Add a nice example of using stdio pipes

Cargo.toml

@@ -221,6 +221,11 @@ name = "wasi"
 path = "examples/wasi.rs"
 required-features = ["cranelift", "wasi"]
 
+[[example]]
+name = "wasi-pipes"
+path = "examples/wasi_pipes.rs"
+required-features = ["cranelift", "wasi"]
+
 [[example]]
 name = "table"
 path = "examples/table.rs"

examples/README.md

@@ -346,6 +346,20 @@ example.
 
    </details>
 
+2. [**WASI Pipes**][wasi-pipes], builds on the WASI example to show off
+   stdio piping in Wasmer.
+
+   _Keywords_: wasi, system, interface
+
+   <details>
+   <summary><em>Execute the example</em></summary>
+
+   ```shell
+   $ cargo run --example wasi-pipes --release --features "cranelift,wasi"
+   ```
+
+   </details>
+
 [engine-jit]: ./engine_jit.rs
 [engine-native]: ./engine_native.rs
 [engine-headless]: ./engine_headless.rs
@@ -360,6 +374,7 @@ example.
 [imported-function]: ./imports_function.rs
 [instance]: ./instance.rs
 [wasi]: ./wasi.rs
+[wasi-pipes]: ./wasi_pipes.rs
 [table]: ./table.rs
 [memory]: ./memory.rs
 [`wasmer-compiler-singlepass`]: https://github.com/wasmerio/wasmer/tree/master/lib/compiler-singlepass

examples/wasi_pipes.rs

@@ -0,0 +1,86 @@
+//! Piping to and from a WASI compiled WebAssembly module with Wasmer.
+//!
+//! This example builds on the WASI example, showing how you can pipe to and
+//! from a WebAssembly module.
+//!
+//! You can run the example directly by executing in Wasmer root:
+//!
+//! ```shell
+//! cargo run --example wasi-pipes --release --features "cranelift,wasi"
+//! ```
+//!
+//! Ready?
+
+use wasmer::{Instance, Module, Store};
+use wasmer_compiler_cranelift::Cranelift;
+use wasmer_engine_jit::JIT;
+use wasmer_wasi::{Pipe, WasiState};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let wasm_path = concat!(
+        env!("CARGO_MANIFEST_DIR"),
+        "/tests/wasi-wast/wasi/unstable/pipe_reverse.wasm"
+    );
+    // Let's declare the Wasm module with the text representation.
+    let wasm_bytes = std::fs::read(wasm_path)?;
+
+    // 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 store = Store::new(&JIT::new(&Cranelift::default()).engine());
+
+    println!("Compiling module...");
+    // Let's compile the Wasm module.
+    let module = Module::new(&store, wasm_bytes)?;
+
+    println!("Creating `WasiEnv`...");
+    // First, we create the `WasiEnv` with the stdio pipes
+    let input = Pipe::new();
+    let output = Pipe::new();
+    let mut wasi_env = WasiState::new("hello")
+        .stdin(Box::new(input))
+        .stdout(Box::new(output))
+        .finalize()?;
+
+    println!("Instantiating module with WASI imports...");
+    // Then, we get the import object related to our WASI
+    // and attach it to the Wasm instance.
+    let import_object = wasi_env.import_object(&module)?;
+    let instance = Instance::new(&module, &import_object)?;
+
+    // WASI requires to explicitly set the memory for the `WasiEnv`
+    wasi_env.set_memory(instance.exports.get_memory("memory")?.clone());
+
+    let msg = "racecar go zoom";
+    println!("Writing \"{}\" to the WASI stdin...", msg);
+    // To write to the stdin, we need a mutable reference to the pipe
+    let mut state = wasi_env.state();
+    let wasi_stdin = state.fs.stdin_mut()?.as_mut().unwrap();
+    // Then we can write to it!
+    writeln!(wasi_stdin, "{}", msg)?;
+    // Forgetting to drop state will deadlock `start.call()` later on!
+    drop(state);
+
+    println!("Call WASI `_start` function...");
+    // And we just call the `_start` function!
+    let start = instance.exports.get_function("_start")?;
+    start.call(&[])?;
+
+    println!("Reading from the WASI stdout...");
+    // To read from the stdout, we again need a mutable reference to the pipe
+    let mut state = wasi_env.state();
+    let wasi_stdout = state.fs.stdout_mut()?.as_mut().unwrap();
+    // Then we can read from it!
+    let mut buf = String::new();
+    wasi_stdout.read_to_string(&mut buf)?;
+    println!("Read \"{}\" from the WASI stdout!", buf.trim());
+
+    Ok(())
+}
+
+#[test]
+#[cfg(feature = "wasi")]
+fn test_wasi() -> Result<(), Box<dyn std::error::Error>> {
+    main()
+}

tests/wasi-wast/wasi/snapshot1/pipe_reverse.wast

@@ -0,0 +1,6 @@
+;; This file was generated by https://github.com/wasmerio/wasi-tests
+
+(wasi_test "pipe_reverse.wasm"
+  (assert_return (i64.const 0))
+  (assert_stdout "\n")
+)

tests/wasi-wast/wasi/unstable/pipe_reverse.wast

@@ -0,0 +1,6 @@
+;; This file was generated by https://github.com/wasmerio/wasi-tests
+
+(wasi_test "pipe_reverse.wasm"
+  (assert_return (i64.const 0))
+  (assert_stdout "\n")
+)