XPL2 protocol foundation: wire framing, typed API, KA_PING, GS_JC_VERSION

Add Xpl2Protocol namespace with buildMessage/parseMessage for wire
serialization. Replace raw send/receive API on Xpl2Client with typed
protocol methods and internal dispatch. Auto-reply to KA_PING on all
sockets (qDebug only). Add GS_JC_VERSION as first typed command with
controllerId, firmwareVersion, hardwareVersion, printheadCount properties.

Upgrade mock server from echo to line-based command dispatch with 1s
KA_PING timer and canned GS_JC_VERSION response. Unknown commands
produce qWarning instead of echo.

Overhaul demo: remove raw send UI and port config, add wireDebug
toggle and Get JC Version button.

1 files changed, 128 insertions, 0 deletions

diff --git a/src/Xpl2Protocol.cpp b/src/Xpl2Protocol.cpp
new file mode 100644
index 0000000..9ee7f4f
--- /dev/null
+++ b/src/Xpl2Protocol.cpp
@@ -0,0 +1,128 @@
+/**
+ * @file   Xpl2Protocol.cpp
+ * @brief  Wire framing for the XPL2 printhead protocol.
+ */
+#include "Xpl2Protocol.h"
+
+#include <QMetaType>
+
+namespace Xpl2Protocol
+{
+
+QByteArray
+buildMessage (const QByteArray &command, const QVariantList &params)
+{
+  QByteArray msg = command;
+
+  for (const QVariant &p : params)
+    {
+      msg += ',';
+
+      switch (p.typeId ())
+        {
+        case QMetaType::Bool:
+          msg += p.toBool () ? '1' : '0';
+          break;
+        case QMetaType::Int:
+        case QMetaType::LongLong:
+          msg += QByteArray::number (p.toLongLong ());
+          break;
+        case QMetaType::UInt:
+        case QMetaType::ULongLong:
+          msg += QByteArray::number (p.toULongLong ());
+          break;
+        case QMetaType::Float:
+        case QMetaType::Double:
+          msg += QByteArray::number (p.toDouble (), 'g', 10);
+          break;
+        default:
+          msg += '"';
+          msg += p.toString ().toUtf8 ();
+          msg += '"';
+          break;
+        }
+    }
+
+  msg += Terminator;
+  return msg;
+}
+
+static QList<QByteArray>
+splitFields (const QByteArray &data)
+{
+  QList<QByteArray> fields;
+  QByteArray current;
+  bool inQuotes = false;
+
+  for (int i = 0; i < data.size (); ++i)
+    {
+      char c = data.at (i);
+
+      if (c == '"')
+        {
+          inQuotes = !inQuotes;
+          current += c;
+        }
+      else if (c == ',' && !inQuotes)
+        {
+          fields.append (current);
+          current.clear ();
+        }
+      else
+        {
+          current += c;
+        }
+    }
+
+  if (!current.isEmpty ())
+    fields.append (current);
+
+  return fields;
+}
+
+static QVariant
+parseField (const QByteArray &field)
+{
+  if (field.size () >= 2 && field.front () == '"' && field.back () == '"')
+    return QString::fromUtf8 (field.mid (1, field.size () - 2));
+
+  bool ok = false;
+
+  int intVal = field.toInt (&ok);
+  if (ok)
+    return intVal;
+
+  double dblVal = field.toDouble (&ok);
+  if (ok)
+    return dblVal;
+
+  return QString::fromUtf8 (field);
+}
+
+ParsedMessage
+parseMessage (const QByteArray &raw)
+{
+  QByteArray data = raw;
+
+  /* Strip terminator. */
+  while (!data.isEmpty () && data.back () == Terminator)
+    data.chop (1);
+
+  if (data.isEmpty ())
+    return {};
+
+  QList<QByteArray> fields = splitFields (data);
+  if (fields.isEmpty ())
+    return {};
+
+  ParsedMessage msg;
+  msg.command = fields.takeFirst ();
+  msg.valid = true;
+
+  for (const QByteArray &f : fields)
+    msg.params.append (parseField (f));
+
+  return msg;
+}
+
+} // namespace Xpl2Protocol