PYTHON-5713 Allow using OP_MSG exclusively

pymongo/asynchronous/command_cursor.py

@@ -24,14 +24,13 @@
     NoReturn,
     Optional,
     Sequence,
-    Union,
 )
 
 from bson import CodecOptions, _convert_raw_document_lists_to_streams
 from pymongo.asynchronous.cursor_base import _AsyncCursorBase, _ConnectionManager
 from pymongo.cursor_shared import _CURSOR_CLOSED_ERRORS
 from pymongo.errors import ConnectionFailure, InvalidOperation, OperationFailure
-from pymongo.message import _GetMore, _OpMsg, _OpReply, _RawBatchGetMore
+from pymongo.message import _GetMore, _OpMsg, _RawBatchGetMore
 from pymongo.response import PinnedResponse
 from pymongo.typings import _Address, _DocumentOut, _DocumentType
 
@@ -145,7 +144,7 @@ async def _maybe_pin_connection(self, conn: AsyncConnection) -> None:
 
     def _unpack_response(
         self,
-        response: Union[_OpReply, _OpMsg],
+        response: _OpMsg,
         cursor_id: Optional[int],
         codec_options: CodecOptions[Mapping[str, Any]],
         user_fields: Optional[Mapping[str, Any]] = None,
@@ -189,15 +188,10 @@ async def _send_message(self, operation: _GetMore) -> None:
         if isinstance(response, PinnedResponse):
             if not self._sock_mgr:
                 self._sock_mgr = _ConnectionManager(response.conn, response.more_to_come)  # type: ignore[arg-type]
-        if response.from_command:
-            cursor = response.docs[0]["cursor"]
-            documents = cursor["nextBatch"]
-            self._postbatchresumetoken = cursor.get("postBatchResumeToken")
-            self._id = cursor["id"]
-        else:
-            documents = response.docs
-            assert isinstance(response.data, _OpReply)
-            self._id = response.data.cursor_id
+        cursor = response.docs[0]["cursor"]
+        documents = cursor["nextBatch"]
+        self._postbatchresumetoken = cursor.get("postBatchResumeToken")
+        self._id = cursor["id"]
 
         if self._id == 0:
             await self.close()
@@ -333,7 +327,7 @@ def __init__(
 
     def _unpack_response(  # type: ignore[override]
         self,
-        response: Union[_OpReply, _OpMsg],
+        response: _OpMsg,
         cursor_id: Optional[int],
         codec_options: CodecOptions[dict[str, Any]],
         user_fields: Optional[Mapping[str, Any]] = None,

pymongo/asynchronous/cursor.py

@@ -48,7 +48,6 @@
 from pymongo.message import (
     _GetMore,
     _OpMsg,
-    _OpReply,
     _Query,
     _RawBatchGetMore,
     _RawBatchQuery,
@@ -864,7 +863,7 @@ def collation(self, collation: Optional[_CollationIn]) -> AsyncCursor[_DocumentT
 
     def _unpack_response(
         self,
-        response: Union[_OpReply, _OpMsg],
+        response: _OpMsg,
         cursor_id: Optional[int],
         codec_options: CodecOptions,  # type: ignore[type-arg]
         user_fields: Optional[Mapping[str, Any]] = None,
@@ -1020,29 +1019,23 @@ async def _send_message(self, operation: Union[_Query, _GetMore]) -> None:
 
         cmd_name = operation.name
         docs = response.docs
-        if response.from_command:
-            if cmd_name != "explain":
-                cursor = docs[0]["cursor"]
-                self._id = cursor["id"]
-                if cmd_name == "find":
-                    documents = cursor["firstBatch"]
-                    # Update the namespace used for future getMore commands.
-                    ns = cursor.get("ns")
-                    if ns:
-                        self._dbname, self._collname = ns.split(".", 1)
-                else:
-                    documents = cursor["nextBatch"]
-                self._data = deque(documents)
-                self._retrieved += len(documents)
+        if cmd_name != "explain":
+            cursor = docs[0]["cursor"]
+            self._id = cursor["id"]
+            if cmd_name == "find":
+                documents = cursor["firstBatch"]
+                # Update the namespace used for future getMore commands.
+                ns = cursor.get("ns")
+                if ns:
+                    self._dbname, self._collname = ns.split(".", 1)
             else:
-                self._id = 0
-                self._data = deque(docs)
-                self._retrieved += len(docs)
+                documents = cursor["nextBatch"]
+            self._data = deque(documents)
+            self._retrieved += len(documents)
         else:
-            assert isinstance(response.data, _OpReply)
-            self._id = response.data.cursor_id
+            self._id = 0
             self._data = deque(docs)
-            self._retrieved += response.data.number_returned
+            self._retrieved += len(docs)
 
