Sniff the wasm magic bytes, rather than relying on the filename extension.

cranelift/src/wasm.rs

@@ -11,7 +11,6 @@ use cretonne::settings::FlagsOrIsa;
 use std::fs::File;
 use std::error::Error;
 use std::io;
-use std::io::prelude::*;
 use std::path::Path;
 use std::process::Command;
 use tempdir::TempDir;
@@ -78,18 +77,10 @@ fn handle_module(
     terminal.fg(term::color::MAGENTA).unwrap();
     vprint!(flag_verbose, "Translating... ");
     terminal.reset().unwrap();
-    let data = match path.extension() {
-        None => {
-            return Err(String::from("the file extension is not wasm or wat"));
-        }
-        Some(ext) => {
-            match ext.to_str() {
-                Some("wasm") => {
-                    read_to_end(path.clone()).map_err(|err| {
+    let mut data = read_to_end(path.clone()).map_err(|err| {
         String::from(err.description())
-                    })?
-                }
-                Some("wat") => {
+    })?;
+    if !data.starts_with(&[b'\0', b'a', b's', b'm']) {
         let tmp_dir = TempDir::new("cretonne-wasm").unwrap();
         let file_path = tmp_dir.path().join("module.wasm");
         File::create(file_path.clone()).unwrap();
@@ -103,16 +94,10 @@ fn handle_module(
             } else {
                 return Err(String::from(e.description()));
             })?;
-                    read_to_end(file_path).map_err(
+        data = read_to_end(file_path).map_err(
             |err| String::from(err.description()),
-                    )?
+        )?;
     }
-                None | Some(&_) => {
-                    return Err(String::from("the file extension is not wasm or wat"));
-                }
-            }
-        }
-    };
     let mut dummy_runtime = DummyRuntime::with_flags(fisa.flags.clone());
     let translation = {
         let runtime: &mut WasmRuntime = &mut dummy_runtime;