add docker network prune

`docker network prune` prunes unused networks, including overlay ones.
`docker system prune` also prunes unused networks.

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
Upstream-commit: 7e24c16086a9a4f38e241e51837f2be4877c04a6
Component: engine

components/engine/daemon/cluster.go

@@ -0,0 +1,12 @@
+package daemon
+
+import (
+	apitypes "github.com/docker/docker/api/types"
+)
+
+// Cluster is the interface for github.com/docker/docker/daemon/cluster.(*Cluster).
+type Cluster interface {
+	GetNetwork(input string) (apitypes.NetworkResource, error)
+	GetNetworks() ([]apitypes.NetworkResource, error)
+	RemoveNetwork(input string) error
+}

components/engine/daemon/daemon.go

@@ -102,6 +102,7 @@ type Daemon struct {
 	containerdRemote          libcontainerd.Remote
 	defaultIsolation          containertypes.Isolation // Default isolation mode on Windows
 	clusterProvider           cluster.Provider
+	cluster                   Cluster
 }
 
 // HasExperimental returns whether the experimental features of the daemon are enabled or not
@@ -1234,3 +1235,13 @@ func copyBlkioEntry(entries []*containerd.BlkioStatsEntry) []types.BlkioStatEntr
 	}
 	return out
 }
+
+// GetCluster returns the cluster
+func (daemon *Daemon) GetCluster() Cluster {
+	return daemon.cluster
+}
+
+// SetCluster sets the cluster
+func (daemon *Daemon) SetCluster(cluster Cluster) {
+	daemon.cluster = cluster
+}

components/engine/daemon/prune.go

@@ -1,6 +1,8 @@
 package daemon
 
 import (
+	"regexp"
+
 	"github.com/Sirupsen/logrus"
 	"github.com/docker/distribution/digest"
 	"github.com/docker/docker/api/types"
@@ -8,7 +10,9 @@ import (
 	"github.com/docker/docker/layer"
 	"github.com/docker/docker/pkg/directory"
 	"github.com/docker/docker/reference"
+	"github.com/docker/docker/runconfig"
 	"github.com/docker/docker/volume"
+	"github.com/docker/libnetwork"
 )
 
 // ContainersPrune removes unused containers
@@ -150,3 +154,72 @@ func (daemon *Daemon) ImagesPrune(config *types.ImagesPruneConfig) (*types.Image
 
 	return rep, nil
 }
+
+// localNetworksPrune removes unused local networks
+func (daemon *Daemon) localNetworksPrune(config *types.NetworksPruneConfig) (*types.NetworksPruneReport, error) {
+	rep := &types.NetworksPruneReport{}
+	var err error
+	// When the function returns true, the walk will stop.
+	l := func(nw libnetwork.Network) bool {
+		nwName := nw.Name()
+		predefined := runconfig.IsPreDefinedNetwork(nwName)
+		if !predefined && len(nw.Endpoints()) == 0 {
+			if err = daemon.DeleteNetwork(nw.ID()); err != nil {
+				logrus.Warnf("could not remove network %s: %v", nwName, err)
+				return false
+			}
+			rep.NetworksDeleted = append(rep.NetworksDeleted, nwName)
+		}
+		return false
+	}
+	daemon.netController.WalkNetworks(l)
+	return rep, err
+}
+
+// clusterNetworksPrune removes unused cluster networks
+func (daemon *Daemon) clusterNetworksPrune(config *types.NetworksPruneConfig) (*types.NetworksPruneReport, error) {
+	rep := &types.NetworksPruneReport{}
+	cluster := daemon.GetCluster()
+	networks, err := cluster.GetNetworks()
+	if err != nil {
+		return rep, err
+	}
+	networkIsInUse := regexp.MustCompile(`network ([[:alnum:]]+) is in use`)
+	for _, nw := range networks {
+		if nw.Name == "ingress" {
+			continue
+		}
+		// https://github.com/docker/docker/issues/24186
+		// `docker network inspect` unfortunately displays ONLY those containers that are local to that node.
+		// So we try to remove it anyway and check the error
+		err = cluster.RemoveNetwork(nw.ID)
+		if err != nil {
+			// we can safely ignore the "network .. is in use" error
+			match := networkIsInUse.FindStringSubmatch(err.Error())
+			if len(match) != 2 || match[1] != nw.ID {
+				logrus.Warnf("could not remove network %s: %v", nw.Name, err)
+			}
+			continue
+		}
+		rep.NetworksDeleted = append(rep.NetworksDeleted, nw.Name)
+	}
+	return rep, nil
+}
+
+// NetworksPrune removes unused networks
+func (daemon *Daemon) NetworksPrune(config *types.NetworksPruneConfig) (*types.NetworksPruneReport, error) {
+	rep := &types.NetworksPruneReport{}
+	clusterRep, err := daemon.clusterNetworksPrune(config)
+	if err != nil {
+		logrus.Warnf("could not remove cluster networks: %v", err)
+	} else {
+		rep.NetworksDeleted = append(rep.NetworksDeleted, clusterRep.NetworksDeleted...)
+	}
+	localRep, err := daemon.localNetworksPrune(config)
+	if err != nil {
+		logrus.Warnf("could not remove local networks: %v", err)
+	} else {
+		rep.NetworksDeleted = append(rep.NetworksDeleted, localRep.NetworksDeleted...)
+	}
+	return rep, err
+}