rcCount
} refreshCountsEnum;
+/**
+ * Flags indicating which staleness algorithm has been applied.
+ */
typedef struct {
- bool expires;
- bool min;
- bool lmfactor;
- bool max;
+ bool expires; ///< Expires: header absolute timestamp limit
+ bool min; ///< Heuristic minimum age limited
+ bool lmfactor; ///< Last-Modified with heuristic determines limit
+ bool max; ///< Configured maximum age limit
} stale_flags;
/*
const char *proto;
int total;
int status[STALE_DEFAULT + 1];
-}
-
-refreshCounts[rcCount];
+} refreshCounts[rcCount];
/*
* Defaults:
/**
* Calculate how stale the response is (or will be at the check_time).
- * Staleness calculation is based on the following: (1) response
- * expiration time, (2) age greater than configured maximum, (3)
- * last-modified factor, and (4) age less than configured minimum.
+ *
+ * We try the following ways until one gives a result:
+ *
+ * 1. response expiration time, if one was set
+ * 2. age greater than configured maximum
+ * 3. last-modified factor algorithm
+ * 4. age less than configured minimum
+ * 5. default (stale)
+ *
+ * \param entry the StoreEntry being examined
+ * \param check_time the time (maybe future) at which we want to know whether $
+ * \param age the age of the entry at check_time
+ * \param R the refresh_pattern rule that matched this entry
+ * \param sf small struct to indicate reason for stale/fresh decision
*
* \retval -1 If the response is fresh.
- * \retval >0 Otherwise return it's staleness.
+ * \retval >0 The amount of staleness.
* \retval 0 NOTE return value of 0 means the response is stale.
- *
- * The 'stale_flags' structure is used to tell the calling function
- * _why_ this response is fresh or stale. Its used, for example,
- * when the admin wants to override expiration and last-modified
- * times.
*/
static int
refreshStaleness(const StoreEntry * entry, time_t check_time, const time_t age, const RefreshPattern * R, stale_flags * sf)
{
- /** \par
- * Check for an explicit expiration time (Expires: header).
- */
+ // 1. If the cached object has an explicit expiration time, then we rely on this and
+ // completely ignore the Min, Percent and Max values in the refresh_pattern.
if (entry->expires > -1) {
sf->expires = true;
}
}
- /** \par
- * Use local heuristics to determine staleness. Start with the
- * max age from the refresh_pattern rule.
- */
+ debugs(22, 3, "No explicit expiry given, using heuristics to determine freshness");
+
+ // 2. If the entry is older than the maximum age in the refresh_pattern, it is STALE.
if (age > R->max) {
debugs(22, 3, "STALE: age " << age << " > max " << R->max << " ");
sf->max = true;
return (age - R->max);
}
- /** \par
- * Try the last-modified factor algorithm: refresh_pattern n% percentage of Last-Modified: age.
- */
+ // 3. If there is a Last-Modified header, try the last-modified factor algorithm.
if (entry->lastmod > -1 && entry->timestamp > entry->lastmod) {
- /*
- * stale_age is the Age of the response when it became/becomes
- * stale according to the last-modified factor algorithm.
+
+ /* lastmod_delta is the difference between the last-modified date of the response
+ * and the time we cached it. It's how "old" the response was when we got it.
+ */
+ time_t lastmod_delta = entry->timestamp - entry->lastmod;
+
+ /* stale_age is the age of the response when it became/becomes stale according to
+ * the last-modified factor algorithm. It's how long we can consider the response
+ * fresh from the time we cached it.
*/
- time_t stale_age = static_cast<time_t>((entry->timestamp - entry->lastmod) * R->pct);
+ time_t stale_age = static_cast<time_t>(lastmod_delta * R->pct);
+
+ debugs(22,3, "Last modified " << lastmod_delta << " sec before we cached it, L-M factor " <<
+ (100.0 * R->pct) << "% = " << stale_age << " sec freshness lifetime");
sf->lmfactor = true;
if (age >= stale_age) {
}
}
- /** \par
- * Finally, if all else fails; staleness is determined by the refresh_pattern
- * configured minimum age.
