From ae956e624fa6ba1a3d9bb7b6f47418e8dcbc7fae Mon Sep 17 00:00:00 2001
From: Marius Wensing <wensing@uni-wuppertal.de>
Date: Wed, 4 Sep 2019 10:32:53 +0200
Subject: [PATCH] changing behaviour of parsePacket: returns -1 if no packet
 has been received, otherwise the length of the packet this fixes reception of
 zero-length packets

---
 examples/CANReceiver/CANReceiver.ino | 2 +-
 src/CANController.cpp                | 2 +-
 src/ESP32SJA1000.cpp                 | 2 +-
 src/MCP2515.cpp                      | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/examples/CANReceiver/CANReceiver.ino b/examples/CANReceiver/CANReceiver.ino
index fca49e4..08d7deb 100644
--- a/examples/CANReceiver/CANReceiver.ino
+++ b/examples/CANReceiver/CANReceiver.ino
@@ -20,7 +20,7 @@ void loop() {
   // try to parse packet
   int packetSize = CAN.parsePacket();
 
-  if (packetSize) {
+  if (packetSize >= 0) {
     // received a packet
     Serial.print("Received ");
 
diff --git a/src/CANController.cpp b/src/CANController.cpp
index 0890eec..ecc9680 100644
--- a/src/CANController.cpp
+++ b/src/CANController.cpp
@@ -109,7 +109,7 @@ int CANControllerClass::endPacket()
 
 int CANControllerClass::parsePacket()
 {
-  return 0;
+  return -1;
 }
 
 long CANControllerClass::packetId()
diff --git a/src/ESP32SJA1000.cpp b/src/ESP32SJA1000.cpp
index 3c56fba..cbe62b7 100644
--- a/src/ESP32SJA1000.cpp
+++ b/src/ESP32SJA1000.cpp
@@ -219,7 +219,7 @@ int ESP32SJA1000Class::parsePacket()
 {
   if ((readRegister(REG_SR) & 0x01) != 0x01) {
     // no packet
-    return 0;
+    return -1;
   }
 
   _rxExtended = (readRegister(REG_SFF) & 0x80) ? true : false;
diff --git a/src/MCP2515.cpp b/src/MCP2515.cpp
index aa46051..93f0d42 100644
--- a/src/MCP2515.cpp
+++ b/src/MCP2515.cpp
@@ -225,7 +225,7 @@ int MCP2515Class::parsePacket()
     _rxExtended = false;
     _rxRtr = false;
     _rxLength = 0;
-    return 0;
+    return -1;
   }
 
   _rxExtended = (readRegister(REG_RXBnSIDL(n)) & FLAG_IDE) ? true : false;