README.md

@@ -67,6 +67,12 @@ go run ./cmd/gbrgames validate                     # what CI runs on every push
 go run ./cmd/gbrgames import admin-games.export.json  # pull templates from GET /api/v1/admin/games
 ```
 
+`go run ./cmd/gbrgames inspect-image -game <id>` pulls the game's Docker image and reads what it needs
+without starting the game: its user, home folder permissions, ports, tools and startup scripts. It then
+checks the template against that, e.g. an image built around its own user needs `containerUser`, and a
+startup command must read settings under the names the node gives them (`RCONPort` arrives as
+`RCONPORT`). Boot tests run it first, so these fail in seconds. `-json` prints the facts for tooling.
+
 Besides the schemas, `validate` checks that each folder name matches its `id`, that referenced config
 keys exist, that consents don't default to accepted, and that no credentials or private network
 addresses end up in a template.

cmd/gbrgames/inspect.go

@@ -0,0 +1,506 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// Facts about a game server image, read without starting the game: Docker metadata plus one short probe
+// (no network) for users, home folder permissions, tools and startup scripts. The template checks and,
+// later, the AI builder work from these instead of guessing from web search.
+type imageFacts struct {
+	Image        string            `json:"image"`
+	User         string            `json:"user"` // image's USER; "" = root
+	Env          map[string]string `json:"env"`
+	ExposedPorts []string          `json:"exposedPorts"`
+	Volumes      []string          `json:"volumes"`
+	Entrypoint   []string          `json:"entrypoint"`
+	Cmd          []string          `json:"cmd"`
+	WorkingDir   string            `json:"workingDir"`
+	Users        []imageUser       `json:"users"`   // regular accounts (uid 1000-64999)
+	Homes        []homeDir         `json:"homes"`   // /home/* and /root
+	Tools        map[string]string `json:"tools"`   // e.g. java -> /usr/bin/java
+	Scripts      map[string]string `json:"scripts"` // startup scripts, path -> content (truncated)
+	EnvRead      []string          `json:"envRead"` // variables those scripts read
+	ProbeError   string            `json:"probeError,omitempty"`
+	// What the node needs to run this image: set when the image is built around a user other than 1000:1000
+	SuggestedContainerUser string `json:"suggestedContainerUser,omitempty"`
+	SuggestionReason       string `json:"suggestionReason,omitempty"`
+}
+
+type imageUser struct {
+	Name string `json:"name"`
+	UID  int    `json:"uid"`
+	GID  int    `json:"gid"`
+	Home string `json:"home"`
+}
+
+type homeDir struct {
+	Path string `json:"path"`
+	UID  int    `json:"uid"`
+	GID  int    `json:"gid"`
+	Mode string `json:"mode"` // octal, e.g. "700"
+}
+
+const (
+	nodeUser       = "1000:1000"
+	maxScriptBytes = 60000
+	probeMarker    = "@@gbr-probe@@"
+)
+
+// Variables every shell or runtime provides; reading them says nothing about the game.
+var commonEnv = map[string]bool{
+	"HOME": true, "PATH": true, "USER": true, "PWD": true, "SHELL": true, "TERM": true, "HOSTNAME": true,
+	"LANG": true, "LC_ALL": true, "UID": true, "GID": true, "IFS": true, "OLDPWD": true, "TMPDIR": true,
+	"XDG_RUNTIME_DIR": true, "LD_LIBRARY_PATH": true, "DEBIAN_FRONTEND": true, "BASH_SOURCE": true,
+}
+
+var (
+	envRef     = regexp.MustCompile(`\$\{?([A-Z][A-Z0-9_]{2,})\b`)
+	camelSplit = regexp.MustCompile(`([a-z])([A-Z]+)`)
+	absPath    = regexp.MustCompile(`(?:^|[\s'"=;&|(])(/[A-Za-z0-9_./-]+)`)
+	// ${VAR:-x} / ${VAR-x}: the command copes when VAR is unset
+	defaultedRef = regexp.MustCompile(`\$\{([A-Z][A-Z0-9_]{2,}):?-`)
+	// VAR=... or export VAR=... inside the command
+	assignedVars = regexp.MustCompile(`(?:^|[\s;&|(])(?:export\s+)?([A-Z][A-Z0-9_]{2,})=`)
+)
+
+func uidOf(user string) string {
+	uid, _, _ := strings.Cut(user, ":")
+	return uid
+}
+
+// envName is the environment variable a config key reaches the container as: the node-agent's
+// toUpperSnakeCase (RCONPort -> RCONPORT, ServerAdminPassword -> SERVER_ADMIN_PASSWORD).