- */
+ // 4. If the entry is not as old as the minimum age in the refresh_pattern, it is FRESH.
if (age < R->min) {
- debugs(22, 3, "FRESH: age " << age << " < min " << R->min);
+ debugs(22, 3, "FRESH: age (" << age << " sec) is less than configured minimum (" << R->min << " sec)");
sf->min = true;
return -1;
}
- debugs(22, 3, "STALE: age " << age << " >= min " << R->min);
+ // 5. default is stale, by the amount we missed the minimum by
+ debugs(22, 3, "STALE: No explicit expiry, no last modified, and older than configured minimum.");
return (age - R->min);
}
-/**
- * \retval 1 if the entry must be revalidated within delta seconds
- * \retval 0 otherwise
+/** Checks whether a store entry is fresh or stale, and why.
+ *
+ * This is where all aspects of request, response and squid configuration
+ * meet to decide whether a response is cacheable or not:
+ *
+ * 1. Client request headers that affect cacheability, e.g.
+ * - Cache-Control: no-cache
+ * - Cache-Control: max-age=N
+ * - Cache-Control: max-stale[=N]
+ * - Pragma: no-cache
+ *
+ * 2. Server response headers that affect cacheability, e.g.
+ * - Age:
+ * - Cache-Control: proxy-revalidate
+ * - Cache-Control: must-revalidate
+ * - Cache-Control: no-cache
+ * - Cache-Control: max-age=N
+ * - Cache-Control: s-maxage=N
+ * - Date:
+ * - Expires:
+ * - Last-Modified:
+ *
+ * 3. Configuration options, e.g.
+ * - reload-into-ims (refresh_pattern)
+ * - ignore-reload (refresh_pattern)
+ * - refresh-ims (refresh_pattern)
+ * - override-lastmod (refresh_pattern)
+ * - override-expire (refresh_pattern)
+ * - reload_into_ims (global option)
+ * - refresh_all_ims (global option)
+ *
+ * \returns a status code (from enum above):
+ * - FRESH_REQUEST_MAX_STALE_ALL
+ * - FRESH_REQUEST_MAX_STALE_VALUE
+ * - FRESH_EXPIRES
+ * - FRESH_LMFACTOR_RULE
+ * - FRESH_MIN_RULE
+ * - FRESH_OVERRIDE_EXPIRES
+ * - FRESH_OVERRIDE_LASTMOD
+ * - STALE_MUST_REVALIDATE
+ * - STALE_RELOAD_INTO_IMS
+ * - STALE_FORCED_RELOAD
+ * - STALE_EXCEEDS_REQUEST_MAX_AGE_VALUE
+ * - STALE_EXPIRES
+ * - STALE_MAX_RULE
+ * - STALE_LMFACTOR_RULE
+ * - STALE_MAX_STALE
+ * - STALE_DEFAULT
+ *
+ * \note request may be NULL (e.g. for cache digests build)
*
- * note: request maybe null (e.g. for cache digests build)
+ * \note the store entry being examined is not necessarily cached (e.g. if
+ * this response is being evaluated for the first time)
*/
static int
refreshCheck(const StoreEntry * entry, HttpRequest * request, time_t delta)
{
- const RefreshPattern *R;
const char *uri = NULL;
time_t age = 0;
time_t check_time = squid_curtime + delta;
int staleness;
stale_flags sf;
+ // get the URL of this entry, if there is one
if (entry->mem_obj)
uri = entry->mem_obj->storeId();
else if (request)
uri = urlCanonical(request);
- debugs(22, 3, "refreshCheck: '" << (uri ? uri : "<none>") << "'");
+ debugs(22, 3, "checking freshness of '" << (uri ? uri : "<none>") << "'");
+ // age is not necessarily the age now, but the age at the given check_time
if (check_time > entry->timestamp)
age = check_time - entry->timestamp;
// FIXME: what to do when age < 0 or counter overflow?
assert(age >= 0);
- R = uri ? refreshLimits(uri) : refreshUncompiledPattern(".");
-
+ /* We need a refresh rule. In order of preference:
+ *
+ * 1. the rule that matches this URI by regex
+ * 2. the "." rule from the config file
+ * 3. the default "." rule
+ */
+ const RefreshPattern *R = uri ? refreshLimits(uri) : refreshUncompiledPattern(".");
if (NULL == R)
R = &DefaultRefresh;
- debugs(22, 3, "refreshCheck: Matched '" << R->pattern << " " <<
+ debugs(22, 3, "Matched '" << R->pattern << " " <<
(int) R->min << " " << (int) (100.0 * R->pct) << "%% " <<
(int) R->max << "'");
entry->mem_obj->getReply()->cache_control->hasStaleIfError() &&
entry->mem_obj->getReply()->cache_control->staleIfError() < staleness) {
- debugs(22, 3, "refreshCheck: stale-if-error period expired.");
+ debugs(22, 3, "stale-if-error period expired. Will produce error if validation fails.");
request->flags.failOnValidationError = true;
}
+ /* If the origin server specified either of:
+ * Cache-Control: must-revalidate
+ * Cache-Control: proxy-revalidate
+ * the spec says the response must always be revalidated if stale.
