Prepare for multiple text formats

Pass content type down to text parser.

Add layer of indirection in front of text parser,
and rename to avoid future clashes.

Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>

Makefile

@@ -17,8 +17,7 @@ STATICCHECK_IGNORE = \
   github.com/prometheus/prometheus/discovery/kubernetes/kubernetes.go:SA1019 \
   github.com/prometheus/prometheus/discovery/kubernetes/node.go:SA1019 \
   github.com/prometheus/prometheus/documentation/examples/remote_storage/remote_storage_adapter/main.go:SA1019 \
-  github.com/prometheus/prometheus/pkg/textparse/lex.l.go:SA4006 \
+  github.com/prometheus/prometheus/pkg/textparse/promlex.l.go:SA4006 \
-  github.com/prometheus/prometheus/pkg/textparse/lex.l.go:SA4006 \
   github.com/prometheus/prometheus/pkg/pool/pool.go:SA6002 \
   github.com/prometheus/prometheus/promql/engine.go:SA6002 \
   github.com/prometheus/prometheus/prompb/rpc.pb.gw.go:SA1019

pkg/textparse/interface.go

@@ -0,0 +1,76 @@
+// Copyright 2017 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package textparse
+
+import (
+	"github.com/prometheus/prometheus/pkg/labels"
+)
+
+// Parser parses samples from a byte slice of samples in the official
+// Prometheus text exposition format.
+type Parser interface {
+	// Series returns the bytes of the series, the timestamp if set, and the value
+	// of the current sample.
+	Series() ([]byte, *int64, float64)
+
+	// Help returns the metric name and help text in the current entry.
+	// Must only be called after Next returned a help entry.
+	// The returned byte slices become invalid after the next call to Next.
+	Help() ([]byte, []byte)
+
+	// Type returns the metric name and type in the current entry.
+	// Must only be called after Next returned a type entry.
+	// The returned byte slices become invalid after the next call to Next.
+	Type() ([]byte, MetricType)
+
+	// Comment returns the text of the current comment.
+	// Must only be called after Next returned a comment entry.
+	// The returned byte slice becomes invalid after the next call to Next.
+	Comment() []byte
+
+	// Metric writes the labels of the current sample into the passed labels.
+	// It returns the string from which the metric was parsed.
+	Metric(l *labels.Labels) string
+
+	// Next advances the parser to the next sample. It returns false if no
+	// more samples were read or an error occurred.
+	Next() (Entry, error)
+}
+
+// New returns a new parser of the byte slice.
+func New(b []byte, contentType string) Parser {
+	return NewPromParser(b)
+}
+
+// Entry represents the type of a parsed entry.
+type Entry int
+
+const (
+	EntryInvalid Entry = -1
+	EntryType    Entry = 0
+	EntryHelp    Entry = 1
+	EntrySeries  Entry = 2
+	EntryComment Entry = 3
+)
+
+// MetricType represents metric type values.
+type MetricType string
+
+const (
+	MetricTypeCounter   = "counter"
+	MetricTypeGauge     = "gauge"
+	MetricTypeHistogram = "histogram"
+	MetricTypeSummary   = "summary"
+	MetricTypeUntyped   = "untyped"
+)

pkg/textparse/promlex.l

@@ -32,7 +32,7 @@ const (
 // Lex is called by the parser generated by "go tool yacc" to obtain each
 // token. The method is opened before the matching rules block and closed at
 // the end of the file.
-func (l *lexer) Lex() token {
+func (l *promlexer) Lex() token {
     if l.i >= len(l.b) {
         return tEOF
     }
@@ -87,7 +87,7 @@ C     [^\n]
     return tInvalid
 }
 
-func (l *lexer) consumeComment() token {
+func (l *promlexer) consumeComment() token {
     for c := l.cur(); ; c = l.next() {
         switch c {
         case 0:

pkg/textparse/promlex.l.go

@@ -1,4 +1,4 @@
-// CAUTION: Generated file - DO NOT EDIT.
+// Code generated by golex. DO NOT EDIT.
 
