init
This commit is contained in:
r4
245
extractor/youtube/youtube_decrypt.go
Normal file
245
extractor/youtube/youtube_decrypt.go
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package youtube
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import (
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exutil "git.nobrain.org/r4/dischord/extractor/util"
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"encoding/json"
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"errors"
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"io"
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"net/http"
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"regexp"
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"strconv"
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"strings"
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)
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var (
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ErrDecryptGettingFunctionName = errors.New("error getting signature decryption function name")
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ErrDecryptGettingFunction = errors.New("error getting signature decryption function")
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ErrDecryptGettingOpTable = errors.New("error getting signature decryption operation table")
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ErrGettingBaseJs = errors.New("unable to get base.js")
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)
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type decryptorOp struct {
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fn func(a *string, b int)
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arg int
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}
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type decryptor struct {
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// base.js version ID, used for caching
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versionId string
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// The actual decryption algorithm can be split up into a list of known
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// operations
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ops []decryptorOp
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}
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func (d *decryptor) decrypt(input string) (string, error) {
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if err := updateDecryptor(d); err != nil {
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return "", err
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}
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s := input
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for _, op := range d.ops {
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op.fn(&s, op.arg)
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}
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return s, nil
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}
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type configData struct {
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PlayerJsUrl string `json:"PLAYER_JS_URL"`
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}
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func updateDecryptor(d *decryptor) error {
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prefix := "(function() {window.ytplayer={};\nytcfg.set("
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endStr := ");"
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// Get base.js URL
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var url string
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var funcErr error
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err := exutil.GetHTMLScriptFunc("https://www.youtube.com", false, func(code string) bool {
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if strings.HasPrefix(code, prefix) {
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// Cut out the JSON part
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code = code[len(prefix):]
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end := strings.Index(code, endStr)
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if end == -1 {
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funcErr = ErrGettingBaseJs
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return false
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}
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// Parse config data
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var data configData
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if err := json.Unmarshal([]byte(code[:end]), &data); err != nil {
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funcErr = ErrGettingBaseJs
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return false
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}
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url = "https://www.youtube.com" + data.PlayerJsUrl
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return false
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}
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return true
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})
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if err != nil {
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return err
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}
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if funcErr != nil {
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return err
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}
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// Get base.js version ID
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sp := strings.SplitN(strings.TrimPrefix(url, "/s/player/"), "/", 2)
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if len(sp) != 2 {
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return ErrGettingBaseJs
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}
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verId := sp[0]
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if d.versionId == verId {
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// Decryptor already up-to-date
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return nil
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}
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// Get base.js contents
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resp, err := http.Get(url)
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if err != nil {
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return err
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}
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defer resp.Body.Close()
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if resp.StatusCode != 200 {
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return ErrGettingBaseJs
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}
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// Copy contents to buffer
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buf := new(strings.Builder)
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_, err = io.Copy(buf, resp.Body)
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if err != nil {
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return err
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}
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// Get decryption operations
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ops, err := getDecryptOps(buf.String())
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if err != nil {
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return err
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}
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d.versionId = verId
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d.ops = ops
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return nil
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}
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var decryptFunctionNameRegexp = regexp.MustCompile(`[a-zA-Z]*&&\([a-zA-Z]*=([a-zA-Z]*)\(decodeURIComponent\([a-zA-Z]*\)\),[a-zA-Z]*\.set\([a-zA-Z]*,encodeURIComponent\([a-zA-Z]*\)\)\)`)
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func getDecryptFunction(baseJs string) (string, error) {
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idx := decryptFunctionNameRegexp.FindSubmatchIndex([]byte(baseJs))
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if len(idx) != 4 {
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return "", ErrDecryptGettingFunctionName
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}
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fnName := baseJs[idx[2]:idx[3]]
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startMatch := fnName + `=function(a){a=a.split("");`
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endMatch := `;return a.join("")};`
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start := strings.Index(baseJs, startMatch)
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if start == -1 {
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return "", ErrDecryptGettingFunction
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}
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fn := baseJs[start+len(startMatch):]
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end := strings.Index(fn, endMatch)
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if start == -1 {
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return "", ErrDecryptGettingFunction
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}
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return fn[:end], nil
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}
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func getDecryptOps(baseJs string) ([]decryptorOp, error) {
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// Extract main decryptor function JS
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decrFn, err := getDecryptFunction(baseJs)
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if err != nil {
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return nil, err
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}
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// Get decyptor operation JS
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var ops string
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{
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sp := strings.SplitN(decrFn, ".", 2)
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if len(sp) != 2 {
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return nil, ErrDecryptGettingOpTable
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}
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opsObjName := sp[0]
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startMatch := `var ` + opsObjName + `={`
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endMatch := `};`
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start := strings.Index(baseJs, startMatch)
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if start == -1 {
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return nil, ErrDecryptGettingOpTable
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}
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ops = baseJs[start+len(startMatch):]
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end := strings.Index(ops, endMatch)
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if start == -1 {
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return nil, ErrDecryptGettingOpTable
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}
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ops = ops[:end]
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}
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// Make a decryptor operation table that associates the operation
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// names with a specific action on an input string
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opTable := make(map[string]func(a *string, b int))
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{
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lns := strings.Split(ops, "\n")
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if len(lns) != 3 {
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return nil, ErrDecryptGettingOpTable
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}
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for _, ln := range lns {
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sp := strings.Split(ln, ":")
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if len(sp) != 2 {
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return nil, ErrDecryptGettingOpTable
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}
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name := sp[0]
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fn := sp[1]
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switch {
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case strings.HasPrefix(fn, `function(a){a.reverse()}`):
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opTable[name] = func(a *string, b int) {
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// Reverse a
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var res string
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for _, c := range *a {
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res = string(c) + res
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}
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*a = res
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}
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case strings.HasPrefix(fn, `function(a,b){var c=a[0];a[0]=a[b%a.length];a[b%a.length]=c}`):
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opTable[name] = func(a *string, b int) {
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// Swap a[0] and a[b % len(a)]
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c := []byte(*a)
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c[0], c[b%len(*a)] = c[b%len(*a)], c[0]
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*a = string(c)
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}
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case strings.HasPrefix(fn, `function(a,b){a.splice(0,b)}`):
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opTable[name] = func(a *string, b int) {
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// Slice off all elements of a up to a[b]
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*a = (*a)[b:]
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}
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}
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}
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}
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// Parse all operations in the main decryptor function and return them in
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// order
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var res []decryptorOp
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for _, fn := range strings.Split(decrFn, ";") {
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sp := strings.SplitN(fn, ".", 2)
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if len(sp) != 2 {
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return nil, ErrDecryptGettingOpTable
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}
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sp = strings.SplitN(sp[1], "(", 2)
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if len(sp) != 2 {
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return nil, ErrDecryptGettingOpTable
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}
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name := sp[0]
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argS := strings.TrimSuffix(strings.TrimPrefix(sp[1], "a,"), ")")
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arg, err := strconv.Atoi(argS)
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if err != nil {
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return nil, ErrDecryptGettingOpTable
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}
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callableOp, exists := opTable[name]
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if !exists {
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return nil, ErrDecryptGettingOpTable
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}
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res = append(res, decryptorOp{callableOp, arg})
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}
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return res, nil
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}
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