Maintenance: improve error codes in IP routing

cmd/gluetun/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -45,6 +46,10 @@ var (
 	buildDate = "an unknown date"
 )
 
+var (
+	errSetupRouting = errors.New("cannot setup routing")
+)
+
 func main() {
 	buildInfo := models.BuildInformation{
 		Version:   version,
@@ -204,12 +209,12 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 	firewallConf.SetNetworkInformation(defaultInterface, defaultGateway, localNetworks, defaultIP)
 
 	if err := routingConf.Setup(); err != nil {
-		return err
+		return fmt.Errorf("%w: %s", errSetupRouting, err)
 	}
 	defer func() {
 		routingConf.SetVerbose(false)
 		if err := routingConf.TearDown(); err != nil {
-			logger.Error(err)
+			logger.Error("cannot teardown routing: " + err.Error())
 		}
 	}()
 

internal/routing/enable.go

@@ -1,28 +1,33 @@
 package routing
 
 import (
+	"errors"
 	"fmt"
 	"net"
 )
 
-var (
-	ErrSetup    = fmt.Errorf("cannot setup routing")
-	ErrTeardown = fmt.Errorf("cannot teardown routing")
-)
-
 const (
 	table    = 200
 	priority = 100
 )
 
+var (
+	ErrDefaultIP          = errors.New("cannot get default IP address")
+	ErrDefaultRoute       = errors.New("cannot get default route")
+	ErrIPRuleAdd          = errors.New("cannot add IP rule")
+	ErrIPRuleDelete       = errors.New("cannot delete IP rule")
+	ErrRouteAdd           = errors.New("cannot add route")
+	ErrSubnetsOutboundSet = errors.New("cannot set outbound subnets routes")
+)
+
 func (r *routing) Setup() (err error) {
 	defaultIP, err := r.DefaultIP()
 	if err != nil {
-		return fmt.Errorf("%s: %w", ErrSetup, err)
+		return fmt.Errorf("%w: %s", ErrDefaultIP, err)
 	}
 	defaultInterfaceName, defaultGateway, err := r.DefaultRoute()
 	if err != nil {
-		return fmt.Errorf("%s: %w", ErrSetup, err)
+		return fmt.Errorf("%w: %s", ErrDefaultRoute, err)
 	}
 
 	defer func() {
@@ -30,22 +35,22 @@ func (r *routing) Setup() (err error) {
 			return
 		}
 		if err := r.TearDown(); err != nil {
-			r.logger.Error(err)
+			r.logger.Error("cannot reverse routing changes: " + err.Error())
 		}
 	}()
 	if err := r.addIPRule(defaultIP, table, priority); err != nil {
-		return fmt.Errorf("%s: %w", ErrSetup, err)
+		return fmt.Errorf("%w: %s", ErrIPRuleAdd, err)
 	}
 	defaultDestination := net.IPNet{IP: net.IPv4(0, 0, 0, 0), Mask: net.IPv4Mask(0, 0, 0, 0)}
 	if err := r.addRouteVia(defaultDestination, defaultGateway, defaultInterfaceName, table); err != nil {
-		return fmt.Errorf("%s: %w", ErrSetup, err)
+		return fmt.Errorf("%w: %s", ErrRouteAdd, err)
 	}
 
 	r.stateMutex.RLock()
 	outboundSubnets := r.outboundSubnets
 	r.stateMutex.RUnlock()
 	if err := r.setOutboundRoutes(outboundSubnets, defaultInterfaceName, defaultGateway); err != nil {
-		return fmt.Errorf("%s: %w", ErrSetup, err)
+		return fmt.Errorf("%w: %s", ErrSubnetsOutboundSet, err)
 	}
 
 	return nil
@@ -54,23 +59,23 @@ func (r *routing) Setup() (err error) {
 func (r *routing) TearDown() error {
 	defaultIP, err := r.DefaultIP()
 	if err != nil {
-		return fmt.Errorf("%s: %w", ErrTeardown, err)
+		return fmt.Errorf("%w: %s", ErrDefaultIP, err)
 	}
 	defaultInterfaceName, defaultGateway, err := r.DefaultRoute()
 	if err != nil {
-		return fmt.Errorf("%s: %w", ErrTeardown, err)
+		return fmt.Errorf("%w: %s", ErrDefaultRoute, err)
 	}
 
