chore!(firewall): iptables logger level is set at FIREWALL_IPTABLES_LOG_LEVEL

- firewall log level is still fully controlled by `LOG_LEVEL`
- iptables log level defaults to `info` even if global log level is `debug` to minimize the amount of debug logs
- iptables log level is only set to debug if retro-compatible `FIREWALL_DEBUG=on` or if `FIREWALL_IPTABLES_LOG_LEVEL=debug`

internal/configuration/settings/iptables.go

@@ -0,0 +1,67 @@
+package settings
+
+import (
+	"fmt"
+
+	"github.com/qdm12/gosettings"
+	"github.com/qdm12/gosettings/reader"
+	"github.com/qdm12/gotree"
+	"github.com/qdm12/log"
+)
+
+// Iptables contains settings to customize iptables.
+type Iptables struct {
+	LogLevel string
+}
+
+func (i Iptables) validate() (err error) {
+	_, err = log.ParseLevel(i.LogLevel)
+	if err != nil {
+		return fmt.Errorf("log level: %w", err)
+	}
+
+	return nil
+}
+
+func (i *Iptables) copy() (copied Iptables) {
+	return Iptables{
+		LogLevel: i.LogLevel,
+	}
+}
+
+func (i *Iptables) overrideWith(other Iptables) {
+	i.LogLevel = gosettings.OverrideWithComparable(i.LogLevel, other.LogLevel)
+}
+
+func (i *Iptables) setDefaults(globalLogLevel string) {
+	defaultLevel := globalLogLevel
+	if defaultLevel == log.LevelDebug.String() {
+		// Given iptables debug logger is quite verbose, we only turn it to debug level
+		// if it is explicitly asked to be at debug level; even if the global logger is
+		// at the debug level, we keep iptables at info level by default.
+		defaultLevel = log.LevelInfo.String()
+	}
+	i.LogLevel = gosettings.DefaultComparable(i.LogLevel, defaultLevel)
+}
+
+func (i Iptables) String() string {
+	return i.toLinesNode().String()
+}
+
+func (i Iptables) toLinesNode() (node *gotree.Node) {
+	node = gotree.New("Iptables settings:")
+	node.Appendf("Log level: %s", i.LogLevel)
+	return node
+}
+
+func (i *Iptables) read(r *reader.Reader) (err error) {
+	debugMode, err := r.BoolPtr("FIREWALL_DEBUG", reader.IsRetro("FIREWALL_IPTABLES_LOG_LEVEL"))
+	if err != nil {
+		return err
+	}
+	if debugMode != nil && *debugMode {
+		i.LogLevel = log.LevelDebug.String()
+	}
+	i.LogLevel = r.String("FIREWALL_IPTABLES_LOG_LEVEL")
+	return nil
+}