[17464] Improve auto gaps in data sharing

src/cpp/rtps/DataSharing/DataSharingListener.cpp

@@ -157,16 +157,16 @@ void DataSharingListener::process_new_data ()
             pool->get_next_unread_payload(ch, last_sequence, last_payload);
             has_new_payload = ch.sequenceNumber != c_SequenceNumber_Unknown;
 
-            if (has_new_payload)
+            if (has_new_payload && ch.sequenceNumber > SequenceNumber_t(0, 0))
             {
-                if (last_sequence != c_SequenceNumber_Unknown && ch.sequenceNumber != last_sequence + 1)
+                if (last_sequence != c_SequenceNumber_Unknown && ch.sequenceNumber > last_sequence + 1)
                 {
                     EPROSIMA_LOG_WARNING(RTPS_READER, "GAP (" << last_sequence + 1 << " - " << ch.sequenceNumber - 1 << ")"
                                                               << " detected on datasharing writer " << pool->writer());
                     reader_->processGapMsg(pool->writer(), last_sequence + 1, SequenceNumberSet_t(ch.sequenceNumber));
                 }
 
-                if (last_sequence == c_SequenceNumber_Unknown && ch.sequenceNumber != SequenceNumber_t(0, 1))
+                if (last_sequence == c_SequenceNumber_Unknown && ch.sequenceNumber > SequenceNumber_t(0, 1))
                 {
                     EPROSIMA_LOG_INFO(RTPS_READER, "First change with SN " << ch.sequenceNumber
                                                                            << " detected on datasharing writer " <<

src/cpp/rtps/DataSharing/ReaderPool.hpp

@@ -192,6 +192,12 @@ class ReaderPool : public DataSharingPayloadPool
                 continue;
             }
 
+            if (last_sn_ != c_SequenceNumber_Unknown && last_sn_ >= cache_change.sequenceNumber)
+            {
+                // Sequence number went backwards, it was most probably overriden.
+                continue;
+            }
+
             if (!ensure_reading_reference_is_in_bounds())
             {
                 // We may have been taken over and read a payload that is too far forward. Discard and continue

src/cpp/rtps/reader/StatefulReader.cpp

@@ -851,7 +851,7 @@ bool StatefulReader::processGapMsg(
     WriterProxy* pWP = nullptr;
 
     std::unique_lock<RecursiveTimedMutex> lock(mp_mutex);
-    if (!is_alive_)
+    if (!is_alive_ || gapStart < SequenceNumber_t(0, 1) || gapList.base() <= gapStart)
     {
         return false;
     }
@@ -860,9 +860,9 @@ bool StatefulReader::processGapMsg(
     {
         // TODO (Miguel C): Refactor this inside WriterProxy
         SequenceNumber_t auxSN;
-        SequenceNumber_t finalSN = gapList.base() - 1;
+        SequenceNumber_t finalSN = gapList.base();
         History::const_iterator history_iterator = mp_history->changesBegin();
-        for (auxSN = gapStart; auxSN <= finalSN; auxSN++)
+        for (auxSN = gapStart; auxSN < finalSN; auxSN++)
         {
             if (pWP->irrelevant_change_set(auxSN))
             {

test/blackbox/common/RTPSBlackboxTestsBasic.cpp

@@ -866,6 +866,35 @@ TEST(RTPS, MultithreadedWriterCreation)
     RTPSDomain::stopAll();
 }
 
+/* Regression Test for improving gaps processing
+ *  https://github.com/eProsima/Fast-DDS/pull/3343
+ */
+TEST(RTPS, RTPSCorrectGAPProcessing)
+{
+    RTPSWithRegistrationReader<HelloWorldPubSubType> reader(TEST_TOPIC_NAME);
+    RTPSWithRegistrationWriter<HelloWorldPubSubType> writer(TEST_TOPIC_NAME);
+
+    reader.durability(eprosima::fastrtps::rtps::DurabilityKind_t::TRANSIENT_LOCAL).
+            reliability(eprosima::fastrtps::rtps::ReliabilityKind_t::RELIABLE).init();
+
+    ASSERT_TRUE(reader.isInitialized());
+
+    writer.durability(eprosima::fastrtps::rtps::DurabilityKind_t::TRANSIENT_LOCAL).
+            reliability(eprosima::fastrtps::rtps::ReliabilityKind_t::RELIABLE).init();
+
+    ASSERT_TRUE(writer.isInitialized());
+
+    reader.wait_discovery();
+    writer.wait_discovery();
+
+    SequenceNumberSet_t seq_set(SequenceNumber_t(0, 0));
+
+    //! GAP Message check
+    RTPSReader& native_reader = reader.get_native_reader();
+    ASSERT_NO_FATAL_FAILURE(native_reader.processGapMsg(writer.guid(), {0, 0}, seq_set));
+}
+
+
 class CustomReaderDataFilter : public eprosima::fastdds::rtps::IReaderDataFilter
 {
 public:

test/blackbox/common/RTPSWithRegistrationReader.hpp

@@ -527,6 +527,11 @@ class RTPSWithRegistrationReader
         return reader_->getGuid();
     }
 
+    eprosima::fastrtps::rtps::RTPSReader& get_native_reader() const
+    {
+        return *reader_;
+    }
+
 private:
 
     void receive_one(