diff --git a/IPython/kernel/adapter.py b/IPython/kernel/adapter.py
new file mode 100644
index 0000000..615ac47
--- /dev/null
+++ b/IPython/kernel/adapter.py
@@ -0,0 +1,295 @@
+"""Adapters for IPython msg spec versions."""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+import json
+
+from IPython.core.release import kernel_protocol_version, kernel_protocol_version_info
+from IPython.utils.tokenutil import token_at_cursor
+
+
+def code_to_line(code, cursor_pos):
+ """Turn a multiline code block and cursor position into a single line
+ and new cursor position.
+
+ For adapting complete_ and object_info_requests.
+ """
+ for line in code.splitlines(True):
+ n = len(line)
+ if cursor_pos > n:
+ cursor_pos -= n
+ else:
+ break
+ return line, cursor_pos
+
+
+class Adapter(object):
+ """Base class for adapting messages
+
+ Override message_type(msg) methods to create adapters.
+ """
+
+ msg_type_map = {}
+
+ def update_header(self, msg):
+ return msg
+
+ def update_metadata(self, msg):
+ return msg
+
+ def update_msg_type(self, msg):
+ header = msg['header']
+ msg_type = header['msg_type']
+ if msg_type in self.msg_type_map:
+ msg['msg_type'] = header['msg_type'] = self.msg_type_map[msg_type]
+ return msg
+
+ def __call__(self, msg):
+ msg = self.update_header(msg)
+ msg = self.update_metadata(msg)
+ msg = self.update_msg_type(msg)
+ header = msg['header']
+
+ handler = getattr(self, header['msg_type'], None)
+ if handler is None:
+ return msg
+ return handler(msg)
+
+def _version_str_to_list(version):
+ """convert a version string to a list of ints
+
+ non-int segments are excluded
+ """
+ v = []
+ for part in content[key].split('.'):
+ try:
+ v.append(int(part))
+ except ValueError:
+ pass
+ return v
+
+class V5toV4(Adapter):
+ """Adapt msg protocol v5 to v4"""
+
+ version = '4.1'
+
+ msg_type_map = {
+ 'execute_result' : 'pyout',
+ 'execute_input' : 'pyin',
+ 'error' : 'pyerr',
+ 'inspect_request' : 'object_info_request',
+ 'inspect_reply' : 'object_info_reply',
+ }
+
+ def update_header(self, msg):
+ msg['header'].pop('version', None)
+ return msg
+
+ # shell channel
+
+ def kernel_info_reply(self, msg):
+ content = msg['content']
+ content.pop('banner', None)
+ for key in ('language_version', 'protocol_version'):
+ if key in content:
+ content[key] = _version_str_to_list(content[key])
+ if content.pop('implementation', '') == 'ipython' \
+ and 'implementation_version' in content:
+ content['ipython_version'] = content.pop('implmentation_version')
+ content.pop('implementation_version', None)
+ content.setdefault("implmentation", content['language'])
+ return msg
+
+ def execute_request(self, msg):
+ content = msg['content']
+ content.setdefault('user_variables', [])
+ return msg
+
+ def execute_reply(self, msg):
+ content = msg['content']
+ content.setdefault('user_variables', {})
+ # TODO: handle payloads
+ return msg
+
+ def complete_request(self, msg):
+ content = msg['content']
+ code = content['code']
+ cursor_pos = content['cursor_pos']
+ line, cursor_pos = code_to_line(code, cursor_pos)
+
+ new_content = msg['content'] = {}
+ new_content['text'] = ''
+ new_content['line'] = line
+ new_content['blob'] = None
+ new_content['cursor_pos'] = cursor_pos
+ return msg
+
+ def complete_reply(self, msg):
+ content = msg['content']
+ cursor_start = content.pop('cursor_start')
+ cursor_end = content.pop('cursor_end')
+ match_len = cursor_end - cursor_start
+ content['matched_text'] = content['matches'][0][:match_len]
+ content.pop('metadata', None)
+ return msg
+
+ def object_info_request(self, msg):
+ content = msg['content']
+ code = content['code']
+ cursor_pos = content['cursor_pos']
+ line, cursor_pos = code_to_line(code, cursor_pos)
+
+ new_content = msg['content'] = {}
+ new_content['name'] = token_at_cursor(code, cursor_pos)
+ new_content['detail_level'] = content['detail_level']
+ return msg
+
