Gustavo Leite de Mendonça Chaves > SVN-Hooks > SVN::Hooks

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Module Version: 1.27   Source  

NAME ^

SVN::Hooks - Framework for implementing Subversion hooks

VERSION ^

version 1.27

SYNOPSIS ^

A single script can implement several hooks:

        #!/usr/bin/perl

        use SVN::Hooks;

        START_COMMIT {
            my ($repo_path, $username, $capabilities) = @_;
            # ...
        };

        PRE_COMMIT {
            my ($svnlook) = @_;
            # ...
        };

        run_hook($0, @ARGV);

Or you can use already implemented hooks via plugins:

        #!/usr/bin/perl

        use SVN::Hooks;
        use SVN::Hooks::DenyFilenames;
        use SVN::Hooks::DenyChanges;
        use SVN::Hooks::CheckProperty;
        ...

        run_hook($0, @ARGV);

INTRODUCTION ^

In order to really understand what this is all about you need to understand Subversion http://subversion.apache.org/ and its hooks. You can read everything about this in the svnbook, a.k.a. Version Control with Subversion, at http://svnbook.red-bean.com/nightly/en/index.html.

Subversion is a version control system, and as such it is used to keep historical revisions of files and directories. Each revision maintains information about all the changes introduced since the previous one: date, author, log message, files changed, files renamed, etc.

Subversion uses a client/server model. The server maintains the repository, which is the database containing all the historical information we talked about above. Users use a Subversion client tool to query and change the repository but also to maintain one or more working areas. A working area is a directory in the user machine containing a copy of a particular revision of the repository. The user can use the client tool to make all sorts of changes in his working area and to "commit" them all in an atomic operation that bumps the repository to a new revision.

A hook is a specifically named program that is called by the Subversion server during the execution of some operations. There are exactly nine hooks which must reside under the hooks directory in the repository. When you create a new repository, you get nine template files in this directory, all of them having the .tmpl suffix and helpful instructions inside explaining how to convert them into working hooks.

When Subversion is performing a commit operation on behalf of a client, for example, it calls the start-commit hook, then the pre-commit hook, and then the post-commit hook. The first two can gather all sorts of information about the specific commit transaction being performed and decide to reject it in case it doesn't comply to specified policies. The post-commit can be used to log or alert interested parties about the commit just done.

IMPORTANT NOTE from the svnbook: "For security reasons, the Subversion repository executes hook programs with an empty environment---that is, no environment variables are set at all, not even $PATH (or %PATH%, under Windows). Because of this, many administrators are baffled when their hook program runs fine by hand, but doesn't work when run by Subversion. Be sure to explicitly set any necessary environment variables in your hook program and/or use absolute paths to programs."

There are several useful hook scripts available elsewhere http://svn.apache.org/repos/asf/subversion/trunk/contrib/hook-scripts/, mainly for those three associated with the commit operation. However, when you try to combine the functionality of two or more of those scripts in a single hook you normally end up facing two problems.

Complexity

In order to integrate the funcionality of more than one script you have to write a driver script that's called by Subversion and calls all the other scripts in order, passing to them the arguments they need. Moreover, some of those scripts may have configuration files to read and you may have to maintain several of them.

Inefficiency

This arrangement is inefficient in two ways. First because each script runs as a separate process, which usually have a high startup cost because they are, well, scripts and not binaries. And second, because as each script is called in turn they have no memory of the scripts called before and have to gather the information about the transaction again and again, normally by calling the svnlook command, which spawns yet another process.

SVN::Hooks is a framework for implementing Subversion hooks that tries to solve these problems.

Instead of having separate scripts implementing different functionality you have a single script implementing all the funcionality you need either directly or using some of the existing plugins, which are implemented by Perl modules in the SVN::Hooks:: namespace. This single script can be used to implement all nine standard hooks, because each hook knows when to perform based on the context in which the script was called.

USAGE ^

In the Subversion server, go to the hooks directory under the directory where the repository was created. You should see there the nine hook templates. Create a script there using the SVN::Hooks module.

        $ cd /path/to/repo/hooks

        $ cat >svn-hooks.pl <<END_OF_SCRIPT
        #!/usr/bin/perl

        use SVN::Hooks;

        run_hook($0, @ARGV);

        END_OF_SCRIPT

        $ chmod +x svn-hooks.pl

This script will serve for any hook. Create symbolic links pointing to it for each hook you are interested in. (You may create symbolic links for all nine hooks, but this will make Subversion call the script for all hooked operations, even for those that you may not be interested in. Nothing wrong will happen, but the server will be doing extra work for nothing.)

        $ ln -s svn-hooks.pl start-commit
        $ ln -s svn-hooks.pl pre-commit
        $ ln -s svn-hooks.pl post-commit
        $ ln -s svn-hooks.pl pre-revprop-change

As is the script won't do anything. You have to implement some hooks or use some of the existing ones implemented as plugins. Either way, the script should end with a call to run_hooks passing to it the name with which it wass called ($0) and all the arguments it received (@ARGV).

Implementing Hooks

Implement hooks using one of the nine hook directives below. Each one of them get a single block (anonymous function) as argument. The block will be called by run_hook with proper arguments, as indicated below. These arguments are the ones gotten from @ARGV, with the exception of the ones identified by SVN::Look. These are SVN::Look objects which can be used to grok detailed information about the repository and the current transaction. (Please, refer to the SVN::Look documentation to know how to use it.)