+func envName(key string) string {
+	return strings.ToUpper(camelSplit.ReplaceAllString(key, "${1}_${2}"))
+}
+
+func runInspectImage(args []string) error {
+	fs := flag.NewFlagSet("inspect-image", flag.ExitOnError)
+	gamesDir := fs.String("games", "games", "directory holding one folder per game")
+	gameID := fs.String("game", "", "also check this game's template against the image")
+	asJSON := fs.Bool("json", false, "print the facts as JSON")
+	noPull := fs.Bool("no-pull", false, "use the local image instead of pulling it")
+	fs.Parse(args)
+
+	var game map[string]any
+	image := fs.Arg(0)
+	if *gameID != "" {
+		g, err := loadMap(filepath.Join(*gamesDir, *gameID, "game.yaml"))
+		if err != nil {
+			return err
+		}
+		game = g
+		if image == "" {
+			image, _ = g["defaultDockerImage"].(string)
+		}
+	}
+	if image == "" {
+		return errors.New("inspect-image needs an IMAGE or -game ID")
+	}
+
+	if !*noPull {
+		if out, err := exec.Command("docker", "pull", "-q", image).CombinedOutput(); err != nil {
+			return fmt.Errorf("docker pull %s: %v: %s", image, err, strings.TrimSpace(string(out)))
+		}
+	}
+	facts, err := inspectImage(image, startupScriptPaths(game))
+	if err != nil {
+		return err
+	}
+
+	var problems, notes []string
+	if game != nil {
+		problems, notes = checkTemplate(game, facts)
+	}
+
+	if *asJSON {
+		out := map[string]any{"facts": facts}
+		if game != nil {
+			out["problems"], out["notes"] = problems, notes
+		}
+		b, _ := json.MarshalIndent(out, "", "  ")
+		fmt.Println(string(b))
+	} else {
+		printFacts(facts)
+		if game != nil {
+			fmt.Printf("\nTemplate %s against this image:\n", *gameID)
+			for _, p := range problems {
+				fmt.Println("  PROBLEM  " + p)
+			}
+			for _, n := range notes {
+				fmt.Println("  note     " + n)
+			}
+			if len(problems) == 0 {
+				fmt.Println("  no problems found")
+			}
+		}
+	}
+	if len(problems) > 0 {
+		return fmt.Errorf("%d problem(s) with %s", len(problems), *gameID)
+	}
+	return nil
+}
+
+func inspectImage(image string, extraScripts []string) (*imageFacts, error) {
+	out, err := exec.Command("docker", "image", "inspect", "--format", "{{json .Config}}", image).Output()
+	if err != nil {
+		return nil, fmt.Errorf("docker image inspect %s: %w", image, err)
+	}
+	var cfg struct {
+		User         string
+		Env          []string
+		ExposedPorts map[string]any
+		Volumes      map[string]any
+		Entrypoint   []string
+		Cmd          []string
+		WorkingDir   string
+	}
+	if err := json.Unmarshal(out, &cfg); err != nil {
+		return nil, fmt.Errorf("parse image config: %w", err)
+	}
+	f := &imageFacts{
+		Image: image, User: cfg.User, Env: map[string]string{}, Entrypoint: cfg.Entrypoint, Cmd: cfg.Cmd,
+		WorkingDir: cfg.WorkingDir, ExposedPorts: sortedSet(cfg.ExposedPorts), Volumes: sortedSet(cfg.Volumes),
+		Tools: map[string]string{}, Scripts: map[string]string{},
+	}
+	for _, kv := range cfg.Env {
+		if k, v, ok := strings.Cut(kv, "="); ok {
+			f.Env[k] = v
+		}
+	}
+
+	scripts := append(append([]string{}, firstWord(cfg.Entrypoint), firstWord(cfg.Cmd)), extraScripts...)
