add IPFS loader support.. use cloudflare instead of the ipfs.io

one because the IPv6 address seems to hang often right now..

casimport/__init__.py

@@ -23,6 +23,7 @@
 # SUCH DAMAGE.
 
 import contextlib
+import functools
 import glob
 import hashlib
 import importlib.resources
@@ -32,11 +33,27 @@ import pathlib
 import shutil
 import sys
 import tempfile
-import urllib
+import urllib.request
 
 from importlib.abc import MetaPathFinder, Loader
 from importlib.machinery import ModuleSpec
 
+def _printanyexc(f):
+	'''Prints any exception that gets raised by the wrapped function.'''
+
+	@functools.wraps(f)
+	def wrapper(*args, **kwargs):
+		try:
+			return f(*args, **kwargs)
+		except Exception:
+			import traceback
+
+			traceback.print_exc()
+
+			raise
+
+	return wrapper
+
 @contextlib.contextmanager
 def tempset(obj, key, value):
 	'''A context (with) manager for changing the value of an item in a
@@ -88,6 +105,26 @@ def tempattrset(obj, key, value):
 		else:
 			delattr(obj, key)
 
+class IPFSCAS(object):
+	gwhost = 'gateway.ipfs.io'
+	gwhost = 'cloudflare-ipfs.com'
+
+	def make_url(self, url):
+		return urllib.parse.urlunparse(('https', self.gwhost,
+		    '/ipfs/' + url.netloc) + ('', ) * 3)
+
+	def fetch_data(self, url):
+		if url.scheme != 'ipfs':
+			raise ValueError('cannot handle scheme %s' %
+			    repr(url.scheme))
+		gwurl = self.make_url(url)
+
+		with urllib.request.urlopen(gwurl) as req:
+			if req.status // 100 != 2:
+				raise RuntimeError('bad fetch')
+
+			return req.read()
+
 class FileDirCAS(object):
 	'''A file loader for CAS that operates on a directory.  It looks
 	at files, caches their hash, and loads them upon request.'''
@@ -296,6 +333,7 @@ def defaultinit(casf):
 	cachedir.mkdir(exist_ok=True)
 
 	casf.register(FileDirCAS(cachedir))
+	casf.register(IPFSCAS())
 
 # The global version
 _casfinder = CASFinder()
@@ -423,6 +461,9 @@ class Test(unittest.TestCase):
 				# it can be imported
 				from cas.v1_f_330884aa2febb5e19fb7194ec6a69ed11dd3d77122f1a5175ee93e73cf0161c3 import hello
 
+				# and that the last loader is the IPFSCAS
+				self.assertIsInstance(f._loaders[-1], IPFSCAS)
+
 			with CASFinder() as f:
 				defaultinit(f)
 
@@ -514,6 +555,35 @@ class Test(unittest.TestCase):
 		finally:
 			sys.path.remove(fixdir)
 
+	@mock.patch('urllib.request.urlopen')
+	def test_ipfscasloader(self, uomock):
+		# prep return test data
+		with open(self.fixtures / 'hello.py') as fp:
+			# that returns the correct data
+			ipfsdata = fp.read()
+
+		# that the ipfs CAS loader
+		ipfs = IPFSCAS()
+
+		# that the request is successfull
+		uomock.return_value.__enter__.return_value.status = 200
+
+		# and returns the correct data
+		uomock.return_value.__enter__.return_value.read.return_value = ipfsdata
+
+		# that when called
+		hashurl = urllib.parse.urlparse('ipfs://bafkreibtbcckul7lwxqz7nyzj3dknhwrdxj5o4jc6gsroxxjhzz46albym')
+		data = ipfs.fetch_data(hashurl)
+
+		# it opens the correct url
+		uomock.assert_called_with('https://cloudflare-ipfs.com/ipfs/bafkreibtbcckul7lwxqz7nyzj3dknhwrdxj5o4jc6gsroxxjhzz46albym')
+
+		# and returns the correct data
+		self.assertEqual(data, ipfsdata)
+
+		with self.assertRaises(ValueError):
+			ipfs.fetch_data(urllib.parse.urlparse('hash://sha256/asldfkj'))
+
 	def test_overlappingaliases(self):
 		# make sure that an aliases file is consistent and does not
 		# override other urls.  That is that any hashes are