From e4ce04bab42a325bbffe7d83e759a2b99e185c8d Mon Sep 17 00:00:00 2001
From: Pat Hickey <pat@moreproductive.org>
Date: Fri, 5 Feb 2021 17:50:20 -0800
Subject: [PATCH] WasiCtx: default to empty/sink stdio files rather than throw

the test harness now uses the empty stdin file. I tested manually that
the sink stdout & stderr files work, but theres no test in tree at the
moment
---
 .../tests/wasm_tests/runtime/cap_std_sync.rs  |  3 +-
 crates/wasi-common/src/ctx.rs                 | 37 +++++++------------
 2 files changed, 15 insertions(+), 25 deletions(-)

diff --git a/crates/test-programs/tests/wasm_tests/runtime/cap_std_sync.rs b/crates/test-programs/tests/wasm_tests/runtime/cap_std_sync.rs
index 089d393ea3..5900e6a19c 100644
--- a/crates/test-programs/tests/wasm_tests/runtime/cap_std_sync.rs
+++ b/crates/test-programs/tests/wasm_tests/runtime/cap_std_sync.rs
@@ -1,7 +1,7 @@
 use anyhow::Context;
 use std::path::Path;
 use wasi_cap_std_sync::WasiCtxBuilder;
-use wasi_common::pipe::{ReadPipe, WritePipe};
+use wasi_common::pipe::WritePipe;
 use wasmtime::{Linker, Module, Store};
 
 pub fn instantiate(data: &[u8], bin_name: &str, workspace: Option<&Path>) -> anyhow::Result<()> {
@@ -18,7 +18,6 @@ pub fn instantiate(data: &[u8], bin_name: &str, workspace: Option<&Path>) -> any
         builder = builder
             .arg(bin_name)?
             .arg(".")?
-            .stdin(Box::new(ReadPipe::from(Vec::new())))
             .stdout(Box::new(stdout.clone()))
             .stderr(Box::new(stderr.clone()));
 
diff --git a/crates/wasi-common/src/ctx.rs b/crates/wasi-common/src/ctx.rs
index 20a9ef7064..cdf89fb890 100644
--- a/crates/wasi-common/src/ctx.rs
+++ b/crates/wasi-common/src/ctx.rs
@@ -65,16 +65,19 @@ pub struct WasiCtxBuilder(WasiCtx);
 impl WasiCtxBuilder {
     pub fn build(self) -> Result<WasiCtx, Error> {
         use crate::file::TableFileExt;
-        let t = self.0.table();
-        for (fd, name) in ["stdin", "stdout", "stderr"].iter().enumerate() {
-            if t.get_file(fd as u32).is_err() {
-                return Err(anyhow::anyhow!(
-                    "Cannot build WasiCtx: Missing required file `{}`",
-                    name
-                ));
+        // Default to an empty readpipe for stdin:
+        if self.0.table().get_file(0).is_err() {
+            let stdin = crate::pipe::ReadPipe::new(std::io::empty());
+            self.0.insert_file(0, Box::new(stdin), FileCaps::all());
+        }
+        // Default to a sink writepipe for stdout, stderr:
+        for stdio_write in &[1, 2] {
+            if self.0.table().get_file(*stdio_write).is_err() {
+                let output_file = crate::pipe::WritePipe::new(std::io::sink());
+                self.0
+                    .insert_file(*stdio_write, Box::new(output_file), FileCaps::all());
             }
         }
-        drop(t);
         Ok(self.0)
     }
 
@@ -89,29 +92,17 @@ impl WasiCtxBuilder {
     }
 
     pub fn stdin(self, f: Box<dyn WasiFile>) -> Self {
-        self.0.insert_file(
-            0,
-            f,
-            FileCaps::READ | FileCaps::POLL_READWRITE, // XXX fixme: more rights are ok, but this is read-only
-        );
+        self.0.insert_file(0, f, FileCaps::all());
         self
     }
 
     pub fn stdout(self, f: Box<dyn WasiFile>) -> Self {
-        self.0.insert_file(
-            1,
-            f,
-            FileCaps::WRITE | FileCaps::POLL_READWRITE, // XXX fixme: more rights are ok, but this is append only
-        );
+        self.0.insert_file(1, f, FileCaps::all());
         self
     }
 
     pub fn stderr(self, f: Box<dyn WasiFile>) -> Self {
-        self.0.insert_file(
-            2,
-            f,
-            FileCaps::WRITE | FileCaps::POLL_READWRITE, // XXX fixme: more rights are ok, but this is append only
-        );
+        self.0.insert_file(2, f, FileCaps::all());
         self
     }