[discover-scanner] allow filtering based on a user given bloom filter indexes (#5075)

This commit enhances the filtering behavior of Discover Scan. When
filtering is enabled, MLE Discovery Responses with steering data
(bloom filter) not containing a set of bloom filter indexes are
filtered. This commit updates the `DiscoverScanner::Discover()` to
allow filter indexes used for filtering to be optionally specified by
the caller. It can be set to NULL (for default behavior) where the
hash of factory-assigned EUI64 of the device would be used to derive
the bloom filter indexes

src/core/api/thread_api.cpp

@@ -457,8 +457,9 @@ otError otThreadDiscover(otInstance *             aInstance,
 {
     Instance &instance = *static_cast<Instance *>(aInstance);
 
-    return instance.Get<Mle::DiscoverScanner>().Discover(static_cast<Mac::ChannelMask>(aScanChannels), aPanId, aJoiner,
-                                                         aEnableEui64Filtering, aCallback, aCallbackContext);
+    return instance.Get<Mle::DiscoverScanner>().Discover(
+        static_cast<Mac::ChannelMask>(aScanChannels), aPanId, aJoiner, aEnableEui64Filtering,
+        /* aFilterIndexes (use hash of factory EUI64) */ NULL, aCallback, aCallbackContext);
 }
 
 bool otThreadIsDiscoverInProgress(otInstance *aInstance)

src/core/meshcop/joiner.cpp

@@ -124,6 +124,7 @@ otError Joiner::Start(const char *     aPskd,
 
     SuccessOrExit(error = Get<Mle::DiscoverScanner>().Discover(Mac::ChannelMask(0), Get<Mac::Mac>().GetPanId(),
                                                                /* aJoiner */ true, /* aEnableFiltering */ true,
+                                                               /* aFilterIndexes (use hash of factory EUI64) */ NULL,
                                                                HandleDiscoverResult, this));
     mCallback = aCallback;
     mContext  = aContext;

src/core/thread/discover_scanner.cpp

@@ -62,6 +62,7 @@ otError DiscoverScanner::Discover(const Mac::ChannelMask &aScanChannels,
                                   uint16_t                aPanId,
                                   bool                    aJoiner,
                                   bool                    aEnableFiltering,
+                                  const FilterIndexes *   aFilterIndexes,
                                   Handler                 aCallback,
                                   void *                  aContext)
 {
@@ -76,12 +77,18 @@ otError DiscoverScanner::Discover(const Mac::ChannelMask &aScanChannels,
 
     if (mEnableFiltering)
     {
-        Mac::ExtAddress extAddress;
+        if (aFilterIndexes == NULL)
+        {
+            Mac::ExtAddress extAddress;
 
-        Get<Radio>().GetIeeeEui64(extAddress);
-        MeshCoP::ComputeJoinerId(extAddress, extAddress);
-
-        MeshCoP::SteeringData::CalculateHashBitIndexes(extAddress, mFilterIndexes);
+            Get<Radio>().GetIeeeEui64(extAddress);
+            MeshCoP::ComputeJoinerId(extAddress, extAddress);
+            MeshCoP::SteeringData::CalculateHashBitIndexes(extAddress, mFilterIndexes);
+        }
+        else
+        {
+            mFilterIndexes = *aFilterIndexes;
+        }
     }
 
     mHandler            = aCallback;

src/core/thread/discover_scanner.hpp

@@ -82,6 +82,16 @@ public:
      */
     typedef otHandleActiveScanResult Handler;
 
+    /**
+     * This type represents the filter indexes, i.e., hash bit index values for the bloom filter (calculated from a
+     * Joiner ID).
+     *
+     * This is used when filtering is enabled during Discover Scan, i.e., received MLE Discovery Responses with steering
+     * data (bloom filter) not containing the given indexes are filtered.
+     *
+     */
+    typedef MeshCoP::SteeringData::HashBitIndexes FilterIndexes;
+
     /**
      * This constructor initializes the object.
      *
@@ -96,7 +106,10 @@ public:
      * @param[in]  aScanChannels      Channel mask listing channels to scan (if empty, use all supported channels).
      * @param[in]  aPanId             The PAN ID filter (set to Broadcast PAN to disable filter).
      * @param[in]  aJoiner            Value of the Joiner Flag in the Discovery Request TLV.
-     * @param[in]  aEnableFiltering   Enable filtering MLE Discovery Responses that don't match our factory EUI64.
+     * @param[in]  aEnableFiltering   Enable filtering MLE Discovery Responses with steering data not containing a
+     *                                given filter indexes.
+     * @param[in]  aFilterIndexes     A pointer to `FilterIndexes` to use for filtering (when enabled).
+     *                                If set to NULL, filter indexes are derived from hash of factory-assigned EUI64.
      * @param[in]  aHandler           A pointer to a function that is called on receiving an MLE Discovery Response.
      * @param[in]  aContext           A pointer to arbitrary context information.
      *
@@ -109,6 +122,7 @@ public:
                      Mac::PanId              aPanId,
                      bool                    aJoiner,
                      bool                    aEnableFiltering,
+                     const FilterIndexes *   aFilterIndexes,
                      Handler                 aHandler,
                      void *                  aContext);
 
@@ -140,15 +154,15 @@ private:
     static void HandleTimer(Timer &aTimer);
     void        HandleTimer(void);
 
-    Handler                               mHandler;
-    void *                                mHandlerContext;
-    TimerMilli                            mTimer;
-    MeshCoP::SteeringData::HashBitIndexes mFilterIndexes;
-    Mac::ChannelMask                      mScanChannels;
-    State                                 mState;
-    uint8_t                               mScanChannel;
-    bool                                  mEnableFiltering : 1;
-    bool                                  mShouldRestorePanId : 1;
+    Handler          mHandler;
+    void *           mHandlerContext;
+    TimerMilli       mTimer;
+    FilterIndexes    mFilterIndexes;
+    Mac::ChannelMask mScanChannels;
+    State            mState;
+    uint8_t          mScanChannel;
+    bool             mEnableFiltering : 1;
+    bool             mShouldRestorePanId : 1;
 };
 
 } // namespace Mle