vfs: add vfs/poll-interval rc command

This command can be used to query the current status of the
poll-interval option and also update the value.

vfs/rc.go

@@ -3,6 +3,7 @@ package vfs
 import (
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/ncw/rclone/fs"
 	"github.com/ncw/rclone/fs/rc"
@@ -166,6 +167,128 @@ starting with dir will refresh that directory, eg
 If the parameter recursive=true is given the whole directory tree
 will get refreshed. This refresh will use --fast-list if enabled.
 
+`,
+	})
+	rc.Add(rc.Call{
+		Path:  "vfs/poll-interval",
+		Fn:    rcPollFunc(vfs),
+		Title: "Get the status or update the value of the poll-interval option.",
+		Help: `
+Without any parameter given this returns the current status of the
+poll-interval setting.
+
+When the interval=duration parameter is set, the poll-interval value
+is updated and the polling function is notified.
+Setting interval=0 disables poll-interval.
+
+    rclone rc vfs/poll-interval interval=5m
+
+The timeout=duration parameter can be used to specify a time to wait
+for the current poll function to apply the new value.
+If timeout is less or equal 0, which is the default, wait indefinitely.
+
+The new poll-interval value will only be active when the timeout is
+not reached.
+
+If poll-interval is updated or disabled temporarily, some changes
+might not get picked up by the polling function, depending on the
+used remote.
 `,
 	})
 }
+
+func rcPollFunc(vfs *VFS) (rcPollFunc rc.Func) {
+	getDuration := func(k string, v interface{}) (time.Duration, error) {
+		s, ok := v.(string)
+		if !ok {
+			return 0, errors.Errorf("value must be string %q=%v", k, v)
+		}
+		interval, err := fs.ParseDuration(s)
+		if err != nil {
+			return 0, errors.Wrap(err, "parse duration")
+		}
+		return interval, nil
+	}
+	getInterval := func(in rc.Params) (time.Duration, bool, error) {
+		k := "interval"
+		v, ok := in[k]
+		if !ok {
+			return 0, false, nil
+		}
+		interval, err := getDuration(k, v)
+		if err != nil {
+			return 0, true, err
+		}
+		if interval < 0 {
+			return 0, true, errors.New("interval must be >= 0")
+		}
+		delete(in, k)
+		return interval, true, nil
+	}
+	getTimeout := func(in rc.Params) (time.Duration, error) {
+		k := "timeout"
+		v, ok := in[k]
+		if !ok {
+			return 10 * time.Second, nil
+		}
+		timeout, err := getDuration(k, v)
+		if err != nil {
+			return 0, err
+		}
+		delete(in, k)
+		return timeout, nil
+	}
+
+	_status := func(in rc.Params) (out rc.Params, err error) {
+		for k, v := range in {
+			return nil, errors.Errorf("invalid parameter: %s=%s", k, v)
+		}
+		return rc.Params{
+			"enabled":   vfs.Opt.PollInterval != 0,
+			"supported": vfs.pollChan != nil,
+			"interval": map[string]interface{}{
+				"raw":     vfs.Opt.PollInterval,
+				"seconds": vfs.Opt.PollInterval / time.Second,
+				"string":  vfs.Opt.PollInterval.String(),
+			},
+		}, nil
+	}
+	return func(in rc.Params) (out rc.Params, err error) {
+		interval, intervalPresent, err := getInterval(in)
+		if err != nil {
+			return nil, err
+		}
+		timeout, err := getTimeout(in)
+		if err != nil {
+			return nil, err
+		}
+		for k, v := range in {
+			return nil, errors.Errorf("invalid parameter: %s=%s", k, v)
+		}
+		if vfs.pollChan == nil {
+			return nil, errors.New("poll-interval is not supported by this remote")
+		}
+
+		if !intervalPresent {
+			return _status(in)
+		}
+		var timeoutHit bool
+		var timeoutChan <-chan time.Time
+		if timeout > 0 {
+			timer := time.NewTimer(timeout)
+			defer timer.Stop()
+			timeoutChan = timer.C
+		}
+		select {
+		case vfs.pollChan <- interval:
+			vfs.Opt.PollInterval = interval
+		case <-timeoutChan:
+			timeoutHit = true
+		}
+		out, err = _status(in)
+		if out != nil {
+			out["timeout"] = timeoutHit
+		}
+		return
+	}
+}