view contrib/win32/hgwebdir_wsgi.py @ 27142:060f83d219b9

extensions: refuse to load extensions if minimum hg version not met

As the author of several 3rd party extensions, I frequently see bug
reports from users attempting to run my extension with an old version
of Mercurial that I no longer support in my extension. Oftentimes, the
extension will import just fine. But as soon as we run extsetup(),
reposetup(), or get into the guts of a wrapped function, we encounter
an exception and abort. Today, Mercurial will print a message about
extensions that don't have a "testedwith" declaring explicit
compatibility with the current version.

The existing mechanism is a good start. But it isn't as robust as I
would like. Specifically, Mercurial assumes compatibility by default.
This means extension authors must perform compatibility checking in
their extsetup() or we wait and see if we encounter an abort at
runtime. And, compatibility checking can involve a lot of code and
lots of error checking. It's a lot of effort for extension authors.

Oftentimes, extension authors know which versions of Mercurial there
extension works on and more importantly where it is broken.

This patch introduces a magic "minimumhgversion" attribute in
extensions. When found, the extension loading mechanism will compare
the declared version against the current Mercurial version. If the
extension explicitly states we require a newer Mercurial version, a
warning is printed and the extension isn't loaded beyond importing
the Python module. This causes a graceful failure while alerting
the user of the compatibility issue.

I would be receptive to the idea of making the failure more fatal.
However, care would need to be taken to not criple every hg command.
e.g. the user may use `hg config` to fix the hgrc and if we aborted
trying to run that, the user would effectively be locked out of `hg`!

A potential future improvement to this functionality would be to catch
ImportError for the extension/module and parse the source code for
"minimumhgversion = 'XXX'" and do similar checking. This way we could
give more information about why the extension failed to load.

# 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
    win32traceutil.SetupForPrint # silence unused import warning

# 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 ISAPIParameters, HandleCommandLine
    params = ISAPIParameters()
    HandleCommandLine(params)