Deprecated NPN (#820)

* Deprecated NPN

* arithmetic is hard

* oops

* oops

CHANGELOG.rst

@@ -18,7 +18,9 @@ Backward-incompatible changes:
 Deprecations:
 ^^^^^^^^^^^^^
 
-*none*
+- Deprecated ``OpenSSL.SSL.Context.set_npn_advertise_callback``, ``OpenSSL.SSL.Context.set_npn_select_callback``, and ``OpenSSL.SSL.Connection.get_next_proto_negotiated``.
+  ALPN should be used instead.
+  `#820 <https://github.com/pyca/pyopenssl/pull/820>`_
 
 
 Changes:

src/OpenSSL/SSL.py

@@ -1,5 +1,6 @@
 import os
 import socket
+import warnings
 from sys import platform
 from functools import wraps, partial
 from itertools import count, chain
@@ -626,6 +627,11 @@ def SSLeay_version(type):
     return _ffi.string(_lib.SSLeay_version(type))
 
 
+def _warn_npn():
+    warnings.warn("NPN is deprecated. Protocols should switch to using ALPN.",
+                  DeprecationWarning, stacklevel=3)
+
+
 def _make_requires(flag, error):
     """
     Builds a decorator that ensures that functions that rely on OpenSSL
@@ -1415,6 +1421,7 @@ def set_npn_advertise_callback(self, callback):
 
         .. versionadded:: 0.15
         """
+        _warn_npn()
         self._npn_advertise_helper = _NpnAdvertiseHelper(callback)
         self._npn_advertise_callback = self._npn_advertise_helper.callback
         _lib.SSL_CTX_set_next_protos_advertised_cb(
@@ -1433,6 +1440,7 @@ def set_npn_select_callback(self, callback):
 
         .. versionadded:: 0.15
         """
+        _warn_npn()
         self._npn_select_helper = _NpnSelectHelper(callback)
         self._npn_select_callback = self._npn_select_helper.callback
         _lib.SSL_CTX_set_next_proto_select_cb(
@@ -2437,6 +2445,7 @@ def get_next_proto_negotiated(self):
 
         .. versionadded:: 0.15
         """
+        _warn_npn()
         data = _ffi.new("unsigned char **")
         data_len = _ffi.new("unsigned int *")