public String verify(JarFile jar, String... algorithms) throws IOException {
    if (algorithms == null || algorithms.length == 0) algorithms = new String[] {"MD5", "SHA"};
    else if (algorithms.length == 1 && algorithms[0].equals("-")) return null;

    try {
      Manifest m = jar.getManifest();
      if (m.getEntries().isEmpty()) return "No name sections";

      for (Enumeration<JarEntry> e = jar.entries(); e.hasMoreElements(); ) {
        JarEntry je = e.nextElement();
        if (MANIFEST_ENTRY.matcher(je.getName()).matches()) continue;

        Attributes nameSection = m.getAttributes(je.getName());
        if (nameSection == null) return "No name section for " + je.getName();

        for (String algorithm : algorithms) {
          try {
            MessageDigest md = MessageDigest.getInstance(algorithm);
            String expected = nameSection.getValue(algorithm + "-Digest");
            if (expected != null) {
              byte digest[] = Base64.decodeBase64(expected);
              copy(jar.getInputStream(je), md);
              if (!Arrays.equals(digest, md.digest()))
                return "Invalid digest for "
                    + je.getName()
                    + ", "
                    + expected
                    + " != "
                    + Base64.encodeBase64(md.digest());
            } else reporter.error("could not find digest for " + algorithm + "-Digest");
          } catch (NoSuchAlgorithmException nsae) {
            return "Missing digest algorithm " + algorithm;
          }
        }
      }
    } catch (Exception e) {
      return "Failed to verify due to exception: " + e.getMessage();
    }
    return null;
  }
  public CommandData parseCommandData(ArtifactData artifact) throws Exception {
    File source = new File(artifact.file);
    if (!source.isFile()) throw new FileNotFoundException();

    CommandData data = new CommandData();
    data.sha = artifact.sha;
    data.jpmRepoDir = repoDir.getCanonicalPath();
    JarFile jar = new JarFile(source);
    try {
      reporter.trace("Parsing %s", source);
      Manifest m = jar.getManifest();
      Attributes main = m.getMainAttributes();
      data.name = data.bsn = main.getValue("Bundle-SymbolicName");
      String version = main.getValue("Bundle-Version");
      if (version == null) data.version = Version.LOWEST;
      else data.version = new Version(version);

      data.main = main.getValue("Main-Class");
      data.description = main.getValue("Bundle-Description");
      data.title = main.getValue("JPM-Name");

      reporter.trace("name " + data.name + " " + data.main + " " + data.title);
      DependencyCollector path = new DependencyCollector(this);
      path.add(artifact);
      DependencyCollector bundles = new DependencyCollector(this);
      if (main.getValue("JPM-Classpath") != null) {
        Parameters requires = OSGiHeader.parseHeader(main.getValue("JPM-Classpath"));

        for (Map.Entry<String, Attrs> e : requires.entrySet()) {
          path.add(e.getKey(), e.getValue().get("name")); // coordinate
        }
      } else if (!artifact.local) { // No JPM-Classpath, falling back to
        // server's revision
        // Iterable<RevisionRef> closure =
        // library.getClosure(artifact.sha,
        // false);
        // System.out.println("getting closure " + artifact.url + " " +
        // Strings.join("\n",closure));

        // if (closure != null) {
        // for (RevisionRef ref : closure) {
        // path.add(Hex.toHexString(ref.revision));
        // }
        // }
      }

      if (main.getValue("JPM-Runbundles") != null) {
        Parameters jpmrunbundles = OSGiHeader.parseHeader(main.getValue("JPM-Runbundles"));

        for (Map.Entry<String, Attrs> e : jpmrunbundles.entrySet()) {
          bundles.add(e.getKey(), e.getValue().get("name"));
        }
      }

      reporter.trace("collect digests runpath");
      data.dependencies.addAll(path.getDigests());
      reporter.trace("collect digests bundles");
      data.runbundles.addAll(bundles.getDigests());

      Parameters command = OSGiHeader.parseHeader(main.getValue("JPM-Command"));
      if (command.size() > 1) reporter.error("Only one command can be specified");

      for (Map.Entry<String, Attrs> e : command.entrySet()) {
        data.name = e.getKey();

        Attrs attrs = e.getValue();

        if (attrs.containsKey("jvmargs")) data.jvmArgs = attrs.get("jvmargs");

        if (attrs.containsKey("title")) data.title = attrs.get("title");

        if (data.title != null) data.title = data.name;
      }
      return data;
    } finally {
      jar.close();
    }
  }