wasmldr: read module from fd 3 if no path given

This commit makes wasmldr try to read the wasm module from fd3 if no
file path was given. (Since keepldr doesn't currently pass arguments to
wasmldr, this will be the default behavior.)

This means you should be able to run a .wasm module in a keep by doing:

    cargo run -- exec 3< hello.wasm

This behavior will likely change soon, but hey.. Hello World!

Signed-off-by: Will Woods <[email protected]>

internal/wasmldr/src/cli.rs

@@ -24,8 +24,8 @@ pub struct RunOptions {
     // TODO: --inherit-env
     // TODO: --stdin, --stdout, --stderr
     /// Path of the WebAssembly module to run
-    #[structopt(index = 1, required = true, value_name = "MODULE", parse(from_os_str))]
-    pub module: PathBuf,
+    #[structopt(index = 1, value_name = "MODULE", parse(from_os_str))]
+    pub module: Option<PathBuf>,
 
     // NOTE: this has to come last for TrailingVarArg
     /// Arguments to pass to the WebAssembly module

internal/wasmldr/src/main.rs

@@ -36,6 +36,7 @@ use structopt::StructOpt;
 
 use std::fs::File;
 use std::io::Read;
+use std::os::unix::io::{FromRawFd, RawFd};
 
 fn main() {
     // Initialize the logger, taking settings from the default env vars
@@ -47,9 +48,13 @@ fn main() {
     let opts = cli::RunOptions::from_args();
     info!("opts: {:#?}", opts);
 
-    info!("reading {:?}", opts.module);
-    // TODO: don't just panic here...
-    let mut reader = File::open(&opts.module).expect("Unable to open file");
+    let mut reader = if let Some(module) = opts.module {
+        info!("reading module from {:?}", &module);
+        File::open(&module).expect("Unable to open file")
+    } else {
+        info!("reading module from fd 3");
+        unsafe { File::from_raw_fd(RawFd::from(3)) }
+    };
 
     let mut bytes = Vec::new();
     reader