content/sources/jsinterp.py

# This code comes from youtube-dl: https://github.com/rg3/youtube-dl/blob/master/youtube_dl/jsinterp.py

from __future__ import unicode_literals

import json
import operator
import re


_OPERATORS = [
    ('|', operator.or_),
    ('^', operator.xor),
    ('&', operator.and_),
    ('>>', operator.rshift),
    ('<<', operator.lshift),
    ('-', operator.sub),
    ('+', operator.add),
    ('%', operator.mod),
    ('/', operator.truediv),
    ('*', operator.mul),
]
_ASSIGN_OPERATORS = [(op + '=', opfunc) for op, opfunc in _OPERATORS]
_ASSIGN_OPERATORS.append(('=', lambda cur, right: right))

_NAME_RE = r'[a-zA-Z_$][a-zA-Z_$0-9]*'


class JSInterpreter(object):
    def __init__(self, code, objects=None):
        if objects is None:
            objects = {}
        self.code = code
        self._functions = {}
        self._objects = objects

    def interpret_statement(self, stmt, local_vars, allow_recursion=100):
        if allow_recursion < 0:
            print '[JSInterpreter] Recursion limit reached'
            return None

        should_abort = False
        stmt = stmt.lstrip()
        stmt_m = re.match(r'var\s', stmt)
        if stmt_m:
            expr = stmt[len(stmt_m.group(0)):]
        else:
            return_m = re.match(r'return(?:\s+|$)', stmt)
            if return_m:
                expr = stmt[len(return_m.group(0)):]
                should_abort = True
            else:
                # Try interpreting it as an expression
                expr = stmt

        v = self.interpret_expression(expr, local_vars, allow_recursion)
        return v, should_abort

    def interpret_expression(self, expr, local_vars, allow_recursion):
        expr = expr.strip()

        if expr == '':  # Empty expression
            return None

        if expr.startswith('('):
            parens_count = 0
            for m in re.finditer(r'[()]', expr):
                if m.group(0) == '(':
                    parens_count += 1
                else:
                    parens_count -= 1
                    if parens_count == 0:
                        sub_expr = expr[1:m.start()]
                        sub_result = self.interpret_expression(
                            sub_expr, local_vars, allow_recursion)
                        remaining_expr = expr[m.end():].strip()
                        if not remaining_expr:
                            return sub_result
                        else:
                            expr = json.dumps(sub_result) + remaining_expr
                        break
            else:
                print '[JSInterpreter] Premature end of parens in %r' % expr
                return None

        for op, opfunc in _ASSIGN_OPERATORS:
            m = re.match(r'''(?x)
                (?P<out>%s)(?:\[(?P<index>[^\]]+?)\])?
                \s*%s
                (?P<expr>.*)$''' % (_NAME_RE, re.escape(op)), expr)
            if not m:
                continue
            right_val = self.interpret_expression(
                m.group('expr'), local_vars, allow_recursion - 1)

            if m.groupdict().get('index'):
                lvar = local_vars[m.group('out')]
                idx = self.interpret_expression(
                    m.group('index'), local_vars, allow_recursion)
                assert isinstance(idx, int)
                cur = lvar[idx]
                val = opfunc(cur, right_val)
                lvar[idx] = val
                return val
            else:
                cur = local_vars.get(m.group('out'))
                val = opfunc(cur, right_val)
                local_vars[m.group('out')] = val
                return val

        if expr.isdigit():
            return int(expr)

        var_m = re.match(
            r'(?!if|return|true|false)(?P<name>%s)$' % _NAME_RE,
            expr)
        if var_m:
            return local_vars[var_m.group('name')]

        try:
            return json.loads(expr)
        except ValueError:
            pass

        m = re.match(
            r'(?P<var>%s)\.(?P<member>[^(]+)(?:\(+(?P<args>[^()]*)\))?$' % _NAME_RE,
            expr)
        if m:
            variable = m.group('var')
            member = m.group('member')
            arg_str = m.group('args')

            if variable in local_vars:
                obj = local_vars[variable]
            else:
                if variable not in self._objects:
                    self._objects[variable] = self.extract_object(variable)
                obj = self._objects[variable]

