Set time and duration of profile (#18)

Co-authored-by: Felix Geisendörfer <felix@felixge.de>

fgprof.go

@@ -14,6 +14,8 @@ import (
 // that needs to be invoked by the caller to stop the profiling and write the
 // results to w using the given format.
 func Start(w io.Writer, format Format) func() error {
+	startTime := time.Now()
+
 	// Go's CPU profiler uses 100hz, but 99hz might be less likely to result in
 	// accidental synchronization with the program we're profiling.
 	const hz = 99
@@ -39,7 +41,15 @@ func Start(w io.Writer, format Format) func() error {
 
 	return func() error {
 		stopCh <- struct{}{}
-		return writeFormat(w, stackCounts.HumanMap(prof.SelfFrame()), format, hz)
+		endTime := time.Now()
+		return writeFormat(
+			w,
+			stackCounts.HumanMap(prof.SelfFrame()),
+			format,
+			hz,
+			startTime,
+			endTime,
+		)
 	}
 }
 

format.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"sort"
 	"strings"
+	"time"
 
 	"github.com/google/pprof/profile"
 )
@@ -21,12 +22,12 @@ const (
 	FormatPprof Format = "pprof"
 )
 
-func writeFormat(w io.Writer, s map[string]int, f Format, hz int) error {
+func writeFormat(w io.Writer, s map[string]int, f Format, hz int, startTime, endTime time.Time) error {
 	switch f {
 	case FormatFolded:
 		return writeFolded(w, s)
 	case FormatPprof:
-		return toPprof(s, hz).Write(w)
+		return toPprof(s, hz, startTime, endTime).Write(w)
 	default:
 		return fmt.Errorf("unknown format: %q", f)
 	}
@@ -42,14 +43,16 @@ func writeFolded(w io.Writer, s map[string]int) error {
 	return nil
 }
 
-func toPprof(s map[string]int, hz int) *profile.Profile {
+func toPprof(s map[string]int, hz int, startTime, endTime time.Time) *profile.Profile {
 	functionID := uint64(1)
 	locationID := uint64(1)
 	line := int64(1)
 
 	p := &profile.Profile{}
 	m := &profile.Mapping{ID: 1, HasFunctions: true}
 	p.Period = int64(1e9 / hz) // Number of nanoseconds between samples.
+	p.TimeNanos = startTime.UnixNano()
+	p.DurationNanos = int64(endTime.Sub(startTime))
 	p.Mapping = []*profile.Mapping{m}
 	p.SampleType = []*profile.ValueType{
 		{

format_test.go

@@ -3,6 +3,7 @@ package fgprof
 import (
 	"strings"
 	"testing"
+	"time"
 )
 
 func Test_toPprof(t *testing.T) {
@@ -11,14 +12,22 @@ func Test_toPprof(t *testing.T) {
 		"foo":     1,
 	}
 
-	p := toPprof(s, 99)
+	before := time.Local
+	defer func() { time.Local = before }()
+	time.Local = time.UTC
+
+	start := time.Date(2022, 8, 27, 14, 32, 23, 0, time.UTC)
+	end := start.Add(time.Second)
+	p := toPprof(s, 99, start, end)
 	if err := p.CheckValid(); err != nil {
 		t.Fatal(err)
 	}
 
 	want := strings.TrimSpace(`
 PeriodType: wallclock nanoseconds
 Period: 10101010
+Time: 2022-08-27 14:32:23 +0000 UTC
+Duration: 1s
 Samples:
 samples/count time/nanoseconds
           1   10101010: 1