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HttpComponents HttpClient - Cache
/*
* ====================================================================
* 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
* The {@link CachingHttpClient} is meant to be a drop-in replacement for
* a {@link DefaultHttpClient} that transparently adds client-side caching.
* The current implementation is conditionally compliant with HTTP/1.1
* (meaning all the MUST and MUST NOTs are obeyed), although quite a lot,
* though not all, of the SHOULDs and SHOULD NOTs are obeyed too. Generally
* speaking, you construct a {@code CachingHttpClient} by providing a
* "backend" {@link HttpClient} used for making actual network requests and
* provide an {@link HttpCacheStorage} instance to use for holding onto
* cached responses. Additional configuration options can be provided by
* passing in a {@link CacheConfig}. Note that all of the usual client
* related configuration you want to do vis-a-vis timeouts and connection
* pools should be done on this backend client before constructing a {@code
* CachingHttpClient} from it.
*
* Generally speaking, the {@code CachingHttpClient} is implemented as a
* Decorator
* of the backend client; for any incoming request it attempts to satisfy
* it from the cache, but if it can't, or if it needs to revalidate a stale
* cache entry, it will use the backend client to make an actual request.
* However, a proper HTTP/1.1 cache won't change the semantics of a request
* and response; in particular, if you issue an unconditional request you
* will get a full response (although it may be served to you from the cache,
* or the cache may make a conditional request on your behalf to the origin).
* This notion of "semantic transparency" means you should be able to drop
* a {@link CachingHttpClient} into an existing application without breaking
* anything.
*
* Folks that would like to experiment with alternative storage backends
* should look at the {@link HttpCacheStorage} interface and the related
* package documentation there. You may also be interested in the provided
* {@link org.apache.http.impl.client.cache.ehcache.EhcacheHttpCacheStorage
* EhCache} and {@link
* org.apache.http.impl.client.cache.memcached.MemcachedHttpCacheStorage
* memcached} storage backends.
*
* @since 4.1
*/
@ThreadSafe // So long as the responseCache implementation is threadsafe
public class CachingHttpClient implements HttpClient {
/**
* This is the name under which the {@link
* org.apache.http.client.cache.CacheResponseStatus} of a request
* (for example, whether it resulted in a cache hit) will be recorded if an
* {@link HttpContext} is provided during execution.
*/
public static final String CACHE_RESPONSE_STATUS = "http.cache.response.status";
private final static boolean SUPPORTS_RANGE_AND_CONTENT_RANGE_HEADERS = false;
private final AtomicLong cacheHits = new AtomicLong();
private final AtomicLong cacheMisses = new AtomicLong();
private final AtomicLong cacheUpdates = new AtomicLong();
private final Map viaHeaders = new HashMap(4);
private final HttpClient backend;
private final HttpCache responseCache;
private final CacheValidityPolicy validityPolicy;
private final ResponseCachingPolicy responseCachingPolicy;
private final CachedHttpResponseGenerator responseGenerator;
private final CacheableRequestPolicy cacheableRequestPolicy;
private final CachedResponseSuitabilityChecker suitabilityChecker;
private final ConditionalRequestBuilder conditionalRequestBuilder;
private final long maxObjectSizeBytes;
private final boolean sharedCache;
private final ResponseProtocolCompliance responseCompliance;
private final RequestProtocolCompliance requestCompliance;
private final AsynchronousValidator asynchRevalidator;
private final Log log = LogFactory.getLog(getClass());
CachingHttpClient(
HttpClient client,
HttpCache cache,
CacheConfig config) {
super();
if (client == null) {
throw new IllegalArgumentException("HttpClient may not be null");
}
if (cache == null) {
throw new IllegalArgumentException("HttpCache may not be null");
}
if (config == null) {
throw new IllegalArgumentException("CacheConfig may not be null");
}
this.maxObjectSizeBytes = config.getMaxObjectSize();
this.sharedCache = config.isSharedCache();
this.backend = client;
this.responseCache = cache;
this.validityPolicy = new CacheValidityPolicy();
this.responseCachingPolicy = new ResponseCachingPolicy(maxObjectSizeBytes, sharedCache);
this.responseGenerator = new CachedHttpResponseGenerator(this.validityPolicy);
this.cacheableRequestPolicy = new CacheableRequestPolicy();
this.suitabilityChecker = new CachedResponseSuitabilityChecker(this.validityPolicy, config);
this.conditionalRequestBuilder = new ConditionalRequestBuilder();
this.responseCompliance = new ResponseProtocolCompliance();
this.requestCompliance = new RequestProtocolCompliance();
this.asynchRevalidator = makeAsynchronousValidator(config);
}
/**
* Constructs a {@code CachingHttpClient} with default caching settings that
* stores cache entries in memory and uses a vanilla {@link DefaultHttpClient}
* for backend requests.
