non-releases/trunk_before_flattening/src/java/org/apache/cocoon/matching/MountTableMatcher.java

/*
 * Copyright 1999-2005 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.cocoon.matching;

import org.apache.avalon.framework.configuration.Configuration;
import org.apache.avalon.framework.configuration.DefaultConfigurationBuilder;
import org.apache.avalon.framework.logger.AbstractLogEnabled;
import org.apache.avalon.framework.parameters.ParameterException;
import org.apache.avalon.framework.parameters.Parameterizable;
import org.apache.avalon.framework.parameters.Parameters;
import org.apache.avalon.framework.service.ServiceException;
import org.apache.avalon.framework.service.ServiceManager;
import org.apache.avalon.framework.service.Serviceable;
import org.apache.avalon.framework.thread.ThreadSafe;

import org.apache.cocoon.components.source.SourceUtil;
import org.apache.cocoon.environment.ObjectModelHelper;
import org.apache.cocoon.environment.Request;
import org.apache.cocoon.sitemap.PatternException;

import org.apache.excalibur.source.Source;
import org.apache.excalibur.source.SourceResolver;
import org.apache.excalibur.source.SourceValidity;

import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

/**
 * A matcher that manages a "mount table", allowing to add subsitemaps to a Cocoon application without
 * modifying the main sitemap. This is especially useful for prototypes and demos where installing
 * a separate instance of Cocoon is overkill.
 * <p>
 * The mount table is an xml file which has a format similar to the <code>map:mount</code> syntax:
 * <pre>
 *   &lt;mount-table&gt;
 *     &lt;mount uri-prefix="foo" src="file://path/to/foo/directory/"/&gt;
 *     &lt;mount uri-prefix="bar/baz" src="file://path/to/bar-baz/directory/"/&gt;
 *   &lt;/mount-table&gt;
 * </pre>
 * The matcher will scan the mount table for an "uri-prefix" value matching the beginning of the current
 * request URI, and if found, succeed and populate the "src" and "uri-prefix" sitemap variables.
 * <p>
 * Usage in the sitemap is therefore as follows:
 * <pre>
 *   &lt;map:match type="mount-table" pattern="path/to/mount-table.xml"&gt;
 *     &lt;map:mount uri-prefix="{uri-prefix}" src="{src}"/&gt;
 *   &lt;/map:match&gt;
 * </pre>
 * <p>
 * This matcher accepts a single configuration parameter, indicating if missing mount tables should be
 * silently ignored (defaults is <code>false</code>, meaning "don't ignore"):
 * <pre>
 *   &lt;map:matcher type="mount-table" src="org.apache.cocoon.matching.MountTableMatcher"&gt;
 *     &lt;map:parameter name="ignore-missing-tables" value="true"/&gt;
 *   &lt;/map:matcher&gt;
 * </pre>
 * <p>
 * This configuration is used in the main sitemap of Cocoon samples, to allow users to define their own mount
 * table, but not fail if it does not exist.
 *
 * @version $Id$
 */
public class MountTableMatcher extends AbstractLogEnabled
                               implements Matcher, ThreadSafe, Serviceable, Parameterizable {

    private ServiceManager manager;
    private SourceResolver resolver;
    private Map mountTables = Collections.synchronizedMap(new HashMap());
    private boolean ignoreMissingTables;

    public void service(ServiceManager manager) throws ServiceException {
        this.manager = manager;
        this.resolver = (SourceResolver) this.manager.lookup(SourceResolver.ROLE);
    }

    public void parameterize(Parameters params) throws ParameterException {
        this.ignoreMissingTables = params.getParameterAsBoolean("ignore-missing-tables", false);
    }

    private Map getMountTable(String src) throws Exception {
        Source source = null;
        try {
            source = this.resolver.resolveURI(src);
            final String uri = source.getURI();

            // Check if source exists
            // FIXME: source.exists() returns true in the case of an OSGI bundle uri,
            // For example if uri=bundle://11/../mount-table.xml, exists() returns true
            // but the Source is unusable
            if (!source.exists()) {
                if (this.ignoreMissingTables) {
                    return Collections.EMPTY_MAP;
                } else {
                    throw new PatternException("Mount table does not exist: '" + uri + "'");
                }
            }

            // Source exists
            Object[] values = (Object[]) this.mountTables.get(uri);
            if (values != null) {
                // Check validity
                SourceValidity oldValidity = (SourceValidity) values[1];

                int valid = oldValidity != null ? oldValidity.isValid() : SourceValidity.INVALID;
                if (valid == SourceValidity.VALID) {
                    // Valid without needing the new validity
                    return (Map) values[0];
                }

                if (valid == SourceValidity.UNKNOWN &&
                        oldValidity.isValid(source.getValidity()) == SourceValidity.VALID) {
                    // Valid after comparing with the new validity
                    return (Map) values[0];
                }

                // Invalid: fallback below to read the mount table
            } else {
                values = new Object[2];
            }

            // Read the mount table
            Map mounts = new HashMap();
            DefaultConfigurationBuilder builder = new DefaultConfigurationBuilder();
            Configuration config = builder.build(SourceUtil.getInputSource(source));

            Configuration[] children = config.getChildren();
            for (int i = 0; i < children.length; i++) {
                Configuration child = children[i];
                if ("mount".equals(child.getName())) {
                    String prefix = children[i].getAttribute("uri-prefix");
                    // Append a '/' at the end of a not-empty prefix
                    // this avoids flat uri matching which would cause
                    // exceptions in the sub sitemap!
                    if (!prefix.endsWith("/") && prefix.length() != 0) {
                        prefix = prefix + '/';
                    }
                    mounts.put(prefix, children[i].getAttribute("src"));
                } else {
                    throw new PatternException(
                        "Unexpected element '" + child.getName() + "' (awaiting 'mount'), at " + child.getLocation());
                }
            }
            values[0] = mounts;
            values[1] = source.getValidity();

            // Cache it with the source validity
            this.mountTables.put(uri, values);

            return mounts;

        } catch (SecurityException e) {
            if (this.ignoreMissingTables) {
                return Collections.EMPTY_MAP;
            } else {
                throw new PatternException("Mount table is not accessible: '" + src + "' (" + e + ")");
            }

        } finally {
            if (source != null) {
                this.resolver.release(source);
            }
        }
    }

    public Map match(String pattern, Map objectModel, Parameters parameters) throws PatternException {
        Map mounts;
        try {
            mounts = getMountTable(pattern);
        } catch (PatternException pe) {
            throw pe;
        } catch (Exception e) {
            throw new PatternException(e);
        }

        // Get the request URI
        Request request = ObjectModelHelper.getRequest(objectModel);
        String uri = request.getSitemapURI();

        // and search for a matching prefix
        Iterator iter = mounts.entrySet().iterator();
        while (iter.hasNext()) {
            Map.Entry entry = (Map.Entry) iter.next();
            String prefix = (String) entry.getKey();
            if (uri.startsWith(prefix)) {
                // Found it
                Map result = new HashMap(2);
                result.put("uri-prefix", prefix);
                result.put("src", entry.getValue());

                // Return immediately
                return result;
            }
        }

        // Not found
        return null;
    }
}