Enable exporting inbound group session keys

A pair of functions which allow you to export the megolm keys for an inbound
group session, so that an application can save/restore them.

2 files changed, 48 insertions, 1 deletions

diff --git a/python/olm/__main__.py b/python/olm/__main__.py
index eb76301..f195591 100755
--- a/python/olm/__main__.py
+++ b/python/olm/__main__.py
@@ -277,6 +277,27 @@ def build_arg_parser():
                                type=argparse.FileType('wb'), nargs='?',
                                default=sys.stdout)
     group_decrypt.set_defaults(func=do_group_decrypt)
+
+
+    export_inbound_group = commands.add_parser(
+        "export_inbound_group",
+        help="Export the keys for an inbound group session",
+    )
+    export_inbound_group.add_argument(
+        "session_file", help="Local inbound group session file",
+    )
+    export_inbound_group.add_argument(
+        "export_file", help="File to export to (default stdout)",
+        type=argparse.FileType('w'), nargs='?',
+        default=sys.stdout,
+    )
+    export_inbound_group.add_argument(
+        "--message_index",
+        help="Index to export session at. Defaults to the earliest known index",
+        type=int,
+    )
+    export_inbound_group.set_defaults(func=do_export_inbound_group)
+
     return parser
 
 def do_outbound_group(args):
@@ -333,6 +354,15 @@ def do_group_decrypt(args):
         f.write(session.pickle(args.key))
     args.plaintext_file.write(plaintext)
 
+def do_export_inbound_group(args):
+    session = InboundGroupSession()
+    session.unpickle(args.key, read_base64_file(args.session_file))
+    index = args.message_index
+    if index is None:
+        # default to first known index
+        index = session.first_known_index()
+    args.export_file.write(session.export_session(index))
+
 if __name__ == '__main__':
     parser = build_arg_parser()
     args = parser.parse_args()
diff --git a/python/olm/inbound_group_session.py b/python/olm/inbound_group_session.py
index 27a569c..67906b2 100644
--- a/python/olm/inbound_group_session.py
+++ b/python/olm/inbound_group_session.py
@@ -49,6 +49,13 @@ inbound_group_session_function(
 inbound_group_session_function(lib.olm_inbound_group_session_id_length)
 inbound_group_session_function(lib.olm_inbound_group_session_id, c_void_p, c_size_t)
 
+lib.olm_inbound_group_session_first_known_index.argtypes = (c_void_p,)
+lib.olm_inbound_group_session_first_known_index.restypes = c_uint32
+
+inbound_group_session_function(lib.olm_export_inbound_group_session_length)
+inbound_group_session_function(lib.olm_export_inbound_group_session, c_void_p, c_size_t, c_uint32)
+
+
 class InboundGroupSession(object):
     def __init__(self):
         self.buf = create_string_buffer(lib.olm_inbound_group_session_size())
@@ -95,5 +102,15 @@ class InboundGroupSession(object):
     def session_id(self):
         id_length = lib.olm_inbound_group_session_id_length(self.ptr)
         id_buffer = create_string_buffer(id_length)
-        lib.olm_inbound_group_session_id(self.ptr, id_buffer, id_length);
+        lib.olm_inbound_group_session_id(self.ptr, id_buffer, id_length)
         return id_buffer.raw
+
+    def first_known_index(self):
+        return lib.olm_inbound_group_session_first_known_index(self.ptr)
+
+    def export_session(self, message_index):
+        length = lib.olm_export_inbound_group_session_length(self.ptr)
+        buffer = create_string_buffer(length)
+        lib.olm_export_inbound_group_session(self.ptr, buffer, length,
+                                             message_index)
+        return buffer.raw