*/
public CachingHttpClient() {
this(new DefaultHttpClient(),
new BasicHttpCache(),
new CacheConfig());
}
/**
* Constructs a {@code CachingHttpClient} with the given caching options that
* stores cache entries in memory and uses a vanilla {@link DefaultHttpClient}
* for backend requests.
* @param config cache module options
*/
public CachingHttpClient(CacheConfig config) {
this(new DefaultHttpClient(),
new BasicHttpCache(config),
config);
}
/**
* Constructs a {@code CachingHttpClient} with default caching settings that
* stores cache entries in memory and uses the given {@link HttpClient}
* for backend requests.
* @param client used to make origin requests
*/
public CachingHttpClient(HttpClient client) {
this(client,
new BasicHttpCache(),
new CacheConfig());
}
/**
* Constructs a {@code CachingHttpClient} with the given caching options that
* stores cache entries in memory and uses the given {@link HttpClient}
* for backend requests.
* @param config cache module options
* @param client used to make origin requests
*/
public CachingHttpClient(HttpClient client, CacheConfig config) {
this(client,
new BasicHttpCache(config),
config);
}
/**
* Constructs a {@code CachingHttpClient} with the given caching options
* that stores cache entries in the provided storage backend and uses
* the given {@link HttpClient} for backend requests. However, cached
* response bodies are managed using the given {@link ResourceFactory}.
* @param client used to make origin requests
* @param resourceFactory how to manage cached response bodies
* @param storage where to store cache entries
* @param config cache module options
*/
public CachingHttpClient(
HttpClient client,
ResourceFactory resourceFactory,
HttpCacheStorage storage,
CacheConfig config) {
this(client,
new BasicHttpCache(resourceFactory, storage, config),
config);
}
/**
* Constructs a {@code CachingHttpClient} with the given caching options
* that stores cache entries in the provided storage backend and uses
* the given {@link HttpClient} for backend requests.
* @param client used to make origin requests
* @param storage where to store cache entries
* @param config cache module options
*/
public CachingHttpClient(
HttpClient client,
HttpCacheStorage storage,
CacheConfig config) {
this(client,
new BasicHttpCache(new HeapResourceFactory(), storage, config),
config);
}
CachingHttpClient(
HttpClient backend,
CacheValidityPolicy validityPolicy,
ResponseCachingPolicy responseCachingPolicy,
HttpCache responseCache,
CachedHttpResponseGenerator responseGenerator,
CacheableRequestPolicy cacheableRequestPolicy,
CachedResponseSuitabilityChecker suitabilityChecker,
ConditionalRequestBuilder conditionalRequestBuilder,
ResponseProtocolCompliance responseCompliance,
RequestProtocolCompliance requestCompliance) {
CacheConfig config = new CacheConfig();
this.maxObjectSizeBytes = config.getMaxObjectSize();
this.sharedCache = config.isSharedCache();
this.backend = backend;
this.validityPolicy = validityPolicy;
this.responseCachingPolicy = responseCachingPolicy;
this.responseCache = responseCache;
this.responseGenerator = responseGenerator;
this.cacheableRequestPolicy = cacheableRequestPolicy;
this.suitabilityChecker = suitabilityChecker;
this.conditionalRequestBuilder = conditionalRequestBuilder;
this.responseCompliance = responseCompliance;
this.requestCompliance = requestCompliance;
this.asynchRevalidator = makeAsynchronousValidator(config);
}
private AsynchronousValidator makeAsynchronousValidator(
CacheConfig config) {
if (config.getAsynchronousWorkersMax() > 0) {
return new AsynchronousValidator(this, config);
}
return null;
}
/**
* Reports the number of times that the cache successfully responded
* to an {@link HttpRequest} without contacting the origin server.
