move scli's UntilInterrupted() here

Makefile

@@ -1,8 +1,11 @@
-
 lint: .golangci.yml
 	golangci-lint run
 
+wait-demo:
+	# Doesn't work with tinygo (yet) because undefined symbol: _os/signal.signal_enable...
+	go run -tags no_net,no_json ./sampleTool/ -wait arg1 arg2
+
 .golangci.yml: Makefile
 	curl -fsS -o .golangci.yml https://raw.githubusercontent.com/fortio/workflows/main/golangci.yml
 
-.PHONY: lint
+.PHONY: lint wait-demo

cli.go

@@ -17,8 +17,10 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"os/signal"
 	"path/filepath"
 	"strings"
+	"syscall"
 
 	"fortio.org/log"
 	"fortio.org/version"
@@ -253,3 +255,20 @@ func PluralExt(i int, noun string, ext string) string {
 	}
 	return noun + ext
 }
+
+// UntilInterrupted runs forever or until interrupted (ctrl-c or shutdown signal (kill -INT or -TERM)).
+// Kubernetes for instance sends a SIGTERM before killing a pod.
+// You can place your clean shutdown code after this call in the main().
+// This assumes there is another go routine doing something (like a server).
+func UntilInterrupted() {
+	// if UntilInterrupted is called, it implies there should be another goroutine at least.
+	// so we put back that logging (vs what log.SetDefaultsForClientTools() does).
+	log.Config.GoroutineID = true
+	// listen for interrupt signal
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
+	// Block until a signal is received.
+	log.LogVf("Waiting for interrupt signal...")
+	<-c
+	log.Warnf("Interrupt received.")
+}

sampleTool/main.go

@@ -9,6 +9,8 @@ import (
 
 func main() {
 	myFlag := flag.String("myflag", "default", "my flag")
+	doWait := flag.Bool("wait", false, "wait for ^C before exiting")
+
 	cli.MinArgs = 2
 	cli.MaxArgs = 4
 	cli.Main() // Will have either called cli.ExitFunction or everything is valid
@@ -21,4 +23,9 @@ func main() {
 		log.Str("myflag", *myFlag),
 		log.Attr("num_args", len(flag.Args())),
 		log.Attr("args", flag.Args()))
+	if *doWait {
+		log.Infof("Waiting for ^C (or kill) to exit")
+		cli.UntilInterrupted()
+		log.Infof("Now done...")
+	}
 }