Provide alternate device paths info for USB cameras (#1519)

This is primarily for use on Linux to get by-id or by-path device names.

This information is now part of UsbCameraInfo.

A new entry point was added to UsbCamera to get that camera's UsbCameraInfo.

The alternate paths are also returned in EnumerateUsbCameras.

cscore/src/main/native/cpp/MjpegServerImpl.cpp

@@ -413,6 +413,15 @@ void MjpegServerImpl::ConnThread::SendHTML(wpi::raw_ostream& os,
     }
   }
 
+  status = 0;
+  auto info = GetUsbCameraInfo(Instance::GetInstance().FindSource(source).first,
+                               &status);
+  if (status == CS_OK) {
+    os << "<p>USB device path: " << info.path << '\n';
+    for (auto&& path : info.otherPaths)
+      os << "<p>Alternate device path: " << path << '\n';
+  }
+
   os << "<p>Supported Video Modes:</p>\n";
   os << "<table cols=\"4\" style=\"border: 1px solid black\">\n";
   os << "<tr><th>Pixel Format</th>"

cscore/src/main/native/cpp/UsbCameraImplCommon.cpp

@@ -12,6 +12,25 @@
 
 using namespace cs;
 
+static void ConvertToC(CS_UsbCameraInfo* out, const UsbCameraInfo& in) {
+  out->dev = in.dev;
+  out->path = ConvertToC(in.path);
+  out->name = ConvertToC(in.name);
+  out->otherPaths = static_cast<char**>(
+      wpi::CheckedMalloc(in.otherPaths.size() * sizeof(char*)));
+  out->otherPathsCount = in.otherPaths.size();
+  for (size_t i = 0; i < in.otherPaths.size(); ++i)
+    out->otherPaths[i] = cs::ConvertToC(in.otherPaths[i]);
+}
+
+static void FreeUsbCameraInfo(CS_UsbCameraInfo* info) {
+  std::free(info->path);
+  std::free(info->name);
+  for (int i = 0; i < info->otherPathsCount; ++i)
+    std::free(info->otherPaths[i]);
+  std::free(info->otherPaths);
+}
+
 extern "C" {
 
 CS_Source CS_CreateUsbCameraDev(const char* name, int dev, CS_Status* status) {
@@ -27,26 +46,34 @@ char* CS_GetUsbCameraPath(CS_Source source, CS_Status* status) {
   return ConvertToC(cs::GetUsbCameraPath(source, status));
 }
 
+CS_UsbCameraInfo* CS_GetUsbCameraInfo(CS_Source source, CS_Status* status) {
+  auto info = cs::GetUsbCameraInfo(source, status);
+  if (*status != CS_OK) return nullptr;
+  CS_UsbCameraInfo* out = static_cast<CS_UsbCameraInfo*>(
+      wpi::CheckedMalloc(sizeof(CS_UsbCameraInfo)));
+  ConvertToC(out, info);
+  return out;
+}
+
 CS_UsbCameraInfo* CS_EnumerateUsbCameras(int* count, CS_Status* status) {
   auto cameras = cs::EnumerateUsbCameras(status);
   CS_UsbCameraInfo* out = static_cast<CS_UsbCameraInfo*>(
       wpi::CheckedMalloc(cameras.size() * sizeof(CS_UsbCameraInfo)));
   *count = cameras.size();
-  for (size_t i = 0; i < cameras.size(); ++i) {
-    out[i].dev = cameras[i].dev;
-    out[i].path = ConvertToC(cameras[i].path);
-    out[i].name = ConvertToC(cameras[i].name);
-  }
+  for (size_t i = 0; i < cameras.size(); ++i) ConvertToC(&out[i], cameras[i]);
   return out;
 }
 
 void CS_FreeEnumeratedUsbCameras(CS_UsbCameraInfo* cameras, int count) {
   if (!cameras) return;
-  for (int i = 0; i < count; ++i) {
-    std::free(cameras[i].path);
-    std::free(cameras[i].name);
-  }
+  for (int i = 0; i < count; ++i) FreeUsbCameraInfo(&cameras[i]);
   std::free(cameras);
 }
 
+void CS_FreeUsbCameraInfo(CS_UsbCameraInfo* info) {
+  if (!info) return;
+  FreeUsbCameraInfo(info);
+  std::free(info);
+}
+
 }  // extern "C"

cscore/src/main/native/cpp/jni/CameraServerJNI.cpp

@@ -185,11 +185,14 @@ static inline bool CheckStatus(JNIEnv* env, CS_Status status) {
 
 static jobject MakeJObject(JNIEnv* env, const cs::UsbCameraInfo& info) {
   static jmethodID constructor = env->GetMethodID(
-      usbCameraInfoCls, "<init>", "(ILjava/lang/String;Ljava/lang/String;)V");
+      usbCameraInfoCls, "<init>",
+      "(ILjava/lang/String;Ljava/lang/String;[Ljava/lang/String;)V");
   JLocal<jstring> path(env, MakeJString(env, info.path));
   JLocal<jstring> name(env, MakeJString(env, info.name));
+  JLocal<jobjectArray> otherPaths(env, MakeJStringArray(env, info.otherPaths));
   return env->NewObject(usbCameraInfoCls, constructor,
-                        static_cast<jint>(info.dev), path.obj(), name.obj());
+                        static_cast<jint>(info.dev), path.obj(), name.obj(),
+                        otherPaths.obj());
 }
 
 static jobject MakeJObject(JNIEnv* env, const cs::VideoMode& videoMode) {
@@ -975,6 +978,21 @@ Java_edu_wpi_cscore_CameraServerJNI_getUsbCameraPath
   return MakeJString(env, str);
 }
 
+/*
+ * Class:     edu_wpi_cscore_CameraServerJNI
+ * Method:    getUsbCameraInfo
+ * Signature: (I)Ljava/lang/Object;
+ */
+JNIEXPORT jobject JNICALL
+Java_edu_wpi_cscore_CameraServerJNI_getUsbCameraInfo
+  (JNIEnv* env, jclass, jint source)
+{
+  CS_Status status = 0;
+  auto info = cs::GetUsbCameraInfo(source, &status);
+  if (!CheckStatus(env, status)) return nullptr;
+  return MakeJObject(env, info);
+}
+
 /*
  * Class:     edu_wpi_cscore_CameraServerJNI
  * Method:    getHttpCameraKind