Redirect TFile::Open() calls to XRootD protocol if possible

io/io/src/TFile.cxx

@@ -76,7 +76,8 @@ The structure of a directory is shown in TDirectoryFile::TDirectoryFile
 #include <errno.h>
 #include <sys/stat.h>
 #ifndef WIN32
-#   include <unistd.h>
+#include <unistd.h>
+#include <sys/xattr.h>
 #else
 #   define ssize_t int
 #   include <io.h>
@@ -150,6 +151,11 @@ Bool_t   TFile::fgOnlyStaged = kFALSE;
 ROOT::Internal::RConcurrentHashColl TFile::fgTsSIHashes;
 #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
+
 const Int_t kBEGIN = 100;
 
 ClassImp(TFile);
@@ -4030,6 +4036,18 @@ TFile *TFile::Open(const char *url, Option_t *options, const char *ftitle,
       return f;
    }
 
+#ifdef R__UNIX
+   { // If the file has an extended attribute with the XRootD URL, try it first
+      ssize_t len = getxattr(url, "eos.url.xroot", nullptr, 0);
+      if (len > 0) {
+         std::string xurl(len, 0);
+         if (getxattr(url, "eos.url.xroot", xurl.data(), len) == len)
+            if ((f = TFile::Open(xurl.c_str(), options, ftitle, compress, netopt)))
+               return f;
+      }
+   }
+#endif
+
    TString expandedUrl(url);
    gSystem->ExpandPathName(expandedUrl);