[dbus] fix Scan return type and match introspect (#1814)

The dbus encoding and decoding methods were attempting to send the
incorrect amount of data over dbus. This breaks the dbus introspect
contract and causes runtime errors.

To fix the issue:
- Re-introduce the entire `ActiveScanResult` data structure to the
  introspect document.
- Coerce the RSSI value into an int16 when encoding and decoding
  an `ActiveScanResult`.

src/dbus/common/dbus_message_helper.hpp

@@ -212,8 +212,8 @@ template <> struct DBusTypeTrait<ChildInfo>
 template <> struct DBusTypeTrait<ActiveScanResult>
 {
     // struct of { uint64, string, uint64, array<uint8>, uint16, uint16, uint8,
-    //             uint8, uint8, uint8, bool, bool }
-    static constexpr const char *TYPE_AS_STRING = "(tstayqqyyyybb)";
+    //             int16, uint8, uint8, bool, bool }
+    static constexpr const char *TYPE_AS_STRING = "(tstayqqynyybb)";
 };
 
 template <> struct DBusTypeTrait<EnergyScanResult>

src/dbus/common/dbus_message_helper_openthread.cpp

@@ -54,6 +54,10 @@ otbrError DBusMessageExtract(DBusMessageIter *aIter, ActiveScanResult &aScanResu
     DBusMessageIter sub;
     otbrError       error = OTBR_ERROR_NONE;
 
+    // Local variable to help convert an RSSI value.
+    // Dbus doesn't have the concept of a signed byte
+    int16_t rssi = 0;
+
     VerifyOrExit(dbus_message_iter_get_arg_type(aIter) == DBUS_TYPE_STRUCT, error = OTBR_ERROR_DBUS);
     dbus_message_iter_recurse(aIter, &sub);
 
@@ -64,12 +68,16 @@ otbrError DBusMessageExtract(DBusMessageIter *aIter, ActiveScanResult &aScanResu
     SuccessOrExit(error = DBusMessageExtract(&sub, aScanResult.mPanId));
     SuccessOrExit(error = DBusMessageExtract(&sub, aScanResult.mJoinerUdpPort));
     SuccessOrExit(error = DBusMessageExtract(&sub, aScanResult.mChannel));
-    SuccessOrExit(error = DBusMessageExtract(&sub, aScanResult.mRssi));
+    SuccessOrExit(error = DBusMessageExtract<int16_t>(&sub, rssi));
     SuccessOrExit(error = DBusMessageExtract(&sub, aScanResult.mLqi));
     SuccessOrExit(error = DBusMessageExtract(&sub, aScanResult.mVersion));
     SuccessOrExit(error = DBusMessageExtract(&sub, aScanResult.mIsNative));
     SuccessOrExit(error = DBusMessageExtract(&sub, aScanResult.mDiscover));
 
+    // Double check the value is within int8 bounds and cast back
+    VerifyOrExit((rssi <= INT8_MAX) && (rssi >= INT8_MIN), error = OTBR_ERROR_PARSE);
+    aScanResult.mRssi = static_cast<int8_t>(rssi);
+
     dbus_message_iter_next(aIter);
     error = OTBR_ERROR_NONE;
 exit:
@@ -89,7 +97,10 @@ otbrError DBusMessageEncode(DBusMessageIter *aIter, const ActiveScanResult &aSca
     SuccessOrExit(error = DBusMessageEncode(&sub, aScanResult.mPanId));
     SuccessOrExit(error = DBusMessageEncode(&sub, aScanResult.mJoinerUdpPort));
     SuccessOrExit(error = DBusMessageEncode(&sub, aScanResult.mChannel));
-    SuccessOrExit(error = DBusMessageEncode(&sub, aScanResult.mRssi));
+
+    // Dbus doesn't have a signed byte, cast into an int16
+    SuccessOrExit(error = DBusMessageEncode(&sub, static_cast<int16_t>(aScanResult.mRssi)));
+
     SuccessOrExit(error = DBusMessageEncode(&sub, aScanResult.mLqi));
     SuccessOrExit(error = DBusMessageEncode(&sub, aScanResult.mVersion));
     SuccessOrExit(error = DBusMessageEncode(&sub, aScanResult.mIsNative));

src/dbus/server/introspect.xml

@@ -9,15 +9,22 @@
       <literallayout>
         struct {
           uint64 ext_address
+          string network_name
+          uint64 ext_panid
+          uint8[] steering_data
           uint16 panid
-          uint16 channel
-          uint16 rssi
+          uint16 joiner_udp_port
+          uint8 channel
+          int16 rssi
           uint8 lqi
+          uint8 version
+          bool is_native
+          bool is_joinable
         }
       </literallayout>
     -->
     <method name="Scan">
-      <arg name="scan_result" type="a(tqqqy)" direction="out"/>
+      <arg name="scan_result" type="a(tstayqqynyybb)" direction="out"/>
     </method>
 
     <!-- Energy Scan: Perform a Thread energy scan.