         if self._id == 0:
             # Don't wait for garbage collection to call __del__, return the
@@ -1195,7 +1188,7 @@ def __init__(
 
     def _unpack_response(
         self,
-        response: Union[_OpReply, _OpMsg],
+        response: _OpMsg,
         cursor_id: Optional[int],
         codec_options: CodecOptions[Mapping[str, Any]],
         user_fields: Optional[Mapping[str, Any]] = None,

pymongo/asynchronous/network.py

@@ -62,7 +62,7 @@ async def command(
     conn: AsyncConnection,
     dbname: str,
     spec: MutableMapping[str, Any],
-    is_mongos: bool,
+    is_mongos: bool,  # noqa: ARG001
     read_preference: Optional[_ServerMode],
     codec_options: CodecOptions[_DocumentType],
     session: Optional[AsyncClientSession],
@@ -76,7 +76,6 @@ async def command(
     parse_write_concern_error: bool = False,
     collation: Optional[_CollationIn] = None,
     compression_ctx: Union[SnappyContext, ZlibContext, ZstdContext, None] = None,
-    use_op_msg: bool = False,
     unacknowledged: bool = False,
     user_fields: Optional[Mapping[str, Any]] = None,
     exhaust_allowed: bool = False,
@@ -102,22 +101,17 @@ async def command(
         field in the command response.
     :param collation: The collation for this command.
     :param compression_ctx: optional compression Context.
-    :param use_op_msg: True if we should use OP_MSG.
     :param unacknowledged: True if this is an unacknowledged command.
     :param user_fields: Response fields that should be decoded
         using the TypeDecoders from codec_options, passed to
         bson._decode_all_selective.
     :param exhaust_allowed: True if we should enable OP_MSG exhaustAllowed.
     """
     name = next(iter(spec))
-    ns = dbname + ".$cmd"
     speculative_hello = False
 
     # Publish the original command document, perhaps with lsid and $clusterTime.
     orig = spec
-    if is_mongos and not use_op_msg:
-        assert read_preference is not None
-        spec = message._maybe_add_read_preference(spec, read_preference)
     if read_concern and not (session and session.in_transaction):
         if read_concern.level:
             spec["readConcern"] = read_concern.document
@@ -142,20 +136,15 @@ async def command(
         conn.apply_timeout(client, spec)
     _csot.apply_write_concern(spec, write_concern)
 
-    if use_op_msg:
-        flags = _OpMsg.MORE_TO_COME if unacknowledged else 0
-        flags |= _OpMsg.EXHAUST_ALLOWED if exhaust_allowed else 0
-        request_id, msg, size, max_doc_size = message._op_msg(
-            flags, spec, dbname, read_preference, codec_options, ctx=compression_ctx
-        )
-        # If this is an unacknowledged write then make sure the encoded doc(s)
-        # are small enough, otherwise rely on the server to return an error.
-        if unacknowledged and max_bson_size is not None and max_doc_size > max_bson_size:
-            message._raise_document_too_large(name, size, max_bson_size)
-    else:
-        request_id, msg, size = message._query(
-            0, ns, 0, -1, spec, None, codec_options, compression_ctx
-        )
+    flags = _OpMsg.MORE_TO_COME if unacknowledged else 0
+    flags |= _OpMsg.EXHAUST_ALLOWED if exhaust_allowed else 0
+    request_id, msg, size, max_doc_size = message._op_msg(
+        flags, spec, dbname, read_preference, codec_options, ctx=compression_ctx
+    )
+    # If this is an unacknowledged write then make sure the encoded doc(s)
+    # are small enough, otherwise rely on the server to return an error.
+    if unacknowledged and max_bson_size is not None and max_doc_size > max_bson_size:
+        message._raise_document_too_large(name, size, max_bson_size)
 
     if max_bson_size is not None and size > max_bson_size + message._COMMAND_OVERHEAD:
         message._raise_document_too_large(name, size, max_bson_size + message._COMMAND_OVERHEAD)
@@ -190,7 +179,7 @@ async def command(
 