 	defaultNet := net.IPNet{IP: net.IPv4(0, 0, 0, 0), Mask: net.IPv4Mask(0, 0, 0, 0)}
 	if err := r.deleteRouteVia(defaultNet, defaultGateway, defaultInterfaceName, table); err != nil {
-		return fmt.Errorf("%s: %w", ErrTeardown, err)
+		return fmt.Errorf("%w: %s", ErrRouteDelete, err)
 	}
 	if err := r.deleteIPRule(defaultIP, table, priority); err != nil {
-		return fmt.Errorf("%s: %w", ErrTeardown, err)
+		return fmt.Errorf("%w: %s", ErrIPRuleDelete, err)
 	}
 
 	if err := r.setOutboundRoutes(nil, defaultInterfaceName, defaultGateway); err != nil {
-		return fmt.Errorf("%s: %w", ErrSetup, err)
+		return fmt.Errorf("%w: %s", ErrSubnetsOutboundSet, err)
 	}
 
 	return nil

internal/routing/mutate.go

@@ -2,12 +2,20 @@ package routing
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"net"
 
 	"github.com/vishvananda/netlink"
 )
 
+var (
+	ErrRouteReplace = errors.New("cannot replace route")
+	ErrRouteDelete  = errors.New("cannot delete route")
+	ErrRuleAdd      = errors.New("cannot add routing rule")
+	ErrRuleDel      = errors.New("cannot delete routing rule")
+)
+
 func (r *routing) addRouteVia(destination net.IPNet, gateway net.IP, iface string, table int) error {
 	destinationStr := destination.String()
 	if r.verbose {
@@ -19,7 +27,7 @@ func (r *routing) addRouteVia(destination net.IPNet, gateway net.IP, iface strin
 
 	link, err := netlink.LinkByName(iface)
 	if err != nil {
-		return fmt.Errorf("cannot add route for %s: %w", destinationStr, err)
+		return fmt.Errorf("%w: interface %s: %s", ErrLinkByName, iface, err)
 	}
 	route := netlink.Route{
 		Dst:       &destination,
@@ -28,7 +36,8 @@ func (r *routing) addRouteVia(destination net.IPNet, gateway net.IP, iface strin
 		Table:     table,
 	}
 	if err := netlink.RouteReplace(&route); err != nil {
-		return fmt.Errorf("cannot add route for %s: %w", destinationStr, err)
+		return fmt.Errorf("%w: for subnet %s at interface %s: %s",
+			ErrRouteReplace, destinationStr, iface, err)
 	}
 	return nil
 }
@@ -44,7 +53,7 @@ func (r *routing) deleteRouteVia(destination net.IPNet, gateway net.IP, iface st
 
 	link, err := netlink.LinkByName(iface)
 	if err != nil {
-		return fmt.Errorf("cannot delete route for %s: %w", destinationStr, err)
+		return fmt.Errorf("%w: for interface %s: %s", ErrLinkByName, iface, err)
 	}
 	route := netlink.Route{
 		Dst:       &destination,
@@ -53,7 +62,8 @@ func (r *routing) deleteRouteVia(destination net.IPNet, gateway net.IP, iface st
 		Table:     table,
 	}
 	if err := netlink.RouteDel(&route); err != nil {
-		return fmt.Errorf("cannot delete route for %s: %w", destinationStr, err)
+		return fmt.Errorf("%w: for subnet %s at interface %s: %s",
+			ErrRouteDelete, destinationStr, iface, err)
 	}
 	return nil
 }
@@ -71,7 +81,7 @@ func (r *routing) addIPRule(src net.IP, table, priority int) error {
 
 	rules, err := netlink.RuleList(netlink.FAMILY_ALL)
 	if err != nil {
-		return fmt.Errorf("cannot add ip rule: %w", err)
+		return fmt.Errorf("%w: %s", ErrRulesList, err)
 	}
 	for _, existingRule := range rules {
 		if existingRule.Src != nil &&
@@ -83,7 +93,10 @@ func (r *routing) addIPRule(src net.IP, table, priority int) error {
 		}
 	}
 
-	return netlink.RuleAdd(rule)
+	if err := netlink.RuleAdd(rule); err != nil {
+		return fmt.Errorf("%w: for rule %q: %s", ErrRuleAdd, rule, err)
+	}
+	return nil
 }
 
 func (r *routing) deleteIPRule(src net.IP, table, priority int) error {
@@ -99,7 +112,7 @@ func (r *routing) deleteIPRule(src net.IP, table, priority int) error {
 
