view contrib/win32/hgwebdir_wsgi.py @ 20742:3681de20b0a7

parsers: fail fast if Python has wrong minor version (issue4110)

This change causes an informative ImportError to be raised when importing
the parsers extension module if the minor version of the currently-running
Python interpreter doesn't match that of the Python used when compiling
the extension module.

This change also exposes a parsers.versionerrortext constant in the
C implementation of the module.  Its presence can be used to determine
whether this behavior is present in a version of the module.  The value
of the constant is the leading text of the ImportError raised and is set
to "Python minor version mismatch".

Here is an example of what the new error looks like:

  Traceback (most recent call last):
    File "test.py", line 1, in <module>
      import mercurial.parsers
  ImportError: Python minor version mismatch: The Mercurial extension
  modules were compiled with Python 2.7.6, but Mercurial is currently using
  Python with sys.hexversion=33883888: Python 2.5.6
  (r256:88840, Nov 18 2012, 05:37:10)
  [GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))]
   at: /opt/local/Library/Frameworks/Python.framework/Versions/2.5/Resources/
    Python.app/Contents/MacOS/Python

The reason for raising an error in this scenario is that Python's C API
is known not to be compatible from minor version to minor version, even
if sys.api_version is the same.  See for example this Python bug report
about incompatibilities between 2.5 and 2.6+:

  http://bugs.python.org/issue8118

These incompatibilities can cause Mercurial to break in mysterious,
unforeseen ways.  For example, when Mercurial compiled with Python 2.7 was
run with 2.5, the following crash occurred when running "hg status":

  http://bz.selenic.com/show_bug.cgi?id=4110

After this crash was fixed, running with Python 2.5 no longer crashes, but
the following puzzling behavior still occurs:

    $ hg status
      ...
      File ".../mercurial/changelog.py", line 123, in __init__
        revlog.revlog.__init__(self, opener, "00changelog.i")
      File ".../mercurial/revlog.py", line 251, in __init__
        d = self._io.parseindex(i, self._inline)
      File ".../mercurial/revlog.py", line 158, in parseindex
        index, cache = parsers.parse_index2(data, inline)
    TypeError: data is not a string

which can be reproduced more simply with:

    import mercurial.parsers as parsers
    parsers.parse_index2("", True)

Both the crash and the TypeError occurred because the Python C API's
PyString_Check() returns the wrong value when the C header files from
Python 2.7 are run with Python 2.5.  This is an example of an
incompatibility of the sort mentioned in the Python bug report above.

Failing fast with an informative error message results in a better user
experience in cases like the above.  The information in the ImportError
also simplifies troubleshooting for those on Mercurial mailing lists, the
bug tracker, etc.

This patch only adds the version check to parsers.c, which is sufficient
to affect command-line commands like "hg status" and "hg summary".
An idea for a future improvement is to move the version-checking C code
to a more central location, and have it run when importing all
Mercurial extension modules and not just parsers.c.

# An example WSGI script for IIS/isapi-wsgi to export multiple hgweb repos
# Copyright 2010 Sune Foldager <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
#
# Requirements:
# - Python 2.6
# - PyWin32 build 214 or newer
# - Mercurial installed from source (python setup.py install)
# - IIS 7
#
# Earlier versions will in general work as well, but the PyWin32 version is
# necessary for win32traceutil to work correctly.
#
#
# Installation and use:
#
# - Download the isapi-wsgi source and run python setup.py install:
#   http://code.google.com/p/isapi-wsgi/
#
# - Run this script (i.e. python hgwebdir_wsgi.py) to get a shim dll. The
#   shim is identical for all scripts, so you can just copy and rename one
#   from an earlier run, if you wish.
#
# - Setup an IIS application where your hgwebdir is to be served from.
#   On 64-bit systems, make sure it's assigned a 32-bit app pool.
#
# - In the application, setup a wildcard script handler mapping of type
#   IsapiModule with the shim dll as its executable. This file MUST reside
#   in the same directory as the shim. Remove all other handlers, if you wish.
#
# - Make sure the ISAPI and CGI restrictions (configured globally on the
#   web server) includes the shim dll, to allow it to run.
#
# - Adjust the configuration variables below to match your needs.
#

# Configuration file location
hgweb_config = r'c:\src\iis\hg\hgweb.config'

# Global settings for IIS path translation
path_strip = 0   # Strip this many path elements off (when using url rewrite)
path_prefix = 1  # This many path elements are prefixes (depends on the
                 # virtual path of the IIS application).

import sys

# Adjust python path if this is not a system-wide install
#sys.path.insert(0, r'c:\path\to\python\lib')

# Enable tracing. Run 'python -m win32traceutil' to debug
if getattr(sys, 'isapidllhandle', None) is not None:
    import win32traceutil

# To serve pages in local charset instead of UTF-8, remove the two lines below
import os
os.environ['HGENCODING'] = 'UTF-8'


import isapi_wsgi
from mercurial import demandimport; demandimport.enable()
from mercurial.hgweb.hgwebdir_mod import hgwebdir

# Example tweak: Replace isapi_wsgi's handler to provide better error message
# Other stuff could also be done here, like logging errors etc.
class WsgiHandler(isapi_wsgi.IsapiWsgiHandler):
    error_status = '500 Internal Server Error' # less silly error message

isapi_wsgi.IsapiWsgiHandler = WsgiHandler

# Only create the hgwebdir instance once
application = hgwebdir(hgweb_config)

def handler(environ, start_response):

    # Translate IIS's weird URLs
    url = environ['SCRIPT_NAME'] + environ['PATH_INFO']
    paths = url[1:].split('/')[path_strip:]
    script_name = '/' + '/'.join(paths[:path_prefix])
    path_info = '/'.join(paths[path_prefix:])
    if path_info:
        path_info = '/' + path_info
    environ['SCRIPT_NAME'] = script_name
    environ['PATH_INFO'] = path_info

    return application(environ, start_response)

def __ExtensionFactory__():
    return isapi_wsgi.ISAPISimpleHandler(handler)

if __name__=='__main__':
    from isapi.install import *
    params = ISAPIParameters()
    HandleCommandLine(params)