { .. }=> 2,
+            _ => {
+                dbg!(operator);
+
+                0
+            }
+        }
+    });
+    let mut compiler_config = Cranelift::default();
+    compiler_config.push_middleware(Arc::new(metering));
+    let store = Store::new(&JIT::new(&compiler_config).engine());
+
+    println!("Compiling module...");
+    // Let's compile the Wasm module.
+    let module = Module::new(&store, wasm_bytes)?;
+
+    // Create an empty import object.
+    let import_object = imports! {};
+
+    println!("Instantiating module...");
+    // Let's instantiate the Wasm module.
+    let instance = Instance::new(&module, &import_object)?;
+
+    // We now have an instance ready to be used.
+    //
+    // From an `Instance` we can retrieve any exported entities.
+    // Each of these entities is covered in others examples.
+    //
+    // Here we are retrieving the exported function. We won't go into details here
+    // as the main focus of this example is to show how to create an instance out
+    // of a Wasm module and have basic interactions with it.
+    let add_one = instance
+        .exports
+        .get_function("add_one")?
+        .native::<i32, i32>()?;
+
+    println!("Calling `add_one` function...");
+    let result = add_one.call(1)?;
+
+    println!("Results of `add_one`: {:?}", result);
+    assert_eq!(result, 2);
+
+    Ok(())
+}
+
+#[test]
+fn test_exported_function() -> Result<(), Box<dyn std::error::Error>> {
+    main()
+}