 // Copyright 2017 The Prometheus Authors
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -33,7 +33,7 @@ const (
 // Lex is called by the parser generated by "go tool yacc" to obtain each
 // token. The method is opened before the matching rules block and closed at
 // the end of the file.
-func (l *lexer) Lex() token {
+func (l *promlexer) Lex() token {
 	if l.i >= len(l.b) {
 		return tEOF
 	}
@@ -537,7 +537,7 @@ yyabort: // no lexem recognized
 	return tInvalid
 }
 
-func (l *lexer) consumeComment() token {
+func (l *promlexer) consumeComment() token {
 	for c := l.cur(); ; c = l.next() {
 		switch c {
 		case 0:

pkg/textparse/promparse.go

@@ -12,9 +12,8 @@
 // limitations under the License.
 
 //go:generate go get github.com/cznic/golex
-//go:generate golex -o=lex.l.go lex.l
+//go:generate golex -o=promlex.l.go promlex.l
 
-// Package textparse contains an efficient parser for the Prometheus text format.
 package textparse
 
 import (
@@ -32,7 +31,7 @@ import (
 	"github.com/prometheus/prometheus/pkg/value"
 )
 
-type lexer struct {
+type promlexer struct {
 	b     []byte
 	i     int
 	start int
@@ -106,16 +105,16 @@ func (t token) String() string {
 }
 
 // buf returns the buffer of the current token.
-func (l *lexer) buf() []byte {
+func (l *promlexer) buf() []byte {
 	return l.b[l.start:l.i]
 }
 
-func (l *lexer) cur() byte {
+func (l *promlexer) cur() byte {
 	return l.b[l.i]
 }
 
-// next advances the lexer to the next character.
+// next advances the promlexer to the next character.
-func (l *lexer) next() byte {
+func (l *promlexer) next() byte {
 	l.i++
 	if l.i >= len(l.b) {
 		l.err = io.EOF
@@ -129,14 +128,14 @@ func (l *lexer) next() byte {
 	return l.b[l.i]
 }
 
-func (l *lexer) Error(es string) {
+func (l *promlexer) Error(es string) {
 	l.err = errors.New(es)
 }
 
-// Parser parses samples from a byte slice of samples in the official
+// PromParser parses samples from a byte slice of samples in the official
 // Prometheus text exposition format.
-type Parser struct {
+type PromParser struct {
-	l       *lexer
+	l       *promlexer
 	series  []byte
 	text    []byte
 	mtype   MetricType
@@ -148,13 +147,13 @@ type Parser struct {
 }
 
 // New returns a new parser of the byte slice.
-func New(b []byte) *Parser {
+func NewPromParser(b []byte) Parser {
-	return &Parser{l: &lexer{b: append(b, '\n')}}
+	return &PromParser{l: &promlexer{b: append(b, '\n')}}
 }
 
 // Series returns the bytes of the series, the timestamp if set, and the value
 // of the current sample.
-func (p *Parser) Series() ([]byte, *int64, float64) {
+func (p *PromParser) Series() ([]byte, *int64, float64) {
 	if p.hasTS {
 		return p.series, &p.ts, p.val
 	}
@@ -164,7 +163,7 @@ func (p *Parser) Series() ([]byte, *int64, float64) {
 // Help returns the metric name and help text in the current entry.
 // Must only be called after Next returned a help entry.
 // The returned byte slices become invalid after the next call to Next.
-func (p *Parser) Help() ([]byte, []byte) {
+func (p *PromParser) Help() ([]byte, []byte) {
 	m := p.l.b[p.offsets[0]:p.offsets[1]]
 
 	// Replacer causes allocations. Replace only when necessary.
@@ -177,20 +176,20 @@ func (p *Parser) Help() ([]byte, []byte) {
 // Type returns the metric name and type in the current entry.
 // Must only be called after Next returned a type entry.
 // The returned byte slices become invalid after the next call to Next.
-func (p *Parser) Type() ([]byte, MetricType) {
+func (p *PromParser) Type() ([]byte, MetricType) {
 	return p.l.b[p.offsets[0]:p.offsets[1]], p.mtype
 }
 
