Split crates and clean up structure of codebase (#294)

Co-authored-by: Jiahao XU <Jiahao_XU@outlook.com>

crates/detect-wasi/src/lib.rs

@@ -0,0 +1,42 @@
+use std::{
+    fs::File,
+    io::{Result, Write},
+    process::Command,
+};
+#[cfg(unix)]
+use std::{fs::Permissions, os::unix::fs::PermissionsExt};
+
+use tempfile::tempdir;
+
+const WASI_PROGRAM: &[u8] = include_bytes!("miniwasi.wasm");
+
+/// Detect the ability to run WASI
+///
+/// This attempts to run a small embedded WASI program, and returns true if no errors happened.
+/// Errors returned by the `Result` are I/O errors from the establishment of the context, not
+/// errors from the run attempt.
+///
+/// On Linux, you can configure your system to run WASI programs using a binfmt directive. Under
+/// systemd, write the below to `/etc/binfmt.d/wasi.conf`, with `/usr/bin/wasmtime` optionally
+/// replaced with the path to your WASI runtime of choice:
+///
+/// ```plain
+/// :wasi:M::\x00asm::/usr/bin/wasmtime:
+/// ```
+pub fn detect_wasi_runability() -> Result<bool> {
+    let progdir = tempdir()?;
+    let prog = progdir.path().join("miniwasi.wasm");
+
+    {
+        let mut progfile = File::create(&prog)?;
+        progfile.write_all(WASI_PROGRAM)?;
+
+        #[cfg(unix)]
+        progfile.set_permissions(Permissions::from_mode(0o777))?;
+    }
+
+    match Command::new(prog).output() {
+        Ok(out) => Ok(out.status.success() && out.stdout.is_empty() && out.stderr.is_empty()),
+        Err(_) => Ok(false),
+    }
+}