filesystem example (#2236)

examples/wasi-fs/main.rs

@@ -0,0 +1,46 @@
+//! Example of running a wasi binary in a memory filesystem
+
+// The corresponding wasm binary can be built with:
+// `cargo build -p example-wasi-fs-wasm --target wasm32-wasi`
+//
+// then you can execute this example with `cargo run --example wasi-fs`
+
+use anyhow::Result;
+use std::collections::HashMap;
+use wasmtime::*;
+use wasmtime_wasi::virtfs::{VecFileContents, VirtualDirEntry};
+use wasmtime_wasi::{Wasi, WasiCtxBuilder};
+
+fn main() -> Result<()> {
+    tracing_subscriber::FmtSubscriber::builder()
+        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
+        .with_ansi(true)
+        .init();
+
+    let store = Store::default();
+    let mut linker = Linker::new(&store);
+
+    // Create an instance of `Wasi` which contains a `WasiCtx`. Note that
+    // `WasiCtx` provides a number of ways to configure what the target program
+    // will have access to.
+    let entry = VirtualDirEntry::File(Box::new(VecFileContents::with_content(
+        "world".as_bytes().to_owned(),
+    )));
+    let mut map = HashMap::new();
+    map.insert("test.txt".to_string(), entry);
+    let dir = VirtualDirEntry::Directory(map);
+    let ctx = WasiCtxBuilder::new()
+        .inherit_stdout()
+        .inherit_stderr()
+        .preopened_virt(dir, ".")
+        .build()?;
+    let wasi = Wasi::new(&store, ctx);
+    wasi.add_to_linker(&mut linker)?;
+
+    // Instantiate our module with the imports we've created, and run it.
+    let module = Module::from_file(store.engine(), "target/wasm32-wasi/debug/wasi-fs.wasm")?;
+    linker.module("", &module)?;
+    linker.get_default("")?.get0::<()>()?()?;
+
+    Ok(())
+}