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Agner

Agner is a rebar-friendly Erlang package index inspired by Clojars and Homebrew.

Essentially, Agner is an index of Erlang packages with some extra capabilities such as versioning, downloads and so on.

Agner is a shorthand for A Giant Nebula of Erlang Repositories. It also pays homage to the Danish statistician Agner Krarup Erlang.

Motivation

By now, there is a large set of Erlang tools and libraries out there, all of them highly useful. The problem however is to provide an index of these packages, so other people

  • Know of their existence
  • Can easily use a package in their own projects

Agner aims to provide such an index, by focusing on a number of points:

  • The index is loose in the sense that anyone can overlay the index and add their own packages to the repository
  • The tool is as simple as possible, utilizing git (for the time being) to maintain the indexes
  • Recognize the ideas of simplicity Joe Armstrong had in mind on the erlang-questions@ mailing list the 22-Jul-2010

Use

This section introduces the terminology of Agner:

  • index/indices: Where Agner finds its package index. Usually this is a github user with one or more packages among the users git repositories.
  • package: A separate library or program indentified by the index. It is a .agner repository underneath the index-user, so one example would be agner/gproc.agner specifying a package for the gproc library undernath the agner-user.
  • project: A software project, program or library, that contains the actual source code for the program or library. In the example, this is esl/gproc on github.
  • release: A release of a package signifying a point in time where the package was deemed to be in a certain state. Is usually used when a new version of the software is released to the general public so you can refer to package X version Y
  • flavour: A moving target of a package with some specified behaviour. It is used for tracking the development of a package over time. Common flavours include the @master flavour, used to track the development branch of a package and the @release flavour, used to track the latest release of the package.

Command invocation

agner list [-d/--descriptions]

Will list all agner-packages. With the -d or --descriptions option, it will also print out the descriptions of the packages, for easy grepping to find relevant packages.

agner spec PACKAGE [-v/--version package_version] [-b/--browser] 
                   [-h/--homepage]

Will print a specification of a given package on stdout. If the optional version constraint is given (for example agner spec gproc -v @release) then the output is of that version. By default, the @master flavour is chosen.

If -b or --browser is used, it will also open browser with the specification file in its respective .agner repository.

If -h or --homepage is present, it will also open browser with the package's homepage.

agner fetch PACKAGE [DESTDIR] [-v/--version package_version]

Fetch a given PACKAGE to either the current directory or, optionally, to the DESTDIR directory. The version constraint is as were the case for agner spec.

agner versions PACKAGE

List the versions of the given PACKAGE

agner verify [SPEC FILENAME (agner.config by default)]

Verify specification file for correctness; intended to be used to package maintainers to simplify their workflow. Currently checks whether 1) specification is a valid file that can be parsed, 2) the URL can be fetched. In the future it will also offer a deeper analysis of specification correctness.

Packaging

Package organization

When Agner is invoked, it will scan its indices for package lists. The default index is "agner", which is located at https://github.com/agner/. The index is scanned by looking for Agner repositories which are normal (github) repositories suffixed with .agner. An example is the repository https://github.com/agner/getopt.agner which contains the package details of the getopt package.

It is important to nail down that there are three balls in the air:

  • The index user, who has a list of
  • .agner repositories, which points to
  • Erlang software projects

By making a split between the repository containing the project and the repository containing the package, we make it easy to identify .agner repositories, and we enable a simple way to make the project live in another source control system, for instance Mercurial (hg). It is also way easier to keep the (small) .agner repositories in an index and in the long run, it provisions for local caching.

Further indices can be added to Agner through the environment (TODO: flesh out how that is done). Indices are searched in the order of specification, allowing for overriding of a given index. This allows you to create local indices or special indices for your own use, or try something out on top of other indices.

The multiple indices approach solves authorization questions by solving it "the git way". You put trust in the indices you add to Agner, so if you don't trust an index, you can simply refrain from adding it. The main "agner" index is intended to be the official source, but we recognize that individuals might have reasons to overlay another index on top. By having a loose index-construction, we hope to alleviate some of the problems with access rights.

Package names

Package name is just either a package name such as mochiweb, or (in case of github indices, it might also take a form of account/package, for example yrashk/misultin). We use package names to identify a given package in Agner - but versions of the package is naturally not part of its name. This allows for packages to exist in multiple versions at a time.

Versions

Agner has two kinds of versions:

  • Release versions, normally something like 1.2.0, represented using tags in .agner repos.
  • Flavour versions, normally something like @release, represented using branches in .agner repos. Note the prefix of "@".

