add a tls_prefix parameter to utils.request

This assumes that a backend only ever connects to a single domain, because we
set the fingerprint on the whole session

vdirsyncer/utils/__init__.py

@@ -12,6 +12,7 @@ import os
 import click
 
 import requests
+from requests.packages.urllib3.poolmanager import PoolManager
 
 from .. import exceptions, log
 from .compat import iteritems, urlparse
@@ -178,8 +179,23 @@ def _password_from_keyring(username, resource):
         key = new_key
 
 
+class _FingerprintAdapter(requests.adapters.HTTPAdapter):
+    def __init__(self, fingerprint=None, **kwargs):
+        self.fingerprint = str(fingerprint)
+        super(_FingerprintAdapter, self).__init__(**kwargs)
+
+    def send(self, *args, **kwargs):
+        return super(_FingerprintAdapter, self).send(*args, **kwargs)
+
+    def init_poolmanager(self, connections, maxsize, block=False):
+        self.poolmanager = PoolManager(num_pools=connections,
+                                       maxsize=maxsize,
+                                       block=block,
+                                       assert_fingerprint=self.fingerprint)
+
+
 def request(method, url, data=None, headers=None, auth=None, verify=None,
-            session=None, latin1_fallback=True):
+            session=None, latin1_fallback=True, tls_fingerprint=None):
     '''
     Wrapper method for requests, to ease logging and mocking. Parameters should
     be the same as for ``requests.request``, except:
@@ -194,9 +210,16 @@ def request(method, url, data=None, headers=None, auth=None, verify=None,
     '''
 
     if session is None:
-        func = requests.request
-    else:
-        func = session.request
+        session = requests.Session()
+
+    if tls_fingerprint is not None:
+        https_prefix = 'https://'
+
+        if not isinstance(session.adapters[https_prefix], _FingerprintAdapter):
+            fingerprint_adapter = _FingerprintAdapter(tls_fingerprint)
+            session.mount(https_prefix, fingerprint_adapter)
+
+    func = session.request
 
     logger.debug(u'{} {}'.format(method, url))
     logger.debug(headers)