* @return the number of cache hits
*/
public long getCacheHits() {
return cacheHits.get();
}
/**
* Reports the number of times that the cache contacted the origin
* server because it had no appropriate response cached.
* @return the number of cache misses
*/
public long getCacheMisses() {
return cacheMisses.get();
}
/**
* Reports the number of times that the cache was able to satisfy
* a response by revalidating an existing but stale cache entry.
* @return the number of cache revalidations
*/
public long getCacheUpdates() {
return cacheUpdates.get();
}
public HttpResponse execute(HttpHost target, HttpRequest request) throws IOException {
HttpContext defaultContext = null;
return execute(target, request, defaultContext);
}
public T execute(HttpHost target, HttpRequest request,
ResponseHandler responseHandler) throws IOException {
return execute(target, request, responseHandler, null);
}
public T execute(HttpHost target, HttpRequest request,
ResponseHandler responseHandler, HttpContext context) throws IOException {
HttpResponse resp = execute(target, request, context);
return handleAndConsume(responseHandler,resp);
}
public HttpResponse execute(HttpUriRequest request) throws IOException {
HttpContext context = null;
return execute(request, context);
}
public HttpResponse execute(HttpUriRequest request, HttpContext context) throws IOException {
URI uri = request.getURI();
HttpHost httpHost = new HttpHost(uri.getHost(), uri.getPort(), uri.getScheme());
return execute(httpHost, request, context);
}
public T execute(HttpUriRequest request, ResponseHandler responseHandler)
throws IOException {
return execute(request, responseHandler, null);
}
public T execute(HttpUriRequest request, ResponseHandler responseHandler,
HttpContext context) throws IOException {
HttpResponse resp = execute(request, context);
return handleAndConsume(responseHandler, resp);
}
private T handleAndConsume(
final ResponseHandler responseHandler,
HttpResponse response) throws Error, IOException {
T result;
try {
result = responseHandler.handleResponse(response);
} catch (Exception t) {
HttpEntity entity = response.getEntity();
try {
EntityUtils.consume(entity);
} catch (Exception t2) {
// Log this exception. The original exception is more
// important and will be thrown to the caller.
this.log.warn("Error consuming content after an exception.", t2);
}
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
}
if (t instanceof IOException) {
throw (IOException) t;
}
throw new UndeclaredThrowableException(t);
}
// Handling the response was successful. Ensure that the content has
// been fully consumed.
HttpEntity entity = response.getEntity();
EntityUtils.consume(entity);
return result;
}
public ClientConnectionManager getConnectionManager() {
return backend.getConnectionManager();
}
public HttpParams getParams() {
return backend.getParams();
}
public HttpResponse execute(HttpHost target, HttpRequest request, HttpContext context)
throws IOException {
// default response context
setResponseStatus(context, CacheResponseStatus.CACHE_MISS);
String via = generateViaHeader(request);
if (clientRequestsOurOptions(request)) {
setResponseStatus(context, CacheResponseStatus.CACHE_MODULE_RESPONSE);
return new OptionsHttp11Response();
}
HttpResponse fatalErrorResponse = getFatallyNoncompliantResponse(
request, context);
if (fatalErrorResponse != null) return fatalErrorResponse;
request = requestCompliance.makeRequestCompliant(request);
request.addHeader("Via",via);
flushEntriesInvalidatedByRequest(target, request);
