Fix caching of requests with relative end time.

The logic to determine whether a cache file was stale was wrong when
the end time was relative.  More specifically, as long as the `end'
parameter was given, the cached file wouldn't be regenerated.  Also
the mtime of the cached file was compared against the end time of the
request instead of being compared to the current time to determine how
old the file is.

Change-Id: I77b810b26566f6b1fa9fc3bfffc1b862d16aa660

src/tsd/GraphHandler.java

@@ -133,7 +133,7 @@ private void doGraph(final TSDB tsdb, final HttpQuery query)
  final int max_age = (end_time > now ? 0 // (1)
  : (end_time < now - Const.MAX_TIMESPAN ? 86400 // (2)
  : (int) (end_time - start_time) >> 10)); // (3)
- if (isDiskCacheHit(query, max_age, end_time, basepath)) {
+ if (isDiskCacheHit(query, max_age, basepath)) {
  return;
  }
  Query[] tsdbqueries;
@@ -332,16 +332,13 @@ private String getGnuplotBasePath(final HttpQuery query) {
  * @param query The query to serve.
  * @param max_age The maximum time (in seconds) we wanna allow clients to
  * cache the result in case of a cache hit.
- * @param end_time The UNIX timestamp corresponding to the {@code end}
- * query string parameter, or corresponding to "now" if it wasn't given.
  * @param basepath The base path used for the Gnuplot files.
  * @return {@code true} if this request was served from disk (in which
  * case processing can stop here), {@code false} otherwise (in which case
  * the query needs to be processed).
  */
  private boolean isDiskCacheHit(final HttpQuery query,
  final int max_age,
- final long end_time,
  final String basepath) throws IOException {
  final String cachepath = basepath + (query.hasQueryStringParam("ascii")
  ? ".dat" : ".png");
@@ -354,13 +351,11 @@ private boolean isDiskCacheHit(final HttpQuery query,
  + bytes + " bytes) to be valid. Ignoring it.");
  return false;
  }
- logInfo(query, "Found cached file @ " + cachepath + " bytes: " + bytes);
- if (staleCacheFile(query, max_age, end_time, cachedfile)) {
+ if (staleCacheFile(query, max_age, cachedfile)) {
  return false;
  }
  if (query.hasQueryStringParam("json")) {
- StringBuilder json = loadCachedJson(query, max_age, end_time,
- basepath);
+ StringBuilder json = loadCachedJson(query, max_age, basepath);
  if (json == null) {
  json = new StringBuilder(32);
  json.append("{\"timing\":");
@@ -381,8 +376,7 @@ private boolean isDiskCacheHit(final HttpQuery query,
  }
  // We didn't find an image. Do a negative cache check. If we've seen
  // this query before but there was no result, we at least wrote the JSON.
- final StringBuilder json = loadCachedJson(query, max_age, end_time,
- basepath);
+ final StringBuilder json = loadCachedJson(query, max_age, basepath);
  // If we don't have a JSON file it's a complete cache miss. If we have
  // one, and it says 0 data points were plotted, it's a negative cache hit.
  if (json == null || !json.toString().contains("\"plotted\":0")) {
@@ -408,23 +402,22 @@ private boolean isDiskCacheHit(final HttpQuery query,
  * @param query The query to serve.
  * @param max_age The maximum time (in seconds) we wanna allow clients to
  * cache the result in case of a cache hit.
- * @param end_time The UNIX timestamp corresponding to the {@code end}
- * query string parameter, or corresponding to "now" if it wasn't given.
  * @param cachedfile The file to check for staleness.
  */
  private boolean staleCacheFile(final HttpQuery query,
  final long max_age,
- final long end_time,
  final File cachedfile) {
  // Queries that don't specify an end-time must be handled carefully,
  // since time passes and we may need to regenerate the results in case
  // new data points have arrived in the mean time.
- if (!query.hasQueryStringParam("end")) {
+ final String end = query.getQueryStringParam("end");
+ if (end == null || end.endsWith("ago")) {
+ // How many seconds stale?
  final long mtime = cachedfile.lastModified() / 1000;
- final long staleness = end_time - mtime; // How many seconds stale?
+ final long staleness = System.currentTimeMillis() / 1000 - mtime;
  if (staleness < 0) { // Can happen if the mtime is "in the future".
  logWarn(query, "Not using file @ " + cachedfile + " with weird"
- + " mtime=" + mtime + " > request end_time=" + end_time);
+ + " mtime in the future: " + mtime);
  return true;
  }
  // If our graph is older than 0.1% of the duration of the request,
@@ -487,8 +480,6 @@ private static byte[] readFile(final HttpQuery query,
  * @param query The query to serve.
  * @param max_age The maximum time (in seconds) we wanna allow clients to
  * cache the result in case of a cache hit.
- * @param end_time The UNIX timestamp corresponding to the {@code end}
- * query string parameter, or corresponding to "now" if it wasn't given.
  * @param basepath The base path used for the Gnuplot files.
  * @return {@code null} in case no file was found, or the contents of the
  * file if it was found. In case some contents was found, it is truncated
@@ -497,12 +488,10 @@ private static byte[] readFile(final HttpQuery query,
  */
  private StringBuilder loadCachedJson(final HttpQuery query,
  final long max_age,
- final long end_time,
  final String basepath) {
  final String json_path = basepath + ".json";
  File json_cache = new File(json_path);
- if (!json_cache.exists() || staleCacheFile(query, max_age, end_time,
- json_cache)) {
+ if (!json_cache.exists() || staleCacheFile(query, max_age, json_cache)) {
  return null;
  }
  final byte[] json = readFile(query, json_cache, 4096);