hltDiff: add protections against missing or empty input files

HLTrigger/Tools/bin/BuildFile.xml

@@ -15,6 +15,7 @@
 <bin name="hltDiff" file="hltDiff.cc">
   <use name="jemalloc"/>
   <use name="boost"/>
+  <use name="boost_filesystem"/>
   <use name="FWCore/Common"/>
   <use name="FWCore/Framework"/>
   <use name="FWCore/Utilities"/>

HLTrigger/Tools/bin/hltDiff.cc

@@ -16,6 +16,7 @@
 #include <getopt.h>
 
 #include <boost/algorithm/string.hpp>
+#include <boost/filesystem.hpp>
 
 #include "FWCore/Common/interface/TriggerNames.h"
 #include "FWCore/Utilities/interface/InputTag.h"
@@ -471,17 +472,55 @@ std::ostream & operator<<(std::ostream & out, TriggerDiff diff) {
 }
 
 
+bool check_file(std::string const & file) {
+  boost::filesystem::path p(file);
+
+  // check if the file exists
+  if (not boost::filesystem::exists(p))
+    return false;
+
+  // resolve the file name to canonical form
+  p = boost::filesystem::canonical(p);
+  if (not boost::filesystem::exists(p))
+    return false;
+
+  // check for a regular file
+  if (not boost::filesystem::is_regular_file(p))
+    return false;
+
+  return true;
+}
+
+
+bool check_files(std::vector<std::string> const & files) {
+  bool flag = true;
+  for (auto const & file: files)
+    if (not check_file(file)) {
+      flag = false;
+      std::cerr << "hltDiff: error: file " << file << " does not exist, or is not a regular file." << std::endl;
+    }
+  return flag;
+}
+
+
 void compare(std::vector<std::string> const & old_files, std::string const & old_process,
              std::vector<std::string> const & new_files, std::string const & new_process,
              unsigned int max_events, bool ignore_prescales, int verbose) {
 
-  std::shared_ptr<fwlite::ChainEvent> old_events = std::make_shared<fwlite::ChainEvent>(old_files);
+  std::shared_ptr<fwlite::ChainEvent> old_events;
   std::shared_ptr<fwlite::ChainEvent> new_events;
 
+  if (check_files(old_files))
+    old_events = std::make_shared<fwlite::ChainEvent>(old_files);
+  else
+    return;
+
   if (new_files.size() == 1 and new_files[0] == "-")
     new_events = old_events;
-  else
+  else if (check_files(new_files))
     new_events = std::make_shared<fwlite::ChainEvent>(new_files);
+  else
+    return;
 
   std::unique_ptr<HLTConfigDataEx> old_config_data;
   std::unique_ptr<HLTConfigDataEx> new_config_data;
@@ -629,10 +668,14 @@ void compare(std::vector<std::string> const & old_files, std::string const & old
       break;
   }
 
-  std::cout << "Found " << affected << " events out of " << counter << " with differences:\n" << std::endl;
-  std::cout << std::setw(12) << "Events" << std::setw(12) << "Accepted" << std::setw(12) << "Gained" << std::setw(12) << "Lost" << std::setw(12) << "Other" << "  " << "Trigger" << std::endl;
-  for (unsigned int p = 0; p < old_config->size(); ++p)
-    std::cout << std::setw(12) << counter << differences[p] << "  " << old_config->triggerName(p) << std::endl;
+  if (not counter) {
+    std::cout << "There are no common events between the old and new files." << std::endl;
+  } else {
+    std::cout << "Found " << affected << " events out of " << counter << " with differences:\n" << std::endl;
+    std::cout << std::setw(12) << "Events" << std::setw(12) << "Accepted" << std::setw(12) << "Gained" << std::setw(12) << "Lost" << std::setw(12) << "Other" << "  " << "Trigger" << std::endl;
+    for (unsigned int p = 0; p < old_config->size(); ++p)
+      std::cout << std::setw(12) << counter << differences[p] << "  " << old_config->triggerName(p) << std::endl;
+  }
 }