+	probe, err := runProbe(image, scripts)
+	if err != nil {
+		f.ProbeError = err.Error()
+	} else {
+		parseProbe(f, probe)
+	}
+	suggestContainerUser(f)
+	return f, nil
+}
+
+// runProbe reads users, home folders, tools and scripts from inside the image. --network none: the probe
+// never needs the internet, and the image's own entrypoint is bypassed so nothing of the game starts.
+func runProbe(image string, scripts []string) (string, error) {
+	script := `
+m="` + probeMarker + `"
+echo "$m passwd"; cat /etc/passwd 2>/dev/null
+echo "$m homes"; for d in /home/* /root; do [ -d "$d" ] && stat -c '%n|%u|%g|%a' "$d" 2>/dev/null; done
+echo "$m tools"
+for t in java steamcmd steamcmd.sh proton wine wine64 bash python3 node dotnet; do p=$(command -v "$t" 2>/dev/null) && echo "$t|$p"; done
+for d in /home/*/steamcmd /opt/steamcmd /steamcmd /usr/games/steamcmd; do [ -e "$d" ] && echo "steamcmd-dir|$d"; done
+for s in "$@"; do
+  [ -n "$s" ] || continue
+  p=$(command -v "$s" 2>/dev/null || echo "$s")
+  [ -f "$p" ] || continue
+  [ "$(head -c 2 "$p")" = "#!" ] || continue
+  echo "$m script $p"; head -c ` + strconv.Itoa(maxScriptBytes) + ` "$p"; echo
+done
+`
+	args := append([]string{"run", "--rm", "--network", "none", "--entrypoint", "sh", image, "-c", script, "probe"}, scripts...)
+	cmd := exec.Command("docker", args...)
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout, cmd.Stderr = &stdout, &stderr
+	if err := cmd.Run(); err != nil && stdout.Len() == 0 {
+		return "", fmt.Errorf("probe could not run a shell in the image: %v %s", err, strings.TrimSpace(stderr.String()))
+	}
+	return stdout.String(), nil
+}
+
+func parseProbe(f *imageFacts, out string) {
+	section, scriptPath := "", ""
+	var script strings.Builder
+	flush := func() {
+		if scriptPath != "" {
+			f.Scripts[scriptPath] = script.String()
+		}
+		scriptPath = ""
+		script.Reset()
+	}
+	for _, line := range strings.Split(out, "\n") {
+		if rest, ok := strings.CutPrefix(line, probeMarker+" "); ok {
+			flush()
+			section = rest
+			if p, ok := strings.CutPrefix(rest, "script "); ok {
+				section, scriptPath = "script", p
+			}
+			continue
+		}
+		switch section {
+		case "passwd":
+			parts := strings.Split(line, ":")
+			if len(parts) < 6 {
+				continue
+			}
+			uid, _ := strconv.Atoi(parts[2])
+			gid, _ := strconv.Atoi(parts[3])
+			if uid >= 1000 && uid < 65000 {
+				f.Users = append(f.Users, imageUser{Name: parts[0], UID: uid, GID: gid, Home: parts[5]})
+			}
+		case "homes":
+			parts := strings.Split(line, "|")
+			if len(parts) == 4 {
+				uid, _ := strconv.Atoi(parts[1])
+				gid, _ := strconv.Atoi(parts[2])
+				f.Homes = append(f.Homes, homeDir{Path: parts[0], UID: uid, GID: gid, Mode: parts[3]})
+			}
+		case "tools":
+			if name, path, ok := strings.Cut(line, "|"); ok {
+				f.Tools[name] = path
+			}
+		case "script":
+			script.WriteString(line + "\n")
+		}
+	}
+	flush()
+
+	seen := map[string]bool{}
+	for _, body := range f.Scripts {
+		for _, m := range envRef.FindAllStringSubmatch(body, -1) {
+			if !commonEnv[m[1]] {
+				seen[m[1]] = true
+			}
+		}
+	}
+	f.EnvRead = sortedKeysBool(seen)
+}
+
+// suggestContainerUser works out whether the image only works as a specific user. Images either declare
+// it (USER) or are built around an account whose home folder nobody else may enter (ARK's gameserver,
+// uid 25000, with /home/gameserver at 700).
