Add example of communication using protobuf messages

Add the protobuf example that emulates the work of dummy sensors that
send data to the sensor client. The example uses UDP sockets to send
datagrams that contain protobuf messages. Messages consist of two
layers:
 - The Type-Length-Value wrapping message that specifies the the
   message type and allows to verify the message size.
 - Sensor message that contains a sensor data.

The example intends to show how to generate the code from the protobuf
schema and use it in simple UDP signalling protocol on both sender and
receiver sides.

Both client and emulator have simple UI implemented using QtWidgets.

Task-number: QTBUG-109598
Pick-to: 6.5
Change-Id: I13e2c5bcd995b8aa6d873c495a7bd83f6651a061
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

1 files changed, 18 insertions, 0 deletions

diff --git a/examples/protobuf/sensors/tlv.proto b/examples/protobuf/sensors/tlv.proto
new file mode 100644
index 0000000..3d268c3
--- /dev/null
+++ b/examples/protobuf/sensors/tlv.proto
@@ -0,0 +1,18 @@
+syntax = "proto3";
+
+//! [0]
+package qt.examples.sensors.tlv;
+
+enum MessageType {
+    Coordinates = 0;
+    Temperature = 1;
+    WarningNotification = 2;
+}
+
+// Protobuf messages imply inline data size.
+message TlvMessage
+{
+    MessageType type = 1;
+    bytes value = 2;
+}
+//! [0]