if (!cacheableRequestPolicy.isServableFromCache(request)) {
log.debug("Request is not servable from cache");
return callBackend(target, request, context);
}
HttpCacheEntry entry = satisfyFromCache(target, request);
if (entry == null) {
log.debug("Cache miss");
return handleCacheMiss(target, request, context);
}
return handleCacheHit(target, request, context, entry);
}
private HttpResponse handleCacheHit(HttpHost target, HttpRequest request,
HttpContext context, HttpCacheEntry entry)
throws ClientProtocolException, IOException {
recordCacheHit(target, request);
HttpResponse out = null;
Date now = getCurrentDate();
if (suitabilityChecker.canCachedResponseBeUsed(target, request, entry, now)) {
log.debug("Cache hit");
out = generateCachedResponse(request, context, entry, now);
} else if (!mayCallBackend(request)) {
log.debug("Cache entry not suitable but only-if-cached requested");
out = generateGatewayTimeout(context);
} else if (validityPolicy.isRevalidatable(entry)
&& !(entry.getStatusCode() == HttpStatus.SC_NOT_MODIFIED
&& !suitabilityChecker.isConditional(request))) {
log.debug("Revalidating cache entry");
return revalidateCacheEntry(target, request, context, entry, now);
} else {
log.debug("Cache entry not usable; calling backend");
return callBackend(target, request, context);
}
if (context != null) {
context.setAttribute(ExecutionContext.HTTP_TARGET_HOST, target);
context.setAttribute(ExecutionContext.HTTP_REQUEST, request);
context.setAttribute(ExecutionContext.HTTP_RESPONSE, out);
context.setAttribute(ExecutionContext.HTTP_REQ_SENT, true);
}
return out;
}
private HttpResponse revalidateCacheEntry(HttpHost target,
HttpRequest request, HttpContext context, HttpCacheEntry entry,
Date now) throws ClientProtocolException {
try {
if (asynchRevalidator != null
&& !staleResponseNotAllowed(request, entry, now)
&& validityPolicy.mayReturnStaleWhileRevalidating(entry, now)) {
log.trace("Serving stale with asynchronous revalidation");
final HttpResponse resp = generateCachedResponse(request, context, entry, now);
asynchRevalidator.revalidateCacheEntry(target, request, context, entry);
return resp;
}
return revalidateCacheEntry(target, request, context, entry);
} catch (IOException ioex) {
return handleRevalidationFailure(request, context, entry, now);
} catch (ProtocolException e) {
throw new ClientProtocolException(e);
}
}
private HttpResponse handleCacheMiss(HttpHost target, HttpRequest request,
HttpContext context) throws IOException {
recordCacheMiss(target, request);
if (!mayCallBackend(request)) {
return new BasicHttpResponse(HttpVersion.HTTP_1_1, HttpStatus.SC_GATEWAY_TIMEOUT,
"Gateway Timeout");
}
Map variants =
getExistingCacheVariants(target, request);
if (variants != null && variants.size() > 0) {
return negotiateResponseFromVariants(target, request, context, variants);
}
return callBackend(target, request, context);
}
private HttpCacheEntry satisfyFromCache(HttpHost target, HttpRequest request) {
HttpCacheEntry entry = null;
try {
entry = responseCache.getCacheEntry(target, request);
} catch (IOException ioe) {
log.warn("Unable to retrieve entries from cache", ioe);
}
return entry;
}
private HttpResponse getFatallyNoncompliantResponse(HttpRequest request,
HttpContext context) {
HttpResponse fatalErrorResponse = null;
List fatalError = requestCompliance.requestIsFatallyNonCompliant(request);
for (RequestProtocolError error : fatalError) {
setResponseStatus(context, CacheResponseStatus.CACHE_MODULE_RESPONSE);
fatalErrorResponse = requestCompliance.getErrorForRequest(error);
}
return fatalErrorResponse;
