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>

command/network/cmd.go

@@ -26,6 +26,7 @@ func NewNetworkCommand(dockerCli *command.DockerCli) *cobra.Command {
 		newInspectCommand(dockerCli),
 		newListCommand(dockerCli),
 		newRemoveCommand(dockerCli),
+		NewPruneCommand(dockerCli),
 	)
 	return cmd
 }

command/network/prune.go

@@ -0,0 +1,72 @@
+package network
+
+import (
+	"fmt"
+
+	"golang.org/x/net/context"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/cli"
+	"github.com/docker/docker/cli/command"
+	"github.com/spf13/cobra"
+)
+
+type pruneOptions struct {
+	force bool
+}
+
+// NewPruneCommand returns a new cobra prune command for networks
+func NewPruneCommand(dockerCli *command.DockerCli) *cobra.Command {
+	var opts pruneOptions
+
+	cmd := &cobra.Command{
+		Use:   "prune [OPTIONS]",
+		Short: "Remove all unused networks",
+		Args:  cli.NoArgs,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			output, err := runPrune(dockerCli, opts)
+			if err != nil {
+				return err
+			}
+			if output != "" {
+				fmt.Fprintln(dockerCli.Out(), output)
+			}
+			return nil
+		},
+	}
+
+	flags := cmd.Flags()
+	flags.BoolVarP(&opts.force, "force", "f", false, "Do not prompt for confirmation")
+
+	return cmd
+}
+
+const warning = `WARNING! This will remove all networks not used by at least one container.
+Are you sure you want to continue?`
+
+func runPrune(dockerCli *command.DockerCli, opts pruneOptions) (output string, err error) {
+	if !opts.force && !command.PromptForConfirmation(dockerCli.In(), dockerCli.Out(), warning) {
+		return
+	}
+
+	report, err := dockerCli.Client().NetworksPrune(context.Background(), types.NetworksPruneConfig{})
+	if err != nil {
+		return
+	}
+
+	if len(report.NetworksDeleted) > 0 {
+		output = "Deleted Networks:\n"
+		for _, id := range report.NetworksDeleted {
+			output += id + "\n"
+		}
+	}
+
+	return
+}
+
+// RunPrune calls the Network Prune API
+// This returns the amount of space reclaimed and a detailed output string
+func RunPrune(dockerCli *command.DockerCli) (uint64, string, error) {
+	output, err := runPrune(dockerCli, pruneOptions{force: true})
+	return 0, output, err
+}

command/prune/prune.go

@@ -4,6 +4,7 @@ import (
 	"github.com/docker/docker/cli/command"
 	"github.com/docker/docker/cli/command/container"
 	"github.com/docker/docker/cli/command/image"
+	"github.com/docker/docker/cli/command/network"
 	"github.com/docker/docker/cli/command/volume"
 	"github.com/spf13/cobra"
 )
@@ -23,6 +24,11 @@ func NewImagePruneCommand(dockerCli *command.DockerCli) *cobra.Command {
 	return image.NewPruneCommand(dockerCli)
 }
 
+// NewNetworkPruneCommand returns a cobra prune command for Networks
+func NewNetworkPruneCommand(dockerCli *command.DockerCli) *cobra.Command {
+	return network.NewPruneCommand(dockerCli)
+}
+
 // RunContainerPrune executes a prune command for containers
 func RunContainerPrune(dockerCli *command.DockerCli) (uint64, string, error) {
 	return container.RunPrune(dockerCli)
@@ -37,3 +43,8 @@ func RunVolumePrune(dockerCli *command.DockerCli) (uint64, string, error) {
 func RunImagePrune(dockerCli *command.DockerCli, all bool) (uint64, string, error) {
 	return image.RunPrune(dockerCli, all)
 }
+
+// RunNetworkPrune executes a prune command for networks
+func RunNetworkPrune(dockerCli *command.DockerCli) (uint64, string, error) {
+	return network.RunPrune(dockerCli)
+}

command/system/prune.go

@@ -39,6 +39,7 @@ const (
 	warning = `WARNING! This will remove:
 	- all stopped containers
 	- all volumes not used by at least one container
+	- all networks not used by at least one container
 	%s
 Are you sure you want to continue?`
 
@@ -64,13 +65,14 @@ func runPrune(dockerCli *command.DockerCli, opts pruneOptions) error {
 	for _, pruneFn := range []func(dockerCli *command.DockerCli) (uint64, string, error){
 		prune.RunContainerPrune,
 		prune.RunVolumePrune,
+		prune.RunNetworkPrune,
 	} {
 		spc, output, err := pruneFn(dockerCli)
 		if err != nil {
 			return err
 		}
-		if spc > 0 {
 		spaceReclaimed += spc
+		if output != "" {
 			fmt.Fprintln(dockerCli.Out(), output)
 		}
 	}