Added class-method get_handshake

The Bolt.get_handshake() returns bytes that is used in the version
negotiation.

Author: martin-neotech

neo4j/io/__init__.py

@@ -94,6 +94,15 @@ class Bolt:
 
     PROTOCOL_VERSION = None
 
+    @classmethod
+    def get_handshake(cls):
+        """ Return the supported Bolt versions as bytes.
+        The length is 16 bytes as specified in the Bolt version negotiation.
+        :return: bytes
+        """
+        offered_versions = sorted(cls.protocol_handlers().keys(), reverse=True)[:4]
+        return b"".join(version.to_bytes() for version in offered_versions).ljust(16, b"\x00")
+
     @classmethod
     def protocol_handlers(cls, protocol_version=None):
         """ Return a dictionary of available Bolt protocol handlers,

tests/unit/io/test_class_bolt.py

@@ -48,3 +48,9 @@ def test_class_method_protocol_handlers_with_invalid_protocol_version():
     # python -m pytest tests/unit/io/test_class_bolt.py -s -v -k test_class_method_protocol_handlers_with_invalid_protocol_version
     with pytest.raises(TypeError):
         Bolt.protocol_handlers(protocol_version=2)
+
+
+def test_class_method_get_handshake():
+    # python -m pytest tests/unit/io/test_class_bolt.py -s -v -k test_class_method_get_handshake
+    handshake = Bolt.get_handshake()
+    assert handshake == b"\x00\x00\x00\x04\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00\x00"