fortify: show system info when instance is not specified

This contains useful information not obtainable by external tools.

Signed-off-by: Ophestra <cat@gensokyo.uk>

fst/info.go

@@ -0,0 +1,5 @@
+package fst
+
+type Info struct {
+	User int `json:"user"`
+}

main.go

@@ -16,7 +16,6 @@ import (
 	"git.gensokyo.uk/security/fortify/internal/app"
 	"git.gensokyo.uk/security/fortify/internal/fmsg"
 	"git.gensokyo.uk/security/fortify/internal/linux"
-	"git.gensokyo.uk/security/fortify/internal/state"
 	"git.gensokyo.uk/security/fortify/internal/system"
 )
 
@@ -128,24 +127,20 @@ func main() {
 		// Ignore errors; set is set for ExitOnError.
 		_ = set.Parse(args[1:])
 
-		var (
-			config   *fst.Config
-			instance *state.State
-			name     string
-		)
-
-		if len(set.Args()) != 1 {
-			fmsg.Fatal("show requires 1 argument")
-		} else {
-			name = set.Args()[0]
-			config, instance = tryShort(name)
-		}
-
+		switch len(set.Args()) {
+		case 0: // system
+			printShowSystem(short)
+		case 1: // instance
+			name := set.Args()[0]
+			config, instance := tryShort(name)
 			if config == nil {
 				config = tryPath(name)
 			}
+			printShowInstance(instance, config, short)
+		default:
+			fmsg.Fatal("show requires 1 argument")
+		}
 
-		printShow(instance, config, short)
 		fmsg.Exit(0)
 	case "app": // launch app from configuration file
 		if len(args) < 2 {

print.go

@@ -16,14 +16,37 @@ import (
 	"git.gensokyo.uk/security/fortify/internal/state"
 )
 
-func printShow(instance *state.State, config *fst.Config, short bool) {
-	if flagJSON {
-		v := any(config)
-		if instance != nil {
-			v = instance
+func printShowSystem(short bool) {
+	info := new(fst.Info)
+
+	// get fid by querying uid of aid 0
+	if uid, err := os.Uid(0); err != nil {
+		fmsg.Fatalf("cannot obtain uid from fsu: %v", err)
+	} else {
+		info.User = (uid / 10000) - 100
 	}
 
-		printJSON(v)
+	if flagJSON {
+		printJSON(info)
+		return
+	}
+
+	w := tabwriter.NewWriter(direct.Stdout, 0, 1, 4, ' ', 0)
+
+	fmt.Fprintf(w, "User:\t%d\n", info.User)
+
+	if err := w.Flush(); err != nil {
+		fmsg.Fatalf("cannot flush tabwriter: %v", err)
+	}
+}
+
+func printShowInstance(instance *state.State, config *fst.Config, short bool) {
+	if flagJSON {
+		if instance != nil {
+			printJSON(instance)
+		} else {
+			printJSON(config)
+		}
 		return
 	}