+func suggestContainerUser(f *imageFacts) {
+	if u := strings.TrimSpace(f.User); u != "" && u != "root" && u != "0" {
+		resolved := resolveUser(f, u)
+		if resolved != "" && resolved != nodeUser {
+			f.SuggestedContainerUser = resolved
+			f.SuggestionReason = fmt.Sprintf("the image declares USER %s", u)
+		}
+		return
+	}
+	for _, h := range f.Homes {
+		if h.Path == "/root" || h.UID == 0 || strconv.Itoa(h.UID) == uidOf(nodeUser) {
+			continue
+		}
+		mode, err := strconv.ParseInt(h.Mode, 8, 32)
+		if err != nil || mode&0o005 != 0 { // others can enter it, so 1000:1000 would get in too
+			continue
+		}
+		// The account's own group if it has one; the folder's group otherwise
+		gid := h.GID
+		for _, acc := range f.Users {
+			if acc.UID == h.UID {
+				gid = acc.GID
+			}
+		}
+		f.SuggestedContainerUser = fmt.Sprintf("%d:%d", h.UID, gid)
+		f.SuggestionReason = fmt.Sprintf("%s belongs to uid %d with mode %s, so the node's default %s cannot enter it", h.Path, h.UID, h.Mode, nodeUser)
+		return
+	}
+}
+
+func resolveUser(f *imageFacts, u string) string {
+	name, group, _ := strings.Cut(u, ":")
+	for _, acc := range f.Users {
+		if acc.Name == name || strconv.Itoa(acc.UID) == name {
+			if group == "" {
+				return fmt.Sprintf("%d:%d", acc.UID, acc.GID)
+			}
+			if _, err := strconv.Atoi(group); err == nil {
+				return fmt.Sprintf("%d:%s", acc.UID, group)
+			}
+			return fmt.Sprintf("%d:%d", acc.UID, acc.GID)
+		}
+	}
+	if _, err := strconv.Atoi(name); err == nil {
+		if group == "" {
+			group = name
+		}
+		return name + ":" + group
+	}
+	return ""
+}
+
+// checkTemplate compares a game template with what the image needs. Problems are things that stop or
+// silently break the server; notes are worth a look but often fine.
+func checkTemplate(game map[string]any, f *imageFacts) (problems, notes []string) {
+	set, _ := game["containerUser"].(string)
+	effective := set
+	if effective == "" {
+		effective = nodeUser
+	}
+	// Only the uid decides whether the server can enter its folders; the group may reasonably differ
+	if f.SuggestedContainerUser != "" && uidOf(effective) != uidOf(f.SuggestedContainerUser) {
+		problems = append(problems, fmt.Sprintf("image needs containerUser %q (%s), template runs as %s",
+			f.SuggestedContainerUser, f.SuggestionReason, effective))
+	}
+	if f.ProbeError != "" {
+		notes = append(notes, "could not look inside the image: "+f.ProbeError)
+	}
+
+	// Everything the container will have in its environment: the image's own defaults plus one variable
+	// per config key, named the way the node-agent names them
+	provided := map[string]bool{}
+	for k := range f.Env {
+		provided[k] = true
+	}
+	defaults, _ := game["defaultConfig"].(map[string]any)
+	byLoose := map[string]string{}
+	for key := range defaults {
+		n := envName(key)
+		provided[n] = true
+		byLoose[strings.ReplaceAll(n, "_", "")] = n
+	}
+	if cmd, _ := game["defaultStartupCommand"].(string); cmd != "" {
+		for _, m := range assignedVars.FindAllStringSubmatch(cmd, -1) {
+			provided[m[1]] = true // set by the command itself, e.g. export ASA_START_PARAMS=...
+		}
+		withDefault := map[string]bool{}
+		for _, m := range defaultedRef.FindAllStringSubmatch(cmd, -1) {
+			withDefault[m[1]] = true
+		}
+		for _, v := range uniqueRefs(cmd) {
+			if provided[v] || commonEnv[v] {
+				continue
+			}
+			near, misnamed := byLoose[strings.ReplaceAll(v, "_", "")]
+			switch {
+			case misnamed:
+				// The RCON bug: ${RCON_PORT:-27020} while the RCONPort setting arrives as RCONPORT, so the
+				// default always wins and the owner's setting is silently ignored
+				problems = append(problems, fmt.Sprintf("startup command reads ${%s}, but the setting arrives as %s", v, near))
+			case !withDefault[v]:
+				problems = append(problems, fmt.Sprintf("startup command reads ${%s}, which nothing sets and has no default", v))
+			}
+		}
+	}
+
+	ports, _ := game["defaultPorts"].([]any)
+	templatePorts := map[string]bool{}
+	for _, p := range ports {
+		templatePorts[containerPort(fmt.Sprint(p))] = true
+	}
+	for _, p := range f.ExposedPorts {
+		if !templatePorts[p] {
+			notes = append(notes, fmt.Sprintf("image exposes %s, template does not publish it (fine for RCON/admin ports)", p))
+		}
+	}
+	return problems, notes
+}
+
+// containerPort turns "8211:8211/udp" or "7777/udp" or "25565" into Docker's "8211/udp" form.
