Revert "GODRIVER-3054 Handshake connection should not use legacy for LB"

This reverts commit d77f8cc.

x/mongo/driver/operation.go

@@ -1357,6 +1357,14 @@ func (op Operation) createMsgWireMessage(
 	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.
+func isLegacyHandshake(op Operation, desc description.SelectedServer) bool {
+	isInitialHandshake := desc.WireVersion == nil || desc.WireVersion.Max == 0
+
+	return op.Legacy == LegacyHandshake && isInitialHandshake
+}
+
 func (op Operation) createWireMessage(
 	ctx context.Context,
 	maxTimeMS uint64,
@@ -1365,10 +1373,7 @@ func (op Operation) createWireMessage(
 	conn Connection,
 	requestID int32,
 ) ([]byte, startedInformation, error) {
-	isInitialHandshake := desc.WireVersion == nil || desc.WireVersion.Max == 0
-
-	// Use the OP_LEGACY on non-load-balanced connection handshakes.
-	if op.ServerAPI == nil && desc.Kind != description.LoadBalanced && isInitialHandshake {
+	if isLegacyHandshake(op, desc) {
 		return op.createLegacyHandshakeWireMessage(maxTimeMS, dst, desc)
 	}
 

x/mongo/driver/operation/hello.go

@@ -571,6 +571,14 @@ 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(srvAPI *driver.ServerAPIOptions, deployment driver.Deployment) bool {
+	return srvAPI == nil && deployment.Kind() != description.LoadBalanced
+}
+
 func (h *Hello) createOperation() driver.Operation {
 	op := driver.Operation{
 		Clock:      h.clock,
@@ -584,6 +592,10 @@ func (h *Hello) createOperation() driver.Operation {
 		ServerAPI: h.serverAPI,
 	}
 
+	if isLegacyHandshake(h.serverAPI, h.d) {
+		op.Legacy = driver.LegacyHandshake
+	}
+
 	return op
 }
 
@@ -604,6 +616,10 @@ func (h *Hello) GetHandshakeInformation(ctx context.Context, _ address.Address,
 		ServerAPI: h.serverAPI,
 	}
 
+	if isLegacyHandshake(h.serverAPI, deployment) {
+		op.Legacy = driver.LegacyHandshake
+	}
+
 	if err := op.Execute(ctx); err != nil {
 		return driver.HandshakeInformation{}, err
 	}