 	rules, err := netlink.RuleList(netlink.FAMILY_ALL)
 	if err != nil {
-		return fmt.Errorf("cannot add ip rule: %w", err)
+		return fmt.Errorf("%w: %s", ErrRulesList, err)
 	}
 	for _, existingRule := range rules {
 		if existingRule.Src != nil &&
@@ -107,7 +120,9 @@ func (r *routing) deleteIPRule(src net.IP, table, priority int) error {
 			bytes.Equal(existingRule.Src.Mask, rule.Src.Mask) &&
 			existingRule.Priority == rule.Priority &&
 			existingRule.Table == rule.Table {
-			return netlink.RuleDel(rule)
+			if err := netlink.RuleDel(rule); err != nil {
+				return fmt.Errorf("%w: for rule %q: %s", ErrRuleDel, rule, err)
+			}
 		}
 	}
 	return nil

internal/routing/outboundsubnets.go

@@ -1,14 +1,19 @@
 package routing
 
 import (
+	"errors"
 	"fmt"
 	"net"
 )
 
+var (
+	ErrAddOutboundSubnet = errors.New("cannot add outbound subnet to routes")
+)
+
 func (r *routing) SetOutboundRoutes(outboundSubnets []net.IPNet) error {
 	defaultInterface, defaultGateway, err := r.DefaultRoute()
 	if err != nil {
-		return fmt.Errorf("cannot set oubtound subnets in routing: %w", err)
+		return err
 	}
 	return r.setOutboundRoutes(outboundSubnets, defaultInterface, defaultGateway)
 }
@@ -27,7 +32,7 @@ func (r *routing) setOutboundRoutes(outboundSubnets []net.IPNet,
 
 	r.removeOutboundSubnets(subnetsToRemove, defaultInterfaceName, defaultGateway)
 	if err := r.addOutboundSubnets(subnetsToAdd, defaultInterfaceName, defaultGateway); err != nil {
-		return fmt.Errorf("cannot set outbound subnets in routing: %w", err)
+		return err
 	}
 
 	return nil
@@ -50,7 +55,7 @@ func (r *routing) addOutboundSubnets(subnets []net.IPNet,
 	for _, subnet := range subnets {
 		const table = 0
 		if err := r.addRouteVia(subnet, defaultGateway, defaultInterfaceName, table); err != nil {
-			return fmt.Errorf("cannot add outbound subnet %s to routing: %w", subnet, err)
+			return fmt.Errorf("%w: %s: %s", ErrAddOutboundSubnet, subnet, err)
 		}
 		r.outboundSubnets = append(r.outboundSubnets, subnet)
 	}

internal/routing/reader.go

@@ -2,6 +2,7 @@ package routing
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"net"
 
@@ -15,10 +16,28 @@ type LocalNetwork struct {
 	IP            net.IP
 }
 
+var (
+	ErrInterfaceIPNotFound       = errors.New("IP address not found for interface")
+	ErrInterfaceListAddr         = errors.New("cannot list interface addresses")
+	ErrInterfaceNotFound         = errors.New("network interface not found")
+	ErrLinkByIndex               = errors.New("cannot obtain link by index")
+	ErrLinkByName                = errors.New("cannot obtain link by name")
+	ErrLinkDefaultNotFound       = errors.New("default link not found")
+	ErrLinkList                  = errors.New("cannot list links")
+	ErrLinkLocalNotFound         = errors.New("local link not found")
+	ErrRouteDefaultNotFound      = errors.New("default route not found")
+	ErrRoutesList                = errors.New("cannot list routes")
+	ErrRulesList                 = errors.New("cannot list rules")
+	ErrSubnetDefaultNotFound     = errors.New("default subnet not found")
+	ErrSubnetLocalNotFound       = errors.New("local subnet not found")
+	ErrVPNDestinationIPNotFound  = errors.New("VPN destination IP address not found")
+	ErrVPNLocalGatewayIPNotFound = errors.New("VPN local gateway IP address not found")
+)
+
 func (r *routing) DefaultRoute() (defaultInterface string, defaultGateway net.IP, err error) {
 	routes, err := netlink.RouteList(nil, netlink.FAMILY_ALL)
 	if err != nil {
-		return "", nil, fmt.Errorf("cannot list routes: %w", err)
+		return "", nil, fmt.Errorf("%w: %s", ErrRoutesList, err)
 	}
 	for _, route := range routes {
 		if route.Dst == nil {
@@ -26,7 +45,7 @@ func (r *routing) DefaultRoute() (defaultInterface string, defaultGateway net.IP
 			linkIndex := route.LinkIndex
 			link, err := netlink.LinkByIndex(linkIndex)
 			if err != nil {
-				return "", nil, fmt.Errorf("cannot obtain link with index %d for default route: %w", linkIndex, err)
+				return "", nil, fmt.Errorf("%w: for default route at index %d: %s", ErrLinkByIndex, linkIndex, err)
 			}
 			attributes := link.Attrs()
 			defaultInterface = attributes.Name
@@ -36,13 +55,13 @@ func (r *routing) DefaultRoute() (defaultInterface string, defaultGateway net.IP
 			return defaultInterface, defaultGateway, nil
 		}
 	}
-	return "", nil, fmt.Errorf("cannot find default route in %d routes", len(routes))
+	return "", nil, fmt.Errorf("%w: in %d route(s)", ErrRouteDefaultNotFound, len(routes))
 }
 