The intention is that a release version marks a given point in time where a given version of the code base was released to the general public. When Erlang/OTP is released as OTP-R14B01 for instance, it signifies a release in Agner-terminology. On the other hand, a flavour signifies a moving target. Continuing the OTP-R14B01 example from before, it would be natural to have a @dev flavour which tracks the Erlang/OTP branch called dev. The other important flavour is @release which will track the latest release.

Also, command line utility and agner-enabled rebar will recognize atleast:VERSION format (for example, atleast:1.5.0) and will use the latest version after 'VERSION' (so, if some package already has a version of 1.6, atleast:1.5.0 will select 1.6. This is mostly for scenarios when @release flavour is absent or broken.

How to create relases and flavours

As hinted, a release version is a tag in a .agner repository. So to create a release, you alter the .agner repository to match your liking and then you tag it (with a standard git tag command invocation). Agner will now pick up the change.

Likewise, for a flavour version, you branch the .agner repository and alter the branch so it does what your flavour intended to do. Flavours can be made for anything you would like to track over time. By default, the advice is to create two flavours, @master and @release tracking, respectively, the current development of a project and the latest stable release of that project.

Keeping everything up-to-date is now outsourced to git and you can use usual git-commands to manipulate the .agner repository.

The contents of an .agner package

The .agner package repository contains a file of Erlang-terms, called agner.config. This file looks like this:

{name, "etorrent"}.
{authors, ["Jesper Louis Andersen <jesper.louis.andersen@gmail.com>"]}.
{description, "Etorrent is a bittorrent client implementation in Erlang focusing on fault-tolerance"}.
{homepage, "http://github.com/jlouis/etorrent"}.
{rebar_compatible, true}.
{license, "BSD2", "COPYING"}.
{erlang_versions, [otp_r14b, otp_r14b01, otp_r13b04]}.
{url, {git, "https://github.com/jlouis/etorrent.git", {branch, "master"}}}.

Or in a more generic way:

{name, ProjectName}.
{authors, [Author]}.
{description, ProjectDescription}.
{homepage, ProjectHomepage}.
{rebar_compatible, IsRebarCompatible}.
{license, LicenseType [, LicenseFile]}.
{erlang_versions, [OTPAtom]}.
{url, UrlSpec}.
  • ProjectName :: string() - is the project name. This is usually named the same as the .agner package to minimize confusion.
  • [Author] :: [string()] - Can really be any string, but it is usually the names of the project authors in a list including their email-addresses for easy contact.
  • ProjectDescription :: string() - A description of the project. Used for searching through projects.
  • ProjectHomepage :: string() - The URL of the homepage of the project.
  • IsRebarCompatible :: boolean() - Set to true if this project uses rebar or is compilable by rebar even if it wasn't originally designed for that.
  • LicenseType :: string(), LicenseFile :: string() - Two strings. The first one specifies the general license type of the project and the second string explains where the license is to be found from the top level directory (usually file-names like COPYING or LICENSE are used for this). Please note that LicenseFile is optional.
  • [OTPAtom] :: [otp_rXXb | otp_rXXbYY] - A list of what OTP versions the project can be used with. the XX is a major release number in Erlang/OTP (12,13,14,...) and YY is a minor release number (01, 02, ...).
  • UrlSpec :: {git, URL, GitSpec} - Specifies where to fetch the project. GitSpec has type sha1() | {tag, string()} | {branch, string()} and points to either string-based sha1 representation, a git tag or a git branch respectively. Notice that you can't specify more than one target in this file. To handle multiple versions, you use releases and flavours by altering the .agner repository wherein this configuration file lies.
  • UrlSpec :: {hg, URL, HgRev} - Specifies where to fetch the project. HgSpec has type string() and points to either string-based revision representation

The very latest specification typespecs are available in agner_spec.hrl

Rebar

Agner-compatible rebar is available at agner branch of agner/rebar. Or you can download ready-made rebar from agner itself. We hope to get rebar integration in the upstream with time.

Using it with rebar is fairly simple, it uses rebar's deps feature:

{deps, [
          {typespecs, "0.1", {agner, "typespecs"}},
          {getopt, "0.3.0", {agner, "getopt"}}
       ]}.

You can also specify your own indices:

{agner_indices, [{github, "yourgithubusername"},{github,"agner"}].

Contributing

Please read at the wiki.