expfmt: precompute parsed goautoneg.Accept for well-known Format constants

expfmt/encode.go

@@ -27,6 +27,24 @@ import (
 	"github.com/prometheus/common/model"
 )
 
+var formatToAccept = map[Format]goautoneg.Accept{}
+
+func init() {
+	for _, f := range []Format{
+		FmtText,
+		FmtProtoDelim,
+		FmtProtoText,
+		FmtProtoCompact,
+		FmtOpenMetrics_1_0_0,
+		fmtOpenMetrics_2_0_0,
+		FmtOpenMetrics_0_0_1,
+	} {
+		if parsed := goautoneg.ParseAccept(string(f)); len(parsed) > 0 {
+			formatToAccept[f] = parsed[0]
+		}
+	}
+}
+
 // Encoder types encode metric families into an underlying wire protocol.
 type Encoder interface {
 	Encode(*dto.MetricFamily) error
@@ -81,7 +99,7 @@ func NegotiateIncludingOpenMetrics(h http.Header) Format {
 // format if present in the accepted list, or the first accepted format (or FmtText
 // if accepted is empty).
 func NegotiateAccept(h http.Header, accepted ...Format) Format {
-	escapingScheme := Format(fmt.Sprintf("; escaping=%s", Format(model.NameEscapingScheme.String())))
+	escapingScheme := Format("; escaping=" + model.NameEscapingScheme.String())
 	for _, ac := range goautoneg.ParseAccept(h.Get(hdrAccept)) {
 		if escapeParam := ac.Params[model.EscapingKey]; escapeParam != "" {
 			switch Format(escapeParam) {
@@ -111,11 +129,14 @@ func NegotiateAccept(h http.Header, accepted ...Format) Format {
 
 // matchFormat checks if a parsed accept clause matches a given Format.
 func matchFormat(ac goautoneg.Accept, f Format) bool {
-	parsed := goautoneg.ParseAccept(string(f))
-	if len(parsed) == 0 {
-		return false
+	target, ok := formatToAccept[f]
+	if !ok {
+		parsed := goautoneg.ParseAccept(string(f))
+		if len(parsed) == 0 {
+			return false
+		}
+		target = parsed[0]
 	}
-	target := parsed[0]
 
 	if ac.Type != "*" && ac.Type != target.Type {
 		return false

expfmt/encode_test.go

@@ -547,3 +547,34 @@ func TestDottedEncode(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkNegotiate(b *testing.B) {
+	h := http.Header{}
+	h.Set(hdrAccept, "application/vnd.google.protobuf;proto=io.prometheus.client.MetricFamily;encoding=delimited;q=0.7,text/plain;version=0.0.4;q=0.3,application/json;q=0.1,*/*;q=0.01")
+	b.ReportAllocs()
+	b.ResetTimer()
+	for b.Loop() {
+		_ = Negotiate(h)
+	}
+}
+
+func BenchmarkNegotiateIncludingOpenMetrics(b *testing.B) {
+	h := http.Header{}
+	h.Set(hdrAccept, "application/openmetrics-text;version=1.0.0;q=0.8,application/openmetrics-text;version=0.0.1;q=0.5,text/plain;version=0.0.4;q=0.3,*/*;q=0.1")
+	b.ReportAllocs()
+	b.ResetTimer()
+	for b.Loop() {
+		_ = NegotiateIncludingOpenMetrics(h)
+	}
+}
+
+func BenchmarkNegotiateAccept(b *testing.B) {
+	h := http.Header{}
+	h.Set(hdrAccept, "application/openmetrics-text;version=1.0.0;q=0.8,text/plain;version=0.0.4;q=0.3,*/*;q=0.1")
+	accepted := []Format{FmtOpenMetrics_1_0_0, FmtOpenMetrics_0_0_1, FmtProtoDelim, FmtProtoText, FmtProtoCompact, FmtText}
+	b.ReportAllocs()
+	b.ResetTimer()
+	for b.Loop() {
+		_ = NegotiateAccept(h, accepted...)
+	}
+}