 // Comment returns the text of the current comment.
 // Must only be called after Next returned a comment entry.
 // The returned byte slice becomes invalid after the next call to Next.
-func (p *Parser) Comment() []byte {
+func (p *PromParser) Comment() []byte {
 	return p.text
 }
 
 // Metric writes the labels of the current sample into the passed labels.
 // It returns the string from which the metric was parsed.
-func (p *Parser) Metric(l *labels.Labels) string {
+func (p *PromParser) Metric(l *labels.Labels) string {
 	// Allocate the full immutable string immediately, so we just
 	// have to create references on it below.
 	s := string(p.series)
@@ -221,9 +220,9 @@ func (p *Parser) Metric(l *labels.Labels) string {
 	return s
 }
 
-// nextToken returns the next token from the lexer. It skips over tabs
+// nextToken returns the next token from the promlexer. It skips over tabs
 // and spaces.
-func (p *Parser) nextToken() token {
+func (p *PromParser) nextToken() token {
 	for {
 		if tok := p.l.Lex(); tok != tWhitespace {
 			return tok
@@ -231,35 +230,13 @@ func (p *Parser) nextToken() token {
 	}
 }
 
-// Entry represents the type of a parsed entry.
-type Entry int
-
-const (
-	EntryInvalid Entry = -1
-	EntryType    Entry = 0
-	EntryHelp    Entry = 1
-	EntrySeries  Entry = 2
-	EntryComment Entry = 3
-)
-
-// MetricType represents metric type values.
-type MetricType string
-
-const (
-	MetricTypeCounter   = "counter"
-	MetricTypeGauge     = "gauge"
-	MetricTypeHistogram = "histogram"
-	MetricTypeSummary   = "summary"
-	MetricTypeUntyped   = "untyped"
-)
-
 func parseError(exp string, got token) error {
 	return fmt.Errorf("%s, got %q", exp, got)
 }
 
 // Next advances the parser to the next sample. It returns false if no
 // more samples were read or an error occurred.
-func (p *Parser) Next() (Entry, error) {
+func (p *PromParser) Next() (Entry, error) {
 	var err error
 
 	p.start = p.l.i
@@ -371,7 +348,7 @@ func (p *Parser) Next() (Entry, error) {
 	return EntryInvalid, err
 }
 
-func (p *Parser) parseLVals() error {
+func (p *PromParser) parseLVals() error {
 	t := p.nextToken()
 	for {
 		switch t {
@@ -393,7 +370,7 @@ func (p *Parser) parseLVals() error {
 			return fmt.Errorf("invalid UTF-8 label value")
 		}
 
-		// The lexer ensures the value string is quoted. Strip first
+		// The promlexer ensures the value string is quoted. Strip first
 		// and last character.
 		p.offsets = append(p.offsets, p.l.start+1, p.l.i-1)
 

pkg/textparse/promparse_test.go

@@ -27,7 +27,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestParse(t *testing.T) {
+func TestPromParse(t *testing.T) {
 	input := `# HELP go_gc_duration_seconds A summary of the GC invocation durations.
 # 	TYPE go_gc_duration_seconds summary
 go_gc_duration_seconds{quantile="0"} 4.9351e-05
@@ -164,7 +164,7 @@ testmetric{label="\"bar\""} 1`
 		},
 	}
 
-	p := New([]byte(input))
+	p := NewPromParser([]byte(input))
 	i := 0
 
 	var res labels.Labels
@@ -207,7 +207,7 @@ testmetric{label="\"bar\""} 1`
 	require.Equal(t, len(exp), i)
 }
 
-func TestParseErrors(t *testing.T) {
+func TestPromParseErrors(t *testing.T) {
 	cases := []struct {
 		input string
 		err   string
@@ -247,7 +247,7 @@ func TestParseErrors(t *testing.T) {
 	}
 
 	for i, c := range cases {
-		p := New([]byte(c.input))
+		p := NewPromParser([]byte(c.input))
 		var err error
 		for err == nil {
 			_, err = p.Next()
@@ -257,7 +257,7 @@ func TestParseErrors(t *testing.T) {
 	}
 }
 