This is an example of a script implementing two hooks:

        #!/usr/bin/perl

        use SVN::Hooks;

        # ...

        START_COMMIT {
            my ($repos_path, $username, $capabilities) = @_;

            exists $committers{$username}
                or die "User '$username' is not allowed to commit.\n";

            $capabilities =~ /mergeinfo/
                or die "Your Subversion client does not support mergeinfo capability.\n";
        };

        PRE_COMMIT {
            my ($svnlook) = @_;

            foreach my $added ($svnlook->added()) {
                $added !~ /\.(exe|o|jar|zip)$/
                    or die "Please, don't commit binary files such as '$added'.\n";
            }
        };

        run_hook($0, @ARGV);

Note that the hook directives resemble function definitions but they're not. They are function calls, and as such must end with a semi-colon.

Most of the start-commit and pre-* hooks are used to check some condition. If the condition holds, they must simply end without returning anything. Otherwise, they must die with a suitable error message.

Also note that each hook directive can be called more than once if you need to implement more than one specific hook. The hooks will run in the order they were defined.

Using Plugins

There are several hooks already implemented as plugin modules under the namespace SVN::Hooks::, which you can use. The main ones are described succinctly below. Please, see their own documentation for more details.

SVN::Hooks::AllowPropChange

Allow only specified users make changes in revision properties.

SVN::Hooks::CheckCapability

Check if the Subversion client implements the required capabilities.

SVN::Hooks::CheckJira

Integrate Subversion with the JIRA http://www.atlassian.com/software/jira/ ticketing system.

SVN::Hooks::CheckLog

Check if the log message in a commit conforms to a Regexp.

SVN::Hooks::CheckMimeTypes

Check if the files added to the repository have the svn:mime-type property set. Moreover, for text files, check if the properties svn:eol-style and svn:keywords are also set.

SVN::Hooks::CheckProperty

Check for specific properties for specific kinds of files.

SVN::Hooks::CheckStructure

Check if the files and directories being added to the repository conform to a specific structure.

SVN::Hooks::DenyChanges

Deny the addition, modification, or deletion of specific files and directories in the repository. Usually used to deny modifications in the tags directory.

SVN::Hooks::DenyFilenames

Deny the addition of files which file names doesn't comply with a Regexp. Usually used to disallow some characteres in the filenames.

SVN::Hooks::Notify

Sends notification emails after successful commits.

SVN::Hooks::UpdateConfFile

Allows you to maintain Subversion configuration files versioned in the same repository where they are used. Usually used to maintain the configuration file for the hooks and the repository access control file.

This is an example of a script using some plugins:

        #!/usr/bin/perl

        use SVN::Hooks;
        use SVN::Hooks::CheckProperty;
        use SVN::Hooks::DenyChanges;
        use SVN::Hooks::DenyFilenames;

        # Accept only letters, digits, underlines, periods, and hifens
        DENY_FILENAMES(qr/[^-\/\.\w]/i);

        # Disallow modifications in the tags directory
        DENY_UPDATE(qr:^tags:);

        # OpenOffice.org documents need locks
        CHECK_PROPERTY(qr/\.(?:od[bcfgimpst]|ot[ghpst])$/i => 'svn:needs-lock');

        run_hook($0, @ARGV);

Those directives are implemented and exported by the hooks. Note that using hooks you don't need to be explicit about which one of the nine hooks will be triggered by the directives. This is on purpose, because some plugins can trigger more than one hook. The plugin documentation should tell you which hooks can be triggered so that you know which symbolic links you need to create in the hooks repository directory.

Configuration file

Before calling the hooks, the function run_hook evaluates a file called svn-hooks.conf under the conf directory in the repository, if it exists. Hence, you can choose to put all the directives in this file and not in the script under the hooks directory.

The advantage of this is that you can then manage the configuration file with the SVN::Hooks::UpdateConfFile and have it versioned under the same repository that it controls.

One way to do this is to use this hook script:

        #!/usr/bin/perl

        use SVN::Hooks;
        use SVN::Hooks::UpdateConfFile;
        use ...

        UPDATE_CONF_FILE(
            'conf/svn-hooks.conf' => 'svn-hooks.conf',
            validator             => [qw(/usr/bin/perl -c)],
            rotate                => 2,
        );

        run_hook($0, @ARGV);

Use this hook script and create a directory called conf at the root of the repository (besides the common trunk, branches, and tags directories). Add the svn-hooks.conf file under the conf directory. Then, whenever you commit a new version of the file, the pre-commit hook will validate it sintactically (/usr/bin/perl -c) and copy its new version to the conf/svn-hooks.conf file in the repository. (Read the SVN::Hooks::UpdateConfFile documentation to understand it in details.)

Being a Perl script, it's possible to get fancy with the configuration file, using variables, functions, and whatever. But for most purposes it consists just in a series of configuration directives.

Don't forget to end it with the 1; statement, though, because it's evaluated with a do statement and needs to end with a true expression.

Please, see the plugins documentation to know about the directives.

PLUGIN DEVELOPER TUTORIAL ^

Yet to do.

EXPORT ^

run_hook

This is responsible to invoke the right plugins depending on the context in which it was called.

Its first argument must be the name of the hook that was called. Usually you just pass $0 to it, since it knows to extract the basename of the parameter.

Its second argument must be the path to the directory where the repository was created.

The remaining arguments depend on the hook for which it's being called, like this:

But as these are exactly the arguments Subversion passes when it calls the hooks, you usually call run_hook like this:

        run_hook($0, @ARGV);

AUTHOR ^

Gustavo L. de M. Chaves <gnustavo@cpan.org>

COPYRIGHT AND LICENSE ^

This software is copyright (c) 2014 by CPqD.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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