+ def object_info_reply(self, msg):
+ """inspect_reply can't be easily backward compatible"""
+ msg['content'] = {'found' : False, 'name' : 'unknown'}
+ return msg
+
+ # iopub channel
+
+ def display_data(self, msg):
+ content = msg['content']
+ content.setdefault("source", "display")
+ return msg
+
+ # stdin channel
+
+ def input_request(self, msg):
+ msg['content'].pop('password', None)
+ return msg
+
+def _tuple_to_str(version):
+ return ".".join(map(str, version))
+
+class V4toV5(Adapter):
+ """Convert msg spec V4 to V5"""
+ version = kernel_protocol_version
+
+ # invert message renames above
+ msg_type_map = {v:k for k,v in V5toV4.msg_type_map.items()}
+
+ def update_header(self, msg):
+ msg['header']['version'] = self.version
+ return msg
+
+ # shell channel
+
+ def kernel_info_reply(self, msg):
+ content = msg['content']
+ for key in ('language_version', 'protocol_version', 'ipython_version'):
+ if key in content:
+ content[key] = ".".join(map(str, content[key]))
+
+ if content['language'].startswith('python') and 'ipython_version' in content:
+ content['implementation'] = 'ipython'
+ content['implementation_version'] = content.pop('ipython_version')
+
+ content['banner'] = ''
+ return msg
+
+ def execute_request(self, msg):
+ content = msg['content']
+ user_variables = content.pop('user_variables', [])
+ user_expressions = content.setdefault('user_expressions', {})
+ for v in user_variables:
+ user_expressions[v] = v
+ return msg
+
+ def execute_reply(self, msg):
+ content = msg['content']
+ user_expressions = content.setdefault('user_expressions', {})
+ user_variables = content.pop('user_variables', {})
+ if user_variables:
+ user_expressions.update(user_variables)
+ return msg
+
+ def complete_request(self, msg):
+ old_content = msg['content']
+
+ new_content = msg['content'] = {}
+ new_content['code'] = old_content['line']
+ new_content['cursor_pos'] = old_content['cursor_pos']
+ return msg
+
+ def complete_reply(self, msg):
+ # TODO: complete_reply needs more context than we have
+ # Maybe strip common prefix and give magic cursor_start = cursor_end = 0?
+ content = msg['content'] = {}
+ content['matches'] = []
+ content['cursor_start'] = content['cursor_end'] = 0
+ content['metadata'] = {}
+ return msg
+
+ def inspect_request(self, msg):
+ content = msg['content']
+ name = content['name']
+
+ new_content = msg['content'] = {}
+ new_content['code'] = name
+ new_content['cursor_pos'] = len(name) - 1
+ new_content['detail_level'] = content['detail_level']
+ return msg
+
+ def inspect_reply(self, msg):
+ """inspect_reply can't be easily backward compatible"""
+ msg['content'] = {'found' : False, 'name' : 'unknown'}
+ return msg
+
+ # iopub channel
+
+ def display_data(self, msg):
+ content = msg['content']
+ content.pop("source", None)
+ data = content['data']
+ if 'application/json' in data:
+ data['application/json'] = json.dumps(data['application/json'])
+ return msg
+
+ # stdin channel
+
+ def input_request(self, msg):
+ msg['content'].setdefault('password', False)
+ return msg
+
+
+
+def adapt(msg, to_version=kernel_protocol_version_info[0]):
+ """Adapt a single message to a target version
+
+ Parameters
+ ----------
+
+ msg : dict
+ An IPython message.
+ to_version : int, optional
+ The target major version.
+ If unspecified, adapt to the current version for IPython.
+
+ Returns
+ -------
+
+ msg : dict
+ An IPython message appropriate in the new version.
+ """
+ header = msg['header']
+ if 'version' in header:
+ from_version = int(header['version'].split('.')[0])
+ else:
+ # assume last version before adding the key to the header
+ from_version = 4
+ adapter = adapters.get((from_version, to_version), None)
+ if adapter is None:
+ return msg
+ return adapter(msg)
+
+
+# one adapter per major version from,to
+adapters = {
+ (5,4) : V5toV4(),
+ (4,5) : V4toV5(),
+}
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