CLI version command falls back to Bundle-Version

If the version command cannot read the Implementation-Version of the
containing JAR fall back to read the Bundle-Version header in
MANIFEST.MF. This makes the command working also from the
org.eclipse.jgit.pgm bundle and during development in a host IDE.

Bug: 419087
Change-Id: I4269d1cbd9bf9fd8be6fb4463aecc1c434aa387b
Signed-off-by: Kaloyan Raev <kaloyan.r@zend.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Version.java

 
 package org.eclipse.jgit.pgm;
 
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+import java.net.URLClassLoader;
 import java.text.MessageFormat;
+import java.util.jar.JarFile;
+import java.util.jar.Manifest;
 
 import org.eclipse.jgit.pgm.internal.CLIText;
 
 class Version extends TextBuiltin {
 	@Override
 	protected void run() throws Exception {
-		final Package pkg = getClass().getPackage();
-		if (pkg == null || pkg.getImplementationVersion() == null)
+		// read the Implementation-Version from Manifest
+		String version = getImplementationVersion();
+
+		// if Implementation-Version is not available then try reading
+		// Bundle-Version
+		if (version == null)
+			version = getBundleVersion();
+
+		// if both Implementation-Version and Bundle-Version are not available
+		// then throw an exception
+		if (version == null)
 			throw die(CLIText.get().cannotReadPackageInformation);
 
-		outw.println(MessageFormat.format(CLIText.get().jgitVersion, pkg.getImplementationVersion()));
+		outw.println(MessageFormat.format(CLIText.get().jgitVersion, version));
 	}
 
 	@Override
 	protected final boolean requiresRepository() {
 		return false;
 	}
+
+	private String getImplementationVersion() {
+		Package pkg = getClass().getPackage();
+		return (pkg == null) ? null : pkg.getImplementationVersion();
+	}
+
+	private String getBundleVersion() {
+		ClassLoader cl = getClass().getClassLoader();
+		if (cl instanceof URLClassLoader) {
+			URL url = ((URLClassLoader) cl).findResource(JarFile.MANIFEST_NAME);
+			if (url != null)
+				return getBundleVersion(url);
+		}
+		return null;
+	}
+
+	private static String getBundleVersion(URL url) {
+		try {
+			InputStream is = url.openStream();
+			try {
+				Manifest manifest = new Manifest(is);
+				return manifest.getMainAttributes().getValue("Bundle-Version"); //$NON-NLS-1$
+			} finally {
+				is.close();
+			}
+		} catch (IOException e) {
+			// do nothing - will return null
+		}
+		return null;
+	}
 }