Reorg and add host flag, and catch error when not root:

- A previous workaround done to recover from a panic on nil
    ref is now not needed and removed. The issue was that I assumed
    cli.Exit(err, int) was a way to exit; i.e. it uses os.Exit()
    under the hood. However, it only constructs a struct that implements
    error. Hence, we should return it, not just execute it.

    - Also warn on root and Windows

    - Move IPPool init to setup rather than run

cmd/hvpn-node/hvpn-node.go

@@ -1,10 +1,10 @@
 package main
 
 import (
-	"errors"
 	"fmt"
 	"log/slog"
 	"net/http"
+	"net/netip"
 	"os"
 	"os/signal"
 	"time"
@@ -15,7 +15,13 @@ import (
 	hvpnnode3 "gitea.hbanafa.com/HeshamTB/hvpn-node3"
 )
 
-var IPPool *hvpnnode3.IPPool
+/*
+   Can change all therse vars to local func vars
+   IPPool can be internal to wglink or other abstraction. As well as
+   POrt, ifname and CIDR and so on. Use Clie.ctx to get the values
+*/
+
+var IPPool hvpnnode3.IPPool
 var VPNIPCIDR string
 var PrivateKeyPath cli.Path
 var InterfaceName string
@@ -30,6 +36,13 @@ func main() {
     // TODO: Define error exit codes
     slog.SetLogLoggerLevel(slog.LevelDebug)
 
+    uid := os.Getuid()
+    if uid == -1 {
+        slog.Warn("Running on windows! whatrr u doing?")
+    } else if uid == 0 {
+        slog.Warn("Running as root! avoid running as root by setting CAP_NET_ADMIN")
+    }
+
     app := createCliApp()
     err := app.Run(os.Args)
     if err != nil {
@@ -40,27 +53,8 @@ func main() {
 
 }
 
-func run() {
-    IPPool, err := hvpnnode3.NewPool(VPNIPCIDR)
-    if err != nil {
-        slog.Error(fmt.Sprintf("main.IPPool: %s", err))
-        os.Exit(1)
-    }
-    slog.Info(fmt.Sprintf("Init ip pool %s", VPNIPCIDR))
-
-    testVip, err := IPPool.Allocate()
-    if err != nil {
-        slog.Error("main.testVip: ", err)
-        os.Exit(1)
-    }
-
-    slog.Info(fmt.Sprintf("main.testVip: IP Pool Test IP: %s", testVip.String()))
-    err = IPPool.Free(testVip)
-    if err != nil {
-        slog.Error("main.testVip: Could not free test Vip from IPPool!", err)
-        os.Exit(1)
-    }
-    slog.Info("main.testVip: Test IP Freed")
+func run(ctx *cli.Context) {
+    slog.Debug("Starting run()")
 
     apiMux := http.NewServeMux()
     apiMux.HandleFunc("GET /peer", hvpnnode3.HandleGetPeer(wgLink))
@@ -71,7 +65,11 @@ func run() {
     handler = hvpnnode3.HttpLogHandler2(handler)
 
     port := fmt.Sprintf("%d", httpPort)
-    host := "0.0.0.0"
+    host := ctx.String("host")
+    if host == "" {
+        slog.Info("Host is not set. Using 0.0.0.0")
+        host = "0.0.0.0"
+    }
     hostPort := fmt.Sprintf("%s:%s", host, port)
 
     slog.Info(fmt.Sprintf("Starting HVPN node on %s", hostPort))
@@ -156,6 +154,20 @@ func createCliApp() *cli.App {
     }
     app.Flags = append(app.Flags, &wgPort)
 
+    httpListenAddr := cli.StringFlag{
+        Name: "host",
+        Usage: "IP address to listen on for HTTP API requests",
+        Value: "0.0.0.0",
+        Action: func(ctx *cli.Context, s string) error {
+            _, err := netip.ParseAddr(s)
+            if err != nil {
+                return cli.Exit(fmt.Sprintf("Can not parse %s as a network IP", s), 1)
+            }
+            return nil
+        },
+    }
+    app.Flags = append(app.Flags, &httpListenAddr)
+
     httpPort := cli.IntFlag{
         Name: "http-port",
         Usage: "TCP Port for HTTP API",
@@ -170,7 +182,7 @@ func createCliApp() *cli.App {
         if err != nil {
             return err
         }
-        run()
+        run(ctx)
         return nil
     }
 
@@ -178,6 +190,7 @@ func createCliApp() *cli.App {
 }
 
 func setup() error {
+    slog.Debug("Starting setup()")
     privKeyFile, err := os.Open(PrivateKeyPath)
     if err != nil {
         return cli.Exit(err, 1)
@@ -208,24 +221,14 @@ func setup() error {
         WgPort,
     )
     if err != nil {
+        slog.Warn("Error while initlizing Wireguard netlink and device!")
+        slog.Warn("Ensure to run as root or with CAP_NET_ADMIN")
         return cli.Exit(err, 1)
     }
 
     wgLink = wg
 
-    // this is done to recover from the next call to wgLink.Device call
-    // idk a better way to recover or prevent the panic when running user
-    // does not have root or CAP_NET_ADMIN.
-    defer func() {
-        if r := recover(); r != nil {
-            slog.Error(fmt.Sprint(r))
-            slog.Error("Recovered from panic. Ensure to run as root or with CAP_NET_ADMIN")
-            cli.Exit(errors.New("Recovered from panic. Ensure to run as root or with CAP_NET_ADMIN"),1)
-            os.Exit(-1)
-        }
-    }()
-
-    slog.Info("Wireguard device is setup and running")
+    slog.Info("Wireguard netlink is setup and running")
 
 
     dev, err := wgLink.Device(InterfaceName)
@@ -241,6 +244,29 @@ func setup() error {
         ),
     )
 
+    ipPool, err := hvpnnode3.NewPool(VPNIPCIDR)
+    if err != nil {
+        slog.Error(fmt.Sprintf("main.IPPool: %s", err))
+        os.Exit(1)
+    }
+    slog.Info(fmt.Sprintf("Init ip pool %s", VPNIPCIDR))
+
+    testVip, err := ipPool.Allocate()
+    if err != nil {
+        slog.Error("main.testVip: ", err)
+        os.Exit(1)
+    }
+
+    slog.Info(fmt.Sprintf("main.testVip: IP Pool Test IP: %s", testVip.String()))
+    err = ipPool.Free(testVip)
+    if err != nil {
+        slog.Error("main.testVip: Could not free test Vip from IPPool!", err)
+        os.Exit(1)
+    }
+    slog.Info("main.testVip: Test IP Freed")
+
+    IPPool = ipPool
+
     //defer wgLink.Close()
     c := make(chan os.Signal, 1)
     signal.Notify(c, os.Interrupt, os.Kill)