Make pduFromStream work on big endian (again)

reinterpret_cast<char *>(&code) works on little endian, but not on big
endian, because code is an int (4 bytes value).

I fixed this bug earlier in afb7f76efafcb04e430168416d9d74113bde13bc,
but it was added back in 2c0bb738e988d84f36169e0103d051745b678479.

[ChangeLog][QModbusPdu] Fix reading from stream on big endian systems

Pick-to: 6.4 6.3 6.2 5.15
Change-Id: Ic432d5c86aac40ec2acdc07b4c4881967a023966
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

2 files changed, 20 insertions, 2 deletions

diff --git a/src/serialbus/qmodbuspdu.cpp b/src/serialbus/qmodbuspdu.cpp
index c008bf7..d06e75f 100644
--- a/src/serialbus/qmodbuspdu.cpp
+++ b/src/serialbus/qmodbuspdu.cpp
@@ -95,11 +95,12 @@ static QDataStream &pduFromStream(QDataStream &stream, Type type, QModbusPdu *pd
     } raii = { pdu };
 
     QModbusPdu::FunctionCode code = QModbusPdu::FunctionCode::Invalid;
-    if (stream.readRawData(reinterpret_cast<char *>(&code), sizeof(quint8)) != sizeof(quint8))
+    stream >> code;
+    if (stream.status() == QDataStream::ReadPastEnd)
         return stream;
     pdu->setFunctionCode(code);
 
-    if (code == QModbusPdu::Invalid || code == QModbusPdu::UndefinedFunctionCode) // shortcut
+    if (code == QModbusPdu::Invalid) // shortcut
         return stream;
 
     constexpr const int MaxPduDataSize = 252; // in bytes
@@ -598,6 +599,22 @@ void QModbusRequest::registerDataSizeCalculator(FunctionCode fc, CalcFuncPtr cal
 }
 
 /*!
+    \internal
+
+    Reads a FunctionCode from a \a stream.
+    In stream we serialize FunctionCode as one byte, so we use a temporary char
+    variable to make the code work on both little endian and big endian systems.
+    If reading from stream fails, code will retain original value.
+*/
+QDataStream &operator>>(QDataStream &stream, QModbusPdu::FunctionCode &code)
+{
+    char buffer;
+    if (stream.readRawData(&buffer, 1) == 1)
+        code = static_cast<QModbusPdu::FunctionCode>(buffer);
+    return stream;
+}
+
+/*!
     \relates QModbusRequest
 
     Reads a \a pdu from the \a stream and returns a reference to the stream.
diff --git a/src/serialbus/qmodbuspdu.h b/src/serialbus/qmodbuspdu.h
index 60aa6ed..a54e05b 100644
--- a/src/serialbus/qmodbuspdu.h
+++ b/src/serialbus/qmodbuspdu.h
@@ -157,6 +157,7 @@ private:
 };
 Q_SERIALBUS_EXPORT QDebug operator<<(QDebug debug, const QModbusPdu &pdu);
 Q_SERIALBUS_EXPORT QDataStream &operator<<(QDataStream &stream, const QModbusPdu &pdu);
+Q_SERIALBUS_EXPORT QDataStream &operator>>(QDataStream &stream, QModbusPdu::FunctionCode &code);
 
 class Q_SERIALBUS_EXPORT QModbusRequest : public QModbusPdu
 {