}
private Map getExistingCacheVariants(HttpHost target,
HttpRequest request) {
Map variants = null;
try {
variants = responseCache.getVariantCacheEntriesWithEtags(target, request);
} catch (IOException ioe) {
log.warn("Unable to retrieve variant entries from cache", ioe);
}
return variants;
}
private void recordCacheMiss(HttpHost target, HttpRequest request) {
cacheMisses.getAndIncrement();
if (log.isTraceEnabled()) {
RequestLine rl = request.getRequestLine();
log.trace("Cache miss [host: " + target + "; uri: " + rl.getUri() + "]");
}
}
private void recordCacheHit(HttpHost target, HttpRequest request) {
cacheHits.getAndIncrement();
if (log.isTraceEnabled()) {
RequestLine rl = request.getRequestLine();
log.trace("Cache hit [host: " + target + "; uri: " + rl.getUri() + "]");
}
}
private void recordCacheUpdate(HttpContext context) {
cacheUpdates.getAndIncrement();
setResponseStatus(context, CacheResponseStatus.VALIDATED);
}
private void flushEntriesInvalidatedByRequest(HttpHost target,
HttpRequest request) {
try {
responseCache.flushInvalidatedCacheEntriesFor(target, request);
} catch (IOException ioe) {
log.warn("Unable to flush invalidated entries from cache", ioe);
}
}
private HttpResponse generateCachedResponse(HttpRequest request,
HttpContext context, HttpCacheEntry entry, Date now) {
final HttpResponse cachedResponse;
if (request.containsHeader(HeaderConstants.IF_NONE_MATCH)
|| request.containsHeader(HeaderConstants.IF_MODIFIED_SINCE)) {
cachedResponse = responseGenerator.generateNotModifiedResponse(entry);
} else {
cachedResponse = responseGenerator.generateResponse(entry);
}
setResponseStatus(context, CacheResponseStatus.CACHE_HIT);
if (validityPolicy.getStalenessSecs(entry, now) > 0L) {
cachedResponse.addHeader(HeaderConstants.WARNING,"110 localhost \"Response is stale\"");
}
return cachedResponse;
}
private HttpResponse handleRevalidationFailure(HttpRequest request,
HttpContext context, HttpCacheEntry entry, Date now) {
if (staleResponseNotAllowed(request, entry, now)) {
return generateGatewayTimeout(context);
} else {
return unvalidatedCacheHit(context, entry);
}
}
private HttpResponse generateGatewayTimeout(HttpContext context) {
setResponseStatus(context, CacheResponseStatus.CACHE_MODULE_RESPONSE);
return new BasicHttpResponse(HttpVersion.HTTP_1_1,
HttpStatus.SC_GATEWAY_TIMEOUT, "Gateway Timeout");
}
private HttpResponse unvalidatedCacheHit(HttpContext context,
HttpCacheEntry entry) {
final HttpResponse cachedResponse = responseGenerator.generateResponse(entry);
setResponseStatus(context, CacheResponseStatus.CACHE_HIT);
cachedResponse.addHeader(HeaderConstants.WARNING, "111 localhost \"Revalidation failed\"");
return cachedResponse;
}
private boolean staleResponseNotAllowed(HttpRequest request,
HttpCacheEntry entry, Date now) {
return validityPolicy.mustRevalidate(entry)
|| (isSharedCache() && validityPolicy.proxyRevalidate(entry))
|| explicitFreshnessRequest(request, entry, now);
}
private boolean mayCallBackend(HttpRequest request) {
for (Header h: request.getHeaders(HeaderConstants.CACHE_CONTROL)) {
for (HeaderElement elt : h.getElements()) {
if ("only-if-cached".equals(elt.getName())) {
log.trace("Request marked only-if-cached");
return false;
}
}
}
return true;
}
private boolean explicitFreshnessRequest(HttpRequest request, HttpCacheEntry entry, Date now) {
for(Header h : request.getHeaders(HeaderConstants.CACHE_CONTROL)) {
for(HeaderElement elt : h.getElements()) {
if (HeaderConstants.CACHE_CONTROL_MAX_STALE.equals(elt.getName())) {
try {
int maxstale = Integer.parseInt(elt.getValue());
long age = validityPolicy.getCurrentAgeSecs(entry, now);
long lifetime = validityPolicy.getFreshnessLifetimeSecs(entry);
if (age - lifetime > maxstale) return true;
} catch (NumberFormatException nfe) {
return true;
}
} else if (HeaderConstants.CACHE_CONTROL_MIN_FRESH.equals(elt.getName())
|| HeaderConstants.CACHE_CONTROL_MAX_AGE.equals(elt.getName())) {
return true;
}
}
}
return false;
}
private String generateViaHeader(HttpMessage msg) {
final ProtocolVersion pv = msg.getProtocolVersion();
String existingEntry = viaHeaders.get(pv);
if (existingEntry != null) return existingEntry;
final VersionInfo vi = VersionInfo.loadVersionInfo("org.apache.http.client", getClass().getClassLoader());
final String release = (vi != null) ? vi.getRelease() : VersionInfo.UNAVAILABLE;
String value;
if ("http".equalsIgnoreCase(pv.getProtocol())) {
value = String.format("%d.%d localhost (Apache-HttpClient/%s (cache))", pv.getMajor(), pv.getMinor(),
release);
} else {
value = String.format("%s/%d.%d localhost (Apache-HttpClient/%s (cache))", pv.getProtocol(), pv.getMajor(),
pv.getMinor(), release);
}
viaHeaders.put(pv, value);
return value;
}
private void setResponseStatus(final HttpContext context, final CacheResponseStatus value) {
if (context != null) {
context.setAttribute(CACHE_RESPONSE_STATUS, value);
}
}
/**
* Reports whether this {@code CachingHttpClient} implementation
* supports byte-range requests as specified by the {@code Range}
* and {@code Content-Range} headers.
* @return {@code true} if byte-range requests are supported
*/
public boolean supportsRangeAndContentRangeHeaders() {
return SUPPORTS_RANGE_AND_CONTENT_RANGE_HEADERS;
}
/**
* Reports whether this {@code CachingHttpClient} is configured as
* a shared (public) or non-shared (private) cache. See {@link
* CacheConfig#setSharedCache(boolean)}.
* @return {@code true} if we are behaving as a shared (public)
* cache
*/
public boolean isSharedCache() {
return sharedCache;
}
Date getCurrentDate() {
return new Date();
}
boolean clientRequestsOurOptions(HttpRequest request) {
RequestLine line = request.getRequestLine();
if (!HeaderConstants.OPTIONS_METHOD.equals(line.getMethod()))
return false;
if (!"*".equals(line.getUri()))
return false;
if (!"0".equals(request.getFirstHeader(HeaderConstants.MAX_FORWARDS).getValue()))
return false;
return true;
}
HttpResponse callBackend(HttpHost target, HttpRequest request, HttpContext context)
throws IOException {
Date requestDate = getCurrentDate();
log.trace("Calling the backend");
HttpResponse backendResponse = backend.execute(target, request, context);
backendResponse.addHeader("Via", generateViaHeader(backendResponse));
return handleBackendResponse(target, request, requestDate, getCurrentDate(),
backendResponse);
}
private boolean revalidationResponseIsTooOld(HttpResponse backendResponse,
HttpCacheEntry cacheEntry) {
final Header entryDateHeader = cacheEntry.getFirstHeader(HTTP.DATE_HEADER);
final Header responseDateHeader = backendResponse.getFirstHeader(HTTP.DATE_HEADER);
if (entryDateHeader != null && responseDateHeader != null) {
try {
Date entryDate = DateUtils.parseDate(entryDateHeader.getValue());
Date respDate = DateUtils.parseDate(responseDateHeader.getValue());
if (respDate.before(entryDate)) return true;
} catch (DateParseException e) {
// either backend response or cached entry did not have a valid
// Date header, so we can't tell if they are out of order
// according to the origin clock; thus we can skip the
// unconditional retry recommended in 13.2.6 of RFC 2616.
}
}
return false;
}
HttpResponse negotiateResponseFromVariants(HttpHost target,
HttpRequest request, HttpContext context,
Map variants) throws IOException {
HttpRequest conditionalRequest = conditionalRequestBuilder.buildConditionalRequestFromVariants(request, variants);
Date requestDate = getCurrentDate();
HttpResponse backendResponse = backend.execute(target, conditionalRequest, context);
Date responseDate = getCurrentDate();
backendResponse.addHeader("Via", generateViaHeader(backendResponse));
if (backendResponse.getStatusLine().getStatusCode() != HttpStatus.SC_NOT_MODIFIED) {
return handleBackendResponse(target, request, requestDate, responseDate, backendResponse);
}
Header resultEtagHeader = backendResponse.getFirstHeader(HeaderConstants.ETAG);
if (resultEtagHeader == null) {
log.warn("304 response did not contain ETag");
return callBackend(target, request, context);
}
String resultEtag = resultEtagHeader.getValue();
Variant matchingVariant = variants.get(resultEtag);
if (matchingVariant == null) {
log.debug("304 response did not contain ETag matching one sent in If-None-Match");
return callBackend(target, request, context);
}
HttpCacheEntry matchedEntry = matchingVariant.getEntry();
if (revalidationResponseIsTooOld(backendResponse, matchedEntry)) {
EntityUtils.consume(backendResponse.getEntity());
return retryRequestUnconditionally(target, request, context,
matchedEntry);
}
recordCacheUpdate(context);
HttpCacheEntry responseEntry = getUpdatedVariantEntry(target,
conditionalRequest, requestDate, responseDate, backendResponse,
matchingVariant, matchedEntry);
HttpResponse resp = responseGenerator.generateResponse(responseEntry);
tryToUpdateVariantMap(target, request, matchingVariant);
if (shouldSendNotModifiedResponse(request, responseEntry)) {
return responseGenerator.generateNotModifiedResponse(responseEntry);
}
return resp;
}
private HttpResponse retryRequestUnconditionally(HttpHost target,
HttpRequest request, HttpContext context,
HttpCacheEntry matchedEntry) throws IOException {
HttpRequest unconditional = conditionalRequestBuilder
.buildUnconditionalRequest(request, matchedEntry);
return callBackend(target, unconditional, context);
}
private HttpCacheEntry getUpdatedVariantEntry(HttpHost target,
HttpRequest conditionalRequest, Date requestDate,
Date responseDate, HttpResponse backendResponse,
Variant matchingVariant, HttpCacheEntry matchedEntry) {
HttpCacheEntry responseEntry = matchedEntry;
try {
responseEntry = responseCache.updateVariantCacheEntry(target, conditionalRequest,
matchedEntry, backendResponse, requestDate, responseDate, matchingVariant.getCacheKey());
} catch (IOException ioe) {
log.warn("Could not update cache entry", ioe);
}
return responseEntry;
}
private void tryToUpdateVariantMap(HttpHost target, HttpRequest request,
Variant matchingVariant) {
try {
responseCache.reuseVariantEntryFor(target, request, matchingVariant);
} catch (IOException ioe) {
log.warn("Could not update cache entry to reuse variant", ioe);
}
}
private boolean shouldSendNotModifiedResponse(HttpRequest request,
HttpCacheEntry responseEntry) {
return (suitabilityChecker.isConditional(request)
&& suitabilityChecker.allConditionalsMatch(request, responseEntry, new Date()));
}
HttpResponse revalidateCacheEntry(
HttpHost target,
HttpRequest request,
HttpContext context,
HttpCacheEntry cacheEntry) throws IOException, ProtocolException {
HttpRequest conditionalRequest = conditionalRequestBuilder.buildConditionalRequest(request, cacheEntry);
Date requestDate = getCurrentDate();
HttpResponse backendResponse = backend.execute(target, conditionalRequest, context);
Date responseDate = getCurrentDate();
if (revalidationResponseIsTooOld(backendResponse, cacheEntry)) {
EntityUtils.consume(backendResponse.getEntity());
HttpRequest unconditional = conditionalRequestBuilder
.buildUnconditionalRequest(request, cacheEntry);
requestDate = getCurrentDate();
backendResponse = backend.execute(target, unconditional, context);
responseDate = getCurrentDate();
}
backendResponse.addHeader(HeaderConstants.VIA, generateViaHeader(backendResponse));
int statusCode = backendResponse.getStatusLine().getStatusCode();
if (statusCode == HttpStatus.SC_NOT_MODIFIED || statusCode == HttpStatus.SC_OK) {
recordCacheUpdate(context);
}
if (statusCode == HttpStatus.SC_NOT_MODIFIED) {
HttpCacheEntry updatedEntry = responseCache.updateCacheEntry(target, request, cacheEntry,
backendResponse, requestDate, responseDate);
if (suitabilityChecker.isConditional(request)
&& suitabilityChecker.allConditionalsMatch(request, updatedEntry, new Date())) {
return responseGenerator.generateNotModifiedResponse(updatedEntry);
}
return responseGenerator.generateResponse(updatedEntry);
}
if (staleIfErrorAppliesTo(statusCode)
&& !staleResponseNotAllowed(request, cacheEntry, getCurrentDate())
&& validityPolicy.mayReturnStaleIfError(request, cacheEntry, responseDate)) {
final HttpResponse cachedResponse = responseGenerator.generateResponse(cacheEntry);
cachedResponse.addHeader(HeaderConstants.WARNING, "110 localhost \"Response is stale\"");
HttpEntity errorBody = backendResponse.getEntity();
if (errorBody != null) EntityUtils.consume(errorBody);
return cachedResponse;
}
return handleBackendResponse(target, conditionalRequest, requestDate, responseDate,
backendResponse);
}
private boolean staleIfErrorAppliesTo(int statusCode) {
return statusCode == HttpStatus.SC_INTERNAL_SERVER_ERROR
|| statusCode == HttpStatus.SC_BAD_GATEWAY
|| statusCode == HttpStatus.SC_SERVICE_UNAVAILABLE
|| statusCode == HttpStatus.SC_GATEWAY_TIMEOUT;
}
HttpResponse handleBackendResponse(
HttpHost target,
HttpRequest request,
Date requestDate,
Date responseDate,
HttpResponse backendResponse) throws IOException {
log.trace("Handling Backend response");
responseCompliance.ensureProtocolCompliance(request, backendResponse);
boolean cacheable = responseCachingPolicy.isResponseCacheable(request, backendResponse);
responseCache.flushInvalidatedCacheEntriesFor(target, request, backendResponse);
if (cacheable &&
!alreadyHaveNewerCacheEntry(target, request, backendResponse)) {
try {
storeRequestIfModifiedSinceFor304Response(request, backendResponse);
return responseCache.cacheAndReturnResponse(target, request, backendResponse, requestDate,
responseDate);
} catch (IOException ioe) {
log.warn("Unable to store entries in cache", ioe);
}
}
if (!cacheable) {
try {
responseCache.flushCacheEntriesFor(target, request);
} catch (IOException ioe) {
log.warn("Unable to flush invalid cache entries", ioe);
}
}
return backendResponse;
}
/**
* For 304 Not modified responses, adds a "Last-Modified" header with the
* value of the "If-Modified-Since" header passed in the request. This
* header is required to be able to reuse match the cache entry for
* subsequent requests but as defined in http specifications it is not
* included in 304 responses by backend servers. This header will not be
* included in the resulting response.
*/
private void storeRequestIfModifiedSinceFor304Response(
HttpRequest request, HttpResponse backendResponse) {
if (backendResponse.getStatusLine().getStatusCode() == HttpStatus.SC_NOT_MODIFIED) {
Header h = request.getFirstHeader("If-Modified-Since");
if (h != null) {
backendResponse.addHeader("Last-Modified", h.getValue());
}
}
}
private boolean alreadyHaveNewerCacheEntry(HttpHost target, HttpRequest request,
HttpResponse backendResponse) {
HttpCacheEntry existing = null;
try {
existing = responseCache.getCacheEntry(target, request);
} catch (IOException ioe) {
// nop
}
if (existing == null) return false;
Header entryDateHeader = existing.getFirstHeader(HTTP.DATE_HEADER);
if (entryDateHeader == null) return false;
Header responseDateHeader = backendResponse.getFirstHeader(HTTP.DATE_HEADER);
if (responseDateHeader == null) return false;
try {
Date entryDate = DateUtils.parseDate(entryDateHeader.getValue());
Date responseDate = DateUtils.parseDate(responseDateHeader.getValue());
return responseDate.before(entryDate);
} catch (DateParseException e) {
// Empty on Purpose
}
return false;
}
}