shell.py

#!/usr/bin/python
#
# Copyright 2007 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""
An interactive, stateful AJAX shell that runs Python code on the server.

Part of http://code.google.com/p/google-app-engine-samples/.

May be run as a standalone app or in an existing app as an admin-only handler.
Can be used for system administration tasks, as an interactive way to try out
APIs, or as a debugging aid during development.

The logging, os, sys, db, and users modules are imported automatically.

Interpreter state is stored in the datastore so that variables, function
definitions, and other values in the global and local namespaces can be used
across commands.

To use the shell in your app, copy shell.py, static/*, and templates/* into
your app's source directory. Then, copy the URL handlers from app.yaml into
your app.yaml.

TODO: unit tests!
"""

import logging
import new
import os
import pickle
import sys
import pdb
import traceback
import tokenize
import types
import simplejson
import wsgiref.handlers

from StringIO import StringIO

from google.appengine.api import users
from google.appengine.ext import db
from google.appengine.ext import webapp
from google.appengine.ext.webapp import template

sys.path.insert(0, os.path.join(os.getcwd(), 'sympy'))

from sympy import srepr, sstr, pretty, latex

PRINTERS = {
    'repr': srepr,
    'str': sstr,
    'ascii': lambda arg: pretty(arg, use_unicode=False),
    'unicode': lambda arg: pretty(arg, use_unicode=True),
    'latex': lambda arg: latex(arg, mode="equation*"),
}

def gdb():
    """Enter pdb in Google App Engine. """
    pdb.Pdb(stdin=getattr(sys, '__stdin__'),
            stdout=getattr(sys, '__stderr__')).set_trace(sys._getframe().f_back)

# Set to True if stack traces should be shown in the browser, etc.
_DEBUG = True

# The entity kind for shell sessions. Feel free to rename to suit your app.
_SESSION_KIND = '_Shell_Session'

# Types that can't be pickled.
UNPICKLABLE_TYPES = (
  types.ModuleType,
  types.TypeType,
  types.ClassType,
  types.FunctionType,
  )

# Unpicklable statements to seed new sessions with.
INITIAL_UNPICKLABLES = [
  "import logging",
  "import os",
  "import sys",
  "from google.appengine.ext import db",
  "from google.appengine.api import users",
  "from __future__ import division",
  "from sympy import *",
]

PREEXEC = """\
x, y, z, t = symbols('x y z t')
k, m, n = symbols('k m n', integer=True)
f, g, h = symbols('f g h', cls=Function)
"""

PREEXEC_INTERNAL = """\
_ = None
"""

PREEXEC_MESSAGE = """\
from __future__ import division
from sympy import *
""" + PREEXEC

VERBOSE_MESSAGE = """\
These commands were executed:
%(source)s
Documentation can be found at http://www.sympy.org\
"""

def banner(quiet=False):
    from sympy import __version__ as sympy_version
    python_version = "%d.%d.%d" % sys.version_info[:3]

    message = "Python console for SymPy %s (Python %s)\n" % (sympy_version, python_version)

    if not quiet:
        source = ""

        for line in PREEXEC_MESSAGE.split('\n')[:-1]:
            if not line:
                source += '\n'
            else:
                source += '>>> ' + line + '\n'

        message += '\n' + VERBOSE_MESSAGE % {'source': source}

    return message

class Live(object):

    _header = 'Traceback (most recent call last):\n'
    _file = '<string>'

    def traceback(self, offset=None):
        """Return nicely formatted most recent traceback. """
        etype, value, tb = sys.exc_info()

        if tb.tb_next is not None:
            _tb = tb.tb_next
        else:
            _tb = tb

        try:
            if offset is not None:
                lines = traceback.extract_tb(_tb)

                line = lines[0][1] + offset
                lines[0] = (lines[0][0], line) + lines[0][2:]

                text = [self._header]
                text = text + traceback.format_list(lines)
                text = text + traceback.format_exception_only(etype, value)

                line = lines[0][1]
            else:
                text = traceback.format_exception(etype, value, _tb)
                line = _tb.tb_lineno
        finally:
            del tb, _tb

        return ''.join(text), line

    def syntaxerror(self):
        """Return nicely formatted syntax error. """
        etype, value, sys.last_traceback = sys.exc_info()

