scubainit: Restore the default SIGPIPE action

Rust pre-main code may change the SIGPIPE disposition to ignore:
* rust-lang/rust#62569
* rust-lang/rust#97889

We could use the nightly compiler flag -Zon-broken-pipe=inherit to
disable this behavior. Instead, we take the simpler route and restore
the default disposition ourselves.

Fixes #254

scubainit/src/main.rs

@@ -45,6 +45,8 @@ fn run_scubainit() -> Result<()> {
     setup_logging()?;
     info!("Looking Rusty!");
 
+    restore_sigpipe_default()?;
+
     let ctx = process_envvars()?;
 
     if let Some(ref user_info) = ctx.user_info {
@@ -368,3 +370,34 @@ fn setup_logging() -> Result<()> {
         .verbosity(verbosity)
         .init()?)
 }
+
+// Restore the default SIGPIPE action.
+//
+// Rust pre-main code may change the SIGPIPE disposition to ignore:
+// * https://github.com/rust-lang/rust/issues/62569
+// * https://github.com/rust-lang/rust/issues/97889
+//
+// While scubainit doesn't rely on any specific SIGPIPE behavior, the dispositions of ignored
+// signals are inherited through execve and Rust's pre-main code shouldn't influence the process
+// executed by scuba.
+//
+// From man signal(7):
+//
+//   Signal dispositions ...  A child created via fork(2) inherits a copy of its parent's signal
+//   dispositions. During an execve(2), the dispositions of handled signals are reset to the
+//   default; the dispositions of ignored signals are left unchanged.
+//
+// This code may be unnecessary in the future if Rust's execve library function is changed to
+// restore SIGPIPE.
+fn restore_sigpipe_default() -> Result<()> {
+    // Set the SIGPIPE disposition to default (terminate).
+    // SAFETY: No signal handler is provided, only the default action,
+    //         so no additional consideration is needed.
+    unsafe {
+        let result = libc::signal(libc::SIGPIPE, libc::SIG_DFL);
+        if result == libc::SIG_ERR {
+            return Err(std::io::Error::last_os_error().into());
+        }
+    }
+    Ok(())
+}

tests/test_main.py

@@ -278,6 +278,17 @@ def test_redirect_stdin(self) -> None:
         assert_str_equalish(out, test_str)
 
 
+class TestMainSignals(MainTest):
+    def test_sigpipe(self) -> None:
+        """Verify SIGPIPE is handled correctly"""
+        # See https://github.com/JonathonReinhart/scuba/issues/254
+        SCUBA_YML.write_text(f"image: {DOCKER_IMAGE}")
+
+        out, err = run_scuba(["sh", "-c", "yes | echo abcd"])
+        assert_str_equalish(out, "abcd")
+        assert_str_equalish(err, "")
+
+
 class TestMainUser(MainTest):
     def _test_user(
         self,