[youtube] Move JavaScript interpreter into its own module

1 files changed, 113 insertions, 0 deletions

diff --git a/youtube_dl/jsinterp.py b/youtube_dl/jsinterp.py
new file mode 100644
index 000000000..129a4027b
--- /dev/null
+++ b/youtube_dl/jsinterp.py
@@ -0,0 +1,113 @@
+from __future__ import unicode_literals
+
+import re
+
+from .utils import (
+    ExtractorError,
+)
+
+
+class JSInterpreter(object):
+    def __init__(self, code):
+        self.code = code
+        self._functions = {}
+
+    def interpret_statement(self, stmt, local_vars, allow_recursion=20):
+        if allow_recursion < 0:
+            raise ExtractorError('Recursion limit reached')
+
+        if stmt.startswith('var '):
+            stmt = stmt[len('var '):]
+        ass_m = re.match(r'^(?P<out>[a-z]+)(?:\[(?P<index>[^\]]+)\])?' +
+                         r'=(?P<expr>.*)$', stmt)
+        if ass_m:
+            if ass_m.groupdict().get('index'):
+                def assign(val):
+                    lvar = local_vars[ass_m.group('out')]
+                    idx = self.interpret_expression(
+                        ass_m.group('index'), local_vars, allow_recursion)
+                    assert isinstance(idx, int)
+                    lvar[idx] = val
+                    return val
+                expr = ass_m.group('expr')
+            else:
+                def assign(val):
+                    local_vars[ass_m.group('out')] = val
+                    return val
+                expr = ass_m.group('expr')
+        elif stmt.startswith('return '):
+            assign = lambda v: v
+            expr = stmt[len('return '):]
+        else:
+            raise ExtractorError(
+                'Cannot determine left side of statement in %r' % stmt)
+
+        v = self.interpret_expression(expr, local_vars, allow_recursion)
+        return assign(v)
+
+    def interpret_expression(self, expr, local_vars, allow_recursion):
+        if expr.isdigit():
+            return int(expr)
+
+        if expr.isalpha():
+            return local_vars[expr]
+
+        m = re.match(r'^(?P<in>[a-z]+)\.(?P<member>.*)$', expr)
+        if m:
+            member = m.group('member')
+            val = local_vars[m.group('in')]
+            if member == 'split("")':
+                return list(val)
+            if member == 'join("")':
+                return u''.join(val)
+            if member == 'length':
+                return len(val)
+            if member == 'reverse()':
+                return val[::-1]
+            slice_m = re.match(r'slice\((?P<idx>.*)\)', member)
+            if slice_m:
+                idx = self.interpret_expression(
+                    slice_m.group('idx'), local_vars, allow_recursion - 1)
+                return val[idx:]
+
+        m = re.match(
+            r'^(?P<in>[a-z]+)\[(?P<idx>.+)\]$', expr)
+        if m:
+            val = local_vars[m.group('in')]
+            idx = self.interpret_expression(
+                m.group('idx'), local_vars, allow_recursion - 1)
+            return val[idx]
+
+        m = re.match(r'^(?P<a>.+?)(?P<op>[%])(?P<b>.+?)$', expr)
+        if m:
+            a = self.interpret_expression(
+                m.group('a'), local_vars, allow_recursion)
+            b = self.interpret_expression(
+                m.group('b'), local_vars, allow_recursion)
+            return a % b
+
+        m = re.match(
+            r'^(?P<func>[a-zA-Z$]+)\((?P<args>[a-z0-9,]+)\)$', expr)
+        if m:
+            fname = m.group('func')
+            if fname not in self._functions:
+                self._functions[fname] = self.extract_function(fname)
+            argvals = [int(v) if v.isdigit() else local_vars[v]
+                       for v in m.group('args').split(',')]
+            return self._functions[fname](argvals)
+        raise ExtractorError('Unsupported JS expression %r' % expr)
+
+    def extract_function(self, funcname):
+        func_m = re.search(
+            r'function ' + re.escape(funcname) +
+            r'\((?P<args>[a-z,]+)\){(?P<code>[^}]+)}',
+            self.code)
+        argnames = func_m.group('args').split(',')
+
+        def resf(args):
+            local_vars = dict(zip(argnames, args))
+            for stmt in func_m.group('code').split(';'):
+                res = self.interpret_statement(stmt, local_vars)
+            return res
+        return resf
+