go-hep/hep: Release v0.16.0

Release v0.16.0 is fresh from the oven.

This new release introduces a new package, groot, that replaces rootio.

groot is a new package that is meant to replace rootio. For backward compatibility, rootio will remain in the repository for a couple of releases (presumably until v1.0.0.)

groot is the result of refactoring rootio in a couple of more focused packages with clear API boundaries:

• groot/rbase: definitions of basic ROOT classes (Object, Named, ObjString, ...)
• groot/rbytes: definitions of types useful for serializing and deserializing ROOT data buffers, interfaces to interact with ROOT's metadata classes such as StreamerInfo and StreamerElements.
• groot/rcont: definitions of ROOT container types (TList, THashList, TObjArray, TArrayX)
• groot/rdict: definitions of ROOT streamers (TStreamerArtificial, TStreamerLoop, ...)
• groot/rhist: definitions of ROOT types related to histograms and graphs (TH1x, TH2x, TGraph, TGraphErrors, TGraphAsymmErrors)
• groot/riofs: low-level types and functions to deal with opening and creating ROOT files; users should prefer using the groot package to open and create ROOT files
• groot/root: ROOT core interfaces (Object, Named, ObjArray, ...)
• groot/rsrv: exposes HTTP end-point to manipulate ROOT files, plot and create histograms and graphs from files or trees
• groot/rtree: interface to decode, read, concatenate and iterate over ROOT Trees
• groot/rtypes: rtypes contains the means to register types (ROOT ones and user defined ones) with the ROOT type factory system
• groot/rvers: rvers contains the ROOT version and the classes' versions groot is supporting and currently reading.

Interacting with ROOT files should be performed with the groot package:

import "go-hep.org/x/hep/groot"

func F() {
    f1, err := groot.Open("some/file.root")
    f2, err := groot.Create("some/other.root")
}

groot has the needed bootstrap code that allows to automatically import the registration code for all the ROOT types groot knows how to handle.

Here is a quick and dirty Rosetta code for migrating to groot:

• rootio.H1 → groot/rhist.H1
• rootio.H2 → groot/rhist.H2
• rootio.Graph → groot/rhist.Graph
• rootio.Tree → groot/rtree.Tree
• rootio.ChainOf → groot/rtree.ChainOf
• rootio.Scanner → groot/rtree.Scanner
• rootio.File → groot/riofs.File
• rootio.Directory → groot/riofs.Directory
• rootio.Open → groot.Open
• rootio.Create → groot.Create

root-srv has been refactored to extract the pure plot/file interaction machinery from the GUI part. The plot creation and the ROOT file interaction parts have been refactored into a new package go-hep.org/x/hep/groot/rsrv that contains a couple of HTTP end-points that can be reused in third-party packages or applications.

rsrv exposes a REST API that expects JSON requests (OpenFileRequest, PlotH1Request, PlotTreeRequest, ...) and returns JSON responses. The HTTP end-points are attached to the rsrv.Server type.

root-srv can now open ROOT files served over xrootd.

hbook now exposes a Bin method on H{1,2}D to retrieve a bin by its (x,y) coordinates.

Following an issue raised on gonum/plot, hplot now creates histograms with transparent background by default.

Improved test coverage (by adding some more tests.)

The low-level bits for the following requests have been implemented:

• kXR_query
• kXR_prepare
• kXR_endsess
• kXR_locate
• kXR_decrypt
• kXR_admin

The first steps to support the "host" security provider have also been implemented.

We are still missing the implementation for the GSI authentification protocol: still waiting on xrootd to provide specifications for this protocol (progress is tracked here: issue-757.)

Improved test coverage.

We will try to have preliminary support for writing TTrees in the next release. That should be fun.

Interoperability with Apache Arrow Arrays is in the works. It might even prove to be easier to support Apache Arrow first and then implement TTrees writing support on top of that. We will see...

Stay tuned! (and, as always, any kind of help (reviews, patches, nice emails, constructive criticism) deeply appreciated.)