scrape: remove unsafe code

The `yolostring` routine was intended to avoid an allocation when
converting from a `[]byte` to a `string` for map lookup.
However, since 2014 Go has recognized this pattern and does not make
a copy of the data when looking up a map. So the unsafe code is not
necessary.

In line with this, constants like `scrapeHealthMetricName` also become
`[]byte`.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

scrape/scrape.go

@@ -27,7 +27,6 @@ import (
 	"strconv"
 	"sync"
 	"time"
-	"unsafe"
 
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
@@ -1006,8 +1005,8 @@ func (c *scrapeCache) iterDone(flushCache bool) {
 	}
 }
 
-func (c *scrapeCache) get(met string) (*cacheEntry, bool) {
+func (c *scrapeCache) get(met []byte) (*cacheEntry, bool) {
-	e, ok := c.series[met]
+	e, ok := c.series[string(met)]
 	if !ok {
 		return nil, false
 	}
@@ -1015,11 +1014,11 @@ func (c *scrapeCache) get(met string) (*cacheEntry, bool) {
 	return e, true
 }
 
-func (c *scrapeCache) addRef(met string, ref storage.SeriesRef, lset labels.Labels, hash uint64) {
+func (c *scrapeCache) addRef(met []byte, ref storage.SeriesRef, lset labels.Labels, hash uint64) {
 	if ref == 0 {
 		return
 	}
-	c.series[met] = &cacheEntry{ref: ref, lastIter: c.iter, lset: lset, hash: hash}
+	c.series[string(met)] = &cacheEntry{ref: ref, lastIter: c.iter, lset: lset, hash: hash}
 }
 
 func (c *scrapeCache) addDropped(met string) {
@@ -1027,8 +1026,8 @@ func (c *scrapeCache) addDropped(met string) {
 	c.droppedSeries[met] = &iter
 }
 
-func (c *scrapeCache) getDropped(met string) bool {
+func (c *scrapeCache) getDropped(met []byte) bool {
-	iterp, ok := c.droppedSeries[met]
+	iterp, ok := c.droppedSeries[string(met)]
 	if ok {
 		*iterp = c.iter
 	}
@@ -1052,7 +1051,7 @@ func (c *scrapeCache) forEachStale(f func(labels.Labels) bool) {
 func (c *scrapeCache) setType(metric []byte, t textparse.MetricType) {
 	c.metaMtx.Lock()
 
-	e, ok := c.metadata[yoloString(metric)]
+	e, ok := c.metadata[string(metric)]
 	if !ok {
 		e = &metaEntry{Metadata: metadata.Metadata{Type: textparse.MetricTypeUnknown}}
 		c.metadata[string(metric)] = e
@@ -1069,12 +1068,12 @@ func (c *scrapeCache) setType(metric []byte, t textparse.MetricType) {
 func (c *scrapeCache) setHelp(metric, help []byte) {
 	c.metaMtx.Lock()
 
-	e, ok := c.metadata[yoloString(metric)]
+	e, ok := c.metadata[string(metric)]
 	if !ok {
 		e = &metaEntry{Metadata: metadata.Metadata{Type: textparse.MetricTypeUnknown}}
 		c.metadata[string(metric)] = e
 	}
-	if e.Help != yoloString(help) {
+	if e.Help != string(help) {
 		e.Help = string(help)
 		e.lastIterChange = c.iter
 	}
@@ -1086,12 +1085,12 @@ func (c *scrapeCache) setHelp(metric, help []byte) {
 func (c *scrapeCache) setUnit(metric, unit []byte) {
 	c.metaMtx.Lock()
 
-	e, ok := c.metadata[yoloString(metric)]
+	e, ok := c.metadata[string(metric)]
 	if !ok {
 		e = &metaEntry{Metadata: metadata.Metadata{Type: textparse.MetricTypeUnknown}}
 		c.metadata[string(metric)] = e
 	}
-	if e.Unit != yoloString(unit) {
+	if e.Unit != string(unit) {
 		e.Unit = string(unit)
 		e.lastIterChange = c.iter
 	}
@@ -1509,7 +1508,7 @@ func (sl *scrapeLoop) append(app storage.Appender, b []byte, contentType string,
 
 		sl.cache.metaMtx.Lock()
 		defer sl.cache.metaMtx.Unlock()
-		metaEntry, metaOk := sl.cache.metadata[yoloString([]byte(lset.Get(labels.MetricName)))]
+		metaEntry, metaOk := sl.cache.metadata[lset.Get(labels.MetricName)]
 		if metaOk && (isNewSeries || metaEntry.lastIterChange == sl.cache.iter) {
 			metadataChanged = true
 			meta.Type = metaEntry.Type
@@ -1584,10 +1583,10 @@ loop:
 		meta = metadata.Metadata{}
 		metadataChanged = false
 
