ConditionalRequestBuilder.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.util.Set;

import org.apache.http.Header;
import org.apache.http.HeaderElement;
import org.apache.http.HttpRequest;
import org.apache.http.ProtocolException;
import org.apache.http.impl.client.RequestWrapper;

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

/**
 * @since 4.1
 */
@Immutable
class ConditionalRequestBuilder {

	/**
	 * When a {@link HttpCacheEntry} is stale but 'might' be used as a response
	 * to an {@link HttpRequest} we will attempt to revalidate the entry with
	 * the origin. Build the origin {@link HttpRequest} here and return it.
	 * 
	 * @param request
	 *            the original request from the caller
	 * @param cacheEntry
	 *            the entry that needs to be revalidated
	 * @return the wrapped request
	 * @throws ProtocolException
	 *             when I am unable to build a new origin request.
	 */
	public HttpRequest buildConditionalRequest(HttpRequest request,
			HttpCacheEntry cacheEntry) throws ProtocolException {
		RequestWrapper wrapperRequest = new RequestWrapper(request);
		wrapperRequest.resetHeaders();
		Header eTag = cacheEntry.getFirstHeader(HeaderConstants.ETAG);
		if (eTag != null) {
			wrapperRequest.setHeader(HeaderConstants.IF_NONE_MATCH,
					eTag.getValue());
		}
		Header lastModified = cacheEntry
				.getFirstHeader(HeaderConstants.LAST_MODIFIED);
		if (lastModified != null) {
			wrapperRequest.setHeader(HeaderConstants.IF_MODIFIED_SINCE,
					lastModified.getValue());
		}
		boolean mustRevalidate = false;
		for (Header h : cacheEntry.getHeaders(HeaderConstants.CACHE_CONTROL)) {
			for (HeaderElement elt : h.getElements()) {
				if (HeaderConstants.CACHE_CONTROL_MUST_REVALIDATE
						.equalsIgnoreCase(elt.getName())
						|| HeaderConstants.CACHE_CONTROL_PROXY_REVALIDATE
								.equalsIgnoreCase(elt.getName())) {
					mustRevalidate = true;
					break;
				}
			}
		}
		if (mustRevalidate) {
			wrapperRequest.addHeader("Cache-Control", "max-age=0");
		}
		return wrapperRequest;

	}

	/**
	 * When a {@link HttpCacheEntry} does not exist for a specific
	 * {@link HttpRequest} we attempt to see if an existing
	 * {@link HttpCacheEntry} is appropriate by building a conditional
	 * {@link HttpRequest} using the variants' ETag values. If no such values
	 * exist, the request is unmodified
	 * 
	 * @param request
	 *            the original request from the caller
	 * @param cacheEntry
	 *            the entry that needs to be revalidated
	 * @return the wrapped request
	 * @throws ProtocolException
	 *             when I am unable to build a new origin request.
	 */
	public HttpRequest buildConditionalRequestFromVariants(HttpRequest request,
			Set<HttpCacheEntry> variantEntries) throws ProtocolException {
		RequestWrapper wrapperRequest = new RequestWrapper(request);
		wrapperRequest.resetHeaders();

		// we do not support partial content so all etags are used
		StringBuilder etags = new StringBuilder();
		boolean first = true;
		for (HttpCacheEntry entry : variantEntries) {
			Header etagHeader = entry.getFirstHeader(HeaderConstants.ETAG);
			if (etagHeader != null) {
				if (first) {
					etags.append(etagHeader.getValue());
					first = false;
				} else {
					etags.append(",").append(etagHeader.getValue());
				}
			}
		}
		// if first is still true than no variants had a cache entry, return
		// unmodified wrapped request
		if (first) {
			return wrapperRequest;
		}

		wrapperRequest.setHeader(HeaderConstants.IF_NONE_MATCH,
				etags.toString());

		return wrapperRequest;
	}

	/**
	 * Returns a request to unconditionally validate a cache entry with the
	 * origin. In certain cases (due to multiple intervening caches) our cache
	 * may actually receive a response to a normal conditional validation where
	 * the Date header is actually older than that of our current cache entry.
	 * In this case, the protocol recommendation is to retry the validation and
	 * force syncup with the origin.
	 * 
	 * @param request
	 *            client request we are trying to satisfy
	 * @param entry
	 *            existing cache entry we are trying to validate
	 * @return an unconditional validation request
	 * @throws ProtocolException
	 */
	public HttpRequest buildUnconditionalRequest(HttpRequest request,
			HttpCacheEntry entry) throws ProtocolException {
		RequestWrapper wrapped = new RequestWrapper(request);
		wrapped.resetHeaders();
		wrapped.addHeader("Cache-Control", "no-cache");
		wrapped.addHeader("Pragma", "no-cache");
		wrapped.removeHeaders("If-Range");
		wrapped.removeHeaders("If-Match");
		wrapped.removeHeaders("If-None-Match");
		wrapped.removeHeaders("If-Unmodified-Since");
		wrapped.removeHeaders("If-Modified-Since");
		return wrapped;
	}

}