refactor: move decipher to file

decipher.go

@@ -0,0 +1,217 @@
+package youtube
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net/url"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+func (y *Youtube) parseDecipherOpsAndArgs() (operations []string, args []int, err error) {
+	/// try to get whole page
+	client, err := y.getHTTPClient()
+	if err != nil {
+		return nil, nil, fmt.Errorf("get http client error=%s", err)
+	}
+
+	if y.VideoID == "" {
+		return nil, nil, fmt.Errorf("video id is empty , err=%s", err)
+	}
+	embedUrl := fmt.Sprintf("https://youtube.com/embed/%s?hl=en", y.VideoID)
+
+	embeddedPageResp, err := client.Get(embedUrl)
+	if err != nil {
+		return nil, nil, err
+	}
+	defer embeddedPageResp.Body.Close()
+
+	if embeddedPageResp.StatusCode != 200 {
+		return nil, nil, err
+	}
+
+	embeddedPageBodyBytes, err := ioutil.ReadAll(embeddedPageResp.Body)
+	if err != nil {
+		return nil, nil, err
+	}
+	embeddedPage := string(embeddedPageBodyBytes)
+
+	playerConfigPattern := regexp.MustCompile("yt\\.setConfig\\({'PLAYER_CONFIG':(.*)}\\);")
+	playerConfig := playerConfigPattern.FindString(embeddedPage)
+
+	basejsPattern := regexp.MustCompile(`"js":"\\/s\\/player(.*)base\.js`)
+	//eg: "js":\"\/s\/player\/f676c671\/player_ias.vflset\/en_US\/base.js
+	escapedBasejsUrl := basejsPattern.FindString(playerConfig)
+	//eg: ["js", "\/s\/player\/f676c671\/player_ias.vflset\/en_US\/base.js]
+	arr := strings.Split(escapedBasejsUrl, ":\"")
+	basejsUrl := "https://youtube.com" + strings.ReplaceAll(arr[len(arr)-1], "\\", "")
+	basejsUrlResp, err := client.Get(basejsUrl)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	defer basejsUrlResp.Body.Close()
+	if basejsUrlResp.StatusCode != 200 {
+		return nil, nil, err
+	}
+
+	basejsBodyBytes, err := ioutil.ReadAll(basejsUrlResp.Body)
+	if err != nil {
+		return nil, nil, err
+	}
+	basejs := string(basejsBodyBytes)
+
+	// regex to get name of decipher function
+	decipherFuncNamePattern := regexp.MustCompile(`(\w+)=function\(\w+\){(\w+)=(\w+)\.split\(\x22{2}\);.*?return\s+(\w+)\.join\(\x22{2}\)}`)
+
+	// Ft=function(a){a=a.split("");Et.vw(a,2);Et.Zm(a,4);Et.Zm(a,46);Et.vw(a,2);Et.Zm(a,34);Et.Zm(a,59);Et.cn(a,42);return a.join("")} => get Ft
+	arr = decipherFuncNamePattern.FindStringSubmatch(basejs)
+	funcName := arr[1]
+	decipherFuncBodyPattern := regexp.MustCompile(fmt.Sprintf(`[^h\.]%s=function\(\w+\)\{(.*?)\}`, funcName))
+
+	// eg: get a=a.split("");Et.vw(a,2);Et.Zm(a,4);Et.Zm(a,46);Et.vw(a,2);Et.Zm(a,34);Et.Zm(a,59);Et.cn(a,42);return a.join("")
+	arr = decipherFuncBodyPattern.FindStringSubmatch(basejs)
+	decipherFuncBody := arr[1]
+
+	// FuncName in Body => get Et
+	funcNameInBodyRegex := regexp.MustCompile(`(\w+).\w+\(\w+,\d+\);`)
+	arr = funcNameInBodyRegex.FindStringSubmatch(decipherFuncBody)
+	funcNameInBody := arr[1]
+	decipherDefBodyRegex := regexp.MustCompile(fmt.Sprintf(`var\s+%s=\{(\w+:function\(\w+(,\w+)?\)\{(.*?)\}),?\};`, funcNameInBody))
+	re := regexp.MustCompile(`\r?\n`)
+	basejs = re.ReplaceAllString(basejs, "")
+	arr1 := decipherDefBodyRegex.FindStringSubmatch(basejs)
+
+	// eg:  vw:function(a,b){a.splice(0,b)},cn:function(a){a.reverse()},Zm:function(a,b){var c=a[0];a[0]=a[b%a.length];a[b%a.length]=c}
+	decipherDefBody := arr1[1]
+	// eq:  [ a=a.split("") , Et.vw(a,2) , Et.Zm(a,4) , Et.Zm(a,46) , Et.vw(a,2) , Et.Zm(a,34), Et.Zm(a,59) , Et.cn(a,42) , return a.join("") ]