+ */
if (EBIT_TEST(entry->flags, ENTRY_REVALIDATE) && staleness > -1
#if USE_HTTP_VIOLATIONS
&& !R->flags.ignore_must_revalidate
#endif
) {
- debugs(22, 3, "refreshCheck: YES: Must revalidate stale response");
+ debugs(22, 3, "YES: Must revalidate stale object (origin set must-revalidate or proxy-revalidate)");
if (request)
request->flags.failOnValidationError = true;
return STALE_MUST_REVALIDATE;
if (request && !request->flags.ignoreCc) {
HttpHdrCc *cc = request->cache_control;
+ /* If the request is an IMS request, and squid is configured NOT to service this from cache
+ * (either by 'refresh-ims' in the refresh pattern or 'refresh_all_ims on' globally)
+ * then force a reload from the origin.
+ */
if (request->flags.ims && (R->flags.refresh_ims || Config.onoff.refresh_all_ims)) {
- /* The clients no-cache header is changed into a IMS query */
- debugs(22, 3, "refreshCheck: YES: refresh-ims");
+ // The client's no-cache header is changed into a IMS query
+ debugs(22, 3, "YES: Client IMS request forcing revalidation of object (refresh-ims option)");
return STALE_FORCED_RELOAD;
}
#if USE_HTTP_VIOLATIONS
-
- if (!request->flags.noCacheHack()) {
- (void) 0;
- } else if (R->flags.ignore_reload) {
- /* The clients no-cache header is ignored */
- debugs(22, 3, "refreshCheck: MAYBE: ignore-reload");
- } else if (R->flags.reload_into_ims || Config.onoff.reload_into_ims) {
- /* The clients no-cache header is changed into a IMS query */
- debugs(22, 3, "refreshCheck: YES: reload-into-ims");
- return STALE_RELOAD_INTO_IMS;
- } else {
- /* The clients no-cache header is not overridden on this request */
- debugs(22, 3, "refreshCheck: YES: client reload");
- request->flags.noCache = true;
- return STALE_FORCED_RELOAD;
+ /* Normally a client reload request ("Cache-Control: no-cache" or "Pragma: no-cache")
+ * means we must treat this reponse as STALE and fetch a new one.
+ *
+ * However, some options exist to override this behaviour. For example, we might just
+ * revalidate our existing response, or even just serve it up without revalidating it.
+ *
+ * ---- Note on the meaning of nocache_hack -----
+ *
+ * The nocache_hack flag has a very specific and complex meaning:
+ *
+ * (a) this is a reload request ("Cache-Control: no-cache" or "Pragma: no-cache" header)
+ * and (b) the configuration file either has at least one refresh_pattern with
+ * ignore-reload or reload-into-ims (not necessarily the rule matching this request) or
+ * the global reload_into_ims is set to on
+ *
+ * In other words: this is a client reload, and we might need to override
+ * the default behaviour (but we might not).
+ *
+ * "nocache_hack" is a pretty deceptive name for such a complicated meaning.
+ */
+ if (request->flags.noCacheHack()) {
+
+ if (R->flags.ignore_reload) {
+ /* The client's no-cache header is ignored completely - we'll try to serve
+ * what we have (assuming it's still fresh, etc.)
+ */
+ debugs(22, 3, "MAYBE: Ignoring client reload request - trying to serve from cache (ignore-reload option)");
+ } else if (R->flags.reload_into_ims || Config.onoff.reload_into_ims) {
+ /* The client's no-cache header is not honoured completely - we'll just try
+ * to revalidate our cached copy (IMS to origin) instead of fetching a new
+ * copy with an unconditional GET.