        sys.last_type = etype
        sys.last_value = value

        if etype is SyntaxError:
            try:
                msg, (dummy_filename, line, offset, source) = value
            except:
                pass
            else:
                value = SyntaxError(msg, (self._file, line, offset, source))
                sys.last_value = value

        text = [self._header]
        text = text + traceback.format_exception_only(etype, value)

        return ''.join(text), line

    def error(self, stream, error):
        """Write error message to a stream. """
        if stream is not None:
            stream.write(error[0])

    def split(self, source):
        """Extract last logical line from multi-line source code. """
        string = StringIO(source).readline

        try:
            tokens = list(tokenize.generate_tokens(string))
        except (OverflowError, SyntaxError, ValueError, tokenize.TokenError):
            return None, source

        for tok, _, (n, _), _, _ in reversed(tokens):
            if tok == tokenize.NEWLINE:
                lines = source.split('\n')

                exec_source = '\n'.join(lines[:n])
                eval_source = '\n'.join(lines[n:])

                return exec_source, eval_source
        else:
            return None, source

    def compile(self, source, mode):
        """Wrapper over Python's built-in function. """
        return compile(source, self._file, mode)

    def evaluate(self, statement, session, printer=None, stream=None):
        """Evaluate the statement in sessions's globals. """
        # the Python compiler doesn't like network line endings
        source = statement.replace('\r\n', '\n').rstrip()

        # split source code into 'exec' and 'eval' parts
        exec_source, eval_source = self.split(source)

        try:
            self.compile(eval_source, 'eval')
        except (OverflowError, SyntaxError, ValueError):
            exec_source, eval_source = source, None

        if exec_source is not None:
            exec_source += '\n'
        if eval_source is not None:
            eval_source += '\n'

        # create a dedicated module to be used as this statement's __main__
        statement_module = new.module('__main__')

        # use this request's __builtin__, since it changes on each request.
        # this is needed for import statements, among other things.
        import __builtin__
        statement_module.__builtin__ = __builtin__

        # create customized display hook
        stringify_func = printer or sstr

        def displayhook(arg):
            if arg is not None:
                __builtin__._ = None
                print stringify_func(arg)
                __builtin__._ = arg

        old_displayhook = sys.displayhook
        sys.displayhook = displayhook

        # swap in our custom module for __main__. then unpickle the session
        # globals, run the statement, and re-pickle the session globals, all
        # inside it.
        old_main = sys.modules.get('__main__')

        try:
            sys.modules['__main__'] = statement_module
            statement_module.__name__ = '__main__'

            # re-evaluate the unpicklables
            for code in session.unpicklables:
                exec code in statement_module.__dict__

            old_globals = dict(statement_module.__dict__)

            # re-initialize the globals
            session_globals_dict = session.globals_dict()

            for name, val in session_globals_dict.items():
                try:
                    statement_module.__dict__[name] = val
                except:
                    session.remove_global(name)

            # re-initialize '_' special variable
            __builtin__._ = session_globals_dict.get('_')

            # run!
            offset = 0

            try:
                old_stdout = sys.stdout
                old_stderr = sys.stderr

                try:
                    if stream is not None:
                        sys.stdout = stream
                        sys.stderr = stream

                    if exec_source is not None:
                        try:
                            exec_code = self.compile(exec_source, 'exec')
                        except (OverflowError, SyntaxError, ValueError):
                            return self.error(stream, self.syntaxerror())

                        eval(exec_code, statement_module.__dict__)

                    if eval_source is not None:
                        if exec_source is not None:
                            offset = len(exec_source.split('\n'))

                        result = eval(eval_source, statement_module.__dict__)
                        sys.displayhook(result)
                finally:
                    sys.stdout = old_stdout
                    sys.stderr = old_stderr
            except:
                return self.error(stream, self.traceback(offset))

            # extract the new globals that this statement added
            new_globals = {}

            for name, val in statement_module.__dict__.items():
                if name not in old_globals or val != old_globals[name]:
                    new_globals[name] = val

            if True in [isinstance(val, UNPICKLABLE_TYPES) for val in new_globals.values()]:
                # this statement added an unpicklable global. store the statement and
                # the names of all of the globals it added in the unpicklables
                source = ""

                if exec_source:
                    source += exec_source
                if eval_source:
                    source += eval_source

                source += "\n"

                session.add_unpicklable(source, new_globals.keys())
                logging.debug('Storing this statement as an unpicklable.')
            else:
                # this statement didn't add any unpicklables. pickle and store the
                # new globals back into the datastore
                for name, val in new_globals.items():
                    if not name.startswith('__'):
                        try:
                            session.set_global(name, val)
                        except (TypeError, pickle.PicklingError):
                            pass