 func (r *routing) DefaultIP() (ip net.IP, err error) {
 	routes, err := netlink.RouteList(nil, netlink.FAMILY_ALL)
 	if err != nil {
-		return nil, fmt.Errorf("cannot get default IP address: %w", err)
+		return nil, fmt.Errorf("%w: %s", ErrRoutesList, err)
 	}
 
 	defaultLinkName := ""
@@ -51,13 +70,13 @@ func (r *routing) DefaultIP() (ip net.IP, err error) {
 			linkIndex := route.LinkIndex
 			link, err := netlink.LinkByIndex(linkIndex)
 			if err != nil {
-				return nil, fmt.Errorf("cannot get default IP address: %w", err)
+				return nil, fmt.Errorf("%w: for default route at index %d: %s", ErrLinkByIndex, linkIndex, err)
 			}
 			defaultLinkName = link.Attrs().Name
 		}
 	}
 	if len(defaultLinkName) == 0 {
-		return nil, fmt.Errorf("cannot find default link name in %d routes", len(routes))
+		return nil, fmt.Errorf("%w: in %d route(s)", ErrLinkDefaultNotFound, len(routes))
 	}
 
 	return r.assignedIP(defaultLinkName)
@@ -66,7 +85,7 @@ func (r *routing) DefaultIP() (ip net.IP, err error) {
 func (r *routing) LocalSubnet() (defaultSubnet net.IPNet, err error) {
 	routes, err := netlink.RouteList(nil, netlink.FAMILY_ALL)
 	if err != nil {
-		return defaultSubnet, fmt.Errorf("cannot find local subnet: %w", err)
+		return defaultSubnet, fmt.Errorf("%w: %s", ErrRoutesList, err)
 	}
 
 	defaultLinkIndex := -1
@@ -77,7 +96,7 @@ func (r *routing) LocalSubnet() (defaultSubnet net.IPNet, err error) {
 		}
 	}
 	if defaultLinkIndex == -1 {
-		return defaultSubnet, fmt.Errorf("cannot find local subnet: cannot find default link")
+		return defaultSubnet, fmt.Errorf("%w: in %d route(s)", ErrLinkDefaultNotFound, len(routes))
 	}
 
 	for _, route := range routes {
@@ -91,13 +110,13 @@ func (r *routing) LocalSubnet() (defaultSubnet net.IPNet, err error) {
 		return defaultSubnet, nil
 	}
 
-	return defaultSubnet, fmt.Errorf("cannot find default subnet in %d routes", len(routes))
+	return defaultSubnet, fmt.Errorf("%w: in %d routes", ErrSubnetDefaultNotFound, len(routes))
 }
 
 func (r *routing) LocalNetworks() (localNetworks []LocalNetwork, err error) {
 	links, err := netlink.LinkList()
 	if err != nil {
-		return localNetworks, fmt.Errorf("cannot find local subnet: %w", err)
+		return localNetworks, fmt.Errorf("%w: %s", ErrLinkList, err)
 	}
 
 	localLinks := make(map[int]struct{})
@@ -114,12 +133,12 @@ func (r *routing) LocalNetworks() (localNetworks []LocalNetwork, err error) {
 	}
 
 	if len(localLinks) == 0 {
-		return localNetworks, fmt.Errorf("cannot find any local interfaces")
+		return localNetworks, fmt.Errorf("%w: in %d links", ErrLinkLocalNotFound, len(links))
 	}
 
 	routes, err := netlink.RouteList(nil, netlink.FAMILY_V4)
 	if err != nil {
-		return localNetworks, fmt.Errorf("cannot list local routes: %w", err)
+		return localNetworks, fmt.Errorf("%w: %s", ErrRoutesList, err)
 	}
 
 	for _, route := range routes {
@@ -138,14 +157,14 @@ func (r *routing) LocalNetworks() (localNetworks []LocalNetwork, err error) {
 
