internal/trace/v2: add gotraceeventstats utility

Change-Id: Ibf83d74a76edf2fe2896fa1e7f93ab1296fc5d75
Reviewed-on: https://go-review.googlesource.com/c/go/+/583378
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

src/internal/trace/v2/testdata/cmd/gotraceeventstats/main.go

@@ -0,0 +1,136 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"cmp"
+	"encoding/binary"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"slices"
+	"text/tabwriter"
+
+	"internal/trace/v2/event"
+	"internal/trace/v2/raw"
+)
+
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), "Usage: %s [mode]\n", os.Args[0])
+		fmt.Fprintf(flag.CommandLine.Output(), "\n")
+		fmt.Fprintf(flag.CommandLine.Output(), "Accepts a trace at stdin.\n")
+		fmt.Fprintf(flag.CommandLine.Output(), "\n")
+		fmt.Fprintf(flag.CommandLine.Output(), "Supported modes:")
+		fmt.Fprintf(flag.CommandLine.Output(), "\n")
+		fmt.Fprintf(flag.CommandLine.Output(), "* size  - dumps size stats\n")
+		fmt.Fprintf(flag.CommandLine.Output(), "\n")
+		flag.PrintDefaults()
+	}
+	log.SetFlags(0)
+}
+
+func main() {
+	log.SetPrefix("")
+	flag.Parse()
+
+	if flag.NArg() != 1 {
+		log.Print("missing mode argument")
+		flag.Usage()
+		os.Exit(1)
+	}
+	var err error
+	switch mode := flag.Arg(0); mode {
+	case "size":
+		err = printSizeStats(os.Stdin)
+	default:
+		log.Printf("unknown mode %q", mode)
+		flag.Usage()
+		os.Exit(1)
+	}
+	if err != nil {
+		log.Fatalf("error: %v", err)
+		os.Exit(1)
+	}
+}
+
+func printSizeStats(r io.Reader) error {
+	cr := countingReader{Reader: r}
+	tr, err := raw.NewReader(&cr)
+	if err != nil {
+		return err
+	}
+	type eventStats struct {
+		typ   event.Type
+		count int
+		bytes int
+	}
+	var stats [256]eventStats
+	for i := range stats {
+		stats[i].typ = event.Type(i)
+	}
+	eventsRead := 0
+	for {
+		e, err := tr.ReadEvent()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return err
+		}
+		s := &stats[e.Ev]
+		s.count++
+		s.bytes += encodedSize(&e)
+		eventsRead++
+	}
+	slices.SortFunc(stats[:], func(a, b eventStats) int {
+		return cmp.Compare(b.bytes, a.bytes)
+	})
+	specs := tr.Version().Specs()
+	w := tabwriter.NewWriter(os.Stdout, 3, 8, 2, ' ', 0)
+	fmt.Fprintf(w, "Event\tBytes\t%%\tCount\t%%\n")
+	fmt.Fprintf(w, "-\t-\t-\t-\t-\n")
+	for i := range stats {
+		stat := &stats[i]
+		name := ""
+		if int(stat.typ) >= len(specs) {
+			name = fmt.Sprintf("<unknown (%d)>", stat.typ)
+		} else {
+			name = specs[stat.typ].Name
+		}
+		bytesPct := float64(stat.bytes) / float64(cr.bytesRead) * 100
+		countPct := float64(stat.count) / float64(eventsRead) * 100
+		fmt.Fprintf(w, "%s\t%d\t%.2f%%\t%d\t%.2f%%\n", name, stat.bytes, bytesPct, stat.count, countPct)
+	}
+	w.Flush()
+	return nil
+}
+
+func encodedSize(e *raw.Event) int {
+	size := 1
+	var buf [binary.MaxVarintLen64]byte
+	for _, arg := range e.Args {
+		size += binary.PutUvarint(buf[:], arg)
+	}
+	spec := e.Version.Specs()[e.Ev]
+	if spec.HasData {
+		size += binary.PutUvarint(buf[:], uint64(len(e.Data)))
+		size += len(e.Data)
+	}
+	return size
+}
+
+type countingReader struct {
+	io.Reader
+	bytesRead int
+}
+
+func (r *countingReader) Read(b []byte) (int, error) {
+	n, err := r.Reader.Read(b)
+	r.bytesRead += n
+	return n, err
+}