cmd/serve: add serve docker command (#5415)

Fixes #4750

Co-authored-by: Ivan Andreev <ivandeex@gmail.com>

cmd/serve/docker/docker.go

@@ -0,0 +1,72 @@
+// Package docker serves a remote suitable for use with docker volume api
+package docker
+
+import (
+	"context"
+	"path/filepath"
+	"strings"
+	"syscall"
+
+	"github.com/spf13/cobra"
+
+	"github.com/rclone/rclone/cmd"
+	"github.com/rclone/rclone/cmd/mountlib"
+	"github.com/rclone/rclone/fs/config/flags"
+	"github.com/rclone/rclone/vfs"
+	"github.com/rclone/rclone/vfs/vfsflags"
+)
+
+var (
+	pluginName  = "rclone"
+	pluginScope = "local"
+	baseDir     = "/var/lib/docker-volumes/rclone"
+	sockDir     = "/run/docker/plugins"
+	defSpecDir  = "/etc/docker/plugins"
+	stateFile   = "docker-plugin.state"
+	socketAddr  = "" // TCP listening address or empty string for Unix socket
+	socketGid   = syscall.Getgid()
+	canPersist  = false // allows writing to config file
+	forgetState = false
+	noSpec      = false
+)
+
+func init() {
+	cmdFlags := Command.Flags()
+	// Add command specific flags
+	flags.StringVarP(cmdFlags, &baseDir, "base-dir", "", baseDir, "base directory for volumes")
+	flags.StringVarP(cmdFlags, &socketAddr, "socket-addr", "", socketAddr, "<host:port> or absolute path (default: /run/docker/plugins/rclone.sock)")
+	flags.IntVarP(cmdFlags, &socketGid, "socket-gid", "", socketGid, "GID for unix socket (default: current process GID)")
+	flags.BoolVarP(cmdFlags, &forgetState, "forget-state", "", forgetState, "skip restoring previous state")
+	flags.BoolVarP(cmdFlags, &noSpec, "no-spec", "", noSpec, "do not write spec file")
+	// Add common mount/vfs flags
+	mountlib.AddFlags(cmdFlags)
+	vfsflags.AddFlags(cmdFlags)
+}
+
+// Command definition for cobra
+var Command = &cobra.Command{
+	Use:   "docker",
+	Short: `Serve any remote on docker's volume plugin API.`,
+	Long:  strings.ReplaceAll(longHelp, "|", "`") + vfs.Help,
+
+	Run: func(command *cobra.Command, args []string) {
+		cmd.CheckArgs(0, 0, command, args)
+		cmd.Run(false, false, command, func() error {
+			ctx := context.Background()
+			drv, err := NewDriver(ctx, baseDir, nil, nil, false, forgetState)
+			if err != nil {
+				return err
+			}
+			srv := NewServer(drv)
+			if socketAddr == "" {
+				// Listen on unix socket at /run/docker/plugins/<pluginName>.sock
+				return srv.ServeUnix(pluginName, socketGid)
+			}
+			if filepath.IsAbs(socketAddr) {
+				// Listen on unix socket at given path
+				return srv.ServeUnix(socketAddr, socketGid)
+			}
+			return srv.ServeTCP(socketAddr, "", nil, noSpec)
+		})
+	},
+}