[ntpl] Allow XRootD redirection with EOS files

io/io/CMakeLists.txt

@@ -21,6 +21,7 @@ if (uring)
 endif ()
 
 ROOT_LINKER_LIBRARY(RIO
+  src/InternalIOUtils.cxx
   src/RConcurrentHashColl.cxx
   src/RFile.cxx
   src/RRawFile.cxx
@@ -66,6 +67,8 @@ ROOT_LINKER_LIBRARY(RIO
 )
 
 target_include_directories(RIO PRIVATE ${CMAKE_SOURCE_DIR}/core/clib/res)
+# PUBLIC so that dependent libraries e.g. ROOTDataFrame may find the internal header too
+target_include_directories(RIO PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/res>)
 target_link_libraries(RIO PUBLIC ${ROOT_ATOMIC_LIBS})
 target_link_libraries(RIO PRIVATE nlohmann_json::nlohmann_json)
 

io/io/res/ROOT/InternalIOUtils.hxx

@@ -0,0 +1,24 @@
+// Author: Vincenzo Eduardo Padulano (CERN), 08/2026
+
+#ifndef ROOT_IO_UTILS
+#define ROOT_IO_UTILS
+
+#include <optional>
+#include <string>
+#include <string_view>
+
+namespace ROOT::Internal {
+
+/// \brief Get extended attribute value from path
+/// \param path Path to the file to check
+/// \param xattr Extended attribute to evaluate
+/// \return The string containing the extended attribute value if found, std::nullopt otherwise
+std::optional<std::string> GetXAttrVal(std::string_view path, std::string_view xattr);
+
+/// \brief Redirects the input path to the equivalent XRootD URL on EOS
+/// \param inputUrl The input path to redirect
+/// \return The redirected URL in case of successful redirection, std::nullopt otherwise
+std::optional<std::string> GetEOSRedirectedXRootURL(std::string_view inputPath);
+} // namespace ROOT::Internal
+
+#endif

io/io/src/InternalIOUtils.cxx

@@ -0,0 +1,82 @@
+#include "ROOT/InternalIOUtils.hxx"
+
+#include "ROOT/RConfig.hxx" // R__UNIX
+
+#ifdef R__UNIX
+
+#include <ROOT/RLogger.hxx>
+
+ROOT::RLogChannel &InternalLogChannel()
+{
+   static ROOT::RLogChannel sLog("ROOT.Internal");
+   return sLog;
+}
+
+// getxattr
+#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 "ROOT/StringUtils.hxx" // ROOT::StartsWith
+#include "TEnv.h"               // TEnv::GetValue
+#endif
+
+std::optional<std::string>
+ROOT::Internal::GetXAttrVal([[maybe_unused]] std::string_view path, [[maybe_unused]] std::string_view xattr)
+{
+#ifdef R__UNIX
+   // First call to getxattr evaluates the length of the extended attribute value
+   if (auto len = getxattr(path.data(), xattr.data(), nullptr, 0); len >= 0) {
+      std::string xval(len, 0);
+      // Second call extracts the extended attribute value, checking it's of the correct length
+      if (getxattr(path.data(), xattr.data(), xval.data(), len) == len)
+         return xval;
+   }
+#endif
+   return std::nullopt;
+}
+
+std::optional<std::string> ROOT::Internal::GetEOSRedirectedXRootURL([[maybe_unused]] std::string_view inputPath)
+{
+#ifdef R__UNIX
+   if (inputPath.empty() || inputPath.back() == '/')
+      return std::nullopt;
+
+   if (gEnv->GetValue("TFile.CrossProtocolRedirects", 1) != 1)
+      return std::nullopt;
+
+   auto xurl = ROOT::Internal::GetXAttrVal(inputPath, "eos.url.xroot");
+   if (!xurl)
+      return std::nullopt;
+
+   auto baseName = inputPath.substr(inputPath.find_last_of("/") + 1);
+   // Sometimes the `getxattr` call may return an invalid URL due
+   // to the POSIX attribute not being yet completely filled by EOS.
+   if (!std::equal(baseName.crbegin(), baseName.crend(), xurl->crbegin())) {
+      R__LOG_WARNING(InternalLogChannel())
+         << "Could not find path base name '" << baseName << "' in redirected URL '" << *xurl << "'.";
+      return std::nullopt;
+   }
+
+   // Ensure the redirected URL actually starts with the XRootD protocol string
+   if (ROOT::StartsWith(*xurl, "root://") || ROOT::StartsWith(*xurl, "xroot://") ||
+       ROOT::StartsWith(*xurl, "roots://") || ROOT::StartsWith(*xurl, "xroots://"))
+      return xurl;
+   else
+      R__LOG_WARNING(InternalLogChannel())
+         << "Redirected URL '" << *xurl << "' does not begin with any valid XRootD protocol string.";
+
+#endif
+   return std::nullopt;
+}

io/io/src/RRawFile.cxx

@@ -20,6 +20,7 @@
 #include "TError.h"
 #include "TPluginManager.h"
 #include "TROOT.h"
+#include "ROOT/InternalIOUtils.hxx"
 
 #include <algorithm>
 #include <cctype> // for towlower
@@ -68,6 +69,9 @@ ROOT::Internal::RRawFile::Create(std::string_view url, ROptions options)
 #ifdef _WIN32
       return std::unique_ptr<RRawFile>(new RRawFileWin(url, options));
 #else
+      // We're assuming the input url is null-terminated in the next call
+      if (auto xurl = ROOT::Internal::GetEOSRedirectedXRootURL(url))
+         return Create(*xurl, options);
       return std::unique_ptr<RRawFile>(new RRawFileUnix(url, options));
 #endif
    }

io/io/src/TFile.cxx

@@ -171,6 +171,7 @@ The structure of a directory is shown in TDirectoryFile::TDirectoryFile
 #include "TThreadSlots.h"
 #include "TGlobal.h"
 #include "ROOT/RConcurrentHashColl.hxx"
+#include "ROOT/InternalIOUtils.hxx"
 #include <memory>
 #include <cinttypes>
 
