Maint: refactor internal/routing

- Split Go files better
- Reduce public API for exported errors

internal/routing/rules.go

@@ -0,0 +1,73 @@
+package routing
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"net"
+	"strconv"
+
+	"github.com/qdm12/gluetun/internal/netlink"
+)
+
+var (
+	errRulesList = errors.New("cannot list rules")
+)
+
+func (r *Routing) addIPRule(src net.IP, table, priority int) error {
+	r.logger.Debug("ip rule add from " + src.String() +
+		" lookup " + strconv.Itoa(table) +
+		" pref " + strconv.Itoa(priority))
+
+	rule := netlink.NewRule()
+	rule.Src = netlink.NewIPNet(src)
+	rule.Priority = priority
+	rule.Table = table
+
+	rules, err := r.netLinker.RuleList(netlink.FAMILY_ALL)
+	if err != nil {
+		return fmt.Errorf("%w: %s", errRulesList, err)
+	}
+	for _, existingRule := range rules {
+		if existingRule.Src != nil &&
+			existingRule.Src.IP.Equal(rule.Src.IP) &&
+			bytes.Equal(existingRule.Src.Mask, rule.Src.Mask) &&
+			existingRule.Priority == rule.Priority &&
+			existingRule.Table == rule.Table {
+			return nil // already exists
+		}
+	}
+
+	if err := r.netLinker.RuleAdd(rule); err != nil {
+		return fmt.Errorf("%w: for rule: %s", err, rule)
+	}
+	return nil
+}
+
+func (r *Routing) deleteIPRule(src net.IP, table, priority int) error {
+	r.logger.Debug("ip rule del from " + src.String() +
+		" lookup " + strconv.Itoa(table) +
+		" pref " + strconv.Itoa(priority))
+
+	rule := netlink.NewRule()
+	rule.Src = netlink.NewIPNet(src)
+	rule.Priority = priority
+	rule.Table = table
+
+	rules, err := r.netLinker.RuleList(netlink.FAMILY_ALL)
+	if err != nil {
+		return fmt.Errorf("%w: %s", errRulesList, err)
+	}
+	for _, existingRule := range rules {
+		if existingRule.Src != nil &&
+			existingRule.Src.IP.Equal(rule.Src.IP) &&
+			bytes.Equal(existingRule.Src.Mask, rule.Src.Mask) &&
+			existingRule.Priority == rule.Priority &&
+			existingRule.Table == rule.Table {
+			if err := r.netLinker.RuleDel(rule); err != nil {
+				return fmt.Errorf("%w: for rule: %s", err, rule)
+			}
+		}
+	}
+	return nil
+}