new-app: configure jail mail relay and persist the jail's network alias

Two provisioning gaps in new-app:

- The jail's dma.conf inherited the base image's shared SMARTHOST/
  PORT/AUTHPATH, but never got a per-app MAILNAME - without one, dma
  can misroute mail for recipients on the jail's own apex domain as
  local delivery. EnableMail appends a MAILNAME of <app>.skiff.local,
  which can't collide with any real domain an app sends to or from.

- A classic jail's ip4.addr is only a bind restriction, not a route,
  until something aliases it onto a host interface. jail.conf.tmpl
  never set jail(8)'s own `interface` parameter, so nothing ever
  created that alias - confirmed on skiff-freebsd, where the address
  had twice been made to work via an ad hoc `ifconfig alias` that
  didn't survive a reboot. Setting `interface` lets jail(8) manage
  the alias itself, including on every boot.

1 files changed, 17 insertions, 2 deletions

diff --git a/internal/jailmgr/jailmgr.go b/internal/jailmgr/jailmgr.go
index b6a5d28..9ddf9b8 100644
--- a/internal/jailmgr/jailmgr.go
+++ b/internal/jailmgr/jailmgr.go
@@ -16,8 +16,8 @@ import (
 
 // WriteConf renders jail.conf.d/<app>.conf and the jail's own rc.d service
 // script + rc.conf enable line. Called once, from `skiff new-app`.
-func WriteConf(cfg layout.Config, app, ip string) error {
-	conf, err := tmpl.JailConf(tmpl.JailConfData{Name: app, JailRoot: cfg.JailRoot(app), IP: ip})
+func WriteConf(cfg layout.Config, app, ip, iface string) error {
+	conf, err := tmpl.JailConf(tmpl.JailConfData{Name: app, JailRoot: cfg.JailRoot(app), IP: ip, Iface: iface})
 	if err != nil {
 		return err
 	}
@@ -49,6 +49,21 @@ func WriteConf(cfg layout.Config, app, ip string) error {
 	return nil
 }
 
+// EnableMail appends a MAILNAME line to the jail's dma.conf, inherited from
+// the base image's SMARTHOST/PORT/AUTHPATH/SECURETRANSFER/STARTTLS. Called
+// once, from `skiff new-app`.
+func EnableMail(cfg layout.Config, app string) error {
+	f, err := os.OpenFile(cfg.DMAConfPath(app), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return fmt.Errorf("open jail dma.conf: %w", err)
+	}
+	defer f.Close()
+	if _, err := fmt.Fprintf(f, "\nMAILNAME %s.skiff.local\n", app); err != nil {
+		return fmt.Errorf("set MAILNAME in jail dma.conf: %w", err)
+	}
+	return nil
+}
+
 func Start(ctx context.Context, out io.Writer, app string) error {
 	return sh.Run(ctx, out, "", "service", "jail", "start", app)
 }