@@ -3811,34 +3812,16 @@ TFile *TFile::Open(const char *url, Option_t *options, const char *ftitle,
    TString expandedUrl(url);
    gSystem->ExpandPathName(expandedUrl);
 
-#ifdef R__UNIX
-   // If URL is a file on an EOS FUSE mount, attempt redirection to XRootD protocol.
-   if (gEnv->GetValue("TFile.CrossProtocolRedirects", 1) == 1) {
-      TUrl fileurl(expandedUrl, /* default is file */ kTRUE);
-      if (strcmp(fileurl.GetProtocol(), "file") == 0) {
-         ssize_t len = getxattr(fileurl.GetFile(), "eos.url.xroot", nullptr, 0);
-         if (len > 0) {
-            std::string xurl(len, 0);
-            std::string fileNameFromUrl{fileurl.GetFile()};
-            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())) {
-                  if ((f = TFile::Open(xurl.c_str(), options, ftitle, compress, netopt))) {
-                     if (!f->IsZombie()) {
-                        return f;
-                     } else {
-                        delete f;
-                        f = nullptr;
-                     }
-                  }
-               }
-            }
+   if (auto xurl = ROOT::Internal::GetEOSRedirectedXRootURL(expandedUrl)) {
+      if ((f = TFile::Open(xurl->c_str(), options, ftitle, compress, netopt))) {
+         if (!f->IsZombie()) {
+            return f;
+         } else {
+            delete f;
+            f = nullptr;
          }
       }
    }
-#endif
 
    // If a timeout has been specified extract the value and try to apply it (it requires
    // support for asynchronous open, though; the following is completely transparent if

tree/dataframe/src/RLoopManager.cxx

@@ -43,23 +43,8 @@
 #include "ROOT/RSlotStack.hxx"
 #endif
 
-#ifdef R__UNIX
-// Functions needed to perform EOS XRootD redirection in ChangeSpec
-#include "TEnv.h"
+#include "ROOT/InternalIOUtils.hxx"
 #include "TSystem.h"
-#ifndef R__FBSD
-#include <sys/xattr.h>
-#else
-#include <sys/extattr.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
-#endif
 
 #include <algorithm>
 #include <atomic>
@@ -370,37 +355,21 @@ RLoopManager::RLoopManager(ROOT::RDF::Experimental::RDatasetSpec &&spec)
    ChangeSpec(std::move(spec));
 }
 
-#ifdef R__UNIX
 namespace {
 std::optional<std::string> GetRedirectedSampleId(std::string_view path, std::string_view datasetName)
 {
    // Mimick the redirection done in TFile::Open to see if the path points to a FUSE-mounted EOS path.
    // If so, we create a redirected sample ID with the full xroot URL.
    TString expandedUrl(path.data());
    gSystem->ExpandPathName(expandedUrl);
-   if (gEnv->GetValue("TFile.CrossProtocolRedirects", 1) == 1) {
-      TUrl fileurl(expandedUrl, /* default is file */ kTRUE);
-      if (strcmp(fileurl.GetProtocol(), "file") == 0) {
-         ssize_t len = getxattr(fileurl.GetFile(), "eos.url.xroot", nullptr, 0);
-         if (len > 0) {
-            std::string xurl(len, 0);
-            std::string fileNameFromUrl{fileurl.GetFile()};
-            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 xurl + '/' + datasetName.data();
-               }
-            }
-         }
-      }
+   TUrl fileurl(expandedUrl, /* default is file */ kTRUE);
+   if (strcmp(fileurl.GetProtocol(), "file") == 0) {
+      if (auto xurl = ROOT::Internal::GetEOSRedirectedXRootURL(fileurl.GetFile()))
+         return *xurl + '/' + datasetName.data();
    }
-
    return std::nullopt;
 }
 } // namespace
-#endif
 
 /**
  * @brief Changes the internal TTree held by the RLoopManager.
@@ -451,11 +420,10 @@ void RLoopManager::ChangeSpec(ROOT::RDF::Experimental::RDatasetSpec &&spec)
                // is exposed to users via RSampleInfo and DefinePerSample).
                const auto sampleId = files[i] + '/' + trees[i];
                fSampleMap.insert({sampleId, &sample});
-#ifdef R__UNIX
+
                // Also add redirected EOS xroot URL when available
                if (auto redirectedSampleId = GetRedirectedSampleId(files[i], trees[i]))
                   fSampleMap.insert({redirectedSampleId.value(), &sample});
-#endif
             }
          }
          fDataSource = std::make_unique<ROOT::Internal::RDF::RTTreeDS>(std::move(chain), spec.GetFriendInfo());
@@ -473,11 +441,9 @@ void RLoopManager::ChangeSpec(ROOT::RDF::Experimental::RDatasetSpec &&spec)
                fileNames.push_back(files[i]);
                rntupleNames.insert(trees[i]);
 
-#ifdef R__UNIX
                // Also add redirected EOS xroot URL when available
                if (auto redirectedSampleId = GetRedirectedSampleId(files[i], trees[i]))
                   fSampleMap.insert({redirectedSampleId.value(), &sample});
-#endif
             }
          }