Add ALPN support.

OpenSSL/SSL.py

@@ -5,6 +5,7 @@
 from errno import errorcode
 
 from six import text_type as _text_type
+from six import binary_type as _binary_type
 from six import integer_types as integer_types
 from six import int2byte, indexbytes
 
@@ -318,6 +319,56 @@ def wrapper(ssl, out, outlen, in_, inlen, arg):
         )
 
 
+class _ALPNSelectHelper(_CallbackExceptionHelper):
+    """
+    Wrap a callback such that it can be used as an ALPN selection callback.
+    """
+    def __init__(self, callback):
+        _CallbackExceptionHelper.__init__(self)
+
+        @wraps(callback)
+        def wrapper(ssl, out, outlen, in_, inlen, arg):
+            try:
+                conn = Connection._reverse_mapping[ssl]
+
+                # The string passed to us is made up of multiple
+                # length-prefixed bytestrings. We need to split that into a
+                # list.
+                instr = _ffi.buffer(in_, inlen)[:]
+                protolist = []
+                while instr:
+                    encoded_len = indexbytes(instr, 0)
+                    proto = instr[1:encoded_len + 1]
+                    protolist.append(proto)
+                    instr = instr[encoded_len + 1:]
+
+                # Call the callback
+                outstr = callback(conn, protolist)
+
+                if not isinstance(outstr, _binary_type):
+                    raise TypeError("ALPN callback must return a bytestring.")
+
+                # Save our callback arguments on the connection object to make
+                # sure that they don't get freed before OpenSSL can use them.
+                # Then, return them in the appropriate output parameters.
+                conn._alpn_select_callback_args = [
+                    _ffi.new("unsigned char *", len(outstr)),
+                    _ffi.new("unsigned char[]", outstr),
+                ]
+                outlen[0] = conn._alpn_select_callback_args[0][0]
+                out[0] = conn._alpn_select_callback_args[1]
+                return 0
+            except Exception as e:
+                self._problems.append(e)
+                return 2  # SSL_TLSEXT_ERR_ALERT_FATAL
+
+        self.callback = _ffi.callback(
+            "int (*)(SSL *, unsigned char **, unsigned char *, "
+                    "const unsigned char *, unsigned int, void *)",
+            wrapper
+        )
+
+
 def _asFileDescriptor(obj):
     fd = None
     if not isinstance(obj, integer_types):
@@ -348,6 +399,22 @@ def SSLeay_version(type):
 
 
 
+def _requires_alpn(func):
+    """
+    Wraps any function that requires ALPN support in OpenSSL, ensuring that
+    NotImplementedError is raised if ALPN support is not present.
+    """
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        if not _lib.Cryptography_HAS_ALPN:
+            raise NotImplementedError("ALPN not available.")
+
+        return func(*args, **kwargs)
+
+    return wrapper
+
+
+
 class Session(object):
     pass
 
@@ -409,6 +476,8 @@ def __init__(self, method):
         self._npn_advertise_callback = None
         self._npn_select_helper = None
         self._npn_select_callback = None
+        self._alpn_select_helper = None
+        self._alpn_select_callback = None
 
         # SSL_CTX_set_app_data(self->ctx, self);
         # SSL_CTX_set_mode(self->ctx, SSL_MODE_ENABLE_PARTIAL_WRITE |
@@ -923,7 +992,6 @@ def wrapper(ssl, alert, arg):
         _lib.SSL_CTX_set_tlsext_servername_callback(
             self._context, self._tlsext_servername_callback)
 
-
     def set_npn_advertise_callback(self, callback):
         """
         Specify a callback function that will be called when offering `Next
@@ -956,6 +1024,44 @@ def set_npn_select_callback(self, callback):
         _lib.SSL_CTX_set_next_proto_select_cb(
             self._context, self._npn_select_callback, _ffi.NULL)
 
