Utilities and cleanups for socket. (#9576)

- Use c++-17 nodiscard and nested ns.
- Add bind method to socket.
- Remove rabit parameters.

plugin/federated/federated_client.h

@@ -11,9 +11,7 @@
 #include <limits>
 #include <string>
 
-namespace xgboost {
-namespace federated {
-
+namespace xgboost::federated {
 /**
  * @brief A wrapper around the gRPC client.
  */
@@ -112,6 +110,4 @@ class FederatedClient {
   int const rank_;
   uint64_t sequence_number_{};
 };
-
-}  // namespace federated
-}  // namespace xgboost
+}  // namespace xgboost::federated

plugin/federated/federated_communicator.h

@@ -9,9 +9,7 @@
 #include "../../src/common/io.h"
 #include "federated_client.h"
 
-namespace xgboost {
-namespace collective {
-
+namespace xgboost::collective {
 /**
  * @brief A Federated Learning communicator class that handles collective communication.
  */
@@ -118,13 +116,13 @@ class FederatedCommunicator : public Communicator {
    * \brief Get if the communicator is distributed.
    * \return True.
    */
-  bool IsDistributed() const override { return true; }
+  [[nodiscard]] bool IsDistributed() const override { return true; }
 
   /**
    * \brief Get if the communicator is federated.
    * \return True.
    */
-  bool IsFederated() const override { return true; }
+  [[nodiscard]] bool IsFederated() const override { return true; }
 
   /**
    * \brief Perform in-place allgather.
@@ -189,5 +187,4 @@ class FederatedCommunicator : public Communicator {
  private:
   std::unique_ptr<xgboost::federated::FederatedClient> client_{};
 };
-}  // namespace collective
-}  // namespace xgboost
+}  // namespace xgboost::collective

plugin/federated/federated_server.cc

@@ -11,9 +11,7 @@
 
 #include "../../src/common/io.h"
 
-namespace xgboost {
-namespace federated {
-
+namespace xgboost::federated {
 grpc::Status FederatedService::Allgather(grpc::ServerContext*, AllgatherRequest const* request,
                                          AllgatherReply* reply) {
   handler_.Allgather(request->send_buffer().data(), request->send_buffer().size(),
@@ -75,6 +73,4 @@ void RunInsecureServer(int port, int world_size) {
 
   server->Wait();
 }
-
-}  // namespace federated
-}  // namespace xgboost
+}  // namespace xgboost::federated