[hal] Add CAN Stream API to Java through JNI bindings (#4193)

The CAN Stream API allows defining an buffer to receive an
arbitrary set of CAN messages, based on an ID and a mask. Messages
are added to this queue separate of other CAN APIs. This means the
messages can be receive without impacting other APIs such as
vendor APIs.

This enables things like detection of what devices are on the
bus, or custom decoding, without using vendor APIs.

Co-authored-by: Thad House <thadhouse1@gmail.com>

hal/src/main/native/cpp/jni/CANJNI.cpp

@@ -91,4 +91,90 @@ Java_edu_wpi_first_hal_can_CANJNI_getCANStatus
                      txFullCount, receiveErrorCount, transmitErrorCount);
 }
 
+/*
+ * Class:     edu_wpi_first_hal_can_CANJNI
+ * Method:    openCANStreamSession
+ * Signature: (III)I
+ */
+JNIEXPORT jint JNICALL
+Java_edu_wpi_first_hal_can_CANJNI_openCANStreamSession
+  (JNIEnv* env, jclass, jint messageID, jint messageIDMask, jint maxMessages)
+{
+  uint32_t handle = 0;
+  int32_t status = 0;
+  HAL_CAN_OpenStreamSession(&handle, static_cast<uint32_t>(messageID),
+                            static_cast<uint32_t>(messageIDMask),
+                            static_cast<uint32_t>(maxMessages), &status);
+
+  if (!CheckStatus(env, status)) {
+    return static_cast<jint>(0);
+  }
+
+  return static_cast<jint>(handle);
+}
+
+/*
+ * Class:     edu_wpi_first_hal_can_CANJNI
+ * Method:    closeCANStreamSession
+ * Signature: (I)V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_first_hal_can_CANJNI_closeCANStreamSession
+  (JNIEnv* env, jclass, jint sessionHandle)
+{
+  HAL_CAN_CloseStreamSession(static_cast<uint32_t>(sessionHandle));
+}
+
+/*
+ * Class:     edu_wpi_first_hal_can_CANJNI
+ * Method:    readCANStreamSession
+ * Signature: (I[Ljava/lang/Object;I)I
+ */
+JNIEXPORT jint JNICALL
+Java_edu_wpi_first_hal_can_CANJNI_readCANStreamSession
+  (JNIEnv* env, jclass, jint sessionHandle, jobjectArray messages,
+   jint messagesToRead)
+{
+  uint32_t handle = static_cast<uint32_t>(sessionHandle);
+  uint32_t messagesRead = 0;
+
+  wpi::SmallVector<HAL_CANStreamMessage, 16> messageBuffer;
+  messageBuffer.resize_for_overwrite(messagesToRead);
+
+  int32_t status = 0;
+
+  HAL_CAN_ReadStreamSession(handle, messageBuffer.begin(),
+                            static_cast<uint32_t>(messagesToRead),
+                            &messagesRead, &status);
+
+  if (status == HAL_ERR_CANSessionMux_MessageNotFound || messagesRead == 0) {
+    return 0;
+  }
+
+  if (!CheckStatus(env, status)) {
+    return 0;
+  }
+
+  for (int i = 0; i < static_cast<int>(messagesRead); i++) {
+    struct HAL_CANStreamMessage* msg = &messageBuffer[i];
+    JLocal<jobject> elem{
+        env, static_cast<jstring>(env->GetObjectArrayElement(messages, i))};
+    if (!elem) {
+      // TODO decide if should throw
+      continue;
+    }
+    JLocal<jbyteArray> toSetArray{
+        env, SetCANStreamObject(env, elem, msg->dataSize, msg->messageID,
+                                msg->timeStamp)};
+    auto javaLen = env->GetArrayLength(toSetArray);
+    if (javaLen < msg->dataSize) {
+      msg->dataSize = javaLen;
+    }
+    env->SetByteArrayRegion(toSetArray, 0, msg->dataSize,
+                            reinterpret_cast<jbyte*>(msg->data));
+  }
+
+  return static_cast<jint>(messagesRead);
+}
+
 }  // extern "C"