feat(api): allow listening with unix socket

api/main.go

@@ -1,13 +1,17 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io/fs"
 	"log"
 	"net"
 	"net/http"
 	"os"
+	"os/signal"
+	"strconv"
 	"strings"
 	"sync"
 
@@ -27,10 +31,11 @@ const (
 )
 
 type serverConfig struct {
-	ASNDB  string
-	CityDB string
-	Listen string
-	Mode   string
+	ASNDB            string
+	CityDB           string
+	Listen           string
+	Mode             string
+	SocketPermission fs.FileMode
 }
 
 type body struct {
@@ -47,11 +52,17 @@ type bodyError struct {
 }
 
 func main() {
+	perm, err := strconv.ParseUint(getEnvOr("IP_CHECKER_SOCKET_PERMISSION", "0600"), 8, 32)
+	if err != nil {
+		log.Fatal(err)
+	}
+
 	config = serverConfig{
-		ASNDB:  os.Getenv("IP_CHECKER_ASN_DB"),
-		CityDB: os.Getenv("IP_CHECKER_CITY_DB"),
-		Listen: getEnvOr("IP_CHECKER_LISTEN", ":8080"),
-		Mode:   os.Getenv("IP_CHECKER_MODE"),
+		ASNDB:            os.Getenv("IP_CHECKER_ASN_DB"),
+		CityDB:           os.Getenv("IP_CHECKER_CITY_DB"),
+		Listen:           getEnvOr("IP_CHECKER_LISTEN", ":8080"),
+		SocketPermission: fs.FileMode(perm),
+		Mode:             os.Getenv("IP_CHECKER_MODE"),
 	}
 
 	if config.CityDB != "" {
@@ -76,8 +87,40 @@ func main() {
 	}
 
 	http.HandleFunc("/api/v1/ip", handleRequest)
+
 	log.Printf("Starting server on %s", config.Listen)
-	log.Fatal(http.ListenAndServe(config.Listen, nil))
+
+	var srv http.Server
+
+	// graceful shutdown
+	go func() {
+		sigint := make(chan os.Signal, 1)
+		signal.Notify(sigint, os.Interrupt)
+		<-sigint
+
+		srv.Shutdown(context.Background())
+	}()
+
+	if strings.HasPrefix(config.Listen, "unix/") {
+		socketPath := strings.TrimPrefix(config.Listen, "unix/")
+		unixListener, err := net.Listen("unix", socketPath)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		if err := os.Chmod(socketPath, config.SocketPermission); err != nil {
+			log.Fatal(err)
+		}
+
+		if err := srv.Serve(unixListener); err != http.ErrServerClosed {
+			log.Fatal(err)
+		}
+	} else {
+		srv.Addr = config.Listen
+		if err := srv.ListenAndServe(); err != http.ErrServerClosed {
+			log.Fatal(err)
+		}
+	}
 }
 
 func generateJSON(ip string) (body, error) {