-func TestNullByteHandling(t *testing.T) {
+func TestPromNullByteHandling(t *testing.T) {
 	cases := []struct {
 		input string
 		err   string
@@ -297,7 +297,7 @@ func TestNullByteHandling(t *testing.T) {
 	}
 
 	for i, c := range cases {
-		p := New([]byte(c.input))
+		p := NewPromParser([]byte(c.input))
 		var err error
 		for err == nil {
 			_, err = p.Next()
@@ -314,11 +314,11 @@ func TestNullByteHandling(t *testing.T) {
 }
 
 const (
-	testdataSampleCount = 410
+	promtestdataSampleCount = 410
 )
 
-func BenchmarkParse(b *testing.B) {
+func BenchmarkPromParse(b *testing.B) {
-	for _, fn := range []string{"testdata.txt", "testdata.nometa.txt"} {
+	for _, fn := range []string{"promtestdata.txt", "promtestdata.nometa.txt"} {
 		f, err := os.Open(fn)
 		require.NoError(b, err)
 		defer f.Close()
@@ -329,12 +329,12 @@ func BenchmarkParse(b *testing.B) {
 		b.Run("no-decode-metric/"+fn, func(b *testing.B) {
 			total := 0
 
-			b.SetBytes(int64(len(buf) * (b.N / testdataSampleCount)))
+			b.SetBytes(int64(len(buf) * (b.N / promtestdataSampleCount)))
 			b.ReportAllocs()
 			b.ResetTimer()
 
-			for i := 0; i < b.N; i += testdataSampleCount {
+			for i := 0; i < b.N; i += promtestdataSampleCount {
-				p := New(buf)
+				p := NewPromParser(buf)
 
 			Outer:
 				for i < b.N {
@@ -357,12 +357,12 @@ func BenchmarkParse(b *testing.B) {
 		b.Run("decode-metric/"+fn, func(b *testing.B) {
 			total := 0
 
-			b.SetBytes(int64(len(buf) * (b.N / testdataSampleCount)))
+			b.SetBytes(int64(len(buf) * (b.N / promtestdataSampleCount)))
 			b.ReportAllocs()
 			b.ResetTimer()
 
-			for i := 0; i < b.N; i += testdataSampleCount {
+			for i := 0; i < b.N; i += promtestdataSampleCount {
-				p := New(buf)
+				p := NewPromParser(buf)
 
 			Outer:
 				for i < b.N {
@@ -390,12 +390,12 @@ func BenchmarkParse(b *testing.B) {
 			total := 0
 			res := make(labels.Labels, 0, 5)
 
-			b.SetBytes(int64(len(buf) * (b.N / testdataSampleCount)))
+			b.SetBytes(int64(len(buf) * (b.N / promtestdataSampleCount)))
 			b.ReportAllocs()
 			b.ResetTimer()
 
-			for i := 0; i < b.N; i += testdataSampleCount {
+			for i := 0; i < b.N; i += promtestdataSampleCount {
-				p := New(buf)
+				p := NewPromParser(buf)
 
 			Outer:
 				for i < b.N {
@@ -420,13 +420,13 @@ func BenchmarkParse(b *testing.B) {
 			_ = total
 		})
 		b.Run("expfmt-text/"+fn, func(b *testing.B) {
-			b.SetBytes(int64(len(buf) * (b.N / testdataSampleCount)))
+			b.SetBytes(int64(len(buf) * (b.N / promtestdataSampleCount)))
 			b.ReportAllocs()
 			b.ResetTimer()
 
 			total := 0
 
-			for i := 0; i < b.N; i += testdataSampleCount {
+			for i := 0; i < b.N; i += promtestdataSampleCount {
 				var (
 					decSamples = make(model.Vector, 0, 50)
 				)
@@ -450,7 +450,7 @@ func BenchmarkParse(b *testing.B) {
 	}
 }
 func BenchmarkGzip(b *testing.B) {
-	for _, fn := range []string{"testdata.txt", "testdata.nometa.txt"} {
+	for _, fn := range []string{"promtestdata.txt", "promtestdata.nometa.txt"} {
 		b.Run(fn, func(b *testing.B) {
 			f, err := os.Open(fn)
 			require.NoError(b, err)
@@ -466,7 +466,7 @@ func BenchmarkGzip(b *testing.B) {
 			gbuf, err := ioutil.ReadAll(&buf)
 			require.NoError(b, err)
 
