CacheInvalidator.java

/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package com.apigee.sdk.apm.http.impl.client.cache;

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.http.Header;
import org.apache.http.HttpHost;
import org.apache.http.HttpRequest;

import com.apigee.sdk.apm.http.annotation.ThreadSafe;
import com.apigee.sdk.apm.http.client.cache.HeaderConstants;
import com.apigee.sdk.apm.http.client.cache.HttpCacheEntry;
import com.apigee.sdk.apm.http.client.cache.HttpCacheStorage;

/**
 * Given a particular HttpRequest, flush any cache entries that this request
 * would invalidate.
 * 
 * @since 4.1
 */
@ThreadSafe
// so long as the cache implementation is thread-safe
class CacheInvalidator {

	private final HttpCacheStorage storage;
	private final URIExtractor uriExtractor;

	private final Log log = LogFactory.getLog(getClass());

	/**
	 * Create a new {@link CacheInvalidator} for a given {@link HttpCache} and
	 * {@link URIExtractor}.
	 * 
	 * @param uriExtractor
	 *            Provides identifiers for the keys to store cache entries
	 * @param storage
	 *            the cache to store items away in
	 */
	public CacheInvalidator(final URIExtractor uriExtractor,
			final HttpCacheStorage storage) {
		this.uriExtractor = uriExtractor;
		this.storage = storage;
	}

	/**
	 * Remove cache entries from the cache that are no longer fresh or have been
	 * invalidated in some way.
	 * 
	 * @param host
	 *            The backend host we are talking to
	 * @param req
	 *            The HttpRequest to that host
	 */
	public void flushInvalidatedCacheEntries(HttpHost host, HttpRequest req)
			throws IOException {
		if (requestShouldNotBeCached(req)) {
			log.debug("Request should not be cached");

			String theUri = uriExtractor.getURI(host, req);

			HttpCacheEntry parent = storage.getEntry(theUri);

			log.debug("parent entry: " + parent);

			if (parent != null) {
				for (String variantURI : parent.getVariantURIs()) {
					storage.removeEntry(variantURI);
				}
				storage.removeEntry(theUri);
			}
			URL reqURL;
			try {
				reqURL = new URL(theUri);
			} catch (MalformedURLException mue) {
				log.error("Couldn't transform request into valid URL");
				return;
			}
			Header clHdr = req.getFirstHeader("Content-Location");
			if (clHdr != null) {
				String contentLocation = clHdr.getValue();
				if (!flushAbsoluteUriFromSameHost(reqURL, contentLocation)) {
					flushRelativeUriFromSameHost(reqURL, contentLocation);
				}
			}
			Header lHdr = req.getFirstHeader("Location");
			if (lHdr != null) {
				flushAbsoluteUriFromSameHost(reqURL, lHdr.getValue());
			}
		}
	}

	protected void flushUriIfSameHost(URL requestURL, URL targetURL)
			throws IOException {
		URL canonicalTarget = new URL(uriExtractor.canonicalizeUri(targetURL
				.toString()));
		if (canonicalTarget.getAuthority().equalsIgnoreCase(
				requestURL.getAuthority())) {
			storage.removeEntry(canonicalTarget.toString());
		}
	}

	protected void flushRelativeUriFromSameHost(URL reqURL, String relUri)
			throws IOException {
		URL relURL;
		try {
			relURL = new URL(reqURL, relUri);
		} catch (MalformedURLException e) {
			log.debug("Invalid relative URI", e);
			return;
		}
		flushUriIfSameHost(reqURL, relURL);
	}

	protected boolean flushAbsoluteUriFromSameHost(URL reqURL, String uri)
			throws IOException {
		URL absURL;
		try {
			absURL = new URL(uri);
		} catch (MalformedURLException mue) {
			return false;
		}
		flushUriIfSameHost(reqURL, absURL);
		return true;
	}

	protected boolean requestShouldNotBeCached(HttpRequest req) {
		String method = req.getRequestLine().getMethod();
		return notGetOrHeadRequest(method);
	}

	private boolean notGetOrHeadRequest(String method) {
		return !(HeaderConstants.GET_METHOD.equals(method) || HeaderConstants.HEAD_METHOD
				.equals(method));
	}
}