/ 
VCI-0.0.0_1
River stage zero No dependents
/ VCI

NAME

VCI - A generic interface for interacting with various version-control systems.

SYNOPSIS

my $repository = VCI->connect(type => $type, repo => $repo);

DESCRIPTION

This is VCI, the generic Version Control Interface. The goal of VCI is to create a common API that can interface with all version control systems.

VCI uses Moose, so all constructors for all objects are called new (although for VCI itself you'll want to use "connect"), and they all take named parameters as a hash (not a hashref).

Note: The interface of all VCI modules should currently be considered UNSTABLE. I may make breaking changes in order to fix any fundamental design problems that are discovered.

The Structure of VCI

If you aren't sure where to start, you want to first look at "connect" and then at VCI::Abstract::Repository.

The general interface of VCI is described in the various VCI::Abstract modules, and the actual implementations are in modules named after the particular version-control system, but their names start with VCI::VCS. For example, VCI::VCS::CVS.

For example, the methods that you use on a File in your version-control system are described in VCI::Abstract::File, but the actual specific implementation for CVS is in VCI::CVS::File. VCI::CVS::File must implement all of the methods described in VCI::Abstract::File, but it also may implement extension methods whose names start with x_.

Repositories and Projects

A server that contains your version-controlled files is considered a "repository", and is represented by VCI::Abstract::Repository.

An actual set of code that you could check out of the repository is considered a "project", and is represented by VCI::Abstract::Project.

Almost all information that VCI gives is in relation to the project. For example, file paths are relative to the base directory of the project, not the base directory of the entire repository.

VERSION NUMBERING SCHEME

VCI has three-number version numbers, like this:

MAJOR.API.MINOR_DEVEL

Here's what each number means:

MAJOR

As long as this number is 0, major breaking changes may occur to the API all the time. When this becomes 1, the API is stable. For numbers greater than 1, it means we made a major breaking change to the API.

For example, VCI 2.0.0 would have breaking changes for the user or for the drivers, compared to VCI 1.0.1. But VCI 0.1.1 and 0.2.1 could contain breaking changes between them, also, because the first number is still 0.

API

VCI has various features, but the drivers may not implement all of these features. So, when we add new features that drivers must implement, the API number gets incremented.

For example, VCI 0.0.1 doesn't have support for authenticating to repositories, but VCI 0.1.1 might support it.

Drivers will say which VCI API they support. Using a driver that doesn't support the current VCI API may throw an error. Using a driver that supports an API later than the current VCI will throw an error.

MINOR

This indicates a bug-fix release, with the API staying the same.

This will always be 1 or higher unless this is a development release, in which case it will be 0.

DEVEL

If this is an unstable development release, this number will be included. In this case, the MINOR number should almost always be 0.

CLASS METHODS

Constructors

connect
Description

Returns a VCI::Repository object based on your parameters. This is how you "start" using VCI.

Note that you cannot currently connect to repositories that require authentication, as VCI has no way of dealing with usernames or passwords. So you must connect to repositories that don't require authentication, or to which you have already authenticated. Future versions of VCI will support authentication.

Parameters
repo (Required)

This is a string representing the repository you want to connect to, in the exact same format that you'd pass to the command-line interface to your VCS. For example, for CVS this would be the contents of CVSROOT.

type (Required)

What VCI driver you want to use. For example, to use VCI::CVS you'd say CVS for this parameter.

debug

If you'd like VCI to print out a lot of information about what it's doing to STDERR, set this to 1. Different drivers will print out different information.

new

This has the same parameters as connect, but actually returns a VCI object, not a VCI::Repository.

You'll generally want use "connect" instead of this.

Other

api_version

This is for drivers, to indicate what API version they implement.

Returns a hashref with two items:

major - The major version number of the VCI API that this driver implements.

api - The api version numer of the VCI API that this driver implements.

For more information about what these numbers mean, see "VERSION NUMBERING SCHEME".

METHODS

Accessors

All of the fields that connect takes can also be accessed with methods named after them. In addition to the fields that you pass in to new, there are other accessors:

repository

Returns the VCI::Abstract::Repository that this VCI is connected to. Generally you don't want to use this, and you just want to use "connect".

HOW TO GET VCI

VCI is available on CPAN, which is the recommended way to get it.

VCI is also available from my source repository. You can get the latest version by doing:

bzr co http://bzr.everythingsolved.com/vci/

PERFORMANCE

Currently, you should expect good performance on small projects, and bad performance on large projects. This isn't due to the design of VCI itself, but just because many performance optimizations haven't been implemented yet in the various drivers.

As time goes on, performance should improve significantly.