-			k := b.N / testdataSampleCount
+			k := b.N / promtestdataSampleCount
 
 			b.ReportAllocs()
 			b.SetBytes(int64(k) * int64(n))

scrape/scrape.go

@@ -434,7 +434,7 @@ func appender(app storage.Appender, limit int) storage.Appender {
 
 // A scraper retrieves samples and accepts a status report at the end.
 type scraper interface {
-	scrape(ctx context.Context, w io.Writer) error
+	scrape(ctx context.Context, w io.Writer) (string, error)
 	report(start time.Time, dur time.Duration, err error)
 	offset(interval time.Duration) time.Duration
 }
@@ -455,11 +455,11 @@ const acceptHeader = `text/plain;version=0.0.4;q=1,*/*;q=0.1`
 
 var userAgentHeader = fmt.Sprintf("Prometheus/%s", version.Version)
 
-func (s *targetScraper) scrape(ctx context.Context, w io.Writer) error {
+func (s *targetScraper) scrape(ctx context.Context, w io.Writer) (string, error) {
 	if s.req == nil {
 		req, err := http.NewRequest("GET", s.URL().String(), nil)
 		if err != nil {
-			return err
+			return "", err
 		}
 		req.Header.Add("Accept", acceptHeader)
 		req.Header.Add("Accept-Encoding", "gzip")
@@ -471,35 +471,38 @@ func (s *targetScraper) scrape(ctx context.Context, w io.Writer) error {
 
 	resp, err := ctxhttp.Do(ctx, s.client, s.req)
 	if err != nil {
-		return err
+		return "", err
 	}
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		return fmt.Errorf("server returned HTTP status %s", resp.Status)
+		return "", fmt.Errorf("server returned HTTP status %s", resp.Status)
 	}
 
 	if resp.Header.Get("Content-Encoding") != "gzip" {
 		_, err = io.Copy(w, resp.Body)
-		return err
+		return "", err
 	}
 
 	if s.gzipr == nil {
 		s.buf = bufio.NewReader(resp.Body)
 		s.gzipr, err = gzip.NewReader(s.buf)
 		if err != nil {
-			return err
+			return "", err
 		}
 	} else {
 		s.buf.Reset(resp.Body)
 		if err = s.gzipr.Reset(s.buf); err != nil {
-			return err
+			return "", err
 		}
 	}
 
 	_, err = io.Copy(w, s.gzipr)
 	s.gzipr.Close()
-	return err
+	if err != nil {
+		return "", err
+	}
+	return resp.Header.Get("Content-Type"), nil
 }
 
 // A loop can run and be stopped again. It must not be reused after it was stopped.
@@ -789,7 +792,7 @@ mainLoop:
 		b := sl.buffers.Get(sl.lastScrapeSize).([]byte)
 		buf := bytes.NewBuffer(b)
 
-		scrapeErr := sl.scraper.scrape(scrapeCtx, buf)
+		contentType, scrapeErr := sl.scraper.scrape(scrapeCtx, buf)
 		cancel()
 
 		if scrapeErr == nil {
@@ -809,12 +812,12 @@ mainLoop:
 