+func containerPort(p string) string {
+	if i := strings.LastIndex(p, ":"); i >= 0 {
+		p = p[i+1:]
+	}
+	if !strings.Contains(p, "/") {
+		p += "/tcp"
+	}
+	return p
+}
+
+// startupScriptPaths picks absolute paths out of a template's startup command (e.g. ARK's
+// /usr/bin/start_server) so the probe reads those scripts too.
+func startupScriptPaths(game map[string]any) []string {
+	cmd, _ := game["defaultStartupCommand"].(string)
+	var paths []string
+	for _, m := range absPath.FindAllStringSubmatch(cmd, -1) {
+		if p := m[1]; !strings.HasPrefix(p, "/server") && !strings.HasPrefix(p, "/data") && !strings.HasPrefix(p, "/home/") {
+			paths = append(paths, p)
+		}
+	}
+	return paths
+}
+
+func uniqueRefs(s string) []string {
+	seen := map[string]bool{}
+	for _, m := range envRef.FindAllStringSubmatch(s, -1) {
+		seen[m[1]] = true
+	}
+	return sortedKeysBool(seen)
+}
+
+func printFacts(f *imageFacts) {
+	fmt.Printf("Image:        %s\n", f.Image)
+	user := f.User
+	if user == "" {
+		user = "(root)"
+	}
+	fmt.Printf("Default user: %s\n", user)
+	if f.SuggestedContainerUser != "" {
+		fmt.Printf("Needs:        containerUser %q, because %s\n", f.SuggestedContainerUser, f.SuggestionReason)
+	}
+	fmt.Printf("Entrypoint:   %s\n", strings.Join(append(append([]string{}, f.Entrypoint...), f.Cmd...), " "))
+	fmt.Printf("Ports:        %s\n", strings.Join(f.ExposedPorts, ", "))
+	fmt.Printf("Volumes:      %s\n", strings.Join(f.Volumes, ", "))
+	for _, u := range f.Users {
+		fmt.Printf("User:         %s (uid %d, gid %d, home %s)\n", u.Name, u.UID, u.GID, u.Home)
+	}
+	for _, h := range f.Homes {
+		fmt.Printf("Home:         %s owned by %d:%d mode %s\n", h.Path, h.UID, h.GID, h.Mode)
+	}
+	if len(f.Tools) > 0 {
+		var t []string
+		for _, k := range sortedKeysString(f.Tools) {
+			t = append(t, k+"="+f.Tools[k])
+		}
+		fmt.Printf("Tools:        %s\n", strings.Join(t, ", "))
+	}
+	for _, p := range sortedKeysString(f.Scripts) {
+		fmt.Printf("Script:       %s (%d bytes)\n", p, len(f.Scripts[p]))
+	}
+	if len(f.EnvRead) > 0 {
+		fmt.Printf("Scripts read: %s\n", strings.Join(f.EnvRead, ", "))
+	}
+	if len(f.Env) > 0 {
+		fmt.Printf("Image env:    %s\n", strings.Join(sortedKeysString(f.Env), ", "))
+	}
+	if f.ProbeError != "" {
+		fmt.Printf("Probe:        %s\n", f.ProbeError)
+	}
+}
+
+func firstWord(s []string) string {
+	if len(s) == 0 {
+		return ""
+	}
+	return s[0]
+}
+
+func sortedSet(m map[string]any) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}
+
+func sortedKeysBool(m map[string]bool) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}
+
+func sortedKeysString(m map[string]string) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}

cmd/gbrgames/inspect_test.go

@@ -0,0 +1,129 @@
+package main
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+)
+
+func TestEnvNameMatchesNodeAgent(t *testing.T) {
+	for key, want := range map[string]string{
+		"RCONPort":                            "RCONPORT",
+		"ServerAdminPassword":                 "SERVER_ADMIN_PASSWORD",
+		"AllowFlyerCarryPvE":                  "ALLOW_FLYER_CARRY_PV_E",