     try:
         await async_sendall(conn.conn.get_conn, msg)
-        if use_op_msg and unacknowledged:
+        if unacknowledged:
             # Unacknowledged, fake a successful command response.
             reply = None
             response_doc: _DocumentOut = {"ok": 1}

pymongo/asynchronous/pool.py

@@ -102,7 +102,7 @@
         ZlibContext,
         ZstdContext,
     )
-    from pymongo.message import _OpMsg, _OpReply
+    from pymongo.message import _OpMsg
     from pymongo.read_concern import ReadConcern
     from pymongo.read_preferences import _ServerMode
     from pymongo.typings import _Address, _CollationIn
@@ -146,7 +146,6 @@ def __init__(
         self.supports_sessions = False
         self.hello_ok: bool = False
         self.is_mongos = False
-        self.op_msg_enabled = False
         self.listeners = pool.opts._event_listeners
         self.enabled_for_cmap = pool.enabled_for_cmap
         self.enabled_for_logging = pool.enabled_for_logging
@@ -235,13 +234,11 @@ async def unpin(self) -> None:
             await self.close_conn(ConnectionClosedReason.STALE)
 
     def hello_cmd(self) -> dict[str, Any]:
-        # Handshake spec requires us to use OP_MSG+hello command for the
-        # initial handshake in load balanced or stable API mode.
+        # As of PYTHON-5713, always use OP_MSG for the handshake since all
+        # supported servers (MongoDB 4.2+, wire version >= 8) support it.
         if self.opts.server_api or self.hello_ok or self.opts.load_balanced:
-            self.op_msg_enabled = True
             return {HelloCompat.CMD: 1}
-        else:
-            return {HelloCompat.LEGACY_CMD: 1, "helloOk": True}
+        return {HelloCompat.LEGACY_CMD: 1, "helloOk": True}
 
     async def hello(self) -> Hello[dict[str, Any]]:
         return await self._hello(None, None)
@@ -314,7 +311,6 @@ async def _hello(
             ctx = self.compression_settings.get_compression_context(hello.compressors)
             self.compression_context = ctx
 
-        self.op_msg_enabled = True
         self.server_connection_id = hello.connection_id
         if creds:
             self.negotiated_mechs = hello.sasl_supported_mechs
@@ -397,8 +393,7 @@ async def command(
         self.send_cluster_time(spec, session, client)
         listeners = self.listeners if publish_events else None
         unacknowledged = bool(write_concern and not write_concern.acknowledged)
-        if self.op_msg_enabled:
-            self._raise_if_not_writable(unacknowledged)
+        self._raise_if_not_writable(unacknowledged)
         try:
             return await command(
                 self,
@@ -418,7 +413,6 @@ async def command(
                 parse_write_concern_error=parse_write_concern_error,
                 collation=collation,
                 compression_ctx=self.compression_context,
-                use_op_msg=self.op_msg_enabled,
                 unacknowledged=unacknowledged,
                 user_fields=user_fields,
                 exhaust_allowed=exhaust_allowed,
@@ -447,7 +441,7 @@ async def send_message(self, message: bytes, max_doc_size: int) -> None:
         except BaseException as error:
             await self._raise_connection_failure(error)
 
-    async def receive_message(self, request_id: Optional[int]) -> Union[_OpReply, _OpMsg]:
+    async def receive_message(self, request_id: Optional[int]) -> _OpMsg:
         """Receive a raw BSON message or raise ConnectionFailure.
 
         If any exception is raised, the socket is closed.

pymongo/asynchronous/server.py

@@ -265,16 +265,7 @@ async def run_operation(
         duration = datetime.now() - start
         # Must publish in find / getMore / explain command response
         # format.
-        if use_cmd:
-            res = docs[0]
-        elif operation.name == "explain":
-            res = docs[0] if docs else {}
-        else:
-            res = {"cursor": {"id": reply.cursor_id, "ns": operation.namespace()}, "ok": 1}  # type: ignore[union-attr]
-            if operation.name == "find":
-                res["cursor"]["firstBatch"] = docs
-            else:
-                res["cursor"]["nextBatch"] = docs
+        res = docs[0]
         if _COMMAND_LOGGER.isEnabledFor(logging.DEBUG):
             _debug_log(
                 _COMMAND_LOGGER,