Improved socketcand input buffer handling to reduce lost data.

No longer tossing partial frames, saving the data to concat with future data.
On startup there can be some data loss, but after it gets rolling there is none.
Added rough provision to ensure the buffer doesn't get filled with bad data, but
the decodeFrames recursive calls do a pretty good job of getting rid of it so I
haven't seen the buffer grow after millions of frames coming over a UDP-based VPN.

connections/socketcand.cpp

@@ -249,24 +249,38 @@ void SocketCANd::switchToRawMode(int busNum)
     QCoreApplication::processEvents();
 }
 
-void SocketCANd::decodeFrames(QString data, int busNum)
+QString SocketCANd::decodeFrames(QString data, int busNum)
 {
     if (data.indexOf("< frame ") == -1)
     {
-        qDebug() << "Received datagramm doesn't contain any frame: " << data;
+        //qDebug() << "Received datagramm doesn't contain any frame: " << data;
-        return;
+        if (data.indexOf("<") == -1)
+            return "";
+        else
+            return data;
     }
     else
     {
-        QString framePart = data.mid(data.indexOf("< frame "), data.length()); //remove starting beginning of payload if not < frame >
+        int firstIndex = data.indexOf("< frame ");
+        if(firstIndex > 0)
+        {
+            QString framePartial = data.left(firstIndex);
+            qDebug() << "Received datagramm that starts with fragment (missing '< frame'), this should only occur on startup, removing...: " << framePartial;
+        }
+        QString framePart = data.mid(firstIndex, data.length()); //remove starting beginning of payload if not < frame >
         const QString frameStrConst = framePart.left(framePart.indexOf(">")+1);
         QString frameStr = frameStrConst;
         QStringList frameParsed = (frameStr.remove(QRegExp("^<")).remove(QRegExp(">$"))).simplified().split(' ');
 
         if(frameParsed.length() < 2)
         {
-            qDebug() << "Received datagramm is an incomplete frame: " << data;
+            //qDebug() << "Received datagramm is an incomplete frame: " << data;
-            return;
+
+            //ok great, need to leave it in the buffer in case it can be combined with what comes next
+            //but if there was a fragment that did not have a starting token then we don't want it so only return
+            //known good data...again this should only happen on startup, but just in case we need to remove it
+            //so the data buffer doesn't grow uncontrolled.
+            return framePart;
         }
 
         buildFrame.setFrameId(frameParsed[1].toUInt(nullptr, 16));
@@ -281,7 +295,7 @@ void SocketCANd::decodeFrames(QString data, int busNum)
         if(frameParsed.length() < 4)
         {
             qDebug() << "Received frame doesn't contain any data: " << data;
-            return;
+            return data;
         }
 
         int framelength = frameParsed[3].length() * 0.5;
@@ -315,8 +329,12 @@ void SocketCANd::decodeFrames(QString data, int busNum)
         else
             qDebug() << "can't get a frame, capture suspended";
 
+        //take out the data that we just processed and anything that is in front of it
+        //this should keep broken frames from accumulating at in the data buffer
         if (framePart.length() > frameStrConst.length())
-            decodeFrames(framePart.right(framePart.length() - frameStrConst.length()), busNum);
+            return decodeFrames(framePart.right(framePart.length() - frameStrConst.length()), busNum);
+
+        return "";
     }
 }
 
@@ -400,17 +418,30 @@ void SocketCANd::procRXData(QString data, int busNum)
         {
             qDebug() << "Ok found at start of compound message, switching to RAW and decoding immediately";
             rx_state[busNum] = RAWMODE;
-            decodeFrames(data, busNum);
+            unprocessedData = decodeFrames(data, busNum);
         }
         else if(data.indexOf("< ok >", 0, Qt::CaseSensitivity::CaseInsensitive) > 0)
         {
             qDebug() << "Ok found at in middle of compound message, switching to RAW and decoding immediately";
             rx_state[busNum] = RAWMODE;
-            decodeFrames(data, busNum);
+            unprocessedData = decodeFrames(data, busNum);
         }
         break;
     case RAWMODE:
-        decodeFrames(data, busNum);
+        if(!unprocessedData.isEmpty())
+        {
+            //qDebug() << unprocessedData.length() << " bytes of unprocessedData: " << unprocessedData << " adding it to new data: " + data.left(50) + "...";
+        }
+        unprocessedData = decodeFrames(unprocessedData + data, busNum);
+
+        if(unprocessedData.length() > 128)
+        {
+            //the buffer has grown too much we need to clear it out, but what is good logic for that?
+            //the decodeFrames function strips out datat that doesn't have a '< frame' starting token, and in its
+            //recursive calling of itself it strips out data that preceedes valid frames, so this should never happen
+            qDebug() << unprocessedData.length() << " bytes in unprocessedData, something is wrong, clearing...";
+            unprocessedData.clear();
+        }
         break;
     case ISOTP:
         break;

connections/socketcand.h

@@ -57,7 +57,7 @@ private slots:
     void invokeReadTCPData();
     void deviceConnected(int busNum);
     void switchToRawMode(int busNum);
-    void decodeFrames(QString, int busNum);
+    QString decodeFrames(QString, int busNum);
 
 private:
     void procRXData(QString, int busNum);
@@ -76,6 +76,7 @@ protected:
     QByteArray buildData;
     QVarLengthArray<MODE> rx_state;
     CANFrame buildFrame;
+    QString unprocessedData;
 };