CLI: cert get doesn't take over another server's saved name

Each Jarl server has its own certificate names, but a host keeps one
saved NAME.json (and, by default, one /etc/jarl/certs/NAME). Asking a
second server for the same name overwrote the first one's settings and
files, so the first certificate quietly stopped being renewed. Now that
is refused, as is a --dir holding another certificate's files;
--replace takes the name or directory over. A --dir another saved
certificate uses is always refused.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/jarl/certget.go

@@ -114,6 +114,32 @@ func (sc savedCert) save(dir string) error {
 	return writeAtomic(filepath.Join(dir, sc.Name+".json"), append(b, '\n'), 0o600)
 }
 
+// checkCertClash refuses a certificate that would take over what this
+// host keeps for another one: a name saved for another Jarl server
+// (each server has its own names, so the server can't refuse it), or a
+// directory with another certificate's files. saved[i] is sc's saved
+// settings (i < 0: none).
+func checkCertClash(saved []savedCert, i int, sc savedCert, replace bool) error {
+	if i >= 0 && !replace && !sameServer(saved[i].Conn.Server, sc.Conn.Server) {
+		return fmt.Errorf("%s is saved here for the Jarl server %s, not %s: choose another name, or take it over with --replace", sc.Name, saved[i].Conn.Server, sc.Conn.Server)
+	}
+	for j, o := range saved {
+		if j != i && o.Name != sc.Name && filepath.Clean(o.Dir) == filepath.Clean(sc.Dir) {
+			return fmt.Errorf("%s holds the files of %s, saved for %s: give %s another --dir", sc.Dir, o.Name, o.Conn.Server, sc.Name)
+		}
+	}
+	if m, err := readMeta(sc.Dir); err == nil && m.Name != "" && m.Name != sc.Name && !replace {
+		return fmt.Errorf("%s holds the files of the certificate %s: give %s another --dir, or overwrite them with --replace", sc.Dir, m.Name, sc.Name)
+	}
+	return nil
+}
+
+// sameServer reports whether two server addresses name the same jarld.
+func sameServer(a, b string) bool {
+	norm := func(s string) string { return strings.TrimRight(strings.ToLower(s), "/") }
+	return norm(a) == norm(b)
+}
+
 func readMeta(dir string) (*localMeta, error) {
 	b, err := os.ReadFile(filepath.Join(dir, metaFile))
 	if err != nil {
@@ -340,7 +366,7 @@ func runHook(sc savedCert, ci certInfo, renewed bool) error {
 func certGetCmd() *cobra.Command {
 	var domains []string
 	var dir, hook, keyType, configDir string
-	var noSave, force bool
+	var noSave, force, replace bool
 	var wait time.Duration
 	cmd := &cobra.Command{
 		Use:   "get [NAME]",
@@ -365,6 +391,10 @@ readable only by you). 'jarl cert get' without a name then does every
 saved certificate: run it daily (jarl cert schedule does that with a
 systemd timer). Nothing is downloaded until jarld has renewed one.
 
