[ntpl] Allow XRootD redirection with EOS files

Author: vepadulano

io/io/src/RRawFile.cxx

@@ -21,6 +21,28 @@
 #include "TPluginManager.h"
 #include "TROOT.h"
 
+// XRootD protocol redirection
+#ifdef R__UNIX
+
+#ifdef R__FBSD
+#include <sys/extattr.h>
+#else
+#include <sys/xattr.h>
+#endif
+
+#ifdef R__MACOSX
+/* On macOS getxattr takes two extra arguments that should be set to 0 */
+#define getxattr(path, name, value, size) getxattr(path, name, value, size, 0u, 0)
+#endif
+
+#ifdef R__FBSD
+#define getxattr(path, name, value, size) extattr_get_file(path, EXTATTR_NAMESPACE_USER, name, value, size)
+#endif
+
+#include "TEnv.h"
+
+#endif
+
 #include <algorithm>
 #include <cctype> // for towlower
 #include <cerrno>
@@ -68,6 +90,23 @@ ROOT::Internal::RRawFile::Create(std::string_view url, ROptions options)
 #ifdef _WIN32
       return std::unique_ptr<RRawFile>(new RRawFileWin(url, options));
 #else
+      // If URL is a file on an EOS FUSE mount, attempt redirection to XRootD protocol.
+      if (gEnv->GetValue("TFile.CrossProtocolRedirects", 1) == 1) {
+         // At the moment the url parameter can only be the file name
+         ssize_t len = getxattr(url.data(), "eos.url.xroot", nullptr, 0);
+         if (len > 0) {
+            std::string xurl(len, 0);
+            std::string fileNameFromUrl{url.data()};
+            if (getxattr(fileNameFromUrl.c_str(), "eos.url.xroot", &xurl[0], len) == len) {
+               // Sometimes the `getxattr` call may return an invalid URL due
+               // to the POSIX attribute not being yet completely filled by EOS.
+               if (auto baseName = fileNameFromUrl.substr(fileNameFromUrl.find_last_of("/") + 1);
+                   std::equal(baseName.crbegin(), baseName.crend(), xurl.crbegin())) {
+                  return Create(xurl, options);
+               }
+            }
+         }
+      }
       return std::unique_ptr<RRawFile>(new RRawFileUnix(url, options));
 #endif
    }