GATTHandler/DBTDevice (incl Java): Add ping[GATT](), testing device availability via retrieval of GATT info

Issues a ping to the device, validating whether it is still reachable.

This method could be periodically utilized to shorten the underlying OS disconnect period
after turning the device off, which lies within 7-13s.

In case the device is no more reachable, disconnect will be initiated due to the occurring IO error.

+++

Implementation attempts to read the mandatory APPEARANCE CharacteristicValue
of the mandatory GENERIC_ACCESS service.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/direct_bt/GATTHandler.cpp b/src/direct_bt/GATTHandler.cpp
index e744f936..0a5ee71b 100644
--- a/src/direct_bt/GATTHandler.cpp
+++ b/src/direct_bt/GATTHandler.cpp
@@ -899,6 +899,27 @@ std::shared_ptr<GenericAccess> GATTHandler::getGenericAccess(std::vector<GATTSer
 	return res;
 }
 
+bool GATTHandler::ping() {
+    std::shared_ptr<GenericAccess> res = nullptr;
+    for(size_t i=0; i<services.size() && nullptr == res; i++) {
+        std::vector<GATTCharacteristicRef> & genericAccessCharDeclList = services.at(i)->characteristicList;
+        POctets value(32, 0);
+
+        for(size_t i=0; i<genericAccessCharDeclList.size(); i++) {
+            const GATTCharacteristic & charDecl = *genericAccessCharDeclList.at(i);
+            if( _GENERIC_ACCESS != *charDecl.service->type ) {
+                continue;
+            }
+            if( _APPEARANCE == *charDecl.value_type ) {
+                if( readCharacteristicValue(charDecl, value.resize(0)) ) {
+                    return true;
+                }
+            }
+        }
+    }
+    return false;
+}
+
 std::shared_ptr<DeviceInformation> GATTHandler::getDeviceInformation(std::vector<GATTCharacteristicRef> & characteristicDeclList) {
     std::shared_ptr<DeviceInformation> res = nullptr;
     POctets value(number(Defaults::MAX_ATT_MTU), 0);