+A name saved here for another Jarl server isn't taken over, nor a --dir
+holding another certificate's files, unless --replace is given; a --dir
+another saved certificate uses is always refused.
+
 --hook runs with sh after new files are written (and again on the next
 run if it failed), with JARL_CERT_NAME, JARL_CERT_DIR, JARL_CERT_CERT,
 JARL_CERT_CHAIN, JARL_CERT_FULLCHAIN, JARL_CERT_KEY, JARL_CERT_DOMAINS,
@@ -427,6 +457,9 @@ replaced an older certificate).`,
 					}
 					sc.Conn = cn
 				}
+				if err := checkCertClash(saved, i, sc, replace); err != nil {
+					return err
+				}
 				todo = []savedCert{sc}
 			}
 			var results []*getResult
@@ -469,7 +502,7 @@ replaced an older certificate).`,
 			}
 			switch {
 			case len(failed) == 1 && len(todo) == 1:
-				return lastErr // its own exit code (3 forbidden, 6 conflict, ...)
+				return lastErr // its own exit code (3 forbidden, 5 conflict, ...)
 			case len(failed) > 0:
 				return fmt.Errorf("failed: %s", strings.Join(failed, ", "))
 			}
@@ -483,6 +516,7 @@ replaced an older certificate).`,
 	f.StringVar(&keyType, "key-type", "", "key type of a new certificate: ec256 (default), ec384, rsa2048, rsa3072, rsa4096")
 	f.BoolVar(&force, "force", false, "download and run the hook even when this host has the current certificate")
 	f.BoolVar(&noSave, "no-save", false, "don't save the settings for later runs")
+	f.BoolVar(&replace, "replace", false, "take over a name saved here for another Jarl server, or a --dir holding another certificate's files")
 	f.DurationVar(&wait, "wait", 15*time.Minute, "how long to wait while jarld obtains it")
 	f.StringVar(&configDir, "config-dir", "", "where the settings are saved (default /etc/jarl/cert-get as root, ~/.config/jarl/cert-get otherwise)")
 	_ = cmd.RegisterFlagCompletionFunc("key-type", cobra.FixedCompletions([]string{"ec256", "ec384", "rsa2048", "rsa3072", "rsa4096"}, cobra.ShellCompDirectiveNoFileComp))

cmd/jarl/certget_test.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestCheckCertClash(t *testing.T) {
+	tmp := t.TempDir()
+	a := connection{Server: "https://dns-a.example:8053"}
+	b := connection{Server: "https://dns-b.example:8053"}
+	saved := []savedCert{
+		{Name: "proxy", Dir: filepath.Join(tmp, "proxy"), Conn: a},
+		{Name: "mail", Dir: filepath.Join(tmp, "mail"), Conn: a},
+	}
+	// mail's files are on disk; "other" has files but no saved settings.
+	if err := (&localMeta{Name: "mail"}).write(mkdir(t, saved[1].Dir)); err != nil {
+		t.Fatal(err)
+	}
+	if err := (&localMeta{Name: "other"}).write(mkdir(t, filepath.Join(tmp, "other"))); err != nil {
+		t.Fatal(err)
+	}
+	cases := []struct {
+		what    string
+		i       int
+		sc      savedCert
+		replace bool
+		want    string // "" = allowed
+	}{
+		{"same server again", 0, savedCert{Name: "proxy", Dir: saved[0].Dir, Conn: a}, false, ""},
+		{"same server, other spelling", 0, savedCert{Name: "proxy", Dir: saved[0].Dir, Conn: connection{Server: "HTTPS://dns-a.example:8053/"}}, false, ""},
+		{"other server", 0, savedCert{Name: "proxy", Dir: saved[0].Dir, Conn: b}, false, "saved here for the Jarl server"},
+		{"other server, replace", 0, savedCert{Name: "proxy", Dir: saved[0].Dir, Conn: b}, true, ""},
+		{"new name, saved cert's dir", -1, savedCert{Name: "web", Dir: saved[1].Dir, Conn: b}, false, "holds the files of mail"},
+		{"new name, saved cert's dir, replace", -1, savedCert{Name: "web", Dir: saved[1].Dir + "/", Conn: b}, true, "holds the files of mail"},
+		{"new name, unsaved cert's files", -1, savedCert{Name: "web", Dir: filepath.Join(tmp, "other"), Conn: b}, false, "certificate other"},
+		{"new name, unsaved cert's files, replace", -1, savedCert{Name: "web", Dir: filepath.Join(tmp, "other"), Conn: b}, true, ""},
+		{"new name, empty dir", -1, savedCert{Name: "web", Dir: filepath.Join(tmp, "web"), Conn: b}, false, ""},
+	}
+	for _, c := range cases {
+		err := checkCertClash(saved, c.i, c.sc, c.replace)
+		switch {
+		case c.want == "" && err != nil:
+			t.Errorf("%s: %v", c.what, err)
+		case c.want != "" && (err == nil || !strings.Contains(err.Error(), c.want)):
+			t.Errorf("%s: got %v, want %q", c.what, err, c.want)
+		}
+	}
+}
+
+func mkdir(t *testing.T, dir string) string {
+	t.Helper()
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	return dir
+}