Added catch for error from parsing json

- If for some reason the index file on IDAaaS is currupted (eg. being updated) then the error is caught
- Allows for the search to continue on the archive

Co-authored-by: Jonathan Haigh <jonathan.haigh@stfc.ac.uk>

Framework/API/src/FileFinder.cpp

@@ -32,6 +32,7 @@
 #include <boost/algorithm/string.hpp>
 
 #include <filesystem>
+#include <json //value.h>
 
 namespace {
 /// static logger object
@@ -668,6 +669,11 @@ FileFinderImpl::getISISInstrumentDataCachePath(const std::string &cachePathToSea
     } catch (const std::invalid_argument &e) {
       errors += "Data cache: " + std::string(e.what());
       return API::Result<std::string>("", errors);
+
+    } catch (const Json::Exception &e) {
+      errors += "Data cache: Failed parsing to JSON: " + std::string(e.what()) +
+                "Error likely due to accessing instrument index file while it was being updated on IDAaaS.";
+      return API::Result<std::string>("", errors);
     }
 
     if (!std::filesystem::exists(parentDirPath)) {

Framework/API/src/ISISInstrumentDataCache.cpp

@@ -21,7 +21,7 @@ std::string Mantid::API::ISISInstrumentDataCache::getFileParentDirectoryPath(std
   std::string jsonPath = m_dataCachePath + "/" + instrName + "/" + instrName + "_index.json";
   std::ifstream ifstrm{jsonPath};
   if (!ifstrm) {
-    throw std::invalid_argument("Error opennig instrument index file: " + jsonPath);
+    throw std::invalid_argument("Could not open index file: " + jsonPath);
   }
 
   // Read directory path from json file