download: stop using deprecated urlretrieve

src/zc/buildout/download.py

@@ -20,7 +20,7 @@ except ImportError:
 
 try:
     # Python 3
-    from urllib.request import urlretrieve
+    from urllib.request import build_opener, Request
     from urllib.parse import urlparse
 except ImportError:
     # Python 2
@@ -28,8 +28,9 @@ except ImportError:
     from urlparse import urlparse
     from urlparse import urlunparse
     import urllib2
+    from urllib2 import build_opener
 
-    def urlretrieve(url, tmp_path):
+    def Request(url):
         """Work around Python issue 24599 includig basic auth support
         """
         scheme, netloc, path, params, query, frag = urlparse(url)
@@ -42,10 +43,7 @@ except ImportError:
             req.add_header("Authorization", basic)
         else:
             req = urllib2.Request(url)
-        url_obj = urllib2.urlopen(req)
-        with open(tmp_path, 'wb') as fp:
-            fp.write(url_obj.read())
-        return tmp_path, url_obj.info()
+        return req
 
 
 from zc.buildout.easy_install import realpath
@@ -57,6 +55,16 @@ import shutil
 import tempfile
 import zc.buildout
 
+_opener = None
+
+def urlretrieve(url, tmp_path):
+    global _opener
+    if _opener is None:
+        _opener = build_opener()
+    url_obj = _opener.open(Request(url))
+    with open(tmp_path, 'wb') as fp:
+        shutil.copyfileobj(url_obj, fp)
+    return tmp_path, url_obj.info()
 
 class ChecksumError(zc.buildout.UserError):
     pass