python-bson-ext does not encode binary in Apache with mod_wsgi

In a component of MAAS we're using python-bson to dump out structures containing binary data. Everything works fine in development, but breaks in production under Apache.

In Python 2.x (we're using 2.7) it's necessary to wrap str/bytes objects in bson.binary.Binary; the encoder then does an isinstance check and encodes these objects as binary data - or "\x05" e_name binary, from the spec. However, under Apache our binary data is being encoded as string data - or "\x02" e_name string, from the spec. When decoding this becomes a unicode object, which chokes the next part of the MAAS's processing.

I think this is due to the C extension module. Apache and/or mod_wsgi does some weird things with Python contexts (I don't know much about this, just enough to know it can be a problem), and I suspect the PyObject_IsInstance(value, state->Binary) condition in bson/_cbsonmodule.c is failing because state->Binary is referencing a different Binary type than MAAS's code is.

The following are the mod_wsgi directives we're using in Apache:

{{{
WSGIDaemonProcess maas user=maas group=maas processes=2 threads=1 display-name=%{GROUP}

# Without this, defining a tag as a malformed xpath expression will hang
# the region controller.
# See https://techknowhow.library.emory.edu/blogs/branker/2010/07/30/django-lxml-wsgi-and-python-sub-interpreter-magic
WSGIApplicationGroup %{GLOBAL}

WSGIScriptAlias /MAAS /usr/share/maas/wsgi.py
# Preload application when process starts. This will allow publishing
# the MAAS server existence over Avahi.
WSGIImportScript /usr/share/maas/wsgi.py process-group=maas application-group=maas
WSGIPassAuthorization On

<Directory /usr/share/maas/>
    WSGIProcessGroup maas
</Directory>
}}}

$ apt-cache policy apache2 libapache2-mod-wsgi python-bson python-bson-ext
apache2:
  Installed: 2.4.6-2ubuntu2
  Candidate: 2.4.6-2ubuntu2
  Version table:
 *** 2.4.6-2ubuntu2 0
        500 http://gb.archive.ubuntu.com/ubuntu/ saucy/main amd64 Packages
        100 /var/lib/dpkg/status
libapache2-mod-wsgi:
  Installed: 3.4-4
  Candidate: 3.4-4
  Version table:
 *** 3.4-4 0
        500 http://gb.archive.ubuntu.com/ubuntu/ saucy/main amd64 Packages
        100 /var/lib/dpkg/status
python-bson:
  Installed: 2.6-1
  Candidate: 2.6-1
  Version table:
 *** 2.6-1 0
        500 http://gb.archive.ubuntu.com/ubuntu/ saucy/main amd64 Packages
        100 /var/lib/dpkg/status
python-bson-ext:
  Installed: 2.6-1
  Candidate: 2.6-1
  Version table:
 *** 2.6-1 0
        500 http://gb.archive.ubuntu.com/ubuntu/ saucy/main amd64 Packages
        100 /var/lib/dpkg/status