proto: Switch 'compress' type on the wire from Optional[int] to bool

This patch aims to switch the compression parameter to the same
data type that it had before the introduction of msgpack: boolean [1].

1. It’s a smaller size on the wire [2].
2. It simplifies NEO/go code (we don't need to re-implement pythons
   __bool__ in golang to cast Optional[int] into a boolean).
3. It doesn’t complicate NEO/py code: in fact it doesn’t even
   need a protocol change because __bool__ keeps the same.
4. It’s more coherent regarding the protocol: compression can really only
   be either True or False. A compression of any other value than 0 or 1
   is meaningless.

We now need to explicitly cast compression to bool and not forget this when
adding new packets / code, but this is the same what happened to other packet
arguments (last argument of AskStoreTransaction needs to be explicitly cast
to list after switch to msgpack [3]).

---

[1] https://lab.nexedi.com/nexedi/neoppod/-/blob/ee44a3b0/neo/lib/protocol.py#L1113
[2] See msgpack specification: https://github.com/msgpack/msgpack/blob/master/spec.md?plain=1#L166-L178
[3] nexedi/neoppod@9d0bf97a

neo/client/app.py

@@ -528,7 +528,7 @@ class Application(ThreadedApplication):
             checksum = makeChecksum(compressed_data)
             txn_context.data_size += size
         # Store object in tmp cache
-        packet = Packets.AskStoreObject(oid, serial, compression,
+        packet = Packets.AskStoreObject(oid, serial, bool(compression),
             checksum, compressed_data, data_serial, ttid)
         txn_context.data_dict[oid] = data, serial, txn_context.write(
             self, packet, oid, oid=oid, serial=serial)

neo/storage/database/importer.py

@@ -658,7 +658,7 @@ class ImporterDatabaseManager(DatabaseManager):
             next_serial = db._getNextTID(db._getPartition(u_oid), u_oid, u_tid)
             if next_serial:
                 next_serial = p64(next_serial)
-        return (serial, next_serial, 0,
+        return (serial, next_serial, False,
                 util.makeChecksum(value),
                 value,
                 zodb.getDataTid(z_oid, u_tid))

neo/storage/database/manager.py

@@ -935,7 +935,7 @@ class DatabaseManager(object):
             6-tuple: Record content.
                 - record serial (packed)
                 - serial or next record modifying object (packed, None)
-                - compression (boolean-ish, None)
+                - compression (boolean)
                 - checksum (binary string, None)
                 - data (binary string, None)
                 - data_serial (packed, None)
@@ -950,7 +950,7 @@ class DatabaseManager(object):
             return (tid or before_tid) and self.getLastObjectTID(oid) and False
         return (util.p64(serial),
                 None if next_serial is None else util.p64(next_serial),
-                compression, checksum, data,
+                bool(compression), checksum, data,
                 None if data_serial is None else util.p64(data_serial))
 
     @fallback
@@ -973,7 +973,7 @@ class DatabaseManager(object):
         r = self._fetchObject(u64(oid), u64(tid))
         if r:
             serial, compression, checksum, data, data_serial = r
-            return (util.p64(serial), compression, checksum, data,
+            return (util.p64(serial), bool(compression), checksum, data,
                 None if data_serial is None else util.p64(data_serial))
 
     @requires(_getPartitionTable)

neo/storage/handlers/client.py

@@ -120,8 +120,6 @@ class ClientOperationHandler(BaseHandler):
 
     def askStoreObject(self, conn, oid, serial,
             compression, checksum, data, data_serial, ttid):
-        if 1 < compression:
-            raise ProtocolError('invalid compression value')
         # register the transaction
         self.app.tm.register(conn, ttid)
         if data or checksum != ZERO_HASH: