ntcore: Add support for local-only operation (#2204)

StartLocal() causes future calls to StartServer() or StartClient() to have
no effect. StopLocal() re-enables these calls.

ntcore/src/main/native/cpp/Dispatcher.cpp

@@ -115,6 +115,16 @@ DispatcherBase::~DispatcherBase() { Stop(); }
 
 unsigned int DispatcherBase::GetNetworkMode() const { return m_networkMode; }
 
+void DispatcherBase::StartLocal() {
+  {
+    std::scoped_lock lock(m_user_mutex);
+    if (m_active) return;
+    m_active = true;
+  }
+  m_networkMode = NT_NET_MODE_LOCAL;
+  m_storage.SetDispatcher(this, false);
+}
+
 void DispatcherBase::StartServer(
     const Twine& persist_filename,
     std::unique_ptr<wpi::NetworkAcceptor> acceptor) {

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

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2015-2018 FIRST. All Rights Reserved.                        */
+/* Copyright (c) 2015-2019 FIRST. All Rights Reserved.                        */
 /* Open Source Software - may be modified and shared by FRC teams. The code   */
 /* must be accompanied by the FIRST BSD license file in the root directory of */
 /* the project.                                                               */
@@ -48,6 +48,7 @@ class DispatcherBase : public IDispatcher {
   virtual ~DispatcherBase();
 
   unsigned int GetNetworkMode() const;
+  void StartLocal();
   void StartServer(const Twine& persist_filename,
                    std::unique_ptr<wpi::NetworkAcceptor> acceptor);
   void StartClient();

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

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2018 FIRST. All Rights Reserved.                             */
+/* Copyright (c) 2018-2019 FIRST. All Rights Reserved.                        */
 /* Open Source Software - may be modified and shared by FRC teams. The code   */
 /* must be accompanied by the FIRST BSD license file in the root directory of */
 /* the project.                                                               */
@@ -1368,6 +1368,30 @@ Java_edu_wpi_first_networktables_NetworkTablesJNI_getNetworkMode
   return nt::GetNetworkMode(inst);
 }
 
+/*
+ * Class:     edu_wpi_first_networktables_NetworkTablesJNI
+ * Method:    startLocal
+ * Signature: (I)V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_first_networktables_NetworkTablesJNI_startLocal
+  (JNIEnv*, jclass, jint inst)
+{
+  nt::StartLocal(inst);
+}
+
+/*
+ * Class:     edu_wpi_first_networktables_NetworkTablesJNI
+ * Method:    stopLocal
+ * Signature: (I)V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_first_networktables_NetworkTablesJNI_stopLocal
+  (JNIEnv*, jclass, jint inst)
+{
+  nt::StopLocal(inst);
+}
+
 /*
  * Class:     edu_wpi_first_networktables_NetworkTablesJNI
  * Method:    startServer

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

@@ -539,6 +539,10 @@ unsigned int NT_GetNetworkMode(NT_Inst inst) {
   return nt::GetNetworkMode(inst);
 }
 
+void NT_StartLocal(NT_Inst inst) { nt::StartLocal(inst); }
+
+void NT_StopLocal(NT_Inst inst) { nt::StopLocal(inst); }
+
 void NT_StartServer(NT_Inst inst, const char* persist_filename,
                     const char* listen_address, unsigned int port) {
   nt::StartServer(inst, persist_filename, listen_address, port);

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

@@ -742,6 +742,20 @@ unsigned int GetNetworkMode(NT_Inst inst) {
   return ii->dispatcher.GetNetworkMode();
 }
 
+void StartLocal(NT_Inst inst) {
+  auto ii = InstanceImpl::Get(Handle{inst}.GetTypedInst(Handle::kInstance));
+  if (!ii) return;
+
+  ii->dispatcher.StartLocal();
+}
+
+void StopLocal(NT_Inst inst) {
+  auto ii = InstanceImpl::Get(Handle{inst}.GetTypedInst(Handle::kInstance));
+  if (!ii) return;
+
+  ii->dispatcher.Stop();
+}
+
 void StartServer(StringRef persist_filename, const char* listen_address,
                  unsigned int port) {
   auto ii = InstanceImpl::GetDefault();