+ */
+ debugs(22, 3, "YES: Client reload request - cheating, only revalidating with origin (reload-into-ims option)");
+ return STALE_RELOAD_INTO_IMS;
+ } else {
+ /* The client's no-cache header is honoured - we fetch a new copy from origin */
+ debugs(22, 3, "YES: Client reload request - fetching new copy from origin");
+ request->flags.noCache = true;
+ return STALE_FORCED_RELOAD;
+ }
}
-
#endif
+
+ // Check the Cache-Control client request header
if (NULL != cc) {
+
+ // max-age directive
if (cc->hasMaxAge()) {
#if USE_HTTP_VIOLATIONS
+ // Ignore client "Cache-Control: max-age=0" header
if (R->flags.ignore_reload && cc->maxAge() == 0) {
- debugs(22, 3, "refreshCheck: MAYBE: client-max-age = 0 and ignore-reload");
+ debugs(22, 3, "MAYBE: Ignoring client reload request - trying to serve from cache (ignore-reload option)");
} else
#endif
{
- if (cc->maxAge() == 0) {
- debugs(22, 3, "refreshCheck: YES: client-max-age = 0");
- return STALE_EXCEEDS_REQUEST_MAX_AGE_VALUE;
- }
-
- if (age > cc->maxAge()) {
- debugs(22, 3, "refreshCheck: YES: age > client-max-age");
+ // Honour client "Cache-Control: max-age=x" header
+ if (age > cc->maxAge() || cc->maxAge() == 0) {
+ debugs(22, 3, "YES: Revalidating object - client 'Cache-Control: max-age=" << cc->maxAge() << "'");
return STALE_EXCEEDS_REQUEST_MAX_AGE_VALUE;
}
}
}
+ // max-stale directive
if (cc->hasMaxStale() && staleness > -1) {
if (cc->maxStale()==HttpHdrCc::MAX_STALE_ANY) {
- /* max-stale directive without a value */
- debugs(22, 3, "refreshCheck: NO: max-stale wildcard");
+ debugs(22, 3, "NO: Client accepts a stale response of any age - 'Cache-Control: max-stale'");
return FRESH_REQUEST_MAX_STALE_ALL;
} else if (staleness < cc->maxStale()) {
- debugs(22, 3, "refreshCheck: NO: staleness < max-stale");
+ debugs(22, 3, "NO: Client accepts a stale response - 'Cache-Control: max-stale=" << cc->maxStale() << "'");
return FRESH_REQUEST_MAX_STALE_VALUE;
}
}
}
}
+ // If the object is fresh, return the right FRESH_ code
if (-1 == staleness) {
- debugs(22, 3, "refreshCheck: object isn't stale..");
+ debugs(22, 3, "Object isn't stale..");
if (sf.expires) {
- debugs(22, 3, "refreshCheck: returning FRESH_EXPIRES");
+ debugs(22, 3, "returning FRESH_EXPIRES");
return FRESH_EXPIRES;
}
assert(!sf.max);
if (sf.lmfactor) {
- debugs(22, 3, "refreshCheck: returning FRESH_LMFACTOR_RULE");
+ debugs(22, 3, "returning FRESH_LMFACTOR_RULE");
return FRESH_LMFACTOR_RULE;
}
assert(sf.min);
- debugs(22, 3, "refreshCheck: returning FRESH_MIN_RULE");
+ debugs(22, 3, "returning FRESH_MIN_RULE");
return FRESH_MIN_RULE;
}
*/
int max_stale = (R->max_stale >= 0 ? R->max_stale : Config.maxStale);
if ( max_stale >= 0 && staleness > max_stale) {
- debugs(22, 3, "refreshCheck: YES: max-stale limit");
+ debugs(22, 3, "YES: refresh_pattern max-stale=N limit from squid.conf");
if (request)
request->flags.failOnValidationError = true;
return STALE_MAX_STALE;
#if USE_HTTP_VIOLATIONS
if (R->flags.override_expire && age < R->min) {
- debugs(22, 3, "refreshCheck: NO: age < min && override-expire");
+ debugs(22, 3, "NO: Serving from cache - even though explicit expiry has passed, we enforce Min value (override-expire option)");
return FRESH_OVERRIDE_EXPIRES;
}
if (sf.lmfactor) {
#if USE_HTTP_VIOLATIONS
-
if (R->flags.override_lastmod && age < R->min) {
- debugs(22, 3, "refreshCheck: NO: age < min && override-lastmod");
+ debugs(22, 3, "NO: Serving from cache - even though L-M factor says the object is stale, we enforce Min value (override-lastmod option)");
return FRESH_OVERRIDE_LASTMOD;
}
-
#endif
+ debugs(22, 3, "YES: L-M factor says the object is stale'");
return STALE_LMFACTOR_RULE;
}
- debugs(22, 3, "refreshCheck: returning STALE_DEFAULT");
+ debugs(22, 3, "returning STALE_DEFAULT");
return STALE_DEFAULT;
}
-int
+/**
+ * This is called by http.cc once it has received and parsed the origin server's
+ * response headers. It uses the result as part of its algorithm to decide whether a
+ * response should be cached.
