Redesign wasi ctx a bit (bytecodealliance#156)

* redesign wasi ctx and builder

* in ctx, resources are only ever owned by the table
* preopen dirs and stdio are just indexes into the table that we hand to the caller
* builder requires less boxing, in general, takes more impl traits

* tests: rewrite the way we generate tests to not construct store

* uncomment WasiCtx's pool methods

host/Cargo.toml

@@ -22,3 +22,4 @@ tracing-subscriber = { version = "0.3", default-features = false, features = ["e
 test-programs-macros = { path = "../test-programs/macros" }
 test-log = { version = "0.2", default-features = false, features = ["trace"] }
 tempfile = "3.3.0"
+lazy_static = "1"

host/src/env.rs

@@ -15,20 +15,14 @@ impl wasi::environment::Host for WasiCtx {
 impl wasi::preopens::Host for WasiCtx {
     async fn get_stdio(&mut self) -> Result<wasi::preopens::StdioPreopens, anyhow::Error> {
         Ok(wasi::preopens::StdioPreopens {
-            stdin: 0,
-            stdout: 1,
-            stderr: 2,
+            stdin: self.stdin,
+            stdout: self.stdout,
+            stderr: self.stderr,
         })
     }
     async fn get_directories(
         &mut self,
     ) -> Result<Vec<(wasi::filesystem::Descriptor, String)>, anyhow::Error> {
-        // Create new handles to the preopens.
-        let mut results = Vec::new();
-        for (handle, name) in &self.preopens {
-            let desc = self.table.push(Box::new(handle.dup()))?;
-            results.push((desc, name.clone()));
-        }
-        Ok(results)
+        Ok(self.preopens.clone())
     }
 }

host/src/main.rs

@@ -67,16 +67,16 @@ async fn main() -> Result<()> {
 
     let mut builder = WasiCtxBuilder::new()
         .inherit_stdio()
-        .inherit_network()
+        .inherit_network(cap_std::ambient_authority())
         .args(&argv);
 
     for (guest, host) in args.map_dirs {
         let dir = cap_std::fs::Dir::open_ambient_dir(&host, cap_std::ambient_authority())
             .context(format!("opening directory {host:?}"))?;
-        builder = builder.preopened_dir(dir, &guest)?;
+        builder = builder.preopened_dir(dir, &guest);
     }
 
-    let wasi_ctx = builder.build();
+    let wasi_ctx = builder.build()?;
 
     if args.world == "command" {
         run_command(&mut linker, &engine, &component, wasi_ctx).await?;