Feature: add ssr support (#805)

* Refactor ssr stream cipher to expose iv and key

References:
https://github.com/Dreamacro/go-shadowsocks2
https://github.com/sh4d0wfiend/go-shadowsocksr2

* Implement ssr obfs

Reference:
https://github.com/mzz2017/shadowsocksR

* Implement ssr protocol

References:
https://github.com/mzz2017/shadowsocksR
https://github.com/shadowsocksRb/shadowsocksr-libev
https://github.com/shadowsocksr-backup/shadowsocksr

component/ssr/protocol/auth_chain_b.go

@@ -0,0 +1,72 @@
+package protocol
+
+import (
+	"sort"
+
+	"github.com/Dreamacro/clash/component/ssr/tools"
+)
+
+func init() {
+	register("auth_chain_b", newAuthChainB)
+}
+
+func newAuthChainB(b *Base) Protocol {
+	return &authChain{
+		Base:       b,
+		authData:   &authData{},
+		salt:       "auth_chain_b",
+		hmac:       tools.HmacMD5,
+		hashDigest: tools.SHA1Sum,
+		rnd:        authChainBGetRandLen,
+	}
+}
+
+func initDataSize(r *authChain) {
+	random := &r.randomServer
+	random.InitFromBin(r.Key)
+	len := random.Next()%8 + 4
+	r.dataSizeList = make([]int, len)
+	for i := 0; i < int(len); i++ {
+		r.dataSizeList[i] = int(random.Next() % 2340 % 2040 % 1440)
+	}
+	sort.Ints(r.dataSizeList)
+
+	len = random.Next()%16 + 8
+	r.dataSizeList2 = make([]int, len)
+	for i := 0; i < int(len); i++ {
+		r.dataSizeList2[i] = int(random.Next() % 2340 % 2040 % 1440)
+	}
+	sort.Ints(r.dataSizeList2)
+}
+
+func authChainBGetRandLen(dataLength int, random *shift128PlusContext, lastHash []byte, dataSizeList, dataSizeList2 []int, overhead int) int {
+	if dataLength > 1440 {
+		return 0
+	}
+	random.InitFromBinDatalen(lastHash[:16], dataLength)
+	pos := sort.Search(len(dataSizeList), func(i int) bool { return dataSizeList[i] > dataLength+overhead })
+	finalPos := uint64(pos) + random.Next()%uint64(len(dataSizeList))
+	if finalPos < uint64(len(dataSizeList)) {
+		return dataSizeList[finalPos] - dataLength - overhead
+	}
+
+	pos = sort.Search(len(dataSizeList2), func(i int) bool { return dataSizeList2[i] > dataLength+overhead })
+	finalPos = uint64(pos) + random.Next()%uint64(len(dataSizeList2))
+	if finalPos < uint64(len(dataSizeList2)) {
+		return dataSizeList2[finalPos] - dataLength - overhead
+	}
+	if finalPos < uint64(pos+len(dataSizeList2)-1) {
+		return 0
+	}
+
+	if dataLength > 1300 {
+		return int(random.Next() % 31)
+	}
+	if dataLength > 900 {
+		return int(random.Next() % 127)
+	}
+	if dataLength > 400 {
+		return int(random.Next() % 521)
+	}
+	return int(random.Next() % 1021)
+}