ntcore/src/main/native/include/networktables/NetworkTableInstance.h

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2017-2018 FIRST. All Rights Reserved.                        */
+/* Copyright (c) 2017-2019 FIRST. All Rights Reserved.                        */
 /* Open Source Software - may be modified and shared by FRC teams. The code   */
 /* must be accompanied by the FIRST BSD license file in the root directory of */
 /* the project.                                                               */
@@ -61,7 +61,8 @@ class NetworkTableInstance final {
     kNetModeServer = NT_NET_MODE_SERVER,
     kNetModeClient = NT_NET_MODE_CLIENT,
     kNetModeStarting = NT_NET_MODE_STARTING,
-    kNetModeFailure = NT_NET_MODE_FAILURE
+    kNetModeFailure = NT_NET_MODE_FAILURE,
+    kNetModeLocal = NT_NET_MODE_LOCAL
   };
 
   /**
@@ -298,6 +299,19 @@ class NetworkTableInstance final {
    */
   unsigned int GetNetworkMode() const;
 
+  /**
+   * Starts local-only operation.  Prevents calls to StartServer or StartClient
+   * from taking effect.  Has no effect if StartServer or StartClient
+   * has already been called.
+   */
+  void StartLocal();
+
+  /**
+   * Stops local-only operation.  StartServer or StartClient can be called after
+   * this call to start a server or client.
+   */
+  void StopLocal();
+
   /**
    * Starts a server using the specified filename, listening address, and port.
    *

ntcore/src/main/native/include/networktables/NetworkTableInstance.inl

@@ -81,6 +81,10 @@ inline unsigned int NetworkTableInstance::GetNetworkMode() const {
   return ::nt::GetNetworkMode(m_handle);
 }
 
+inline void NetworkTableInstance::StartLocal() { ::nt::StartLocal(m_handle); }
+
+inline void NetworkTableInstance::StopLocal() { ::nt::StopLocal(m_handle); }
+
 inline void NetworkTableInstance::StartServer(const Twine& persist_filename,
                                               const char* listen_address,
                                               unsigned int port) {

ntcore/src/main/native/include/ntcore_c.h

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2015-2018 FIRST. All Rights Reserved.                        */
+/* Copyright (c) 2015-2019 FIRST. All Rights Reserved.                        */
 /* Open Source Software - may be modified and shared by FRC teams. The code   */
 /* must be accompanied by the FIRST BSD license file in the root directory of */
 /* the project.                                                               */
@@ -95,6 +95,7 @@ enum NT_NetworkMode {
   NT_NET_MODE_CLIENT = 0x02,   /* running in client mode */
   NT_NET_MODE_STARTING = 0x04, /* flag for starting (either client or server) */
   NT_NET_MODE_FAILURE = 0x08,  /* flag for failure (either client or server) */
+  NT_NET_MODE_LOCAL = 0x10,    /* running in local-only mode */
 };
 
 /*
@@ -1037,6 +1038,19 @@ void NT_SetNetworkIdentity(NT_Inst inst, const char* name, size_t name_len);
  */
 unsigned int NT_GetNetworkMode(NT_Inst inst);
 
+/**
+ * Starts local-only operation.  Prevents calls to NT_StartServer or
+ * NT_StartClient from taking effect.  Has no effect if NT_StartServer or
+ * NT_StartClient has already been called.
+ */
+void NT_StartLocal(NT_Inst inst);
+
+/**
+ * Stops local-only operation.  NT_StartServer or NT_StartClient can be called
+ * after this call to start a server or client.
+ */
+void NT_StopLocal(NT_Inst inst);
+
 /**
  * Starts a server using the specified filename, listening address, and port.
  *

ntcore/src/main/native/include/ntcore_cpp.h

@@ -1130,6 +1130,19 @@ unsigned int GetNetworkMode();
  */
 unsigned int GetNetworkMode(NT_Inst inst);
 
+/**
+ * Starts local-only operation.  Prevents calls to StartServer or StartClient
+ * from taking effect.  Has no effect if StartServer or StartClient
+ * has already been called.
+ */
+void StartLocal(NT_Inst inst);
+
+/**
+ * Stops local-only operation.  StartServer or StartClient can be called after
+ * this call to start a server or client.
+ */
+void StopLocal(NT_Inst inst);
+
 /**
  * Starts a server using the specified filename, listening address, and port.
  *