backup: Implement network backup

backup/socketbackend.py

@@ -0,0 +1,80 @@
+import json
+import logging, socket, struct
+from typing import Tuple, Iterator
+from urllib.parse import urlparse
+
+from backend import Backend, Change
+from protocol import PacketType, recvall, PKT_CHANGE_TYPES, change_from_packet, packet_from_change, send_packet, recv_packet
+
+class SocketBackend(Backend):
+    def __init__(self, destination: str, create: bool):
+        self.version = None
+        self.prev_version = None
+        self.destination = destination
+        self.url = urlparse(self.destination)
+        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        (host, port) = self.url.path.split(':')
+        logging.info('Initialized socket backend')
+        self.sock.connect((host, int(port)))
+        logging.info('Connected to {}'.format(destination))
+
+    def _send_packet(self, typ: int, payload: bytes) -> None:
+        send_packet(self.sock, typ, payload)
+
+    def _recv_packet(self) -> Tuple[int, bytes]:
+        return recv_packet(self.sock)
+
+    def initialize(self) -> bool:
+        '''
+        Initialize socket backend by request current metadata from server.
+        '''
+        logging.info('Initializing backend')
+        self._send_packet(PacketType.REQ_METADATA, b'')
+        (typ, payload) = self._recv_packet()
+        assert(typ == PacketType.METADATA)
+        self.protocol, self.version, self.prev_version, self.version_count = struct.unpack("!IIIQ", payload)
+        logging.info('Initialized SocketBackend: protocol={}, version={}, prev_version={}, version_count={}'.format(
+            self.protocol, self.version, self.prev_version, self.version_count
+        ))
+        return True
+
+    def add_change(self, entry: Change) -> bool:
+        typ, payload = packet_from_change(entry)
+        self._send_packet(typ, payload)
+        # Wait for change to be acknowledged before continuing.
+        (typ, _) = self._recv_packet()
+        assert(typ == PacketType.ACK)
+        return True
+
+    def rewind(self) -> bool:
+        '''Rewind to previous version.'''
+        version = struct.pack("!I", self.prev_version)
+        self._send_packet(PacketType.REWIND, version)
+        # Wait for change to be acknowledged before continuing.
+        (typ, _) = self._recv_packet()
+        assert(typ == PacketType.ACK)
+        return True
+
+    def stream_changes(self) -> Iterator[Change]:
+        self._send_packet(PacketType.RESTORE, b'')
+        version = -1
+        while True:
+            (typ, payload) = self._recv_packet()
+            if typ in PKT_CHANGE_TYPES:
+                change = change_from_packet(typ, payload)
+                version = change.version
+                yield change
+            elif typ == PacketType.DONE:
+                break
+            else:
+                raise ValueError("Unknown entry type {}".format(typ))
+
+        if version != self.version:
+            raise ValueError("Versions do not match up: restored version {}, backend version {}".format(version, self.version))
+        assert(version == self.version)
+
+    def compact(self):
+        self._send_packet(PacketType.COMPACT, b'')
+        (typ, payload) = self._recv_packet()
+        assert(typ == PacketType.COMPACT_RES)
+        return json.loads(payload.decode())