Add function which checks if an input is a ROOT file

The function Cbm::File::IsRootFile checks if a file with the given name
exists and if this is confirmed it checks if the file is either a ROOT
file or a ROOT file stored in a ZIP file. ROOT is able to handle ROOT
files stored in a ZIP archive.
The function returns true when the file is a ROOT file  and false in
any other case.

core/base/CMakeLists.txt

@@ -57,6 +57,7 @@ report/CbmLatexReportElement.cxx
 utils/CbmUtils.cxx
 utils/CbmGeometryUtils.cxx
 utils/CbmMediaList.cxx
+utils/CbmFileUtils.cxx
 )
 
 Set(LINKDEF CbmBaseLinkDef.h)

core/base/CbmBaseLinkDef.h

@@ -73,4 +73,6 @@
 // can not read the file with the CbmMediaList object. For other platforms there is no
 // problem without the line. So generate the correct streamer info in any way.
 #pragma link C++ class std::pair < TString, TString>;
+
+#pragma link C++ function Cbm::File::IsRootFile( string );
 #endif

core/base/utils/CbmFileUtils.cxx

+#include "CbmFileUtils.h"
+
+#include "FairLogger.h"  // for LOG, info and error
+
+#include "TArchiveFile.h"  // for TArchiveFile
+#include "TFile.h"         // for TFile
+#include "TObjArray.h"
+
+#include <string>      // for string, find, substr
+#include <sys/stat.h>  // for stcuct stat
+
+
+namespace Cbm {
+  namespace File {
+    bool IsRootFile(std::string filename) {
+      // Currently plain root files and root files stored in a zip file are supported.
+      // The destiction between the two is a "#" in the filename string  which separates the
+      // name of the zip file from the name of the root file which is inside the zip file.
+      // In case the filename contains a hash (e.g. multi.zip#file.root) the hash
+      // separates the name of a zipfile (multi.zip) which contains the real root file
+      // (file.root).
+      // This nameing convention (e.g. multi.zip#file.root) is sed by ROOT.
+
+      // If a filename string contains a hash "#"
+      // split the string at the # in the name of the zipfile and
+      // the name of the contained root file.
+      std::string checkFilename {""};
+      std::string membername {""};
+      std::size_t found = filename.find("#");
+      if (found != std::string::npos) {
+        checkFilename = filename.substr(0, found);
+        membername    = filename.substr(found + 1);
+      } else {
+        checkFilename = filename;
+      }
+
+      bool wasfound = kFALSE;
+
+      // Check if the file exist
+      // In case of a root file contained in a zip archive check if the zip file
+      // exist
+      struct stat buffer;
+      if (stat(checkFilename.c_str(), &buffer) == 0) {
+        wasfound = kTRUE;
+      } else {
+        wasfound = kFALSE;
+        LOG(error) << "Input File " << checkFilename << " not found";
+      }
+
+      // In case of a zip archive check if the archive contains the root file
+      if (membername.compare("") != 0) {
+        TFile* fzip = TFile::Open(checkFilename.c_str());
+        if (fzip->IsOpen()) {
+          TArchiveFile* archive = fzip->GetArchive();
+          if (archive) {
+            TObjArray* members = archive->GetMembers();
+            if (members->FindObject(membername.c_str()) == 0) {
+              LOG(error) << "File " << membername << " not found in zipfile "
+                         << checkFilename;
+              wasfound = kFALSE;
+            } else {
+              LOG(info) << "File " << membername << " found in zipfile "
+                        << checkFilename;
+              wasfound = kTRUE;
+            }
+          } else {
+            LOG(error) << "Zipfile " << checkFilename
+                       << " does not contain an archive";
+            wasfound = kFALSE;
+          }
+          fzip->Close();
+          delete fzip;
+        } else {
+          LOG(error) << "Could not open zipfile " << checkFilename;
+          wasfound = kFALSE;
+        }
+      } else {
+        TFile* rootfile = TFile::Open(checkFilename.c_str());
+        if (rootfile->IsOpen()) {
+          LOG(info) << "File " << checkFilename << " is a ROOT file.";
+          wasfound = kTRUE;
+        } else {
+          LOG(error) << "File " << checkFilename << " is no ROOT file.";
+          wasfound = kFALSE;
+        }
+        rootfile->Close();
+        delete rootfile;
+      }
+
+      return wasfound;
+    }
+  }  // namespace File
+}  // namespace Cbm

core/base/utils/CbmFileUtils.h

+#ifndef CBMFILEUTILS_H_
+#define CBMFILEUTILS_H_
+
+#include <string>  // for string
+
+namespace Cbm {
+  namespace File {
+    /**
+     * \brief Check if a the file exist and is a root file
+     * \param[in] filename The filename of the file to be checked
+     * \value     true if file is an existing root file, 0 in any other case
+    **/
+    bool IsRootFile(std::string filename);
+  }  //namespace File
+}  // namespace Cbm
+
+#endif /* CBMFILEUTILS_H_ */