+		"bDisableStructurePlacementCollision": "B_DISABLE_STRUCTURE_PLACEMENT_COLLISION",
+		"RCON_PASSWORD":                       "RCON_PASSWORD",
+		"MaxPlayers":                          "MAX_PLAYERS",
+	} {
+		if got := envName(key); got != want {
+			t.Errorf("envName(%q) = %q, want %q", key, got, want)
+		}
+	}
+}
+
+// Probe output as ARK's image produces it (trimmed)
+const arkProbe = probeMarker + ` passwd
+root:x:0:0:root:/root:/bin/bash
+gameserver:x:25000:25000::/home/gameserver:/bin/bash
+nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
+` + probeMarker + ` homes
+/home/gameserver|25000|1000|700
+/root|0|0|700
+` + probeMarker + ` tools
+bash|/usr/bin/bash
+` + probeMarker + ` script /usr/bin/start_server
+#!/bin/bash
+cd /home/gameserver/steamcmd
+echo "$ASA_START_PARAMS ${ENABLE_DEBUG} $HOME"
+`
+
+func arkFacts() *imageFacts {
+	f := &imageFacts{Env: map[string]string{}, Tools: map[string]string{}, Scripts: map[string]string{}}
+	parseProbe(f, arkProbe)
+	suggestContainerUser(f)
+	return f
+}
+
+func TestProbeParsing(t *testing.T) {
+	f := arkFacts()
+	if len(f.Users) != 1 || f.Users[0].Name != "gameserver" || f.Users[0].UID != 25000 {
+		t.Fatalf("users = %+v", f.Users)
+	}
+	if len(f.Homes) != 2 || f.Homes[0].Mode != "700" {
+		t.Fatalf("homes = %+v", f.Homes)
+	}
+	if !strings.Contains(f.Scripts["/usr/bin/start_server"], "steamcmd") {
+		t.Fatalf("script not captured: %q", f.Scripts)
+	}
+	if want := []string{"ASA_START_PARAMS", "ENABLE_DEBUG"}; !reflect.DeepEqual(f.EnvRead, want) {
+		t.Errorf("envRead = %v, want %v (HOME is common and left out)", f.EnvRead, want)
+	}
+}
+
+func TestSuggestContainerUser(t *testing.T) {
+	// Locked home owned by another uid: use that account, with its own group
+	if f := arkFacts(); f.SuggestedContainerUser != "25000:25000" {
+		t.Errorf("ARK: suggested %q, want 25000:25000", f.SuggestedContainerUser)
+	}
+
+	// uid 1000 images need nothing
+	f := &imageFacts{Homes: []homeDir{{Path: "/home/steam", UID: 1000, GID: 1000, Mode: "700"}}}
+	suggestContainerUser(f)
+	if f.SuggestedContainerUser != "" {
+		t.Errorf("uid 1000 image: suggested %q", f.SuggestedContainerUser)
+	}
+
+	// A home others may enter doesn't force a user
+	f = &imageFacts{Homes: []homeDir{{Path: "/home/app", UID: 2000, GID: 2000, Mode: "755"}}}
+	suggestContainerUser(f)
+	if f.SuggestedContainerUser != "" {
+		t.Errorf("open home: suggested %q", f.SuggestedContainerUser)
+	}
+
+	// A declared USER is resolved through /etc/passwd
+	f = &imageFacts{User: "steam", Users: []imageUser{{Name: "steam", UID: 4242, GID: 4243}}}
+	suggestContainerUser(f)
+	if f.SuggestedContainerUser != "4242:4243" {
+		t.Errorf("declared USER: suggested %q", f.SuggestedContainerUser)
+	}
+}
+
+func TestCheckTemplate(t *testing.T) {
+	f := arkFacts()
+	game := map[string]any{
+		"defaultConfig": map[string]any{"RCONPort": 27020, "MaxPlayers": 70},
+		// Mirrors ARK's old command: ASA_START_PARAMS is assigned, SERVER_MAP has a default, RCON_PORT is the
+		// misnamed one, MAX_PLAYERS is set by a setting, MISSING has no default at all
+		"defaultStartupCommand": `export ASA_START_PARAMS="${ASA_START_PARAMS:-${SERVER_MAP:-TheIsland}?RCONPort=${RCON_PORT:-27020} -Max=${MAX_PLAYERS:-70} ${MISSING}}"`,
