Proof that bindings to nc are immutable.

src/zc/buildout/networkcache.txt

@@ -836,3 +836,155 @@ parse the original url and get the file name:
    ...                       path=globals().get('tmp_dir') +  '/tmp_file',
    ...                       nc_server_path=sample_buildout)
    'id=700c7d5382b01f94e7141'
+
+Buildout bindings to networkcache are immune on slapos.libnetworkcache problems.
+
+Lets prepare networkcache with errors:
+
+  >>> mkdir(sample_buildout, 'damagednc')
+  >>> mkdir(sample_buildout, 'damagednc', 'slapos')
+  >>> write(sample_buildout, 'damagednc', 'slapos', '__init__.py',
+  ... """
+  ... # See http://peak.telecommunity.com/DevCenter/setuptools#namespace-packages
+  ... try:
+  ...     __import__('pkg_resources').declare_namespace(__name__)
+  ... except ImportError:
+  ...     from pkgutil import extend_path
+  ...     __path__ = extend_path(__path__, __name__)
+  ... """)
+  >>> write(sample_buildout, 'damagednc', 'slapos', 'libnetworkcache.py',
+  ... """
+  ... += die during import
+  ... """)
+  >>> write(sample_buildout, 'damagednc', 'setup.py',
+  ... """
+  ... from setuptools import setup, find_packages
+  ...
+  ... setup(
+  ...     name = "slapos.libnetworkcache",
+  ...     namespace_packages=['slapos'],
+  ...     packages=find_packages(),
+  ...     install_requires=['setuptools']
+  ...     )
+  ... """)
+  >>> write(sample_buildout, 'damagednc', 'README.txt', " ")
+
+And install it in buildout:
+
+   >>> write(sample_buildout, 'buildout.cfg',
+   ... '''
+   ... [buildout]
+   ... parts = networkcache
+   ... develop = damagednc
+   ... # Do not register this buildout run
+   ... installed =
+   ...
+   ... [networkcache]
+   ... recipe = zc.recipe.egg
+   ... eggs =
+   ...   slapos.libnetworkcache
+   ...   zc.buildout
+   ... ''')
+   >>> print system(buildout)
+   Develop: '/sample-buildout/damagednc'
+   Installing networkcache.
+   Generated script '/sample-buildout/bin/buildout'.
+
+So lets use such damaged networkcache:
+
+  >>> write(sample_buildout, 'buildout.cfg',
+  ... '''
+  ... [buildout]
+  ...
+  ... networkcache-section = networkcache
+  ... develop = download damagednc
+  ... parts = download
+  ...
+  ... [download]
+  ... recipe = download
+  ... url = %(remote_server_url)shello.txt
+  ...
+  ... [networkcache]
+  ... download-cache-url = %(nc_url)sshacache
+  ... download-dir-url = %(nc_url)sshadir
+  ... ''' % globals())
+  >>> print system(buildout)
+  There was problem while trying to import slapos.libnetworkcache:
+  Traceback (most recent call last):
+  ...
+  SyntaxError: invalid syntax
+  <BLANKLINE>
+  Networkcache forced to be disabled.
+  There was problem while trying to import slapos.libnetworkcache:
+  Traceback (most recent call last):
+  ...
+  SyntaxError: invalid syntax
+  <BLANKLINE>
+  Networkcache forced to be disabled.
+  Develop: '/sample-buildout/download'
+  Develop: '/sample-buildout/damagednc'
+  Unused options for buildout: 'networkcache-section'.
+  Installing download.
+  Downloading http://localhost/hello.txt
+  download: Downloaded http://localhost/hello.txt
+
+If networkcache internally has issues, or its API got changed, buildout will
+still work:
+
+  >>> write(sample_buildout, 'damagednc', 'slapos', 'libnetworkcache.py',
+  ... """
+  ... class NetworkcacheClient(object):
+  ...     def parseUrl(*args, **kwargs):
+  ...         raise Die
+  ...     def __init__(*args, **kwargs):
+  ...         raise Die
+  ...     def upload(*args, **kwargs):
+  ...         raise Die
+  ...     def download(*args, **kwargs):
+  ...         raise Die
+  ...     def select(*args, **kwargs):
+  ...         raise Die
+  ... class UploadError: pass
+  ... class DirectoryNotFound: pass
+  ... """)
+
+  >>> write(sample_buildout, 'buildout.cfg',
+  ... '''
+  ... [buildout]
+  ...
+  ... networkcache-section = networkcache
+  ... develop = download damagednc
+  ... parts = download
+  ...
+  ... [download]
+  ... recipe = download
+  ... url = %(remote_server_url)shello.txt
+  ...
+  ... [networkcache]
+  ... download-cache-url = %(nc_url)sshacache
+  ... download-dir-url = %(nc_url)sshadir
+  ... upload-cache-url = %(nc_url)sshacache
+  ... upload-dir-url = %(nc_url)sshadir
+  ... ''' % globals())
+  >>> print system(buildout)
+  Networkcache enabled.
+  Networkcache download cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
+  Networkcache upload cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
+  Develop: '/sample-buildout/download'
+  Develop: '/sample-buildout/damagednc'
+  Updating download.
+  Downloading http://localhost/hello.txt
+  There was problem while calling method 'download_network_cached':
+  Traceback (most recent call last):
+  ...
+      raise Die
+  NameError: global name 'Die' is not defined
+  <BLANKLINE>
+  Uploading http://localhost/hello.txt into network cache.
+  There was problem while calling method 'upload_network_cached':
+  Traceback (most recent call last):
+  ...
+      raise Die
+  NameError: global name 'Die' is not defined
+  <BLANKLINE>
+  download: Downloaded http://localhost:20863/hello.txt