OperationalDataset: Add ByteSpan extendedPanID

ByteSpans are const references, so we should be able to directly
reference the extendedPanId to send cluster commands if the sender
already owns the OperationalDataset object. This eliminates a copy
and doesn't require the calling object to hold separate memory
for the extended PAN ID when it's already present in the TLV.

src/lib/support/ThreadOperationalDataset.cpp

@@ -288,6 +288,19 @@ CHIP_ERROR OperationalDataset::GetExtendedPanId(uint8_t (&aExtendedPanId)[kSizeE
     return CHIP_ERROR_TLV_TAG_NOT_FOUND;
 }
 
+CHIP_ERROR OperationalDataset::GetExtendedPanIdAsByteSpan(ByteSpan & span) const
+{
+    const ThreadTLV * tlv = Locate(ThreadTLV::kExtendedPanId);
+
+    if (tlv != nullptr)
+    {
+        span = ByteSpan(reinterpret_cast<const uint8_t *>(tlv->GetValue()), tlv->GetLength());
+        return CHIP_NO_ERROR;
+    }
+
+    return CHIP_ERROR_TLV_TAG_NOT_FOUND;
+}
+
 CHIP_ERROR OperationalDataset::SetExtendedPanId(const uint8_t (&aExtendedPanId)[kSizeExtendedPanId])
 {
     ThreadTLV * tlv = MakeRoom(ThreadTLV::kExtendedPanId, sizeof(*tlv) + sizeof(aExtendedPanId));

src/lib/support/ThreadOperationalDataset.h

@@ -113,6 +113,18 @@ class OperationalDataset
      */
     CHIP_ERROR GetExtendedPanId(uint8_t (&aExtendedPanId)[kSizeExtendedPanId]) const;
 
+    /**
+     * This method returns a const ByteSpan to the extended PAN ID in the dataset.
+     * This can be used to pass the extended PAN ID to a cluster command without the use of external memory.
+     *
+     * @param[out]  span  A reference to receive the location of the extended PAN ID.
+     *
+     * @retval CHIP_NO_ERROR                    Successfully retrieved the extended PAN ID.
+     * @retval CHIP_ERROR_TLV_TAG_NOT_FOUND     Thread extended PAN ID is not present in the dataset.
+     *
+     */
+    CHIP_ERROR GetExtendedPanIdAsByteSpan(ByteSpan & span) const;
+
     /**
      * This method sets Thread extended PAN ID to the dataset.
      *

src/lib/support/tests/TestThreadOperationalDataset.cpp

@@ -80,6 +80,11 @@ void TestExtendedPanId(nlTestSuite * inSuite, void * inContext)
     NL_TEST_ASSERT(inSuite, dataset.SetExtendedPanId(kExtendedPanId) == CHIP_NO_ERROR);
     NL_TEST_ASSERT(inSuite, dataset.GetExtendedPanId(extendedPanId) == CHIP_NO_ERROR);
     NL_TEST_ASSERT(inSuite, memcmp(extendedPanId, kExtendedPanId, sizeof(kExtendedPanId)) == 0);
+
+    ByteSpan span;
+    NL_TEST_ASSERT(inSuite, dataset.GetExtendedPanIdAsByteSpan(span) == CHIP_NO_ERROR);
+    NL_TEST_ASSERT(inSuite, span.size() == sizeof(kExtendedPanId));
+    NL_TEST_ASSERT(inSuite, memcmp(extendedPanId, span.data(), sizeof(kExtendedPanId)) == 0);
 }
 
 void TestMasterKey(nlTestSuite * inSuite, void * inContext)