+ *
+ * \retval true if the entry is cacheable, regardless of whether FRESH or STALE
+ * \retval false if the entry is not cacheable
+ *
+ * TODO: this algorithm seems a bit odd and might not be quite right. Verify against HTTPbis.
+ */
+bool
refreshIsCachable(const StoreEntry * entry)
{
/*
if (reason < STALE_MUST_REVALIDATE)
/* Does not need refresh. This is certainly cachable */
- return 1;
+ return true;
if (entry->lastmod < 0)
/* Last modified is needed to do a refresh */
- return 0;
+ return false;
if (entry->mem_obj == NULL)
/* no mem_obj? */
- return 1;
+ return true;
if (entry->getReply() == NULL)
/* no reply? */
- return 1;
+ return true;
if (entry->getReply()->content_length == 0)
/* No use refreshing (caching?) 0 byte objects */
- return 0;
+ return false;
/* This seems to be refreshable. Cache it */
- return 1;
+ return true;
}
/// whether reply is stale if it is a hit
}
}
-/* refreshCheck... functions below are protocol-specific wrappers around
- * refreshCheck() function above */
-
+/**
+ * Protocol-specific wrapper around refreshCheck() function.
+ *
+ * Note the reason for STALE/FRESH then return true/false respectively.
+ *
+ * \retval 1 if STALE
+ * \retval 0 if FRESH
+ */
int
refreshCheckHTTP(const StoreEntry * entry, HttpRequest * request)
{
return (Config.onoff.offline || reason < 200) ? 0 : 1;
}
+/// \see int refreshCheckHTTP(const StoreEntry * entry, HttpRequest * request)
int
refreshCheckICP(const StoreEntry * entry, HttpRequest * request)
{
}
#if USE_HTCP
+/// \see int refreshCheckHTTP(const StoreEntry * entry, HttpRequest * request)
int
refreshCheckHTCP(const StoreEntry * entry, HttpRequest * request)
{
#endif
#if USE_CACHE_DIGESTS
+/// \see int refreshCheckHTTP(const StoreEntry * entry, HttpRequest * request)
int
refreshCheckDigest(const StoreEntry * entry, time_t delta)
{
++ refreshCounts[rcCDigest].status[reason];
return (reason < 200) ? 0 : 1;
}
-
#endif
+/**
+ * Get the configured maximum caching time for objects with this URL
+ * according to refresh_pattern.
+ *
+ * Used by http.cc when generating a upstream requests to ensure that
+ * responses it is given are fresh enough to be worth caching.
+ *
+ * \retval pattern-max if there is a refresh_pattern matching the URL configured.
+ * \retval REFRESH_DEFAULT_MAX if there are no explicit limits configured
+ */
time_t
getMaxAge(const char *url)
{
sum += refreshCountsStatsEntry(sentry, rc, FRESH_EXPIRES, "Fresh: expires time not reached");
sum += refreshCountsStatsEntry(sentry, rc, FRESH_LMFACTOR_RULE, "Fresh: refresh_pattern last-mod factor percentage");
sum += refreshCountsStatsEntry(sentry, rc, FRESH_MIN_RULE, "Fresh: refresh_pattern min value");
- sum += refreshCountsStatsEntry(sentry, rc, FRESH_OVERRIDE_EXPIRES, "Fresh: refresh_pattern override expires");
- sum += refreshCountsStatsEntry(sentry, rc, FRESH_OVERRIDE_LASTMOD, "Fresh: refresh_pattern override lastmod");
+ sum += refreshCountsStatsEntry(sentry, rc, FRESH_OVERRIDE_EXPIRES, "Fresh: refresh_pattern override-expires");
+ sum += refreshCountsStatsEntry(sentry, rc, FRESH_OVERRIDE_LASTMOD, "Fresh: refresh_pattern override-lastmod");
sum += refreshCountsStatsEntry(sentry, rc, STALE_MUST_REVALIDATE, "Stale: response has must-revalidate");
sum += refreshCountsStatsEntry(sentry, rc, STALE_RELOAD_INTO_IMS, "Stale: changed reload into IMS");
sum += refreshCountsStatsEntry(sentry, rc, STALE_FORCED_RELOAD, "Stale: request has no-cache directive");
projects / thirdparty / squid.git / commitdiff
