Xrootd Client integration for Pelican

This repository contains a simple integration between the Xrootd client (XrdCl; used both by the command line tools like xrdcp and the XCache configuration of the server) and Pelican. It uses libcurl to provide generic HTTP functionality and can understand Pelican-specific headers and semantics.

Building and Installing

The plugin requires a C++14 compiler and CMake 3.16 or higher; on RHEL7, this can be provided by the devtoolset-11-toolchain package.

To build and install, after checking out the source code:

mkdir build
cd build
cmake ..
make && make install

Provide the -DCMAKE_INSTALL_PREFIX flag to cmake to override the install location.

Using from the command line

By default, the install drops the plugin configuration into /etc/xrootd/client.plugins.d/; if you do a non-root installation, you must override the location of the client plugin directory with the XRD_PLUGINCONFDIR environment variable.

The xrdcp client disables the HTTP protocol by default; set XRDCP_ALLOW_HTTP=true to enable it.

An example invocation including these two environment variables would be:

XRDCP_ALLOW_HTTP=true XRD_PLUGINCONFDIR=$RELEASE_DIR/etc/xrootd/client.plugins.d/ \
xrdcp -f http://unl-cache.nationalresearchplatform.org:8000/nrp/cachetest/100gfile

where $RELEASE_DIR is set to the value of CMAKE_INSTALL_PREFIX.

Note the install of the xrdcl-http RPM will cause xrdcl-http to be used by default. If this is not desired, remove or comment out /etc/xrootd/client.plugins.d/xrdcl-http-plugin.conf (do not just set enable=false -- the presence of the entry will cause it to match).

To verify the pelican plugin is used, pass -d 3 and look for log messages from XrdClPelican as in:

[2023-12-11 07:39:38.926434 -0600][Debug  ][XrdClPelican      ]
PgRead http://unl-cache.nationalresearchplatform.org:8000/nrp/cachetest/100gfile
(131072 bytes at offset 1132855296)

(line breaks were added for readability).

Using from XCache

Enable the use of the plugin at the system level; ensure the command-line use functions (it may be possible to override solely through the CLI; a system/container level install is simpler).

Add the following two lines to the XRootD server configuration:

pss.setopt DebugLevel 4
pss.origin https://director-caches.osg-htc.org:443

Then issue GET requests to the cache endpoint (substitute localhost below as appropriate):

$ curl http://localhost:8000/nrp/cachetest/100gfile > /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0  100G    0 20.0M    0     0  3320k      0  8:46:18  0:00:06  8:46:12 3967k^C

Adjust for your setup. Note that XRootD 5.6.3 and earlier will crash if a port number is not provided. Once you verify the plugin is working and can download from the cache, we recommend a lower debug level for production use.