Allow hosts
-----------

On some environments the links visited by `zc.buildout` can be forbidden
by paranoiac firewalls. These URL might be on the chain of links
visited by `zc.buildout` whether they are defined in the `find-links` option
or by various eggs in their `url`, `download_url` and `dependency_links` metadata.

It is even harder to track that package_index works like a spider and
might visit links and go to other location.

The `allow-hosts` option provides a way to prevent this, and
works exactly like the one provided in `easy_install`
(see `easy_install allow-hosts option`_).

You can provide a list of allowed host, together with wildcards::

    [buildout]
    ...

    allow-hosts =
        *.python.org
        example.com

Let's create a develop egg in our buildout that specifies
`dependency_links` which points to a server in the outside world::

    >>> mkdir(sample_buildout, 'allowdemo')
    >>> write(sample_buildout, 'allowdemo', 'dependencydemo.py',
    ...       'import eggrecipekss.core')
    >>> write(sample_buildout, 'allowdemo', 'setup.py',
    ... '''from setuptools import setup; setup(
    ...     name='allowdemo', py_modules=['dependencydemo'],
    ...     install_requires = 'kss.core',
    ...     dependency_links = ['http://dist.plone.org'],
    ...     zip_safe=True, version='1')
    ... ''')

Now let's configure the buildout to use the develop egg,
together with some rules that disallow any web site but PyPI and
local files::

    >>> write(sample_buildout, 'buildout.cfg',
    ... '''
    ... [buildout]
    ... develop = allowdemo
    ... parts = eggs
    ... allow-hosts =
    ...     pypi.python.org
    ...
    ... [eggs]
    ... recipe = zc.recipe.egg:eggs
    ... eggs = allowdemo
    ... ''')

Now we can run the buildout and make sure all attempts to dist.plone.org fails::

    >>> print_(system(buildout), end='') # doctest: +ELLIPSIS
    Develop: '/sample-buildout/allowdemo'
    Installing eggs...
    ...
    While:
      Installing eggs.
      Getting distribution for 'kss.core'.
    Error: Couldn't find a distribution for 'kss.core'.

That's what we wanted : this will prevent any attempt to access
unwanted domains. For instance, some packages are listing in their
links `svn://` links. These can lead to error in some cases, and
can therefore be protected like this::

XXX (showcase with a svn:// file)

    >>> write(sample_buildout, 'buildout.cfg',
    ... '''
    ... [buildout]
    ... develop = allowdemo
    ... parts = eggs
    ... allow-hosts =
    ...     ^(!svn://).*
    ...
    ... [eggs]
    ... recipe = zc.recipe.egg:eggs
    ... eggs = allowdemo
    ... ''')

Now we can run the buildout and make sure all attempts to dist.plone.org fails::

    >>> print_(system(buildout), end='') # doctest: +ELLIPSIS
    Develop: '/sample-buildout/allowdemo'
    Installing eggs...
    ...
    While:
      Installing eggs.
      Getting distribution for 'kss.core'.
    Error: Couldn't find a distribution for 'kss.core'.

Test for issues
---------------

Test for 1.0.5 breakage as in https://bugs.launchpad.net/zc.buildout/+bug/239212::

    >>> write(sample_buildout, 'buildout.cfg',
    ... '''
    ... [buildout]
    ... parts=python
    ... foo = ${python:interpreter}
    ...
    ... [python]
    ... recipe=zc.recipe.egg
    ... eggs=zc.buildout
    ... interpreter=python
    ... ''')
    >>> print_('XX'); print_(system(buildout), end='') # doctest: +ELLIPSIS
    X...
    Unused options for buildout: 'foo'.
    Installing python.
    Generated script '/sample-buildout/bin/buildout'.
    Generated interpreter '/sample-buildout/bin/python'.

The bug 239212 above would have got us an *AttributeError* on
*buildout._allow_hosts*.  This was fixed in this changeset:
http://svn.zope.org/zc.buildout/trunk/src/zc/buildout/buildout.py?rev=87309&r1=87277&r2=87309

