Write out JSON on shutdown

main.go

@@ -1,17 +1,20 @@
 package main
 
 import (
+	"context"
 	"embed"
 	"encoding/json"
 	"flag"
 	"fmt"
 	"io/fs"
 	"log"
-	"math/rand/v2"
 	"net/http"
+	"os"
+	"os/signal"
 	"runtime/debug"
 	"strconv"
 	"sync"
+	"syscall"
 	"time"
 
 	"git.chandlerswift.com/chandlerswift/nau-sidewalks/sidewalk"
@@ -20,16 +23,31 @@ import (
 //go:embed static
 var embeddedFiles embed.FS
 
-//go:embed data/sidewalks.json
-var sidewalk_data []byte
-
 var buildInfoJSON []byte
 
 func main() {
 	devel := flag.Bool("devel", false, "Serve from ./static instead of embedded")
 	port := flag.Int("port", 8000, "Port to listen on")
+	dataFile := flag.String("datafile", "", "File to read sidewalk data from (required)")
 	flag.Parse()
+	if *dataFile == "" {
+		panic("datafile arg is required")
+	}
 
+	sidewalkData, err := os.ReadFile(*dataFile)
+	if err != nil {
+		panic(err)
+	}
+
+	// Decode the JSON data
+	var sidewalks []sidewalk.Sidewalk
+	var sidewalksMutex sync.RWMutex
+	if err := json.Unmarshal(sidewalkData, &sidewalks); err != nil {
+		log.Fatalf("Error decoding JSON: %v", err)
+	}
+	sidewalksLen := len(sidewalks)
+
+	// Serve static content
 	if *devel {
 		http.Handle("GET /", http.FileServer(http.Dir("./static")))
 	} else {
@@ -40,17 +58,6 @@ func main() {
 		http.Handle("GET /", http.FileServer(http.FS(frontend)))
 	}
 
-	// Decode the JSON data
-	var sidewalks []sidewalk.Sidewalk
-	var sidewalksMutex sync.RWMutex
-	if err := json.Unmarshal(sidewalk_data, &sidewalks); err != nil {
-		log.Fatalf("Error decoding JSON: %v", err)
-	}
-	sidewalksLen := len(sidewalks)
-	for i := range sidewalks {
-		sidewalks[i].Condition = sidewalk.Condition(rand.IntN(4))
-	}
-
 	initializeBuildInfoJSON()
 	http.HandleFunc("GET /api/version", func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
@@ -87,8 +94,42 @@ func main() {
 		http.Redirect(w, r, "/", http.StatusSeeOther)
 	})
 
-	fmt.Printf("Serving %v sidewalks on :%v\n", &sidewalksLen, *port)
-	panic(http.ListenAndServe(fmt.Sprintf(":%v", *port), nil))
+	server := &http.Server{Addr: fmt.Sprintf(":%v", *port)}
+
+	go func() {
+		fmt.Printf("Serving %v sidewalks on :%v\n", sidewalksLen, *port)
+		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+			log.Fatalf("HTTP server error: %v", err)
+		}
+	}()
+
+	// Listen for OS termination signals
+	stop := make(chan os.Signal, 1)
+	signal.Notify(stop, os.Interrupt, syscall.SIGTERM)
+	<-stop // Block until signal is received
+
+	fmt.Println("\nShutting down server...")
+
+	// write out JSON
+	sidewalksMutex.RLock()
+	f, err := os.Create(*dataFile)
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+	err = json.NewEncoder(f).Encode(sidewalks)
+	if err != nil {
+		panic(err)
+	}
+	sidewalksMutex.RUnlock()
+
+	// graceful shutdown
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	if err := server.Shutdown(ctx); err != nil {
+		log.Fatalf("Server forced to shutdown: %v", err)
+	}
+
 }
 
 func initializeBuildInfoJSON() {