Let a directory's owner follow the account its module runs as (issue 279)

A media manager runs as the puid/pgid its assignment sets per node, but a
declared directory's owner was literal, so a folder the app must write was
refused on a machine whose identity was not the image's default. A
directory's owner now takes ${setting:<key>} (user, or user:group), filled
at composition and refused unless the value is a whole number, and the
module check refuses any other shape or a key the module asks for nowhere
else.

internal/catalogue/setting_into.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 )
 
@@ -15,7 +16,8 @@ import (
 // (novox/hq issues 122, 134). ADR 0112 names the operator as one of the four providers; this is the
 // operator answering.
 //
-// `${setting:<key>}` in a file's content, and in a service's unit name, is filled from the module's settings layers — the mesh's,
+// `${setting:<key>}` in a file's content, in a service's unit name and in a directory's owner (a uid or
+// gid only, issue 279) is filled from the module's settings layers — the mesh's,
 // then this node's — the same layers a mergeable JSON file and a contribution already take, so
 // `settings set <module>` is the one place a person's values go. **Refused when no layer sets it**,
 // naming the key and the remedy: a definition that carried a default for a mail domain would be
@@ -59,6 +61,9 @@ func settingInto(resource map[string]any, layers []Layer, module string) error {
 	if fmt.Sprint(resource["type"]) == "service" {
 		return settingIntoUnit(resource, layers, module)
 	}
+	if fmt.Sprint(resource["type"]) == "directory" {
+		return settingIntoOwner(resource, layers, module)
+	}
 	if fmt.Sprint(resource["type"]) != "file" {
 		return nil
 	}
@@ -143,6 +148,104 @@ func settingIntoUnit(resource map[string]any, layers []Layer, module string) err
 	return nil
 }
 