 		link, err := netlink.LinkByIndex(route.LinkIndex)
 		if err != nil {
-			return localNetworks, fmt.Errorf("cannot get link by index: %w", err)
+			return localNetworks, fmt.Errorf("%w: at index %d: %s", ErrLinkByIndex, route.LinkIndex, err)
 		}
 
 		localNet.InterfaceName = link.Attrs().Name
 
 		ip, err := r.assignedIP(localNet.InterfaceName)
 		if err != nil {
-			return localNetworks, fmt.Errorf("cannot get IP assigned to link: %w", err)
+			return localNetworks, err
 		}
 
 		localNet.IP = ip
@@ -154,7 +173,7 @@ func (r *routing) LocalNetworks() (localNetworks []LocalNetwork, err error) {
 	}
 
 	if len(localNetworks) == 0 {
-		return localNetworks, fmt.Errorf("cannot find any local networks across %d routes", len(routes))
+		return localNetworks, fmt.Errorf("%w: in %d routes", ErrSubnetLocalNotFound, len(routes))
 	}
 
 	return localNetworks, nil
@@ -163,11 +182,11 @@ func (r *routing) LocalNetworks() (localNetworks []LocalNetwork, err error) {
 func (r *routing) assignedIP(interfaceName string) (ip net.IP, err error) {
 	iface, err := net.InterfaceByName(interfaceName)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("%w: %s: %s", ErrInterfaceNotFound, interfaceName, err)
 	}
 	addresses, err := iface.Addrs()
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("%w: %s: %s", ErrInterfaceListAddr, interfaceName, err)
 	}
 	for _, address := range addresses {
 		switch value := address.(type) {
@@ -177,13 +196,14 @@ func (r *routing) assignedIP(interfaceName string) (ip net.IP, err error) {
 			return value.IP, nil
 		}
 	}
-	return nil, fmt.Errorf("IP address not found in addresses of interface %s", interfaceName)
+	return nil, fmt.Errorf("%w: interface %s in %d addresses",
+		ErrInterfaceIPNotFound, interfaceName, len(addresses))
 }
 
 func (r *routing) VPNDestinationIP() (ip net.IP, err error) {
 	routes, err := netlink.RouteList(nil, netlink.FAMILY_ALL)
 	if err != nil {
-		return nil, fmt.Errorf("cannot find VPN destination IP: %w", err)
+		return nil, fmt.Errorf("%w: %s", ErrRoutesList, err)
 	}
 
 	defaultLinkIndex := -1
@@ -194,7 +214,7 @@ func (r *routing) VPNDestinationIP() (ip net.IP, err error) {
 		}
 	}
 	if defaultLinkIndex == -1 {
-		return nil, fmt.Errorf("cannot find VPN destination IP: cannot find default link")
+		return nil, fmt.Errorf("%w: in %d route(s)", ErrLinkDefaultNotFound, len(routes))
 	}
 
 	for _, route := range routes {
@@ -205,18 +225,18 @@ func (r *routing) VPNDestinationIP() (ip net.IP, err error) {
 			return route.Dst.IP, nil
 		}
 	}
-	return nil, fmt.Errorf("cannot find VPN destination IP address from ip routes")
+	return nil, fmt.Errorf("%w: in %d routes", ErrVPNDestinationIPNotFound, len(routes))
 }
 
 func (r *routing) VPNLocalGatewayIP() (ip net.IP, err error) {
 	routes, err := netlink.RouteList(nil, netlink.FAMILY_ALL)
 	if err != nil {
-		return nil, fmt.Errorf("cannot find VPN local gateway IP: %w", err)
+		return nil, fmt.Errorf("%w: %s", ErrRoutesList, err)
 	}
 	for _, route := range routes {
 		link, err := netlink.LinkByIndex(route.LinkIndex)
 		if err != nil {
-			return nil, fmt.Errorf("cannot find VPN local gateway IP: %w", err)
+			return nil, fmt.Errorf("%w: %s", ErrLinkByIndex, err)
 		}
 		interfaceName := link.Attrs().Name
 		if interfaceName == string(constants.TUN) &&
@@ -225,7 +245,7 @@ func (r *routing) VPNLocalGatewayIP() (ip net.IP, err error) {
 			return route.Gw, nil
 		}
 	}
-	return nil, fmt.Errorf("cannot find VPN local gateway IP address from ip routes")
+	return nil, fmt.Errorf("%w: in %d routes", ErrVPNLocalGatewayIPNotFound, len(routes))
 }
 
 func IPIsPrivate(ip net.IP) bool {