GENERAL NOTES FOR VCI::VCS IMPLEMENTORS

This is information for people who want to hack on the internals of VCI or implement a driver for their VCS.

The POD is an API

If the POD of the VCI::Abstract modules says something, that is an API for VCI. Unless the POD specifically says you can change the behavior of a method, you must not deviate from how the POD says the methods and accessors work.

You may add new required attributes to the constructors of various modules, but you must not add required attributes to methods other than what is already specified in the POD for that method.

Extending VCI

VCI provides a base set of functions that are common to all Version-Control Systems, but if your VCS can do special things, feel free to add extension methods.

So that your methods don't conflict with VCI methods, their names should start with x_ (or _x_ for private methods). VCI won't enforce that, but if you don't do it, your module could seriously break in the future if VCI implements a method with the same name as yours.

VCI promises not to have any standard methods or accesors that start with x_ or _x_.

The Design Goals of VCI

In order of priority, the goals of VCI are:

  1. Correctness

  2. Ease of Driver Implementation

  3. To implement as many VCS features as possible, not to only implement the common denominator of all VCSes.

  4. Speed Efficiency

Memory Efficiency is a fourth consideration to be taken into account when writing drivers, but isn't considered as important as the above items.

Correctness

This means that drivers (and VCI) should do exactly what the user asks, without any surprises or side-effects, and should conform fully to all required elements of the API.

If you have doubts about what is "correct", ask yourself the question, "What would be most logical for a web application that views and interacts with a repository?" That is the function that VCI was originally designed for.

Ease of Driver Implementation

VCI is designed to make life easy for implementors. The only things that you must implement are:

build_projects in VCI::Abstract::Repository
build_history in VCI::Abstract::Project
build_contents in VCI::Abstract::Directory
build_revision for VCI::Abstract::Committable objects (File and Directory), for objects that have no revision specified (meaning this is the "HEAD" revision).
build_time for VCI::Abstract::Committable objects that have a revision but no time specified.

That's basically the minimum you have to implement. The more you implement, the faster your VCI driver will be. But it will still be fully correct (if sometimes slow) with only the above implemented.

Many Features, Not the Common Denominator of Features

Many abstractions limit you to the common denominator of all the things they abstract. That is, we could say, "You can only do X with VCI if all VCSes can do X." But that's not the goal of VCI.

Instead, we say, "VCI allows you to do X. If the VCS can't do X, VCI will provide some reasonable default instead."

For example, not all VCSes track if a file is executable. But we provide "is_executable" in VCI::VCS::File, and it behaves sensibly when the VCS doesn't track that information.

Efficiency

In general, VCI strives to be efficient in terms of speed. Working with a version-control system can often be a slow experience, and we don't want to make that any worse than it already is.

This means that individual methods should do the least work possible to return the information that the user needs, and store it internally for later use.

For example, a file in a version control system has a first revision . If there's a fast way to just get the first revision, you should do that.

But if we've already read the whole history of a file, that has information about the first revision in it, so we should just be able to reference the history we already retrieved, instead of asking the version-control system for the first revision all over again.

Order of Implementation

This is just some tips to make your life easier if you're going to implement a driver for your version-control system.

First, you want to implement a method of connecting to your VCS, which means implementing VCI. Then VCI::Abstract::Repository, and then VCI::Abstract::Project.

After that you're probably going to want to implement VCI::Abstract::File and VCI::Abstract::Directory.

Then you can implement VCI::Abstract::History, and now that you have everything, you can implement VCI::Abstract::Commit.

NOTES FOR IMPLEMENTORS OF VCI.pm

In general, you shouldn't override "connect". Also, using before on "connect" probably also isn't a good idea. You could use after, but it mostly just makes sense to implement "build_repository" and leave it at that.

If you do override connect, you must call this connect at some point in your connect.

You must not add new required attributes to connect.

Optional Methods To Implement

build_repository

Returns the VCI::Abstract::Repository object. (This is basically what "connect" returns, so this does the "heavy_lifting" for "connect".)

SEE ALSO

Drivers: VCI::VCS::Svn, VCI::VCS::Bzr, VCI::VCS::Hg, VCI::VCS::Git

TODO

Far more tests need to be written.

Eventually the drivers will be split into their own packages.

Need user and pass support for "connect".

Implement a CVS driver.

BUGS

VCI is very new, and probably has many significant bugs. The code is no better than alpha-quality at this point.

AUTHOR

Max Kanat-Alexander <mkanat@everythingsolved.com>

COPYRIGHT AND LICENSE

Copyright 2007 by Everything Solved, Inc.

http://www.everythingsolved.com

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.