fs: Add --disable flag to disable optional features - fixes #1551

Eg to disable server side copy use `--disable copy`, to see a list of
what you can disable, `--disable help`.

fs/config.go

@@ -100,6 +100,7 @@ var (
 	tpsLimit        = Float64P("tpslimit", "", 0, "Limit HTTP transactions per second to this.")
 	tpsLimitBurst   = IntP("tpslimit-burst", "", 1, "Max burst of transactions for --tpslimit.")
 	bindAddr        = StringP("bind", "", "", "Local address to bind to for outgoing connections, IPv4, IPv6 or name.")
+	disableFeatures = StringP("disable", "", "", "Disable a comma separated list of features.  Use help to see a list.")
 	logLevel        = LogLevelNotice
 	statsLogLevel   = LogLevelInfo
 	bwLimit         BwTimetable
@@ -235,6 +236,7 @@ type ConfigInfo struct {
 	TPSLimit           float64
 	TPSLimitBurst      int
 	BindAddr           net.IP
+	DisableFeatures    []string
 }
 
 // Return the path to the configuration file
@@ -410,6 +412,13 @@ func LoadConfig() {
 		Config.BindAddr = addrs[0]
 	}
 
+	if *disableFeatures != "" {
+		if *disableFeatures == "help" {
+			log.Fatalf("Possible backend features are: %s\n", strings.Join(new(Features).List(), ", "))
+		}
+		Config.DisableFeatures = strings.Split(*disableFeatures, ",")
+	}
+
 	// Load configuration file.
 	var err error
 	ConfigPath, err = filepath.Abs(*configFile)

fs/fs.go

@@ -8,8 +8,10 @@ import (
 	"math"
 	"os"
 	"path/filepath"
+	"reflect"
 	"regexp"
 	"sort"
+	"strings"
 	"time"
 
 	"github.com/pkg/errors"
@@ -347,6 +349,46 @@ type Features struct {
 	ListR ListRFn
 }
 
+// Disable nil's out the named feature.  If it isn't found then it
+// will log a message.
+func (ft *Features) Disable(name string) *Features {
+	v := reflect.ValueOf(ft).Elem()
+	vType := v.Type()
+	for i := 0; i < v.NumField(); i++ {
+		vName := vType.Field(i).Name
+		field := v.Field(i)
+		if strings.EqualFold(name, vName) {
+			if !field.CanSet() {
+				Errorf(nil, "Can't set Feature %q", name)
+			} else {
+				zero := reflect.Zero(field.Type())
+				field.Set(zero)
+				Debugf(nil, "Reset feature %q", name)
+			}
+		}
+	}
+	return ft
+}
+
+// List returns a slice of all the possible feature names
+func (ft *Features) List() (out []string) {
+	v := reflect.ValueOf(ft).Elem()
+	vType := v.Type()
+	for i := 0; i < v.NumField(); i++ {
+		out = append(out, vType.Field(i).Name)
+	}
+	return out
+}
+
+// DisableList nil's out the comma separated list of named features.
+// If it isn't found then it will log a message.
+func (ft *Features) DisableList(list []string) *Features {
+	for _, feature := range list {
+		ft.Disable(strings.TrimSpace(feature))
+	}
+	return ft
+}
+
 // Fill fills in the function pointers in the Features struct from the
 // optional interfaces.  It returns the original updated Features
 // struct passed in.
@@ -387,7 +429,7 @@ func (ft *Features) Fill(f Fs) *Features {
 	if do, ok := f.(ListRer); ok {
 		ft.ListR = do.ListR
 	}
-	return ft
+	return ft.DisableList(Config.DisableFeatures)
 }
 
 // Mask the Features with the Fs passed in
@@ -438,7 +480,7 @@ func (ft *Features) Mask(f Fs) *Features {
 	if mask.ListR == nil {
 		ft.ListR = nil
 	}
-	return ft
+	return ft.DisableList(Config.DisableFeatures)
 }
 
 // Wrap makes a Copy of the features passed in, overriding the UnWrap

fs/fs_test.go

@@ -0,0 +1,54 @@
+package fs
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFeaturesDisable(t *testing.T) {
+	ft := new(Features)
+	ft.Copy = func(src Object, remote string) (Object, error) {
+		return nil, nil
+	}
+	ft.CaseInsensitive = true
+
+	assert.NotNil(t, ft.Copy)
+	assert.Nil(t, ft.Purge)
+	ft.Disable("copy")
+	assert.Nil(t, ft.Copy)
+	assert.Nil(t, ft.Purge)
+
+	assert.True(t, ft.CaseInsensitive)
+	assert.False(t, ft.DuplicateFiles)
+	ft.Disable("caseinsensitive")
+	assert.False(t, ft.CaseInsensitive)
+	assert.False(t, ft.DuplicateFiles)
+}
+
+func TestFeaturesList(t *testing.T) {
+	ft := new(Features)
+	names := strings.Join(ft.List(), ",")
+	assert.True(t, strings.Contains(names, ",Copy,"))
+}
+
+func TestFeaturesDisableList(t *testing.T) {
+	ft := new(Features)
+	ft.Copy = func(src Object, remote string) (Object, error) {
+		return nil, nil
+	}
+	ft.CaseInsensitive = true
+
+	assert.NotNil(t, ft.Copy)
+	assert.Nil(t, ft.Purge)
+	assert.True(t, ft.CaseInsensitive)
+	assert.False(t, ft.DuplicateFiles)
+
+	ft.DisableList([]string{"copy", "caseinsensitive"})
+
+	assert.Nil(t, ft.Copy)
+	assert.Nil(t, ft.Purge)
+	assert.False(t, ft.CaseInsensitive)
+	assert.False(t, ft.DuplicateFiles)
+}