            # save '_' special variable into the datastore
            val = getattr(__builtin__, '_', None)

            try:
                session.set_global('_', val)
            except (TypeError, pickle.PicklingError):
                session.set_global('_', None)
        finally:
            sys.modules['__main__'] = old_main
            sys.displayhook = old_displayhook

            try:
                del __builtin__._
            except AttributeError:
                pass

        session.put()

class Session(db.Model):
  """A shell session. Stores the session's globals.

  Each session globals is stored in one of two places:

  If the global is picklable, it's stored in the parallel globals and
  global_names list properties. (They're parallel lists to work around the
  unfortunate fact that the datastore can't store dictionaries natively.)

  If the global is not picklable (e.g. modules, classes, and functions), or if
  it was created by the same statement that created an unpicklable global,
  it's not stored directly. Instead, the statement is stored in the
  unpicklables list property. On each request, before executing the current
  statement, the unpicklable statements are evaluated to recreate the
  unpicklable globals.

  The unpicklable_names property stores all of the names of globals that were
  added by unpicklable statements. When we pickle and store the globals after
  executing a statement, we skip the ones in unpicklable_names.

  Using Text instead of string is an optimization. We don't query on any of
  these properties, so they don't need to be indexed.
  """
  global_names = db.ListProperty(db.Text)
  globals = db.ListProperty(db.Blob)
  unpicklable_names = db.ListProperty(db.Text)
  unpicklables = db.ListProperty(db.Text)

  def set_global(self, name, value):
    """Adds a global, or updates it if it already exists.

    Also removes the global from the list of unpicklable names.

    Args:
      name: the name of the global to remove
      value: any picklable value
    """
    blob = db.Blob(pickle.dumps(value))

    if name in self.global_names:
      index = self.global_names.index(name)
      self.globals[index] = blob
    else:
      self.global_names.append(db.Text(name))
      self.globals.append(blob)

    self.remove_unpicklable_name(name)

  def remove_global(self, name):
    """Removes a global, if it exists.

    Args:
      name: string, the name of the global to remove
    """
    if name in self.global_names:
      index = self.global_names.index(name)
      del self.global_names[index]
      del self.globals[index]

  def globals_dict(self):
    """Returns a dictionary view of the globals.
    """
    return dict((name, pickle.loads(val))
                for name, val in zip(self.global_names, self.globals))

  def add_unpicklable(self, statement, names):
    """Adds a statement and list of names to the unpicklables.

    Also removes the names from the globals.

    Args:
      statement: string, the statement that created new unpicklable global(s).
      names: list of strings; the names of the globals created by the statement.
    """
    self.unpicklables.append(db.Text(statement))

    for name in names:
      self.remove_global(name)
      if name not in self.unpicklable_names:
        self.unpicklable_names.append(db.Text(name))

  def remove_unpicklable_name(self, name):
    """Removes a name from the list of unpicklable names, if it exists.

    Args:
      name: string, the name of the unpicklable global to remove
    """
    if name in self.unpicklable_names:
      self.unpicklable_names.remove(name)

class FrontPageHandler(webapp.RequestHandler):
    """Creates a new session and renders the ``shell.html`` template. """

    def get(self):
        template_file = os.path.join(os.path.dirname(__file__), 'templates', 'shell.html')

        vars = {
            'server_software': os.environ['SERVER_SOFTWARE'],
            'python_version': sys.version,
            'user': users.get_current_user(),
            'login_url': users.create_login_url('/'),
            'logout_url': users.create_logout_url('/'),
            'banner': banner(),
            'printer': self.request.get('printer').lower() or '',
            'submit': self.request.get('submit').lower() or '',
            'tabWidth': self.request.get('tabWidth').lower() or 'undefined',
        }

        rendered = webapp.template.render(template_file, vars, debug=_DEBUG)
        self.response.out.write(rendered)

class EvaluateHandler(webapp.RequestHandler):
    """Evaluates a Python statement in a given session and returns the result. """

