Truncate times to milliseconds to avoid rounding issues on prometheus

Fixes #212

pkg/promclient/time_truncate.go

@@ -0,0 +1,49 @@
+package promclient
+
+import (
+	"context"
+	"time"
+
+	"github.com/prometheus/client_golang/api"
+	v1 "github.com/prometheus/client_golang/api/prometheus/v1"
+	"github.com/prometheus/common/model"
+	"github.com/prometheus/prometheus/pkg/labels"
+)
+
+func NewTimeTruncate(a API) *TimeTruncate {
+	return &TimeTruncate{a}
+}
+
+const truncateDuration = time.Millisecond
+
+// TimeTruncate is a workaround to https://github.com/jacksontj/promxy/issues/212
+// context: https://github.com/prometheus/prometheus/issues/5972
+// For now we need to truncate the time so that prometheus doesn't round up and return no data <= the timestamp
+// we requested
+type TimeTruncate struct {
+	API
+}
+
+// Query performs a query for the given time.
+func (t *TimeTruncate) Query(ctx context.Context, query string, ts time.Time) (model.Value, api.Warnings, error) {
+	return t.API.Query(ctx, query, ts.Truncate(truncateDuration))
+}
+
+// QueryRange performs a query for the given range.
+func (t *TimeTruncate) QueryRange(ctx context.Context, query string, r v1.Range) (model.Value, api.Warnings, error) {
+	return t.API.QueryRange(ctx, query, v1.Range{
+		Start: r.Start.Truncate(truncateDuration),
+		End:   r.End.Truncate(truncateDuration),
+		Step:  r.Step,
+	})
+}
+
+// Series finds series by label matchers.
+func (t *TimeTruncate) Series(ctx context.Context, matches []string, startTime time.Time, endTime time.Time) ([]model.LabelSet, api.Warnings, error) {
+	return t.API.Series(ctx, matches, startTime.Truncate(truncateDuration), endTime.Truncate(truncateDuration))
+}
+
+// GetValue loads the raw data for a given set of matchers in the time range
+func (t *TimeTruncate) GetValue(ctx context.Context, start, end time.Time, matchers []*labels.Matcher) (model.Value, api.Warnings, error) {
+	return t.API.GetValue(ctx, start.Truncate(truncateDuration), end.Truncate(truncateDuration), matchers)
+}

pkg/proxystorage/proxy.go

@@ -95,7 +95,7 @@ func (p *ProxyStorage) ApplyConfig(c *proxyconfig.Config) error {
 		newState.sgs[i] = tmp
 		apis[i] = tmp
 	}
-	newState.client = promclient.NewMultiAPI(apis, model.TimeFromUnix(0), nil, len(apis))
+	newState.client = promclient.NewTimeTruncate(promclient.NewMultiAPI(apis, model.TimeFromUnix(0), nil, len(apis)))
 
 	if failed {
 		newState.Cancel(nil)