GODRIVER-2935 Add LegacyHandshake operation logic

x/mongo/driver/legacy.go

@@ -19,4 +19,5 @@ const (
 	LegacyKillCursors
 	LegacyListCollections
 	LegacyListIndexes
+	LegacyHandshake
 )

x/mongo/driver/operation.go

@@ -1266,17 +1266,12 @@ func (op Operation) createMsgWireMessage(ctx context.Context, maxTimeMS uint64,
 	return bsoncore.UpdateLength(dst, wmindex, int32(len(dst[wmindex:]))), info, nil
 }
 
-// isLegacyHandshake returns "true" if the operation is the first message of
-// the initial handshake and should use a legacy hello. The requirement for
-// using a legacy hello as defined by the specifications is as follows:
-//
-// > If server API version is not requested and loadBalanced: False, drivers
-// > MUST use legacy hello for the first message of the initial handshake with
-// > the OP_QUERY protocol
+// isLegacyHandshake returns True if the operation is the first message of
+// the initial handshake and should use a legacy hello.
 func isLegacyHandshake(op Operation, desc description.SelectedServer) bool {
 	isInitialHandshake := desc.WireVersion == nil || desc.WireVersion.Max == 0
 
-	return desc.Kind != description.LoadBalanced && op.ServerAPI == nil && isInitialHandshake
+	return op.Legacy == LegacyHandshake && isInitialHandshake
 }
 
 func (op Operation) createWireMessage(
@@ -1937,8 +1932,6 @@ func (op Operation) publishFinishedEvent(ctx context.Context, info finishedInfor
 				logger.KeyFailure, formattedReply)...)
 	}
 
-	//fmt.Println("->", redactFinishedInformationResponse(info))
-
 	// If the finished event cannot be published, return early.
 	if !op.canPublishFinishedEvent(info) {
 		return

x/mongo/driver/operation/hello.go

@@ -537,8 +537,16 @@ func (h *Hello) StreamResponse(ctx context.Context, conn driver.StreamerConnecti
 	return h.createOperation().ExecuteExhaust(ctx, conn)
 }
 
+// isLegacyHandshake returns True if server API version is not requested and
+// loadBalanced is False. If this is the case, then the drivers MUST use legacy
+// hello for the first message of the initial handshake with the OP_QUERY
+// protocol
+func isLegacyHandshake(h *Hello) bool {
+	return h.serverAPI == nil && h.d.Kind() != description.LoadBalanced
+}
+
 func (h *Hello) createOperation() driver.Operation {
-	return driver.Operation{
+	op := driver.Operation{
 		Clock:      h.clock,
 		CommandFn:  h.command,
 		Database:   "admin",
@@ -549,6 +557,12 @@ func (h *Hello) createOperation() driver.Operation {
 		},
 		ServerAPI: h.serverAPI,
 	}
+
+	if isLegacyHandshake(h) {
+		op.Legacy = driver.LegacyHandshake
+	}
+
+	return op
 }
 
 // GetHandshakeInformation performs the MongoDB handshake for the provided connection and returns the relevant