    def _cross_site_headers(self):
        self.response.headers['Access-Control-Allow-Origin'] = '*'
        self.response.headers['Access-Control-Allow-Headers'] = 'Content-Type, X-Requested-With'

    def options(self):
        self._cross_site_headers()

    def post(self):
        self._cross_site_headers()

        try:
            message = simplejson.loads(self.request.body)
        except ValueError:
            self.error(400)
            return

        statement = message.get('statement')

        session_key = message.get('session')
        printer_key = message.get('printer')

        live = Live()

        if session_key is not None:
            try:
                session = Session.get(session_key)
            except db.Error:
                self.error(400)
                return
        else:
            session = Session()
            session.unpicklables = [ db.Text(line) for line in INITIAL_UNPICKLABLES ]
            session_key = session.put()

            live.evaluate(PREEXEC, session)
            live.evaluate(PREEXEC_INTERNAL, session)

        try:
            printer = PRINTERS[printer_key]
        except KeyError:
            printer = None

        stream = StringIO()
        live.evaluate(statement, session, printer, stream)

        result = {
            'session': str(session_key),
            'output': stream.getvalue(),
        }

        self.response.headers['Content-Type'] = 'application/json'
        self.response.out.write(simplejson.dumps(result))

class ShellDsiFrontPageHandler(webapp.RequestHandler):
  """Creates a new session and renders the graphical_shell.html template.
  """

  def get(self):
    # set up the session. TODO: garbage collect old shell sessions
    session_key = self.request.get('session')
    if session_key:
      session = Session.get(session_key)
    else:
      # create a new session
      session = Session()
      session.unpicklables = [db.Text(line) for line in INITIAL_UNPICKLABLES]
      session_key = session.put()

    template_file = os.path.join(os.path.dirname(__file__), 'templates',
                                 'shelldsi.html')
    session_url = '/shelldsi?session=%s' % session_key
    vars = { 'server_software': os.environ['SERVER_SOFTWARE'],
             'python_version': sys.version,
             'session': str(session_key),
             'user': users.get_current_user(),
             'login_url': users.create_login_url(session_url),
             'logout_url': users.create_logout_url(session_url),
             }
    rendered = webapp.template.render(template_file, vars, debug=_DEBUG)
    self.response.out.write(rendered)

class HelpDsiFrontPageHandler(webapp.RequestHandler):
  """Creates a new session and renders the graphical_shell.html template.
  """

  def get(self):
    # set up the session. TODO: garbage collect old shell sessions
    session_key = self.request.get('session')
    if session_key:
      session = Session.get(session_key)
    else:
      # create a new session
      session = Session()
      session.unpicklables = [db.Text(line) for line in INITIAL_UNPICKLABLES]
      session_key = session.put()

    template_file = os.path.join(os.path.dirname(__file__), 'templates',
                                 'helpdsi.html')
    session_url = '/?session=%s' % session_key
    vars = { 'server_software': os.environ['SERVER_SOFTWARE'],
             'python_version': sys.version,
             'session': str(session_key),
             'user': users.get_current_user(),
             'login_url': users.create_login_url(session_url),
             'logout_url': users.create_logout_url(session_url),
             }
    rendered = webapp.template.render(template_file, vars, debug=_DEBUG)
    self.response.out.write(rendered)

class StatementHandler(webapp.RequestHandler):
  """Evaluates a python statement in a given session and returns the result.
  """

  def get(self):
    self.response.headers['Content-Type'] = 'text/plain'

    # extract the statement to be run
    statement = self.request.get('statement')

    # load the session from the datastore
    session = Session.get(self.request.get('session'))

    # setup printing function (srepr, sstr, pretty, upretty, latex)
    key = self.request.get('printer')

    try:
        printer = PRINTERS[key]
    except KeyError:
        printer = None

    # evaluate the statement in session's globals
    evaluate(statement, session, printer, self.response.out)

def main():
  application = webapp.WSGIApplication([
      ('/', FrontPageHandler),
      ('/evaluate', EvaluateHandler),
      ('/shelldsi', ShellDsiFrontPageHandler),
      ('/helpdsi', HelpDsiFrontPageHandler),
      ('/shell.do', StatementHandler),
  ], debug=_DEBUG)

  wsgiref.handlers.CGIHandler().run(application)

if __name__ == '__main__':
  main()