            if arg_str is None:
                # Member access
                if member == 'length':
                    return len(obj)
                return obj[member]

            assert expr.endswith(')')
            # Function call
            if arg_str == '':
                argvals = tuple()
            else:
                argvals = tuple([
                    self.interpret_expression(v, local_vars, allow_recursion)
                    for v in arg_str.split(',')])

            if member == 'split':
                assert argvals == ('',)
                return list(obj)
            if member == 'join':
                assert len(argvals) == 1
                return argvals[0].join(obj)
            if member == 'reverse':
                assert len(argvals) == 0
                obj.reverse()
                return obj
            if member == 'slice':
                assert len(argvals) == 1
                return obj[argvals[0]:]
            if member == 'splice':
                assert isinstance(obj, list)
                index, howMany = argvals
                res = []
                for i in range(index, min(index + howMany, len(obj))):
                    res.append(obj.pop(index))
                return res

            return obj[member](argvals)

        m = re.match(
            r'(?P<in>%s)\[(?P<idx>.+)\]$' % _NAME_RE, expr)
        if m:
            val = local_vars[m.group('in')]
            idx = self.interpret_expression(
                m.group('idx'), local_vars, allow_recursion - 1)
            return val[idx]

        for op, opfunc in _OPERATORS:
            m = re.match(r'(?P<x>.+?)%s(?P<y>.+)' % re.escape(op), expr)
            if not m:
                continue
            x, abort = self.interpret_statement(
                m.group('x'), local_vars, allow_recursion - 1)
            if abort:
                print '[JSInterpreter] Premature left-side return of %s in %r' % (op, expr)
                return None
            y, abort = self.interpret_statement(
                m.group('y'), local_vars, allow_recursion - 1)
            if abort:
                print '[JSInterpreter] Premature right-side return of %s in %r' % (op, expr)
                return None
            return opfunc(x, y)

        m = re.match(
            r'^(?P<func>%s)\((?P<args>[a-zA-Z0-9_$,]+)\)$' % _NAME_RE, expr)
        if m:
            fname = m.group('func')
            argvals = tuple([
                int(v) if v.isdigit() else local_vars[v]
                for v in m.group('args').split(',')])
            if fname not in self._functions:
                self._functions[fname] = self.extract_function(fname)
            return self._functions[fname](argvals)

        print '[JSInterpreter] Unsupported JS expression %r' % expr
        return None

    def extract_object(self, objname):
        obj = {}
        obj_m = re.search(
            (r'(?:var\s+)?%s\s*=\s*\{' % re.escape(objname)) +
            r'\s*(?P<fields>([a-zA-Z$0-9]+\s*:\s*function\(.*?\)\s*\{.*?\}(?:,\s*)?)*)' +
            r'\}\s*;',
            self.code)
        fields = obj_m.group('fields')
        # Currently, it only supports function definitions
        fields_m = re.finditer(
            r'(?P<key>[a-zA-Z$0-9]+)\s*:\s*function'
            r'\((?P<args>[a-z,]+)\){(?P<code>[^}]+)}',
            fields)
        for f in fields_m:
            argnames = f.group('args').split(',')
            obj[f.group('key')] = self.build_function(argnames, f.group('code'))

        return obj

    def extract_function(self, funcname):
        func_m = re.search(
            r'''(?x)
                (?:function\s+%s|[{;,]%s\s*=\s*function|var\s+%s\s*=\s*function)\s*
                \((?P<args>[^)]*)\)\s*
                \{(?P<code>[^}]+)\}''' % (
                re.escape(funcname), re.escape(funcname), re.escape(funcname)),
            self.code)
        if func_m is None:
            print '[JSInterpreter] Could not find JS function %r' % funcname
            return None
        argnames = func_m.group('args').split(',')

        return self.build_function(argnames, func_m.group('code'))

    def call_function(self, funcname, *args):
        f = self.extract_function(funcname)
        return f(args)

    def build_function(self, argnames, code):
        def resf(args):
            local_vars = dict(zip(argnames, args))
            for stmt in code.split(';'):
                res, abort = self.interpret_statement(stmt, local_vars)
                if abort:
                    break
            return res
        return resf