+	}
+	problems, _ := checkTemplate(game, f)
+	joined := strings.Join(problems, "\n")
+	for _, want := range []string{"containerUser \"25000:25000\"", "${RCON_PORT}, but the setting arrives as RCONPORT", "${MISSING}"} {
+		if !strings.Contains(joined, want) {
+			t.Errorf("missing problem %q in:\n%s", want, joined)
+		}
+	}
+	for _, unwanted := range []string{"ASA_START_PARAMS", "SERVER_MAP", "MAX_PLAYERS}"} {
+		if strings.Contains(joined, unwanted) {
+			t.Errorf("false problem about %s in:\n%s", unwanted, joined)
+		}
+	}
+	if len(problems) != 3 {
+		t.Errorf("got %d problems, want 3:\n%s", len(problems), joined)
+	}
+
+	// With the fixes, only the deliberately missing variable is left; 25000:1000 counts (same uid)
+	game["containerUser"] = "25000:1000"
+	game["defaultStartupCommand"] = `export ASA_START_PARAMS="${ASA_START_PARAMS:-x}?RCONPort=${RCONPORT:-27020}"`
+	if problems, _ := checkTemplate(game, f); len(problems) != 0 {
+		t.Errorf("fixed template still has problems: %v", problems)
+	}
+}
+
+func TestContainerPort(t *testing.T) {
+	for in, want := range map[string]string{"8211:8211/udp": "8211/udp", "7777/udp": "7777/udp", "25565": "25565/tcp"} {
+		if got := containerPort(in); got != want {
+			t.Errorf("containerPort(%q) = %q, want %q", in, got, want)
+		}
+	}
+}

cmd/gbrgames/main.go

@@ -4,6 +4,7 @@
 //	go run ./cmd/gbrgames import export.json  # write games/<id>/ from GET /api/v1/admin/games
 //	go run ./cmd/gbrgames export -out p.json  # build the games_published payload CI sends to the panel
 //	go run ./cmd/gbrgames boottest-payload ID # build the deploy message the node-agent's BootTest runs
+//	go run ./cmd/gbrgames inspect-image -game ID   # read the image's facts and check the template against them
 package main
 
 import (
@@ -25,6 +26,8 @@ func main() {
 		err = runExport(os.Args[2:])
 	case "boottest-payload":
 		err = runBootTestPayload(os.Args[2:])
+	case "inspect-image":
+		err = runInspectImage(os.Args[2:])
 	default:
 		usage()
 	}
@@ -35,6 +38,6 @@ func main() {
 }
 
 func usage() {
-	fmt.Fprintln(os.Stderr, "usage: gbrgames validate [-games DIR] | import [-games DIR] [-all] EXPORT.json | export [-repo R] [-commit SHA] [-out FILE] | boottest-payload [-out FILE] ID")
+	fmt.Fprintln(os.Stderr, "usage: gbrgames validate [-games DIR] | import [-games DIR] [-all] EXPORT.json | export [-repo R] [-commit SHA] [-out FILE] | boottest-payload [-out FILE] ID | inspect-image [-game ID] [-json] [-no-pull] [IMAGE]")
 	os.Exit(2)
 }

scripts/boot-test.sh

@@ -23,6 +23,13 @@ go build -o "$gbrgames" ./cmd/gbrgames || exit 1
 passed=() failed=() skipped=()
 for id in "$@"; do
   echo "::group::boot test: $id"
+  # Seconds instead of a full boot: catches templates that can't work with their image (wrong
+  # container user, startup command reading a variable under the wrong name)
+  if ! "$gbrgames" inspect-image -game "$id"; then
+    failed+=("$id")
+    echo "::endgroup::"
+    continue
+  fi
   payload=$("$gbrgames" boottest-payload "$id")
   code=$?
   if [ $code -eq 3 ]; then