fix(signals): loop sigtimedwait() on SIGWINCH (#32)

Our signal-handling looks a little different than resty-cli, which uses
sigaction() to register a signal handler function. rusty-cli uses
sigtimedwait() because the API and control flow is much more convenient.

Previously we were exiting our signal-handling phase after the first
signal was caught, forwarding it to the child process and then
wait4()-ing for it to exit. This is mostly correct, except in the case
of SIGWINCH, which isn't a "you should probably stop now/soon" signal.

To fix this we loop over sigtimedwait() until we get a non-SIGWINCH
signal.

I've also attempted to fix a race condition wherein we could hang if the
child process exited before we could set up our signal blocking mask and
await signal delivery by explicitly checking the child process on each
iteration _before_ blocking for signal delivery.

.github/workflows/test-compat.yml

@@ -174,3 +174,6 @@ jobs:
 
       - name: lua script argv translation
         run: ./tests/lua-arg.sh
+
+      - name: signal-handling
+        run: ./tests/sigwinch.sh

src/run.rs

@@ -46,7 +46,9 @@ fn block_wait(mut proc: Child) -> i32 {
 }
 
 pub(crate) fn run(mut cmd: Command) -> i32 {
-    let proc = match cmd.spawn() {
+    let mask = SigSet::from_iter(SIGNALS);
+
+    let mut proc = match cmd.spawn() {
         Ok(child) => child,
         Err(e) => {
             let prog = cmd.get_program().to_string_lossy();
@@ -55,21 +57,30 @@ pub(crate) fn run(mut cmd: Command) -> i32 {
         }
     };
 
-    let caught = {
-        let mask = SigSet::from_iter(SIGNALS);
-        let old_mask = mask
-            .thread_swap_mask(SIG_BLOCK)
-            .expect("failed to block signals");
+    let old_mask = mask
+        .thread_swap_mask(SIG_BLOCK)
+        .expect("failed to block signals");
 
-        let signal = mask.wait().expect("failed to wait for signal");
+    let caught = loop {
+        // we need to check if the child process has exited some time between
+        // when we set up our signal mask and now
+        if let Ok(Some(_)) = proc.try_wait() {
+            break SIGCHLD;
+        }
 
-        old_mask
-            .thread_set_mask()
-            .expect("failed to restore thread signal mask");
+        let signal = mask.wait().expect("failed to wait for signal");
 
-        signal
+        if signal == SIGWINCH {
+            send_signal(&proc, SIGWINCH);
+        } else {
+            break signal;
+        }
     };
 
+    old_mask
+        .thread_set_mask()
+        .expect("failed to restore thread signal mask");
+
     match caught {
         SIGCHLD => block_wait(proc),
         SIGINT => {

tests/sigwinch.sh

@@ -0,0 +1,74 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+readonly RUSTY=./target/debug/rusty-cli
+readonly RESTY=./resty-cli/bin/resty
+
+test_it() {
+    local -r bin=$1
+    echo "TEST: $bin"
+
+    local tmp; tmp=$(mktemp)
+
+    "$bin" \
+        -e "local fh = io.open('$tmp', 'w+'); fh:write(ngx.config.prefix()); fh:flush(); fh:close()" \
+        -e 'ngx.sleep(60)' \
+    &
+
+    local pid=$!
+
+    while [[ ! -s "$tmp" ]]; do
+        kill -0 "$pid" || {
+            echo "fatal: $pid died while we were waiting"
+            exit 1
+        }
+        sleep 1
+    done
+
+    local prefix; prefix=$(<"$tmp")
+    if [[ -d $prefix ]]; then
+        echo "prefix dir: $prefix"
+    else
+        echo "fatal: nginx prefix dir ($prefix) does not exist at startup"
+        exit 1
+    fi
+
+    echo -n "sending WINCH..."
+    for _ in {1..20}; do
+        echo -n .
+        kill -WINCH "$pid"
+        sleep 0.1
+    done
+
+    echo
+
+    if [[ ! -d $prefix ]]; then
+        echo "fatal: nginx prefix dir ($prefix) does not exist after WINCH"
+    fi
+
+    echo "sending INT..."
+    kill -INT "$pid"
+
+    set +e
+    wait "$pid"
+    ec=$?
+    set -e
+
+    echo "$bin has exited with code: $ec"
+
+    if [[ -d $prefix ]]; then
+        echo "FAILED: nginx prefix dir ($prefix) still exists after stopping"
+        exit 1
+    fi
+
+    if (( ec != 130 )); then
+        echo "FAILED: unexpected exit code ($ec)"
+        exit 1
+    fi
+
+    echo "OK"
+}
+
+test_it "$RESTY"
+test_it "$RUSTY"