LE peripheral - fix a characteristic's length

With Qt's Bluetooth API it's possible to write values with different
lengths into the same characteristic. Imagine this scenario:

   service->writeCharacteristic(handle, QByteArray("abcd"));

and then

   service->writeCharacteristic(handle, QByteArray(2, 0));

If we read from the characteristic later, we get:

   00cd.

A write request in CoreBluetooth is presented as an array of CBATTRequest,
each of them has its offset and value with  length. After processing these
requests we truncate a characteristic's length if needed.

Task-number: QTBUG-56898
Change-Id: I674637eb78c806364d1a89a1db8ab3f31a8800ce
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

1 files changed, 10 insertions, 7 deletions

diff --git a/src/bluetooth/osx/osxbtperipheralmanager.mm b/src/bluetooth/osx/osxbtperipheralmanager.mm
index 1a461be9..03b95667 100644
--- a/src/bluetooth/osx/osxbtperipheralmanager.mm
+++ b/src/bluetooth/osx/osxbtperipheralmanager.mm
@@ -51,7 +51,6 @@
 
 #include <algorithm>
 #include <limits>
-#include <set>
 
 namespace
 {
@@ -584,20 +583,24 @@ bool qt_validate_value_range(const QLowEnergyCharacteristicData &data)
         }
     }
 
-    std::set<QLowEnergyHandle> updated;
+    std::map<QLowEnergyHandle, NSUInteger> updated;
 
     for (CBATTRequest *request in requests) {
         // Transition to 'connected' if needed.
         [self addConnectedCentral:request.central];
-
         const auto charHandle = charMap.key(request.characteristic);
-        updated.insert(charHandle);
+        const auto prevLen = updated[charHandle];
+        updated[charHandle] = std::max(request.offset + request.value.length,
+                                       prevLen);
         [self writeValueForCharacteristic:charHandle withWriteRequest:request];
     }
 
-    for (const auto handle : updated) {
-        emit notifier->characteristicUpdated(handle, qt_bytearray(charValues[handle]));
-        const ObjCStrongReference<NSData> copy([NSData dataWithData:charValues[handle]],
+    for (const auto pair : updated) {
+        const auto handle = pair.first;
+        NSMutableData *value = charValues[handle];
+        value.length = pair.second;
+        emit notifier->characteristicUpdated(handle, qt_bytearray(value));
+        const ObjCStrongReference<NSData> copy([NSData dataWithData:value],
                                                true);
         updateQueue.push_back(UpdateRequest{handle, copy});
     }