[ntcore] Add client disconnect function (#5022)

As setServer doesn't disconnect, it's useful to have a function that
disconnects without needing to completely stop the client.

ntcore/src/main/native/cpp/INetworkClient.h

@@ -18,6 +18,7 @@ class INetworkClient {
 
   virtual void SetServers(
       std::span<const std::pair<std::string, unsigned int>> servers) = 0;
+  virtual void Disconnect() = 0;
 
   virtual void StartDSClient(unsigned int port) = 0;
   virtual void StopDSClient() = 0;

ntcore/src/main/native/cpp/NetworkClient.cpp

@@ -492,6 +492,11 @@ void NetworkClient::SetServers(
   m_impl->SetServers(servers, NT_DEFAULT_PORT4);
 }
 
+void NetworkClient::Disconnect() {
+  m_impl->m_loopRunner.ExecAsync(
+      [this](auto&) { m_impl->Disconnect("requested by application"); });
+}
+
 void NetworkClient::StartDSClient(unsigned int port) {
   m_impl->StartDSClient(port);
 }
@@ -535,6 +540,11 @@ void NetworkClient3::SetServers(
   m_impl->SetServers(servers, NT_DEFAULT_PORT3);
 }
 
+void NetworkClient3::Disconnect() {
+  m_impl->m_loopRunner.ExecAsync(
+      [this](auto&) { m_impl->Disconnect("requested by application"); });
+}
+
 void NetworkClient3::StartDSClient(unsigned int port) {
   m_impl->StartDSClient(port);
 }

ntcore/src/main/native/cpp/NetworkClient.h

@@ -38,6 +38,7 @@ class NetworkClient final : public INetworkClient {
 
   void SetServers(
       std::span<const std::pair<std::string, unsigned int>> servers) final;
+  void Disconnect() final;
 
   void StartDSClient(unsigned int port) final;
   void StopDSClient() final;
@@ -59,6 +60,7 @@ class NetworkClient3 final : public INetworkClient {
 
   void SetServers(
       std::span<const std::pair<std::string, unsigned int>> servers) final;
+  void Disconnect() final;
 
   void StartDSClient(unsigned int port) final;
   void StopDSClient() final;

ntcore/src/main/native/cpp/jni/NetworkTablesJNI.cpp

@@ -1298,6 +1298,18 @@ Java_edu_wpi_first_networktables_NetworkTablesJNI_setServerTeam
   nt::SetServerTeam(inst, team, port);
 }
 
+/*
+ * Class:     edu_wpi_first_networktables_NetworkTablesJNI
+ * Method:    disconnect
+ * Signature: (I)V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_first_networktables_NetworkTablesJNI_disconnect
+  (JNIEnv* env, jclass, jint inst)
+{
+  nt::Disconnect(inst);
+}
+
 /*
  * Class:     edu_wpi_first_networktables_NetworkTablesJNI
  * Method:    startDSClient

ntcore/src/main/native/cpp/ntcore_c.cpp

@@ -537,6 +537,10 @@ void NT_SetServerTeam(NT_Inst inst, unsigned int team, unsigned int port) {
   nt::SetServerTeam(inst, team, port);
 }
 
+void NT_Disconnect(NT_Inst inst) {
+  nt::Disconnect(inst);
+}
+
 void NT_StartDSClient(NT_Inst inst, unsigned int port) {
   nt::StartDSClient(inst, port);
 }

ntcore/src/main/native/cpp/ntcore_cpp.cpp

@@ -685,6 +685,14 @@ void SetServerTeam(NT_Inst inst, unsigned int team, unsigned int port) {
   }
 }
 
+void Disconnect(NT_Inst inst) {
+  if (auto ii = InstanceImpl::GetTyped(inst, Handle::kInstance)) {
+    if (auto client = ii->GetClient()) {
+      client->Disconnect();
+    }
+  }
+}
+
 void StartDSClient(NT_Inst inst, unsigned int port) {
   if (auto ii = InstanceImpl::GetTyped(inst, Handle::kInstance)) {
     if (auto client = ii->GetClient()) {