add registering the writer to the config...

make sure that extra modules don't get loaded..

casimport/__init__.py

@@ -230,6 +230,7 @@ class CASFinder(MetaPathFinder, Loader):
 	def __init__(self):
 		self._loaders = []
 		self._aliases = {}
+		self._writer = None
 
 		if [ x for x in sys.meta_path if
 		    isinstance(x, self.__class__) ]:
@@ -244,6 +245,9 @@ class CASFinder(MetaPathFinder, Loader):
 	def __exit__(self, exc_type, exc_value, traceback):
 		self.disconnect()
 
+	def register_write(self, wr):
+		self._writer = wr
+
 	def load_aliases(self, data):
 		self._aliases.update(self._parsealiases(data))
 
@@ -406,16 +410,17 @@ def defaultinit(casf):
 	modorder = [ x.strip() for x in
 	    cp['casimport']['module_prio'].split(',') ]
 
+	mods = {}
 	for i in modorder:
 		modfun = _supportedmodules[cp[i]['type']]
-		casf.register(modfun(cp[i]))
-
-	cachedir = basedir / 'cache'
-	cachedir.mkdir(parents=True, exist_ok=True)
+		mod = modfun(cp[i])
+		mods[i] = mod
+		casf.register(mod)
 
-	casf.register(FileDirCAS(cachedir))
-	casf.register(IPFSCAS())
-	casf.register(HTTPSCAS())
+	try:
+		casf.register_write(mods[cp['casimport']['write_cache']])
+	except KeyError:
+		pass
 
 def main():
 	# Thoughts on supported features:
@@ -553,6 +558,21 @@ class Test(unittest.TestCase):
 			# and that the second loader is the IPFSCAS
 			self.assertIsInstance(f._loaders[1], IPFSCAS)
 
+	def test_writecache(self):
+		conf = self.fixtures / 'writecache.conf'
+
+		# that w/ a custom config
+		with tempset(os.environ, 'CASIMPORT_CONF', str(conf)), \
+		    CASFinder() as f:
+			# that is gets loaded
+			defaultinit(f)
+
+			# that the first loader is the cache
+			self.assertIsInstance(f._loaders[0], FileDirCAS)
+
+			# and that the stored writer matches
+			self.assertIs(f._writer, f._loaders[0])
+
 	def test_ipfsgwfromconfig(self):
 		gwurl = 'https://www.example.com/somepath/'
 		ipfsconf = dict(gateway=gwurl)
@@ -592,6 +612,9 @@ class Test(unittest.TestCase):
 				# and that the third loader is the HTTPSCAS
 				self.assertIsInstance(f._loaders[2], HTTPSCAS)
 
+				# and that these are the only ones loaded
+				self.assertEqual(len(f._loaders), 3)
+
 			with CASFinder() as f:
 				defaultinit(f)
 

fixtures/writecache.conf

@@ -0,0 +1,15 @@
+[casimport]
+module_prio = homecache, https
+
+write_cache = homecache
+
+[homecache]
+# Default cache is in the user's home directory.
+
+type = cache
+path = ~/.casimport/cache
+
+#size = 10MB
+
+[https]
+type = https