+	decipherFuncs := strings.Split(decipherFuncBody, ";")
+
+	var funcSeq []string
+	var funcArgs []int
+
+	for _, v := range decipherFuncs {
+		//calledFuncNameRegex \w+(?:.|\[)("?\w+(?:")?)\]?\(
+		//eg: Et.vw(a,2) => vw
+		calledFuncNameRegex, err := regexp.Compile(`\w+(?:.|\[)("?\w+(?:")?)\]?\(`)
+		if err != nil {
+			return nil, nil, err
+		}
+		arr := calledFuncNameRegex.FindStringSubmatch(v)
+		if len(arr) < 1 || arr[1] == "" {
+			continue
+		}
+		calledFuncName := arr[1]
+
+		// Et.vw(a,2) => [a, 2]
+		funcArgRegex := regexp.MustCompile(`\(\w+,(\d+)\)`)
+
+		// splice
+		spliceFuncPattern := fmt.Sprintf(`%s:\bfunction\b\([a],b\).(\breturn\b)?.?\w+\.splice`, calledFuncName)
+		if regexp.MustCompile(spliceFuncPattern).MatchString(decipherDefBody) {
+			arr := funcArgRegex.FindStringSubmatch(v)
+			arg, err := strconv.Atoi(arr[1])
+			if err != nil {
+				return nil, nil, err
+			}
+			funcSeq = append(funcSeq, "splice")
+			funcArgs = append(funcArgs, arg)
+			continue
+		}
+
+		// Swap
+		swapFuncPattern := fmt.Sprintf(`%s:\bfunction\b\(\w+\,\w\).\bvar\b.\bc=a\b`, calledFuncName)
+		if regexp.MustCompile(swapFuncPattern).MatchString(decipherDefBody) {
+			arr := funcArgRegex.FindStringSubmatch(v)
+			arg, err := strconv.Atoi(arr[1])
+			if err != nil {
+				return nil, nil, err
+			}
+			funcSeq = append(funcSeq, "swap")
+			funcArgs = append(funcArgs, arg)
+			continue
+		}
+
+		// Reverse
+		reverseFuncPattern := fmt.Sprintf(`%s:\bfunction\b\(\w+\)`, calledFuncName)
+		if regexp.MustCompile(reverseFuncPattern).MatchString(decipherDefBody) {
+			arr := funcArgRegex.FindStringSubmatch(v)
+			arg, err := strconv.Atoi(arr[1])
+			if err != nil {
+				return nil, nil, err
+			}
+			funcSeq = append(funcSeq, "reverse")
+			funcArgs = append(funcArgs, arg)
+			continue
+		}
+	}
+	return funcSeq, funcArgs, nil
+}
+
+func (y *Youtube) decipher(cipher string) (string, error) {
+	queryParams, err := url.ParseQuery(cipher)
+	if err != nil {
+		return "", err
+	}
+	cipherMap := make(map[string]string)
+	for key, value := range queryParams {
+		cipherMap[key] = strings.Join(value, "")
+	}
+	/* eg:
+	    extract decipher from  https://youtube.com/s/player/4fbb4d5b/player_ias.vflset/en_US/base.js
+
+	    var Mt={
+		splice:function(a,b){a.splice(0,b)},
+		reverse:function(a){a.reverse()},
+		EQ:function(a,b){var c=a[0];a[0]=a[b%a.length];a[b%a.length]=c}};
+
+		a=a.split("");
+		Mt.splice(a,3);
+		Mt.EQ(a,39);
+		Mt.splice(a,2);
+		Mt.EQ(a,1);
+		Mt.splice(a,1);
+		Mt.EQ(a,35);
+		Mt.EQ(a,51);
+		Mt.splice(a,2);
+		Mt.reverse(a,52);
+		return a.join("")
+	*/
+
+	s := cipherMap["s"]
+	bs := []byte(s)
+	splice := func(b int) {
+		bs = bs[b:]
+	}
+	swap := func(b int) {
+		pos := b % len(bs)
+		bs[0], bs[pos] = bs[pos], bs[0]
+	}
+	reverse := func(options ...interface{}) {
+		l, r := 0, len(bs)-1
+		for l < r {
+			bs[l], bs[r] = bs[r], bs[l]
+			l++
+			r--
+		}
+	}
+	operations, args, err := y.parseDecipherOpsAndArgs()
+	if err != nil {
+		return "", err
+	}
+	for i, op := range operations {
+		switch op {
+		case "splice":
+			splice(args[i])
+		case "swap":
+			swap(args[i])
+		case "reverse":
+			reverse(args[i])
+		}
+	}
+	cipherMap["s"] = string(bs)
+
+	decipheredUrl := fmt.Sprintf("%s&%s=%s", cipherMap["url"], cipherMap["sp"], cipherMap["s"])
+	return decipheredUrl, nil
+}