Subversion build labels in CruiseControl

I spent some time last week learning about setting up CruiseControl. My motivation was to figure out how to make the subversion revision number part of our build number. Example: say we are on build number 101, cruise kicks off and does a checkout. The code gets updated to revision 1001. That means the build number becomes 101.1001. This mapping from build to revision is useful. Say you had delivered build 85 to the customer, and there is a bug. In order to look at the code in production you need to update your working copy to the production build. If you don't have the revision in the build number you have to go rummaging through logs to find which revision build 85 is, or you can checkout the branch that cruise creates for each build, but for large codebases, that is time consuming. With the build-revision style label you can quickly update to that revision.

Making this happen should be easy, right? Just write a build labelIncrementer plugin that gets the SVN revision. The catch is that in cruise control build numbers are calculated ahead of time. I had made an unfortunate assumption that the build label was calculated at build time and so I wrote an entire plugin to calculate the label I wanted. Then I realized it would never work. Of course this behaviour is documented, but I wasn't bright enough to read that ahead of time. Here is the code to my SVN LabelIncrementer. You can use it but you might be disappointed when your revision numbers in the label are from a previous build. Or you can just skip ahead and read how I ended up satisfying my requirement without writing a plugin.

import net.sourceforge.cruisecontrol.labelincrementers.DefaultLabelIncrementer;
import org.jdom.Element;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class SVNLabelIncrementer extends DefaultLabelIncrementer {
   private String workingCopyPath = ".";

   public String incrementLabel(String oldLabel, Element buildLog) {

       String SVNRev = "";
       try {
           SVNRev = getSvnRevision();
       }
       catch (IOException e) {
           e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
       }

       String label = super.incrementLabel(getNonSubversionPartOfLabel(oldLabel), buildLog);
       if (SVNRev == null || SVNRev.equals(""))
           return label;
       return label + "-" + SVNRev;

   }

   protected String getSvnRevision() throws IOException {
       String rev;
       Process p = null;
       try {
           p = Runtime.getRuntime().exec("svnversion " + workingCopyPath);
           BufferedReader stdInput = new BufferedReader(new
                   InputStreamReader(p.getInputStream()));
           rev = stdInput.readLine();
       }
       finally {
           if (p != null)
               p.destroy();
       }

       return rev;
   }

   public boolean isValidLabel(String label) {
       return super.isValidLabel(getNonSubversionPartOfLabel(label));
   }

   private String getNonSubversionPartOfLabel(String label) {
       int index = label.indexOf("-");
       if (index == -1)
           index = label.length();
       return label.substring(0, index);
   }

   public void setWorkingCopyPath(String path) {
       workingCopyPath = path;
   }

}

Here are my tests for the plugin.

import junit.framework.TestCase;
import org.jdom.Element;

public class SVNLabelIncrementerTest extends TestCase {

   public void testReturnsIncrementedLabelWhenRevNotPresent() {
       SVNLabelIncrementerStub inc = new SVNLabelIncrementerStub();
       assertEquals("FE6.0.2", inc.incrementLabel("FE6.0.1", new Element("foo")));
   }

   public void testReturnsIncrementedLabelAndRevisionWhenRevPresent() {
       SVNLabelIncrementerStub inc = new SVNLabelIncrementerStub();
       inc.setSvnRevision("1");
       assertEquals("FE6.0.2-1", inc.incrementLabel("FE6.0.1", new Element("foo")));
   }

   public void testReturnsIncrementedLabelWhenRevNull() {
       SVNLabelIncrementerStub inc = new SVNLabelIncrementerStub();
       inc.setSvnRevision(null);
       assertEquals("FE6.0.2", inc.incrementLabel("FE6.0.1", new Element("foo")));
   }

   public void testProducesValidLabelWhenRevNotPresent() {
       SVNLabelIncrementerStub inc = new SVNLabelIncrementerStub();
       String label = inc.incrementLabel("FE6.0.1", new Element("foo"));
       assertTrue(inc.isValidLabel(label));
   }

   public void testIncrementsCorrectlyOverSeveralIterations() {
       SVNLabelIncrementerStub inc = new SVNLabelIncrementerStub();
       inc.setSvnRevision("1");
       assertEquals("FE6.0.2-1", inc.incrementLabel("FE6.0.1", new Element("foo")));
       assertEquals("FE6.0.3-1", inc.incrementLabel("FE6.0.2-1", new Element("foo")));
       assertEquals("FE6.0.4-1", inc.incrementLabel("FE6.0.3-1", new Element("foo")));
   }

   public class SVNLabelIncrementerStub extends SVNLabelIncrementer {
       private String revision = "";
       protected String getSvnRevision(){
           return revision;
       }

       public void setSvnRevision(String revision){
           this.revision = revision;
       }
   }
}

There is more than one way to relabel a build. But without doing something gross, like having ant call a script to modify the build number after cruise generates it (you can change build labels in the xml logs that cruise uses to store info about previous builds) I couldn't think of a good way to get the SVN revision into the build label.

Then Andy Slocum came to my rescue with the bright idea of modifying the xsl that creates the html page from the xml logs. He simply added this: (Sorry this is an image, I couldn't figure out how to get wordpress not to supress the xsl.) to the header.xsl file, which cruise uses to generate the header of the build page and PRESTO, the revision appeared. Our build page now looks like this.
Glorious, eh? I've looked at the cruise code. It is actually quite clean and easy to understand. I might take a look at changing the build label to be generated at build time, thus making it possible to use the SVN revision in the label, but I would probably talk to some cruise gurus about it first.