Better handle stuck WebDriver processes

CHANGELOG.md

@@ -16,6 +16,9 @@
 * Adding `getter`, `setter`, and `constructor` methods to enums now results in a compiler error. This was previously erroneously allowed and resulted in invalid JS code gen.
   [#4278](https://github.com/rustwasm/wasm-bindgen/pull/4278)
 
+* Handle stuck and failed WebDriver processes when re-trying to start them.
+  [#4340](https://github.com/rustwasm/wasm-bindgen/pull/4340)
+
 ### Fixed
 
 - Fixed using [JavaScript keyword](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#keywords) as identifiers not being handled correctly.

crates/cli/src/bin/wasm-bindgen-test-runner/headless.rs

@@ -6,10 +6,10 @@ use serde::{Deserialize, Serialize};
 use serde_json::{json, Map, Value as Json};
 use std::env;
 use std::fs::File;
-use std::io::{self, Read};
+use std::io::{BufRead, BufReader, Read};
 use std::net::{SocketAddr, TcpListener, TcpStream};
 use std::path::{Path, PathBuf};
-use std::process::{Child, Command, Stdio};
+use std::process::{Child, ChildStderr, ChildStdout, Command, Stdio};
 use std::thread;
 use std::time::{Duration, Instant};
 use ureq::Agent;
@@ -615,12 +615,6 @@ impl Drop for Client {
     }
 }
 
-fn read<R: Read>(r: &mut R) -> io::Result<Vec<u8>> {
-    let mut dst = Vec::new();
-    r.read_to_end(&mut dst)?;
-    Ok(dst)
-}
-
 fn tab(s: &str) -> String {
     let mut result = String::new();
     for line in s.lines() {
@@ -633,8 +627,8 @@ fn tab(s: &str) -> String {
 
 struct BackgroundChild<'a> {
     child: Child,
-    stdout: Option<thread::JoinHandle<io::Result<Vec<u8>>>>,
-    stderr: Option<thread::JoinHandle<io::Result<Vec<u8>>>>,
+    stdout: BufReader<ChildStdout>,
+    stderr: BufReader<ChildStderr>,
     shell: &'a Shell,
     print_stdio_on_drop: bool,
 }
@@ -652,10 +646,8 @@ impl<'a> BackgroundChild<'a> {
         let mut child = cmd
             .spawn()
             .context(format!("failed to spawn {:?} binary", path))?;
-        let mut stdout = child.stdout.take().unwrap();
-        let mut stderr = child.stderr.take().unwrap();
-        let stdout = Some(thread::spawn(move || read(&mut stdout)));
-        let stderr = Some(thread::spawn(move || read(&mut stderr)));
+        let stdout = BufReader::new(child.stdout.take().unwrap());
+        let stderr = BufReader::new(child.stderr.take().unwrap());
         Ok(BackgroundChild {
             child,
             stdout,
@@ -668,7 +660,11 @@ impl<'a> BackgroundChild<'a> {
     fn has_failed(&mut self) -> bool {
         match self.child.try_wait() {
             Ok(Some(status)) => !status.success(),
-            Ok(None) => false,
+            Ok(None) => self
+                .stderr
+                .fill_buf()
+                .map(|b| !b.is_empty())
+                .unwrap_or(true),
             Err(_) => true,
         }
     }
@@ -685,11 +681,13 @@ impl Drop for BackgroundChild<'_> {
         self.shell.clear();
         println!("driver status: {}", status);
 
-        let stdout = self.stdout.take().unwrap().join().unwrap().unwrap();
+        let mut stdout = Vec::new();
+        self.stdout.read_to_end(&mut stdout).unwrap();
         if !stdout.is_empty() {
             println!("driver stdout:\n{}", tab(&String::from_utf8_lossy(&stdout)));
         }
-        let stderr = self.stderr.take().unwrap().join().unwrap().unwrap();
+        let mut stderr = Vec::new();
+        self.stderr.read_to_end(&mut stderr).unwrap();
         if !stderr.is_empty() {
             println!("driver stderr:\n{}", tab(&String::from_utf8_lossy(&stderr)));
         }