From 1f25b1d6a0dedb19f8e70f06b41c78c1a61e71ae Mon Sep 17 00:00:00 2001
From: Kevin Fox <Kevin.Fox@pnnl.gov>
Date: Tue, 19 Dec 2023 07:48:52 -0800
Subject: [PATCH] Add support for signaling an external process via pid file

Signed-off-by: Kevin Fox <Kevin.Fox@pnnl.gov>
---
 pkg/sidecar/config.go  |  1 +
 pkg/sidecar/sidecar.go | 20 +++++++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/pkg/sidecar/config.go b/pkg/sidecar/config.go
index e83c30bd..82257be8 100644
--- a/pkg/sidecar/config.go
+++ b/pkg/sidecar/config.go
@@ -22,6 +22,7 @@ type Config struct {
 	// where this is the expected format for presented certificates and bundles
 	AddIntermediatesToBundle           bool   `hcl:"add_intermediates_to_bundle"`
 	AddIntermediatesToBundleDeprecated bool   `hcl:"addIntermediatesToBundle"`
+	PidFileName                        string `hcl:"pid_file_name"`
 	SvidFileName                       string `hcl:"svid_file_name"`
 	SvidFileNameDeprecated             string `hcl:"svidFileName"`
 	SvidKeyFileName                    string `hcl:"svid_key_file_name"`
diff --git a/pkg/sidecar/sidecar.go b/pkg/sidecar/sidecar.go
index a9a31a49..5bb9dd98 100644
--- a/pkg/sidecar/sidecar.go
+++ b/pkg/sidecar/sidecar.go
@@ -8,9 +8,11 @@ import (
 	"encoding/json"
 	"encoding/pem"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"os/exec"
 	"path"
+	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -138,7 +140,7 @@ func (s *Sidecar) updateCertificates(svidResponse *workloadapi.X509Context) {
 	}
 	s.config.Log.Info("X.509 certificates updated")
 
-	if s.config.Cmd != "" {
+	if s.config.Cmd != "" || s.config.PidFileName != "" {
 		if err := s.signalProcess(); err != nil {
 			s.config.Log.WithError(err).Error("Unable to signal process")
 		}
@@ -153,6 +155,22 @@ func (s *Sidecar) updateCertificates(svidResponse *workloadapi.X509Context) {
 // signalProcess sends the configured Renew signal to the process running the proxy
 // to reload itself so that the proxy uses the new SVID
 func (s *Sidecar) signalProcess() (err error) {
+	if s.config.PidFileName != "" {
+		atomic.StoreInt32(&s.processRunning, 1)
+		bytes, err := ioutil.ReadFile(s.config.PidFileName)
+		if err != nil {
+			return fmt.Errorf("Failed to read pid file: %s\n%w", s.config.PidFileName, err)
+		}
+		lines := strings.Split(string(bytes), "\n")
+		pid, err := strconv.Atoi(lines[0])
+		if err != nil {
+			return fmt.Errorf("Failed to parse pid file: %s\n%w", s.config.PidFileName, err)
+		}
+		s.process, err = os.FindProcess(pid)
+		if err != nil {
+			return fmt.Errorf("Failed to find process: %d\n%w", pid, err)
+		}
+	}
 	// TODO: is ReloadExternalProcess still used?
 	switch s.config.ReloadExternalProcess {
 	case nil: