okhttp3.internal.cache.CacheStrategy Maven / Gradle / Ivy
/*
* Copyright (C) 2013 Square, Inc.
*
* 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 okhttp3.internal.cache;
import java.util.Date;
import javax.annotation.Nullable;
import okhttp3.CacheControl;
import okhttp3.Headers;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.internal.Internal;
import okhttp3.internal.http.HttpDate;
import okhttp3.internal.http.HttpHeaders;
import okhttp3.internal.http.StatusLine;
import static java.net.HttpURLConnection.HTTP_BAD_METHOD;
import static java.net.HttpURLConnection.HTTP_GONE;
import static java.net.HttpURLConnection.HTTP_MOVED_PERM;
import static java.net.HttpURLConnection.HTTP_MOVED_TEMP;
import static java.net.HttpURLConnection.HTTP_MULT_CHOICE;
import static java.net.HttpURLConnection.HTTP_NOT_AUTHORITATIVE;
import static java.net.HttpURLConnection.HTTP_NOT_FOUND;
import static java.net.HttpURLConnection.HTTP_NOT_IMPLEMENTED;
import static java.net.HttpURLConnection.HTTP_NO_CONTENT;
import static java.net.HttpURLConnection.HTTP_OK;
import static java.net.HttpURLConnection.HTTP_REQ_TOO_LONG;
import static java.util.concurrent.TimeUnit.SECONDS;
/**
* Given a request and cached response, this figures out whether to use the network, the cache, or
* both.
*
* Selecting a cache strategy may add conditions to the request (like the "If-Modified-Since"
* header for conditional GETs) or warnings to the cached response (if the cached data is
* potentially stale).
*/
public final class CacheStrategy {
/** The request to send on the network, or null if this call doesn't use the network. */
public final @Nullable Request networkRequest;
/** The cached response to return or validate; or null if this call doesn't use a cache. */
public final @Nullable Response cacheResponse;
CacheStrategy(Request networkRequest, Response cacheResponse) {
this.networkRequest = networkRequest;
this.cacheResponse = cacheResponse;
}
/** Returns true if {@code response} can be stored to later serve another request. */
public static boolean isCacheable(Response response, Request request) {
// Always go to network for uncacheable response codes (RFC 7231 section 6.1),
// This implementation doesn't support caching partial content.
switch (response.code()) {
case HTTP_OK:
case HTTP_NOT_AUTHORITATIVE:
case HTTP_NO_CONTENT:
case HTTP_MULT_CHOICE:
case HTTP_MOVED_PERM:
case HTTP_NOT_FOUND:
case HTTP_BAD_METHOD:
case HTTP_GONE:
case HTTP_REQ_TOO_LONG:
case HTTP_NOT_IMPLEMENTED:
case StatusLine.HTTP_PERM_REDIRECT:
// These codes can be cached unless headers forbid it.
break;
case HTTP_MOVED_TEMP:
case StatusLine.HTTP_TEMP_REDIRECT:
// These codes can only be cached with the right response headers.
// http://tools.ietf.org/html/rfc7234#section-3
// s-maxage is not checked because OkHttp is a private cache that should ignore s-maxage.
if (response.header("Expires") != null
|| response.cacheControl().maxAgeSeconds() != -1
|| response.cacheControl().isPublic()
|| response.cacheControl().isPrivate()) {
break;
}
// Fall-through.
default:
// All other codes cannot be cached.
return false;
}
// A 'no-store' directive on request or response prevents the response from being cached.
return !response.cacheControl().noStore() && !request.cacheControl().noStore();
}
public static class Factory {
final long nowMillis;
final Request request;
final Response cacheResponse;
/** The server's time when the cached response was served, if known. */
private Date servedDate;
private String servedDateString;
/** The last modified date of the cached response, if known. */
private Date lastModified;
private String lastModifiedString;
/**
* The expiration date of the cached response, if known. If both this field and the max age are
* set, the max age is preferred.
*/
private Date expires;
/**
* Extension header set by OkHttp specifying the timestamp when the cached HTTP request was
* first initiated.
*/
private long sentRequestMillis;
/**
* Extension header set by OkHttp specifying the timestamp when the cached HTTP response was
* first received.
*/
private long receivedResponseMillis;
/** Etag of the cached response. */
private String etag;
/** Age of the cached response. */
private int ageSeconds = -1;
public Factory(long nowMillis, Request request, Response cacheResponse) {
this.nowMillis = nowMillis;
this.request = request;
this.cacheResponse = cacheResponse;
if (cacheResponse != null) {
this.sentRequestMillis = cacheResponse.sentRequestAtMillis();
this.receivedResponseMillis = cacheResponse.receivedResponseAtMillis();
Headers headers = cacheResponse.headers();
for (int i = 0, size = headers.size(); i < size; i++) {
String fieldName = headers.name(i);
String value = headers.value(i);
if ("Date".equalsIgnoreCase(fieldName)) {
servedDate = HttpDate.parse(value);
servedDateString = value;
} else if ("Expires".equalsIgnoreCase(fieldName)) {
expires = HttpDate.parse(value);
} else if ("Last-Modified".equalsIgnoreCase(fieldName)) {
lastModified = HttpDate.parse(value);
lastModifiedString = value;
} else if ("ETag".equalsIgnoreCase(fieldName)) {
etag = value;
} else if ("Age".equalsIgnoreCase(fieldName)) {
ageSeconds = HttpHeaders.parseSeconds(value, -1);
}
}
}
}
/**
* Returns a strategy to satisfy {@code request} using the a cached response {@code response}.
*/
public CacheStrategy get() {
CacheStrategy candidate = getCandidate();
if (candidate.networkRequest != null && request.cacheControl().onlyIfCached()) {
// We're forbidden from using the network and the cache is insufficient.
return new CacheStrategy(null, null);
}
return candidate;
}
/** Returns a strategy to use assuming the request can use the network. */
private CacheStrategy getCandidate() {
// No cached response.
if (cacheResponse == null) {
return new CacheStrategy(request, null);
}
// Drop the cached response if it's missing a required handshake.
if (request.isHttps() && cacheResponse.handshake() == null) {
return new CacheStrategy(request, null);
}
// If this response shouldn't have been stored, it should never be used
// as a response source. This check should be redundant as long as the
// persistence store is well-behaved and the rules are constant.
if (!isCacheable(cacheResponse, request)) {
return new CacheStrategy(request, null);
}
CacheControl requestCaching = request.cacheControl();
if (requestCaching.noCache() || hasConditions(request)) {
return new CacheStrategy(request, null);
}
CacheControl responseCaching = cacheResponse.cacheControl();
long ageMillis = cacheResponseAge();
long freshMillis = computeFreshnessLifetime();
if (requestCaching.maxAgeSeconds() != -1) {
freshMillis = Math.min(freshMillis, SECONDS.toMillis(requestCaching.maxAgeSeconds()));
}
long minFreshMillis = 0;
if (requestCaching.minFreshSeconds() != -1) {
minFreshMillis = SECONDS.toMillis(requestCaching.minFreshSeconds());
}
long maxStaleMillis = 0;
if (!responseCaching.mustRevalidate() && requestCaching.maxStaleSeconds() != -1) {
maxStaleMillis = SECONDS.toMillis(requestCaching.maxStaleSeconds());
}
if (!responseCaching.noCache() && ageMillis + minFreshMillis < freshMillis + maxStaleMillis) {
Response.Builder builder = cacheResponse.newBuilder();
if (ageMillis + minFreshMillis >= freshMillis) {
builder.addHeader("Warning", "110 HttpURLConnection \"Response is stale\"");
}
long oneDayMillis = 24 * 60 * 60 * 1000L;
if (ageMillis > oneDayMillis && isFreshnessLifetimeHeuristic()) {
builder.addHeader("Warning", "113 HttpURLConnection \"Heuristic expiration\"");
}
return new CacheStrategy(null, builder.build());
}
// Find a condition to add to the request. If the condition is satisfied, the response body
// will not be transmitted.
String conditionName;
String conditionValue;
if (etag != null) {
conditionName = "If-None-Match";
conditionValue = etag;
} else if (lastModified != null) {
conditionName = "If-Modified-Since";
conditionValue = lastModifiedString;
} else if (servedDate != null) {
conditionName = "If-Modified-Since";
conditionValue = servedDateString;
} else {
return new CacheStrategy(request, null); // No condition! Make a regular request.
}
Headers.Builder conditionalRequestHeaders = request.headers().newBuilder();
Internal.instance.addLenient(conditionalRequestHeaders, conditionName, conditionValue);
Request conditionalRequest = request.newBuilder()
.headers(conditionalRequestHeaders.build())
.build();
return new CacheStrategy(conditionalRequest, cacheResponse);
}
/**
* Returns the number of milliseconds that the response was fresh for, starting from the served
* date.
*/
private long computeFreshnessLifetime() {
CacheControl responseCaching = cacheResponse.cacheControl();
if (responseCaching.maxAgeSeconds() != -1) {
return SECONDS.toMillis(responseCaching.maxAgeSeconds());
} else if (expires != null) {
long servedMillis = servedDate != null
? servedDate.getTime()
: receivedResponseMillis;
long delta = expires.getTime() - servedMillis;
return delta > 0 ? delta : 0;
} else if (lastModified != null
&& cacheResponse.request().url().query() == null) {
// As recommended by the HTTP RFC and implemented in Firefox, the
// max age of a document should be defaulted to 10% of the
// document's age at the time it was served. Default expiration
// dates aren't used for URIs containing a query.
long servedMillis = servedDate != null
? servedDate.getTime()
: sentRequestMillis;
long delta = servedMillis - lastModified.getTime();
return delta > 0 ? (delta / 10) : 0;
}
return 0;
}
/**
* Returns the current age of the response, in milliseconds. The calculation is specified by RFC
* 7234, 4.2.3 Calculating Age.
*/
private long cacheResponseAge() {
long apparentReceivedAge = servedDate != null
? Math.max(0, receivedResponseMillis - servedDate.getTime())
: 0;
long receivedAge = ageSeconds != -1
? Math.max(apparentReceivedAge, SECONDS.toMillis(ageSeconds))
: apparentReceivedAge;
long responseDuration = receivedResponseMillis - sentRequestMillis;
long residentDuration = nowMillis - receivedResponseMillis;
return receivedAge + responseDuration + residentDuration;
}
/**
* Returns true if computeFreshnessLifetime used a heuristic. If we used a heuristic to serve a
* cached response older than 24 hours, we are required to attach a warning.
*/
private boolean isFreshnessLifetimeHeuristic() {
return cacheResponse.cacheControl().maxAgeSeconds() == -1 && expires == null;
}
/**
* Returns true if the request contains conditions that save the server from sending a response
* that the client has locally. When a request is enqueued with its own conditions, the built-in
* response cache won't be used.
*/
private static boolean hasConditions(Request request) {
return request.header("If-Modified-Since") != null || request.header("If-None-Match") != null;
}
}
}