youtube.lua: add "n" descrambling split compound transformations

A new variant of compound transformation has the Base64 alphabet
generation and the compounding itself as two separate data array
elements, contrary to what was observed so far. Add support for those.

Fixes #26285

share/lua/playlist/youtube.lua

@@ -158,12 +158,14 @@ function n_descramble( nparam, js )
         return len
     end
 
-    -- Common routine shared by the compound transformations,
-    -- compounding the "n" parameter with an input string,
-    -- character by character using a Base64 alphabet.
+    -- Shared core section of compound transformations: it compounds
+    -- the "n" parameter with an input string, character by character,
+    -- using a Base64 alphabet as algebraic modulo group.
     -- var h=f.length;d.forEach(function(l,m,n){this.push(n[m]=f[(f.indexOf(l)-f.indexOf(this[m])+m+h--)%f.length])},e.split(""))
     local compound = function( ntab, str, alphabet )
-        if ntab ~= n or type( str ) ~= "string" then
+        if ntab ~= n or
+           type( str ) ~= "string" or
+           type( alphabet ) ~= "string" then
             return true
         end
         local input = {}
@@ -271,16 +273,44 @@ function n_descramble( nparam, js )
                 "^[^}]-d%.unshift%(f%)}%)},",
             }
         },
-        -- Compound transformations first build a variation of a
-        -- Base64 alphabet, then in a common section, compound the
-        -- "n" parameter with an input string, character by character.
+        -- Here functions with no arguments are not really functions,
+        -- they're constants: treat them as such. These alphabets are
+        -- passed to and used by the compound transformations.
+        alphabet1 = {
+            func = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_",
+            match = {
+                -- function(){for(var d=64,e=[];++d-e.length-32;){switch(d){case 91:d=44;continue;case 123:d=65;break;case 65:d-=18;continue;case 58:d=96;continue;case 46:d=95}e.push(String.fromCharCode(d))}return e}
+                "^function%(%){[^}]-case 58:d=96;",
+            }
+        },
+        alphabet2 = {
+            func = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
+            match = {
+                -- function(){for(var d=64,e=[];++d-e.length-32;)switch(d){case 46:d=95;default:e.push(String.fromCharCode(d));case 94:case 95:case 96:break;case 123:d-=76;case 92:case 93:continue;case 58:d=44;case 91:}return e}
+                "^function%(%){[^}]-case 58:d%-=14;",
+                "^function%(%){[^}]-case 58:d=44;",
+            }
+        },
+        -- Compound transformations are based on a shared core section
+        -- that compounds the "n" parameter with an input string,
+        -- character by character, using a variation of a Base64
+        -- alphabet as algebraic modulo group.
+        compound = {
+            func = compound,
+            match = {
+                -- function(d,e,f){var h=f.length;d.forEach(function(l,m,n){this.push(n[m]=f[(f.indexOf(l)-f.indexOf(this[m])+m+h--)%f.length])},e.split(""))}
+                "^function%(d,e,f%)",
+            }
+        },
+        -- These compound transformation variants first build their
+        -- Base64 alphabet themselves, before using it.
         compound1 = {
             func = function( ntab, str )
                 return compound( ntab, str, "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_" )
             end,
             match = {
                 -- function(d,e){for(var f=64,h=[];++f-h.length-32;)switch(f){case 58:f=96;continue;case 91:f=44;break;case 65:f=47;continue;case 46:f=153;case 123:f-=58;default:h.push(String.fromCharCode(f))} [ compound... ] }
-                "^[^}]-case 58:f=96;",
+                "^function%(d,e%){[^}]-case 58:f=96;",
             }
         },
         compound2 = {
@@ -290,8 +320,8 @@ function n_descramble( nparam, js )
             match = {
                 -- function(d,e){for(var f=64,h=[];++f-h.length-32;){switch(f){case 58:f-=14;case 91:case 92:case 93:continue;case 123:f=47;case 94:case 95:case 96:continue;case 46:f=95}h.push(String.fromCharCode(f))} [ compound... ] }
                 -- function(d,e){for(var f=64,h=[];++f-h.length-32;)switch(f){case 46:f=95;default:h.push(String.fromCharCode(f));case 94:case 95:case 96:break;case 123:f-=76;case 92:case 93:continue;case 58:f=44;case 91:} [ compound... ] }
-                "^[^}]-case 58:f%-=14;",
-                "^[^}]-case 58:f=44;",
+                "^function%(d,e%){[^}]-case 58:f%-=14;",
+                "^function%(d,e%){[^}]-case 58:f=44;",
             }
         },
         -- Fallback
@@ -333,7 +363,9 @@ function n_descramble( nparam, js )
 
             -- Compounding functions use a subfunction, so we need to be
             -- more specific in how much parsed data we consume.
-            if el == trans.compound1.func or el == trans.compound2.func then
+            if el == trans.compound.func or
+               el == trans.compound1.func or
+               el == trans.compound2.func then
                 datac = string.match( datac, '^.-},e%.split%(""%)%)},(.*)$' )
             else
                 datac = string.match( datac, "^.-},(.*)$" )