 		// A failed scrape is the same as an empty scrape,
 		// we still call sl.append to trigger stale markers.
-		total, added, appErr := sl.append(b, start)
+		total, added, appErr := sl.append(b, contentType, start)
 		if appErr != nil {
 			level.Warn(sl.l).Log("msg", "append failed", "err", appErr)
 			// The append failed, probably due to a parse error or sample limit.
 			// Call sl.append again with an empty scrape to trigger stale markers.
-			if _, _, err := sl.append([]byte{}, start); err != nil {
+			if _, _, err := sl.append([]byte{}, "", start); err != nil {
 				level.Warn(sl.l).Log("msg", "append failed", "err", err)
 			}
 		}
@@ -885,7 +888,7 @@ func (sl *scrapeLoop) endOfRunStaleness(last time.Time, ticker *time.Ticker, int
 	// Call sl.append again with an empty scrape to trigger stale markers.
 	// If the target has since been recreated and scraped, the
 	// stale markers will be out of order and ignored.
-	if _, _, err := sl.append([]byte{}, staleTime); err != nil {
+	if _, _, err := sl.append([]byte{}, "", staleTime); err != nil {
 		level.Error(sl.l).Log("msg", "stale append failed", "err", err)
 	}
 	if err := sl.reportStale(staleTime); err != nil {
@@ -921,10 +924,10 @@ func (s samples) Less(i, j int) bool {
 	return s[i].t < s[j].t
 }
 
-func (sl *scrapeLoop) append(b []byte, ts time.Time) (total, added int, err error) {
+func (sl *scrapeLoop) append(b []byte, contentType string, ts time.Time) (total, added int, err error) {
 	var (
 		app            = sl.appender()
-		p              = textparse.New(b)
+		p              = textparse.New(b, contentType)
 		defTime        = timestamp.FromTime(ts)
 		numOutOfOrder  = 0
 		numDuplicates  = 0

scrape/scrape_test.go

@@ -621,7 +621,7 @@ func TestScrapeLoopMetadata(t *testing.T) {
 # other comment
 test_metric 1
 # TYPE test_metric_no_help gauge
-# HELP test_metric_no_type other help text`), time.Now())
+# HELP test_metric_no_type other help text`), "", time.Now())
 	testutil.Ok(t, err)
 	testutil.Equals(t, 1, total)
 
@@ -824,7 +824,7 @@ func TestScrapeLoopAppend(t *testing.T) {
 
 		now := time.Now()
 
-		_, _, err := sl.append([]byte(test.scrapeLabels), now)
+		_, _, err := sl.append([]byte(test.scrapeLabels), "", now)
 		if err != nil {
 			t.Fatalf("Unexpected append error: %s", err)
 		}
@@ -870,7 +870,7 @@ func TestScrapeLoopAppendSampleLimit(t *testing.T) {
 	beforeMetricValue := beforeMetric.GetCounter().GetValue()
 
 	now := time.Now()
-	_, _, err = sl.append([]byte("metric_a 1\nmetric_b 1\nmetric_c 1\n"), now)
+	_, _, err = sl.append([]byte("metric_a 1\nmetric_b 1\nmetric_c 1\n"), "", now)
 	if err != errSampleLimit {
 		t.Fatalf("Did not see expected sample limit error: %s", err)
 	}
@@ -922,11 +922,11 @@ func TestScrapeLoop_ChangingMetricString(t *testing.T) {
 	)
 
 	now := time.Now()
-	_, _, err = sl.append([]byte(`metric_a{a="1",b="1"} 1`), now)
+	_, _, err = sl.append([]byte(`metric_a{a="1",b="1"} 1`), "", now)
 	if err != nil {
 		t.Fatalf("Unexpected append error: %s", err)
 	}
-	_, _, err = sl.append([]byte(`metric_a{b="1",a="1"} 2`), now.Add(time.Minute))
+	_, _, err = sl.append([]byte(`metric_a{b="1",a="1"} 2`), "", now.Add(time.Minute))
 	if err != nil {
 		t.Fatalf("Unexpected append error: %s", err)
 	}
@@ -961,11 +961,11 @@ func TestScrapeLoopAppendStaleness(t *testing.T) {
 	)
 
