util/progresstracking: add Ticker, NewWriter, and CountingWriter

Add three new helpers to the existing progresstracking package:

  - Ticker: spawns a 1 Hz goroutine that calls a report function with
    the current value of an atomic counter and a total. Returns a stop
    function (safe to call multiple times via sync.OnceFunc) that fires
    one final report and blocks until the goroutine exits.

  - NewWriter: wraps an io.Writer and calls onProgress at most once per
    interval with the cumulative byte count.

  - CountingWriter: an io.Writer that atomically counts bytes written,
    for use with Ticker.

These will be used by the appliance flash and OTA update code in
subsequent commits.

Updates #1866

Change-Id: If353cea6506f5351b6fb19bfdb7bc9b78fe7855e
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

clientupdate/clientupdate_gokrazy.go

@@ -15,9 +15,11 @@ import (
 	"net/http"
 	"os"
 	"strings"
+	"time"
 
 	"tailscale.com/clientupdate/distsign"
 	"tailscale.com/types/logger"
+	"tailscale.com/util/progresstracking"
 )
 
 const (
@@ -50,8 +52,9 @@ func gokrazyUpdateFromURL(ctx context.Context, args GokrazyUpdateArgs) error {
 	tmp.Close()
 	defer os.Remove(tmpName)
 
+	logf("downloading %s", args.URL)
 	if args.AllowUnsigned {
-		if err := downloadUnverified(ctx, args.URL, tmpName); err != nil {
+		if err := downloadUnverified(ctx, logf, args.URL, tmpName); err != nil {
 			return err
 		}
 	} else {
@@ -66,6 +69,8 @@ func gokrazyUpdateFromURL(ctx context.Context, args GokrazyUpdateArgs) error {
 	}
 	defer zr.Close()
 
+	logf("download complete")
+
 	gokClient := gokrazyHTTPClient()
 	for _, part := range []struct {
 		name string
@@ -75,6 +80,7 @@ func gokrazyUpdateFromURL(ctx context.Context, args GokrazyUpdateArgs) error {
 		{"boot.img", "/update/boot"},
 		{"mbr.img", "/update/mbr"},
 	} {
+		logf("writing %s...", part.name)
 		if err := putGokrazyGAFMember(ctx, gokClient, zr.File, part.name, part.path); err != nil {
 			return err
 		}
@@ -94,7 +100,7 @@ func gokrazyUpdateFromURL(ctx context.Context, args GokrazyUpdateArgs) error {
 // downloadUnverified saves the GAF at srcURL to dstPath without verifying
 // a signature. It is used only when args.AllowUnsigned is set, for tests
 // that serve the GAF from a fileserver that does not publish distsign.pub.
-func downloadUnverified(ctx context.Context, srcURL, dstPath string) error {
+func downloadUnverified(ctx context.Context, logf logger.Logf, srcURL, dstPath string) error {
 	req, err := http.NewRequestWithContext(ctx, "GET", srcURL, nil)
 	if err != nil {
 		return err
@@ -111,7 +117,13 @@ func downloadUnverified(ctx context.Context, srcURL, dstPath string) error {
 	if err != nil {
 		return err
 	}
-	if _, err := io.Copy(f, res.Body); err != nil {
+	total := res.ContentLength
+	pw := progresstracking.NewWriter(io.Discard, total, time.Second, func(done int64) {
+		if total > 0 {
+			logf("downloading: %d / %d MB (%.0f%%)", done>>20, total>>20, float64(done)/float64(total)*100)
+		}
+	})
+	if _, err := io.Copy(f, io.TeeReader(res.Body, pw)); err != nil {
 		f.Close()
 		return err
 	}

clientupdate/distsign/distsign.go

@@ -60,6 +60,7 @@ import (
 	"tailscale.com/types/logger"
 	"tailscale.com/util/httpm"
 	"tailscale.com/util/must"
+	"tailscale.com/util/progresstracking"
 )
 
 const (
@@ -373,7 +374,10 @@ func (c *Client) download(ctx context.Context, url, dst string, limit int64) ([]
 		return nil, 0, err
 	}
 	defer of.Close()
-	pw := &progressWriter{total: res.ContentLength, logf: c.logf}
+	total := res.ContentLength
+	pw := progresstracking.NewWriter(io.Discard, total, 2*time.Second, func(done int64) {
+		c.logf("Downloaded %v/%v (%.1f%%)", done, total, float64(done)/float64(total)*100)
+	})
 	h := NewPackageHash()
 	n, err := io.Copy(io.MultiWriter(of, h, pw), io.LimitReader(dlRes.Body, limit))
 	if err != nil {
@@ -388,31 +392,10 @@ func (c *Client) download(ctx context.Context, url, dst string, limit int64) ([]
 	if err := of.Close(); err != nil {
 		return nil, n, err
 	}
-	pw.print()
 
 	return h.Sum(nil), h.Len(), nil
 }
 
-type progressWriter struct {
-	done      int64
-	total     int64
-	lastPrint time.Time
-	logf      logger.Logf
-}
-
-func (pw *progressWriter) Write(p []byte) (n int, err error) {
-	pw.done += int64(len(p))
-	if time.Since(pw.lastPrint) > 2*time.Second {
-		pw.print()
-	}
-	return len(p), nil
-}
-
-func (pw *progressWriter) print() {
-	pw.lastPrint = time.Now()
-	pw.logf("Downloaded %v/%v (%.1f%%)", pw.done, pw.total, float64(pw.done)/float64(pw.total)*100)
-}
-
 func parsePrivateKey(data []byte, typeTag string) (ed25519.PrivateKey, error) {
 	b, rest := pem.Decode(data)
 	if b == nil {