+    @_requires_alpn
+    def set_alpn_protos(self, protos):
+        """
+        Specify the clients ALPN protocol list.
+
+        These protocols are offered to the server during protocol negotiation.
+
+        :param protos: A list of the protocols to be offered to the server.
+            This list should be a Python list of bytestrings representing the
+            protocols to offer, e.g. ``[b'http/1.1', b'spdy/2']``.
+        """
+        # Take the list of protocols and join them together, prefixing them
+        # with their lengths.
+        protostr = b''.join(
+            chain.from_iterable((int2byte(len(p)), p) for p in protos)
+        )
+
+        # Build a C string from the list. We don't need to save this off
+        # because OpenSSL immediately copies the data out.
+        input_str = _ffi.new("unsigned char[]", protostr)
+        input_str_len = _ffi.cast("unsigned", len(protostr))
+        _lib.SSL_CTX_set_alpn_protos(self._context, input_str, input_str_len)
+
+    @_requires_alpn
+    def set_alpn_select_callback(self, callback):
+        """
+        Set the callback to handle ALPN protocol choice.
+
+        :param callback: The callback function.  It will be invoked with two
+            arguments: the Connection, and a list of offered protocols as
+            bytestrings, e.g ``[b'http/1.1', b'spdy/2']``.  It should return
+            one of those bytestrings, the chosen protocol.
+        """
+        self._alpn_select_helper = _ALPNSelectHelper(callback)
+        self._alpn_select_callback = self._alpn_select_helper.callback
+        _lib.SSL_CTX_set_alpn_select_cb(
+            self._context, self._alpn_select_callback, _ffi.NULL)
+
 ContextType = Context
 
 
@@ -987,6 +1093,12 @@ def __init__(self, context, socket=None):
         self._npn_advertise_callback_args = None
         self._npn_select_callback_args = None
 
+        # References to strings used for Application Layer Protocol
+        # Negotiation. These strings get copied at some point but it's well
+        # after the callback returns, so we have to hang them somewhere to
+        # avoid them getting freed.
+        self._alpn_select_callback_args = None
+
         self._reverse_mapping[self._ssl] = self
 
         if socket is None:
@@ -1025,6 +1137,8 @@ def _raise_ssl_error(self, ssl, result):
             self._context._npn_advertise_helper.raise_if_problem()
         if self._context._npn_select_helper is not None:
             self._context._npn_select_helper.raise_if_problem()
+        if self._context._alpn_select_helper is not None:
+            self._context._alpn_select_helper.raise_if_problem()
 
         error = _lib.SSL_get_error(ssl, result)
         if error == _lib.SSL_ERROR_WANT_READ:
@@ -1757,6 +1871,46 @@ def get_next_proto_negotiated(self):
 
         return _ffi.buffer(data[0], data_len[0])[:]
 
+    @_requires_alpn
+    def set_alpn_protos(self, protos):
+        """
+        Specify the client's ALPN protocol list.
+
+        These protocols are offered to the server during protocol negotiation.
+
+        :param protos: A list of the protocols to be offered to the server.
+            This list should be a Python list of bytestrings representing the
+            protocols to offer, e.g. ``[b'http/1.1', b'spdy/2']``.
+        """
+        # Take the list of protocols and join them together, prefixing them
+        # with their lengths.
+        protostr = b''.join(
+            chain.from_iterable((int2byte(len(p)), p) for p in protos)
+        )
+
+        # Build a C string from the list. We don't need to save this off
+        # because OpenSSL immediately copies the data out.
+        input_str = _ffi.new("unsigned char[]", protostr)
+        input_str_len = _ffi.cast("unsigned", len(protostr))
+        _lib.SSL_set_alpn_protos(self._ssl, input_str, input_str_len)
+
+
+    def get_alpn_proto_negotiated(self):
+        """Get the protocol that was negotiated by ALPN."""
+        if not _lib.Cryptography_HAS_ALPN:
+            raise NotImplementedError("ALPN not available")
+
+        data = _ffi.new("unsigned char **")
+        data_len = _ffi.new("unsigned int *")
+
+        _lib.SSL_get0_alpn_selected(self._ssl, data, data_len)
+
+        if not data_len:
+            return b''
+
+        return _ffi.buffer(data[0], data_len[0])[:]
+
+
 
 ConnectionType = Connection