 	now := time.Now()
-	_, _, err := sl.append([]byte("metric_a 1\n"), now)
+	_, _, err := sl.append([]byte("metric_a 1\n"), "", now)
 	if err != nil {
 		t.Fatalf("Unexpected append error: %s", err)
 	}
-	_, _, err = sl.append([]byte(""), now.Add(time.Second))
+	_, _, err = sl.append([]byte(""), "", now.Add(time.Second))
 	if err != nil {
 		t.Fatalf("Unexpected append error: %s", err)
 	}
@@ -1006,11 +1006,11 @@ func TestScrapeLoopAppendNoStalenessIfTimestamp(t *testing.T) {
 	)
 
 	now := time.Now()
-	_, _, err := sl.append([]byte("metric_a 1 1000\n"), now)
+	_, _, err := sl.append([]byte("metric_a 1 1000\n"), "", now)
 	if err != nil {
 		t.Fatalf("Unexpected append error: %s", err)
 	}
-	_, _, err = sl.append([]byte(""), now.Add(time.Second))
+	_, _, err = sl.append([]byte(""), "", now.Add(time.Second))
 	if err != nil {
 		t.Fatalf("Unexpected append error: %s", err)
 	}
@@ -1120,7 +1120,7 @@ func TestScrapeLoopAppendGracefullyIfAmendOrOutOfOrderOrOutOfBounds(t *testing.T
 	)
 
 	now := time.Unix(1, 0)
-	_, _, err := sl.append([]byte("out_of_order 1\namend 1\nnormal 1\nout_of_bounds 1\n"), now)
+	_, _, err := sl.append([]byte("out_of_order 1\namend 1\nnormal 1\nout_of_bounds 1\n"), "", now)
 	if err != nil {
 		t.Fatalf("Unexpected append error: %s", err)
 	}
@@ -1153,7 +1153,7 @@ func TestScrapeLoopOutOfBoundsTimeError(t *testing.T) {
 	)
 
 	now := time.Now().Add(20 * time.Minute)
-	total, added, err := sl.append([]byte("normal 1\n"), now)
+	total, added, err := sl.append([]byte("normal 1\n"), "", now)
 	if total != 1 {
 		t.Error("expected 1 metric")
 		return
@@ -1209,7 +1209,7 @@ func TestTargetScraperScrapeOK(t *testing.T) {
 	}
 	var buf bytes.Buffer
 
-	if err := ts.scrape(context.Background(), &buf); err != nil {
+	if _, err := ts.scrape(context.Background(), &buf); err != nil {
 		t.Fatalf("Unexpected scrape error: %s", err)
 	}
 	require.Equal(t, "metric_a 1\nmetric_b 2\n", buf.String())
@@ -1249,7 +1249,7 @@ func TestTargetScrapeScrapeCancel(t *testing.T) {
 	}()
 
 	go func() {
-		if err := ts.scrape(ctx, ioutil.Discard); err != context.Canceled {
+		if _, err := ts.scrape(ctx, ioutil.Discard); err != context.Canceled {
 			errc <- fmt.Errorf("Expected context cancelation error but got: %s", err)
 		}
 		close(errc)
@@ -1291,7 +1291,7 @@ func TestTargetScrapeScrapeNotFound(t *testing.T) {
 		client: http.DefaultClient,
 	}
 
-	if err := ts.scrape(context.Background(), ioutil.Discard); !strings.Contains(err.Error(), "404") {
+	if _, err := ts.scrape(context.Background(), ioutil.Discard); !strings.Contains(err.Error(), "404") {
 		t.Fatalf("Expected \"404 NotFound\" error but got: %s", err)
 	}
 }
@@ -1319,9 +1319,9 @@ func (ts *testScraper) report(start time.Time, duration time.Duration, err error
 	ts.lastError = err
 }
 
-func (ts *testScraper) scrape(ctx context.Context, w io.Writer) error {
+func (ts *testScraper) scrape(ctx context.Context, w io.Writer) (string, error) {
 	if ts.scrapeFunc != nil {
-		return ts.scrapeFunc(ctx, w)
+		return "", ts.scrapeFunc(ctx, w)
 	}
-	return ts.scrapeErr
+	return "", ts.scrapeErr
 }