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 How to write a new SCM provider
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 Maven Team
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 2007-03-27
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How to write a new SCM provider?

* What are the steps to write a new Maven-SCM provider?

  * Define allowed scm urls for this provider

  * Create a class that extends <<<org.apache.maven.scm.provider.ScmProviderRepository>>>
    or <<<org.apache.maven.scm.provider.ScmProviderRepositoryWithHost>>>, this class
    is the corresponding bean of the scm url

  * Create a class that extends <<<org.apache.maven.scm.provider.AbstractScmProvider>>>.
    This class parse the scm url and link all scm commands methods to their
    implementations. Important methods are <<<makeProviderScmRepository()>>>
    and <<<validateScmUrl()>>>

  * Implement all commands and link them in the scm provider class created in
    the step above

  * For each command, implement junit tests that test the command line format

  * For each command, implement TCK tests

  * Test the release plugin with the new provider. For that, you must add the
    dependency to the release plugin and run it

  * Add the dependency to Continuum libs and test the provider with a sample
    project

  * Update the site

  []

  In the next section, we'll see all the steps in details to write a new
  Maven-SCM provider.

* Create a new Maven project for the provider

  Your project need to use some jars from the Maven-SCM framework. Add them to your POM.

+------------------------------------------+
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <parent>
    <artifactId>maven-scm-providers</artifactId>
    <groupId>org.apache.maven.scm</groupId>
    <version>LATEST VERSION OF MAVEN-SCM PROVIDERS MASTER POM</version>
  </parent>

  <artifactId>maven-scm-provider-YOUR_PROVIDER_NAME</artifactId>
  <version>1.0-SNAPSHOT</version>

  <name>My Maven-SCM Provider</name>

  <build>
    <plugins>
      <plugin>
        <groupId>org.codehaus.plexus</groupId>
        <artifactId>plexus-component-metadata</artifactId>
        <version>1.7.1</version>
        <executions>
          <execution>
            <goals>
              <goal>generate-metadata</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>
+------------------------------------------+

  The plexus-component-metadata maven plugin will generate the Plexus meta-data file used by the
  Maven-SCM manager.

* Create an SCM Provider Repository class

  This class will contain all SCM information about your SCM connection
  (user, password, host, port, path...).

+------------------------------------------+
package org.apache.maven.scm.provider.myprovider.repository;

import org.apache.maven.scm.provider.ScmProviderRepository;

public class MyScmProviderRepository
    extends ScmProviderRepository
{
}
+------------------------------------------+

  Before you add more information to this class, you can look at the
  <<<ScmProviderRepository>>> sub-classes, if they are already implemented.

* Create the Provider class

  This class is the central point of the provider. The Maven-SCM framework will
  know only this class in the provider, so this class must validate the scm
  url, populate the <<<ScmProviderRepository>>> and provide all commands
  supported by your provider. We start with a basic class, then we'll add
  commands to it when we implement them.

  Before you start to write your SCM provider, you must define the SCM URLs you
  want to support.

+------------------------------------------+
package org.apache.maven.scm.provider.myprovider;

import org.apache.maven.scm.provider.myprovider.repository.MyScmProviderRepository;

import org.apache.maven.scm.provider.AbstractScmProvider;
import org.apache.maven.scm.provider.ScmProviderRepository;
import org.apache.maven.scm.repository.ScmRepositoryException;

/**
 * @plexus.component role="org.apache.maven.scm.provider.ScmProvider" role-hint="provider_name"
 */
public class MyScmProvider
    extends AbstractScmProvider
{
    public String getScmType()
    {
        return "provider_name";
    }

    /**
     * This method parse the scm URL and return a SCM provider repository.
     * At this point, the scmSpecificUrl is the part after scm:provider_name: in your SCM URL.
     */
    public ScmProviderRepository makeProviderScmRepository( String scmSpecificUrl, char delimiter )
        throws ScmRepositoryException
    {
         MyScmProviderRepository providerRepository = new MyScmProviderRepository();
         //Parse scmSpecificUrl and populate there your provider repository

         return providerRepository;
    }
}
+------------------------------------------+

  The <plexus.component> javadoc tag will be used by the plexus maven plugin,
  declared in the POM, to generate plexus meta-data.
  Generally, we use the string just after <scm:> in the scm URL as the
  <provider_name>.

* Commands implementation

  When you write a new SCM command, you must extend base classes for the
  Maven-SCM framework. We have one base command for each command supported by
  Maven-SCM and each command have an <<<execute>>> method that return an SCM
  result.

+------------------------------------------+
package org.apache.maven.scm.provider.myprovider.command.checkout;

import org.apache.maven.scm.command.checkout.AbstractCheckOutCommand;

public class MyCheckoutCommand
    extends AbstractCheckOutCommand
{
    protected abstract CheckOutScmResult executeCheckOutCommand( ScmProviderRepository repository, ScmFileSet fileSet, String tag )
        throws ScmException
    {
        CheckOutScmResult result = new CheckOutScmResult();

        //Add the code there to run the command
        //If you need to run a native commandline like cvs/svn/cleartool..., look at other providers how to launch it and parse the output

        return result;
    }
}
+------------------------------------------+

* Allow the command in the SCM provider

  Now that your command is implemented, you need to add it in your SCM provider
  (<<<MyScmProvider>>>). Open the provider class and override the method that
  relates to your command.

+------------------------------------------+
public class MyScmProvider
    extends AbstractScmProvider
{
    ...

    protected CheckOutScmResult checkout( ScmRepository repository, ScmFileSet fileSet, CommandParameters params )
        throws ScmException
    {
        MyCheckoutCommand command = new MyCheckoutCommand();
        command.setLogger( getLogger() );
        return (CheckOutScmResult) command.execute( repository.getProviderRepository(), fileSet, params );
    }
}
+------------------------------------------+

* Provider Tests

** Automated tests

  To be sure your provider works as expected, you must implement some tests.
  You can implement two levels of tests:

  * Simple JUnit tests that use your command directly and test that the command
    line you launch in your SCM command is correct

  * Implementation of the TCK. The TCK provides a set of tests that validate
    that your implementation is compatible with the Maven-SCM framework. The
    TCK requires access to the SCM tool.

** Other tests

  You can do manual tests in the real world with the Maven-SCM plugin,
  the maven release plugin, the maven changelog plugin and Continuum.

  It's important to test your SCM provider with these tools, because they are
  used by users that will use your provider.

* Document your provider

  Now that your provider works fine, you must document it (which scm URLs are
  supported, which commands are supported...). You can use the same template
  that is used by the other providers.
