Unified drain support for vmess and shadowsocks (#791)

* Added test for no terminate signal

* unified drain support for vmess and shadowsockets

* drain: add generated file

Co-authored-by: Shelikhoo <xiaokangwang@outlook.com>

common/drain/drain.go

@@ -0,0 +1,10 @@
+package drain
+
+import "io"
+
+//go:generate go run github.com/xtls/xray-core/common/errors/errorgen
+
+type Drainer interface {
+	AcknowledgeReceive(size int)
+	Drain(reader io.Reader) error
+}

common/drain/drainer.go

@@ -0,0 +1,62 @@
+package drain
+
+import (
+	"io"
+	"io/ioutil"
+
+	"github.com/xtls/xray-core/common/dice"
+)
+
+type BehaviorSeedLimitedDrainer struct {
+	DrainSize int
+}
+
+func NewBehaviorSeedLimitedDrainer(behaviorSeed int64, drainFoundation, maxBaseDrainSize, maxRandDrain int) (Drainer, error) {
+	behaviorRand := dice.NewDeterministicDice(behaviorSeed)
+	BaseDrainSize := behaviorRand.Roll(maxBaseDrainSize)
+	RandDrainMax := behaviorRand.Roll(maxRandDrain) + 1
+	RandDrainRolled := dice.Roll(RandDrainMax)
+	DrainSize := drainFoundation + BaseDrainSize + RandDrainRolled
+	return &BehaviorSeedLimitedDrainer{DrainSize: DrainSize}, nil
+}
+
+func (d *BehaviorSeedLimitedDrainer) AcknowledgeReceive(size int) {
+	d.DrainSize -= size
+}
+
+func (d *BehaviorSeedLimitedDrainer) Drain(reader io.Reader) error {
+	if d.DrainSize > 0 {
+		err := drainReadN(reader, d.DrainSize)
+		if err == nil {
+			return newError("drained connection")
+		}
+		return newError("unable to drain connection").Base(err)
+	}
+	return nil
+}
+
+func drainReadN(reader io.Reader, n int) error {
+	_, err := io.CopyN(ioutil.Discard, reader, int64(n))
+	return err
+}
+
+func WithError(drainer Drainer, reader io.Reader, err error) error {
+	drainErr := drainer.Drain(reader)
+	if drainErr == nil {
+		return err
+	}
+	return newError(drainErr).Base(err)
+}
+
+type NopDrainer struct{}
+
+func (n NopDrainer) AcknowledgeReceive(size int) {
+}
+
+func (n NopDrainer) Drain(reader io.Reader) error {
+	return nil
+}
+
+func NewNopDrainer() Drainer {
+	return &NopDrainer{}
+}

common/drain/errors.generated.go

@@ -0,0 +1,9 @@
+package drain
+
+import "github.com/xtls/xray-core/common/errors"
+
+type errPathObjHolder struct{}
+
+func newError(values ...interface{}) *errors.Error {
+	return errors.New(values...).WithPathObj(errPathObjHolder{})
+}