-		if sl.cache.getDropped(yoloString(met)) {
+		if sl.cache.getDropped(met) {
 			continue
 		}
-		ce, ok := sl.cache.get(yoloString(met))
+		ce, ok := sl.cache.get(met)
 		var (
 			ref  storage.SeriesRef
 			lset labels.Labels
@@ -1654,7 +1653,7 @@ loop:
 				// Bypass staleness logic if there is an explicit timestamp.
 				sl.cache.trackStaleness(hash, lset)
 			}
-			sl.cache.addRef(mets, ref, lset, hash)
+			sl.cache.addRef(met, ref, lset, hash)
 			if sampleAdded && sampleLimitErr == nil {
 				seriesAdded++
 			}
@@ -1719,10 +1718,6 @@ loop:
 	return
 }
 
-func yoloString(b []byte) string {
-	return *((*string)(unsafe.Pointer(&b)))
-}
-
 // Adds samples to the appender, checking the error, and then returns the # of samples added,
 // whether the caller should continue to process more samples, and any sample limit errors.
 func (sl *scrapeLoop) checkAddError(ce *cacheEntry, met []byte, tp *int64, err error, sampleLimitErr *error, appErrs *appendErrors) (bool, error) {
@@ -1775,15 +1770,15 @@ func (sl *scrapeLoop) checkAddExemplarError(err error, e exemplar.Exemplar, appE
 
 // The constants are suffixed with the invalid \xff unicode rune to avoid collisions
 // with scraped metrics in the cache.
-const (
+var (
-	scrapeHealthMetricName        = "up" + "\xff"
+	scrapeHealthMetricName        = []byte("up" + "\xff")
-	scrapeDurationMetricName      = "scrape_duration_seconds" + "\xff"
+	scrapeDurationMetricName      = []byte("scrape_duration_seconds" + "\xff")
-	scrapeSamplesMetricName       = "scrape_samples_scraped" + "\xff"
+	scrapeSamplesMetricName       = []byte("scrape_samples_scraped" + "\xff")
-	samplesPostRelabelMetricName  = "scrape_samples_post_metric_relabeling" + "\xff"
+	samplesPostRelabelMetricName  = []byte("scrape_samples_post_metric_relabeling" + "\xff")
-	scrapeSeriesAddedMetricName   = "scrape_series_added" + "\xff"
+	scrapeSeriesAddedMetricName   = []byte("scrape_series_added" + "\xff")
-	scrapeTimeoutMetricName       = "scrape_timeout_seconds" + "\xff"
+	scrapeTimeoutMetricName       = []byte("scrape_timeout_seconds" + "\xff")
-	scrapeSampleLimitMetricName   = "scrape_sample_limit" + "\xff"
+	scrapeSampleLimitMetricName   = []byte("scrape_sample_limit" + "\xff")
-	scrapeBodySizeBytesMetricName = "scrape_body_size_bytes" + "\xff"
+	scrapeBodySizeBytesMetricName = []byte("scrape_body_size_bytes" + "\xff")
 )
 
 func (sl *scrapeLoop) report(app storage.Appender, start time.Time, duration time.Duration, scraped, added, seriesAdded, bytes int, scrapeErr error) (err error) {
@@ -1859,7 +1854,7 @@ func (sl *scrapeLoop) reportStale(app storage.Appender, start time.Time) (err er
 	return
 }
 
-func (sl *scrapeLoop) addReportSample(app storage.Appender, s string, t int64, v float64) error {
+func (sl *scrapeLoop) addReportSample(app storage.Appender, s []byte, t int64, v float64) error {
 	ce, ok := sl.cache.get(s)
 	var ref storage.SeriesRef
 	var lset labels.Labels
@@ -1870,7 +1865,7 @@ func (sl *scrapeLoop) addReportSample(app storage.Appender, s string, t int64, v
 		// The constants are suffixed with the invalid \xff unicode rune to avoid collisions
 		// with scraped metrics in the cache.
 		// We have to drop it when building the actual metric.
-		lset = labels.FromStrings(labels.MetricName, s[:len(s)-1])
+		lset = labels.FromStrings(labels.MetricName, string(s[:len(s)-1]))
 		lset = sl.reportSampleMutator(lset)
 	}
 

scrape/scrape_test.go

@@ -1586,21 +1586,21 @@ func TestScrapeLoopAppendCacheEntryButErrNotFound(t *testing.T) {
 
 	fakeRef := storage.SeriesRef(1)
 	expValue := float64(1)
-	metric := `metric{n="1"} 1`
+	metric := []byte(`metric{n="1"} 1`)
-	p, warning := textparse.New([]byte(metric), "")
+	p, warning := textparse.New(metric, "")
 	require.NoError(t, warning)
 
 	var lset labels.Labels
 	p.Next()
-	mets := p.Metric(&lset)
+	p.Metric(&lset)
 	hash := lset.Hash()
 
 	// Create a fake entry in the cache
-	sl.cache.addRef(mets, fakeRef, lset, hash)
+	sl.cache.addRef(metric, fakeRef, lset, hash)
 	now := time.Now()
 
 	slApp := sl.appender(context.Background())
-	_, _, _, err := sl.append(slApp, []byte(metric), "", now)
+	_, _, _, err := sl.append(slApp, metric, "", now)
 	require.NoError(t, err)
 	require.NoError(t, slApp.Commit())