[irods#7918] replica_truncate: Fix JSON output for some cases

The replica_truncate API has a JSON-based message in its output string
which is meant to communicate error information as well as information
about the replica which was truncated or targeted for truncate. The API
up to this point has only been communicating information back to clients
in the failure cases. It is most useful to communicate the replica
information to the client in the success cases. This change fixes that.

This change also adjusts the JSON output from the case where the target
replica is not in the hierarchy requested by the client via the RESC_NAME_KW.
Before, this case would return the replica information for the replica which
won the vote, but the JSON now returns no replica information because the
replica which the client wanted to target either does not exist or is not
accessible for truncating. Returning the replica information in this case
is incorrect because showing the replica which did win the vote could give
the impression that it was truncated when in fact it was not.

server/api/src/rs_replica_truncate.cpp

@@ -275,7 +275,11 @@ auto rs_replica_truncate(RsComm* _comm, DataObjInp* _inp, char** _out) -> int
                 resource_name,
                 _inp->objPath);
             log_api::error(msg);
-            *_out = strdup(make_json_output(msg, replica).dump().c_str());
+            // Even though we have replica information, do not include it in the output structure. This error case is
+            // specifically about the selected replica not being in the hierarchy descending from the client-requested
+            // resource, so we do not care to include that information in the output. It could give the impression that
+            // the replica from the returned information was truncated when in fact it was not.
+            *_out = strdup(make_json_output(msg).dump().c_str());
             return SYS_REPLICA_INACCESSIBLE;
         }
 
@@ -313,6 +317,9 @@ auto rs_replica_truncate(RsComm* _comm, DataObjInp* _inp, char** _out) -> int
             *_out = strdup(make_json_output(msg, replica).dump().c_str());
             return ec;
         }
+
+        // The output structure is meant to communicate back to the client which replica was truncated.
+        *_out = strdup(make_json_output("", replica).dump().c_str());
     }
     catch (const irods::exception& e) {
         log_api::error("{}: Failed to truncate [{}]: {}", __func__, _inp->objPath, e.client_display_what());