+// A declared directory may be owned by the account its module runs as (novox/hq issue 279).
+//
+// A containerised module runs as the identity its assignment sets per node — its puid and pgid
+// settings, written into the environment file its image reads (ADR 0112, issue 153) — and a directory
+// its app must write, beyond the one its image re-owns at start, was owned by whatever the manifest
+// spelt: right on a machine whose identity matched the image's default, refused by the app on one whose
+// did not. So a directory's `owner` may name the settings that identity is: `${setting:<key>}` for the
+// user alone, `${setting:<user>}:${setting:<group>}` for both, filled from the same layers at
+// composition.
+//
+// **Whole numbers only.** An owner a setting fills is a uid or a gid — never an account's name, never
+// text — so no value can put anything into the ownership the node-engine applies but a number; one that
+// is not is refused at composition, naming the key, and the directory is left as it was. The shape is
+// judged where the manifest is read (OwnerSettingProblems): each side of the colon a whole placeholder
+// or a whole number, and every key one the module itself asks for elsewhere — in a file, a unit, a
+// contribution or a served fact — or declares a default for, so the owner follows the identity its
+// process is told it runs as, never a key that reaches nothing else.
+
+// ownerSide is one side of an owner a setting may fill: a whole placeholder or a whole number.
+var ownerSide = `(?:\$\{setting:[a-z0-9][a-z0-9_.-]*\}|[0-9]+)`
+
+// ownerWithSetting is the only shape an owner holding a setting may have: user, or user:group.
+var ownerWithSetting = regexp.MustCompile(`^` + ownerSide + `(?::` + ownerSide + `)?$`)
+
+// wholeID is whether a value is a uid or a gid: a whole number below the kernel's "no id" (2^32-1).
+func wholeID(v string) bool {
+	if v == "" || strings.TrimLeft(v, "0123456789") != "" {
+		return false
+	}
+	n, err := strconv.ParseUint(v, 10, 32)
+	return err == nil && n < 1<<32-1
+}
+
+// OwnerSettingProblems refuses, where a manifest is read, a directory whose owner carries a setting
+// in any shape but a whole placeholder or number on each side of the colon, or names a key the module
+// asks for nowhere else and declares no default for.
+func OwnerSettingProblems(m Manifest) []string {
+	var problems []string
+	asked := settingKeysAskedOutsideOwners(m)
+	for k := range m.Settings {
+		asked[k] = true
+	}
+	for _, r := range m.Resources {
+		owner, _ := r["owner"].(string)
+		if !strings.Contains(owner, "${setting:") {
+			continue
+		}
+		if fmt.Sprint(r["type"]) != "directory" {
+			// Said by the placeholder sweep: only a directory's owner takes a setting.
+			continue
+		}
+		if !ownerWithSetting.MatchString(owner) {
+			problems = append(problems, fmt.Sprintf("%s: the directory %v's owner %q carries a setting in a shape "+
+				"the mesh does not fill; an owner names the account by number only, each side of the colon a whole "+
+				"${setting:key} or a whole number (${setting:puid}:${setting:pgid}) (novox/hq issue 279)",
+				m.Module, r["id"], owner))
+			continue
+		}
+		for _, key := range settingsUsed(owner) {
+			if !asked[key] {
+				problems = append(problems, fmt.Sprintf("%s: the directory %v's owner says ${setting:%s}, and the "+
+					"module asks for %q nowhere else and declares no default for it: an owner follows the identity "+
+					"the module's process is told it runs as (its identity file's ${setting:%s}), never a key of its "+
+					"own (novox/hq issue 279)", m.Module, r["id"], key, key, key))
+			}
+		}
+	}
+	return problems
+}
+
+// settingIntoOwner fills ${setting:…} in a directory's owner, refusing — with the key and why, the
+// resource left as it was — a key nothing sets and a value that is not a whole number.
+func settingIntoOwner(resource map[string]any, layers []Layer, module string) error {
+	owner, ok := resource["owner"].(string)
+	if !ok {
+		return nil
+	}
+	for _, key := range settingsUsed(owner) {
+		value, set := settingValue(layers, key)
+		if !set {
+			return &UnsetSettingError{Module: module, Setting: key, said: fmt.Sprintf(
+				"%s has a directory %v whose owner says ${setting:%s}, and nothing sets %q for it — an operator's "+
+					"value is the assignment's, never the definition's (novox/hq ADR 0112): "+
+					"`settings set %s <file>` with {%q: …}%s",
+				module, resource["id"], key, key, module, key, orNoSettings(layers))}
+		}
+		v := plainly(value)
+		if !wholeID(v) {
+			return fmt.Errorf("%s: the setting %q is %q, which cannot own the directory %v: an owner a setting "+
+				"names is a uid or a gid, a whole number, never an account's name or other text (novox/hq issue 279)",
+				module, key, v, resource["id"])
+		}
+		owner = strings.ReplaceAll(owner, "${setting:"+key+"}", v)
+	}
+	resource["owner"] = owner
+	return nil
+}
+
 func settingValue(layers []Layer, key string) (any, bool) {
 	var value any
 	set := false
@@ -171,9 +274,25 @@ func orNoSettings(layers []Layer) string {
 	return "; set today: " + strings.Join(keys, ", ")
 }
 
-// settingKeysUsedBy is every key a module's files, contributions and served facts ask for, so a
-// setting that lands in one is not called stray.
+// settingKeysUsedBy is every key a module's files, units, directory owners, contributions and served
+// facts ask for, so a setting that lands in one is not called stray.
 func settingKeysUsedBy(m Manifest) map[string]bool {
+	used := settingKeysAskedOutsideOwners(m)
+	for _, r := range m.Resources {
+		if fmt.Sprint(r["type"]) == "directory" {
+			if owner, ok := r["owner"].(string); ok {
+				for _, k := range settingsUsed(owner) {
+					used[k] = true
+				}
+			}
+		}
+	}
+	return used
+}
+
+// settingKeysAskedOutsideOwners is every key a module's files, units, contributions and served facts
+// ask for: what a directory's owner may follow (OwnerSettingProblems).
+func settingKeysAskedOutsideOwners(m Manifest) map[string]bool {
 	used := map[string]bool{}
 	note := func(s string) {
 		for _, k := range settingsUsed(s) {