fix: wait for unix socket on qmp client creation (#235)

spinifex/utils/pidfile.go

@@ -220,6 +220,26 @@ func WaitForPidFile(instanceID string, timeout time.Duration) (int, error) {
 	}
 }
 
+// WaitForUnixSocket polls until a Unix socket exists at path or the timeout
+// expires. QEMU binds its QMP socket after writing the pidfile, so callers
+// that gate on WaitForPidFile can still race the socket bind under recovery
+// load. Existence is checked via os.Stat rather than a dial probe so we don't
+// consume the listener's accept queue before the real client connects.
+func WaitForUnixSocket(path string, timeout time.Duration) error {
+	deadline := time.Now().Add(timeout)
+	for {
+		if _, err := os.Stat(path); err == nil {
+			return nil
+		} else if !errors.Is(err, os.ErrNotExist) {
+			return err
+		}
+		if time.Now().After(deadline) {
+			return fmt.Errorf("timeout waiting for unix socket %s", path)
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+}
+
 func WaitForPidFileRemoval(instanceID string, timeout time.Duration) error {
 	timeoutCh := time.After(timeout)
 	ticker := time.NewTicker(100 * time.Millisecond)

spinifex/utils/utils_test.go

@@ -185,6 +185,42 @@ func TestWaitForPidFile(t *testing.T) {
 	})
 }
 
+func TestWaitForUnixSocket(t *testing.T) {
+	t.Run("returns nil when socket appears within timeout", func(t *testing.T) {
+		dir := t.TempDir()
+		path := filepath.Join(dir, "appears.sock")
+
+		ln, err := net.Listen("unix", path)
+		require.NoError(t, err)
+		t.Cleanup(func() { _ = ln.Close() })
+
+		require.NoError(t, WaitForUnixSocket(path, time.Second))
+	})
+
+	t.Run("returns error when timeout expires", func(t *testing.T) {
+		dir := t.TempDir()
+		path := filepath.Join(dir, "missing.sock")
+
+		err := WaitForUnixSocket(path, 100*time.Millisecond)
+		require.Error(t, err)
+	})
+
+	t.Run("waits for socket created after a delay", func(t *testing.T) {
+		dir := t.TempDir()
+		path := filepath.Join(dir, "delayed.sock")
+
+		go func() {
+			time.Sleep(150 * time.Millisecond)
+			ln, err := net.Listen("unix", path)
+			if err == nil {
+				t.Cleanup(func() { _ = ln.Close() })
+			}
+		}()
+
+		require.NoError(t, WaitForUnixSocket(path, time.Second))
+	})
+}
+
 func TestUnmarshalJsonPayload(t *testing.T) {
 	type TestStruct struct {
 		Name  string `json:"name"`

spinifex/vm/lifecycle.go

@@ -529,6 +529,14 @@ func (m *Manager) AttachQMP(instance *VM) error {
 // qmp_capabilities handshake. The caller owns starting the heartbeat
 // goroutine on the returned client.
 func newQMPClientWithHandshake(v *VM) (*qmp.QMPClient, error) {
+	// QEMU binds the QMP listening socket after writing its pidfile and parsing
+	// args; under post-reboot recovery load the bind can lag behind startQEMU's
+	// pidfile gate, leaving an "ENOENT on dial" race that tears down the VM
+	// before it finishes coming up. Block briefly so the dial only runs once
+	// the socket inode exists.
+	if err := utils.WaitForUnixSocket(v.Config.QMPSocket, 3*time.Second); err != nil {
+		return nil, fmt.Errorf("connect QMP socket %s: %w", v.Config.QMPSocket, err)
+	}
 	client, err := qmp.NewQMPClient(v.Config.QMPSocket)
 	if err != nil {
 		return nil, fmt.Errorf("connect QMP socket %s: %w", v.Config.QMPSocket, err)

tests/e2e/run-reboot-e2e.sh

@@ -258,13 +258,33 @@ printf '%s' "$KEY_MATERIAL" | put_to_node "$NODE_KEY_PATH"
 node_ssh "chmod 600 $NODE_KEY_PATH" || { fail "chmod key"; exit 1; }
 pass "key pair: reboot-e2e-key"
 
-# Stage user-data on the node (HTTP responder for round-robin verification)
+# Stage user-data on the node (HTTP responder for round-robin verification).
+# Installed as a systemd unit so the responder survives guest VM reboots —
+# nohup-from-cloud-init only runs on first boot (cloud-init's per-instance
+# semaphore) and would leave the app silent after host_reboot, even though
+# OVN/HAProxy recover correctly.
 APP_USER_DATA=$(cat <<'USERDATA'
 #!/bin/bash
+set -e
 INSTANCE_ID=$(hostname)
-mkdir -p /tmp/httpd && cd /tmp/httpd
-echo "{\"instance_id\": \"${INSTANCE_ID}\"}" > index.html
-nohup python3 -m http.server 80 --bind 0.0.0.0 > /dev/null 2>&1 &
+install -d -m 0755 /var/lib/httpd
+echo "{\"instance_id\": \"${INSTANCE_ID}\"}" > /var/lib/httpd/index.html
+cat > /etc/systemd/system/reboot-e2e-httpd.service <<'UNIT'
+[Unit]
+Description=Reboot E2E HTTP responder
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+ExecStart=/usr/bin/python3 -m http.server 80 --bind 0.0.0.0 --directory /var/lib/httpd
+Restart=always
+RestartSec=1
+
+[Install]
+WantedBy=multi-user.target
+UNIT
+systemctl daemon-reload
+systemctl enable --now reboot-e2e-httpd.service
 USERDATA
 )
 printf '%s' "$APP_USER_DATA" | put_to_node "$NODE_USERDATA_PATH"