Add support for OS-specific CA bundle locations

GitHub pull: #19
Suggested-by: Michael Vogt <mvo@ubuntu.com>
Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>

Changelog.rst

@@ -8,6 +8,9 @@ ChangeLog
 OfflineIMAP v6.5.6.1 (YYYY-MM-DD)
 =================================
 
+* Support default CA bundle locations for a couple of
+  known Unix systems (Michael Vogt, GutHub pull #19)
+
 * Create SQLite database directory if it doesn't exist
   yet; warn if path is not a directory (Nick Farrell,
   GutHub pull #102)

offlineimap/repository/IMAP.py

@@ -19,6 +19,7 @@ from offlineimap.repository.Base import BaseRepository
 from offlineimap import folder, imaputil, imapserver, OfflineImapError
 from offlineimap.folder.UIDMaps import MappedIMAPFolder
 from offlineimap.threadutil import ExitNotifyThread
+from offlineimap.utils.distro import get_os_sslcertfile
 from threading import Event
 import os
 from sys import exc_info
@@ -200,7 +201,7 @@ class IMAPRepository(BaseRepository):
 
     def getsslcacertfile(self):
         """Return the absolute path of the CA certfile to use, if any"""
-        cacertfile = self.getconf('sslcacertfile', None)
+        cacertfile = self.getconf('sslcacertfile', get_os_sslcertfile())
         if cacertfile is None:
             return None
         cacertfile = os.path.expanduser(cacertfile)

offlineimap/utils/distro.py

@@ -0,0 +1,74 @@
+# Copyright 2014 Eygene A. Ryabinkin.
+#
+# Module that supports distribution-specific functions.
+
+import platform
+import os
+
+
+# Each dictionary value is either string or some iterable.
+# 
+# For the former we will just return the value, for an iterable
+# we will walk through the values and will return the first
+# one that corresponds to the existing file.
+__DEF_OS_LOCATIONS = {
+    'freebsd': '/usr/local/share/certs/ca-root-nss.crt',
+    'openbsd': None,
+    'netbsd': None,
+    'dragonfly': None,
+    'darwin': [
+      # MacPorts, port curl-ca-bundle
+      '/opt/local/share/curl/curl-ca-bundle.crt',
+    ],
+    'linux-ubuntu': '/etc/ssl/certs/ca-certificates.crt',
+    'linux-debian': '/etc/ssl/certs/ca-certificates.crt',
+    'linux-fedora': '/etc/pki/tls/certs/ca-bundle.crt',
+    'linux-redhat': '/etc/pki/tls/certs/ca-bundle.crt',
+    'linux-suse': '/etc/ssl/ca-bundle.pem',
+}
+
+
+def get_os_name():
+    """
+    Finds out OS name.  For non-Linux system it will be just a plain
+    OS name (like FreeBSD), for Linux it will be "linux-<distro>",
+    where <distro> is the name of the distribution, as returned by
+    the first component of platform.linux_distribution.
+
+    Return value will be all-lowercase to avoid confusion about
+    proper name capitalisation.
+
+    """
+    OS = platform.system().lower()
+
+    if OS.startswith('linux'):
+        DISTRO = platform.linux_distribution()[0]
+        if DISTRO:
+          OS = OS + "-%s" % DISTRO.lower()
+
+    return OS
+
+
+def get_os_sslcertfile():
+    """
+    Finds out the location for the distribution-specific
+    CA certificate file bundle.
+
+    Returns the location of the file or None if there is
+    no known CA certificate file or all known locations
+    correspond to non-existing filesystem objects.
+
+    """
+    OS = get_os_name()
+
+    if OS in __DEF_OS_LOCATIONS:
+        l = __DEF_OS_LOCATIONS[OS]
+        if not hasattr(l, '__iter__'):
+          l = (l, )
+        for f in l:
+          assert (type(f) == type(""))
+          if os.path.exists(f) and \
+            (os.path.isfile(f) or os.path.islink(f)):
+              return f
+
+    return None