build fix; more docs

Author: serges147

libcyphal_demo/src/file_downloader.hpp

@@ -53,7 +53,7 @@ class FileDownloader final
 
         state_.file_size        = 0;
         state_.file_progress    = 0;
-        state_.file_path        = file_path;
+        state_.file_path        = {file_path.data(), file_path.size()};
         state_.start_time       = time_provider_.now();
         state_.file_error.value = uavcan::file::Error_1_0::OK;
 

libcyphal_demo/src/platform/common_helpers.hpp

@@ -94,6 +94,8 @@ struct CommonHelpers
                     }),
                 report_var);
 
+            // "swallows" all transient failures, thus giving a chance
+            // to other redundant media interfaces to continue.
             return cetl::nullopt;
         }
 
@@ -154,6 +156,8 @@ struct CommonHelpers
                     }),
                 report_var);
 
+            // "swallows" all transient failures, thus giving a chance
+            // to other redundant media interfaces to continue.
             return cetl::nullopt;
         }
 

libcyphal_demo/src/transport_bag_can.hpp

@@ -65,6 +65,13 @@ struct TransportBagCan final
         const std::size_t     block_size      = mtu;
         const std::size_t     pool_size       = media_collection_.count() * TxQueueCapacity * block_size;
         media_block_mr_.setup(pool_size, block_size, block_alignment);
+
+        // To support redundancy (multiple homogeneous interfaces), it's important to have a non-default
+        // handler which "swallows" expected transient failures (by returning `nullopt` result).
+        // Otherwise, the default Cyphal behavior will fail/interrupt current and future transfers
+        // if some of its media encounter transient failures - thus breaking the whole redundancy goal,
+        // namely, maintain communication if at least one of the interfaces is still up and running.
+        //
         transport_->setTransientErrorHandler([](auto&) { return cetl::nullopt; });
         // transport_->setTransientErrorHandler(platform::CommonHelpers::Can::transientErrorReporter);