Quietly truncate queries ranging into future (#532)

To fix #472
Grafana queries for current month/year would mostly fail due to
weekly tables not existing into future.
Fix is to detect end of time range is future and quietly change to now
Additionally if begin of time-range is future, then immediately return empty resultset

Author: meccanorak

pkg/chunk/chunk_store.go

@@ -155,6 +155,19 @@ func (c *Store) Get(ctx context.Context, from, through model.Time, allMatchers .
 		return nil, fmt.Errorf("invalid query, through < from (%d < %d)", through, from)
 	}
 
+	now := model.Now()
+	if from.After(now) {
+		// time-span start is in future ... regard as legal
+		util.WithContext(ctx).Debugf("Whole timerange %v..%v in future (now=%v) yield empty resultset", through, from, now)
+		return []local.SeriesIterator{}, nil
+	}
+
+	if through.After(now) {
+		// time-span end is in future ... regard as legal
+		util.WithContext(ctx).Debugf("Adjusting end timerange=%v from future to now=%v", through, now)
+		through = now // Avoid processing future part - otherwise some schemas could fail with eg non-existent table gripes
+	}
+
 	// Fetch metric name chunks if the matcher is of type equal,
 	metricNameMatcher, matchers, ok := util.ExtractMetricNameMatcherFromMatchers(allMatchers)
 	if ok && metricNameMatcher.Type == metric.Equal {

pkg/chunk/chunk_store_test.go

@@ -165,12 +165,30 @@ func TestChunkStore_Get_concrete(t *testing.T) {
 					t.Fatal(err)
 				}
 
-				iterators, err := store.Get(ctx, now.Add(-time.Hour), now, tc.matchers...)
+				// Query with ordinary time-range
+				iterators1, err := store.Get(ctx, now.Add(-time.Hour), now, tc.matchers...)
 				require.NoError(t, err)
 
-				sort.Sort(ByFingerprint(iterators))
-				if !reflect.DeepEqual(tc.expect, iterators) {
-					t.Fatalf("%s: wrong chunks - %s", tc.query, test.Diff(tc.expect, iterators))
+				sort.Sort(ByFingerprint(iterators1))
+				if !reflect.DeepEqual(tc.expect, iterators1) {
+					t.Fatalf("%s: wrong chunks - %s", tc.query, test.Diff(tc.expect, iterators1))
+				}
+
+				// Pushing end of time-range into future should yield exact same resultset
+				iterators2, err := store.Get(ctx, now.Add(-time.Hour), now.Add(time.Hour*24*30), tc.matchers...)
+				require.NoError(t, err)
+
+				sort.Sort(ByFingerprint(iterators2))
+				if !reflect.DeepEqual(tc.expect, iterators2) {
+					t.Fatalf("%s: wrong chunks - %s", tc.query, test.Diff(tc.expect, iterators2))
+				}
+
+				// Query with both begin & end of time-range in future should yield empty resultset
+				iterators3, err := store.Get(ctx, now.Add(time.Hour), now.Add(time.Hour*2), tc.matchers...)
+				require.NoError(t, err)
+				if len(iterators3) != 0 {
+					t.Fatalf("%s: future query should yield empty resultset ... actually got %v chunks: %#v",
+						tc.query, len(iterators3), iterators3)
 				}
 			})
 		}