fix ci.go

build/ci.go

@@ -58,6 +58,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/cespare/cp"
 	"github.com/maticnetwork/bor/internal/build"
 	"github.com/maticnetwork/bor/params"
 )
@@ -137,7 +138,20 @@ var (
 	// Note: yakkety is unsupported because it was officially deprecated on Launchpad.
 	// Note: zesty is unsupported because it was officially deprecated on Launchpad.
 	// Note: artful is unsupported because it was officially deprecated on Launchpad.
-	debDistros = []string{"trusty", "xenial", "bionic", "cosmic", "disco"}
+	// Note: cosmic is unsupported because it was officially deprecated on Launchpad.
+	debDistroGoBoots = map[string]string{
+		"trusty": "golang-1.11",
+		"xenial": "golang-go",
+		"bionic": "golang-go",
+		"disco":  "golang-go",
+		"eoan":   "golang-go",
+		"focal":  "golang-go",
+	}
+
+	debGoBootPaths = map[string]string{
+		"golang-1.11": "/usr/lib/go-1.11",
+		"golang-go":   "/usr/lib/go",
+	}
 )
 
 var GOBIN, _ = filepath.Abs(filepath.Join("build", "bin"))
@@ -201,9 +215,9 @@ func doInstall(cmdline []string) {
 		var minor int
 		fmt.Sscanf(strings.TrimPrefix(runtime.Version(), "go1."), "%d", &minor)
 
-		if minor < 9 {
+		if minor < 11 {
 			log.Println("You have Go version", runtime.Version())
-			log.Println("go-ethereum requires at least Go version 1.9 and cannot")
+			log.Println("go-ethereum requires at least Go version 1.11 and cannot")
 			log.Println("be compiled with an earlier version. Please upgrade your Go installation.")
 			os.Exit(1)
 		}
@@ -213,22 +227,18 @@ func doInstall(cmdline []string) {
 	if flag.NArg() > 0 {
 		packages = flag.Args()
 	}
-	packages = build.ExpandPackagesNoVendor(packages)
 
 	if *arch == "" || *arch == runtime.GOARCH {
 		goinstall := goTool("install", buildFlags(env)...)
+		if runtime.GOARCH == "arm64" {
+			goinstall.Args = append(goinstall.Args, "-p", "1")
+		}
 		goinstall.Args = append(goinstall.Args, "-v")
 		goinstall.Args = append(goinstall.Args, packages...)
 		build.MustRun(goinstall)
 		return
 	}
-	// If we are cross compiling to ARMv5 ARMv6 or ARMv7, clean any previous builds
-	if *arch == "arm" {
-		os.RemoveAll(filepath.Join(runtime.GOROOT(), "pkg", runtime.GOOS+"_arm"))
-		for _, path := range filepath.SplitList(build.GOPATH()) {
-			os.RemoveAll(filepath.Join(path, "pkg", runtime.GOOS+"_arm"))
-		}
-	}
+
 	// Seems we are cross compiling, work around forbidden GOBIN
 	goinstall := goToolArch(*arch, *cc, "install", buildFlags(env)...)
 	goinstall.Args = append(goinstall.Args, "-v")
@@ -278,7 +288,6 @@ func goTool(subcmd string, args ...string) *exec.Cmd {
 
 func goToolArch(arch string, cc string, subcmd string, args ...string) *exec.Cmd {
 	cmd := build.GoTool(subcmd, args...)
-	cmd.Env = []string{"GOPATH=" + build.GOPATH()}
 	if arch == "" || arch == runtime.GOARCH {
 		cmd.Env = append(cmd.Env, "GOBIN="+GOBIN)
 	} else {
@@ -289,7 +298,7 @@ func goToolArch(arch string, cc string, subcmd string, args ...string) *exec.Cmd
 		cmd.Env = append(cmd.Env, "CC="+cc)
 	}
 	for _, e := range os.Environ() {
-		if strings.HasPrefix(e, "GOPATH=") || strings.HasPrefix(e, "GOBIN=") {
+		if strings.HasPrefix(e, "GOBIN=") {
 			continue
 		}
 		cmd.Env = append(cmd.Env, e)
@@ -303,6 +312,7 @@ func goToolArch(arch string, cc string, subcmd string, args ...string) *exec.Cmd
 
 func doTest(cmdline []string) {
 	coverage := flag.Bool("coverage", false, "Whether to record code coverage")
+	verbose := flag.Bool("v", false, "Whether to log verbosely")
 	flag.CommandLine.Parse(cmdline)
 	env := build.Env()
 
@@ -310,7 +320,6 @@ func doTest(cmdline []string) {
 	if len(flag.CommandLine.Args()) > 0 {
 		packages = flag.CommandLine.Args()
 	}
-	packages = build.ExpandPackagesNoVendor(packages)
 
 	// Run the actual tests.
 	// Test a single package at a time. CI builders are slow
@@ -320,44 +329,46 @@ func doTest(cmdline []string) {
 	if *coverage {
 		gotest.Args = append(gotest.Args, "-covermode=atomic", "-cover")
 	}
+	if *verbose {
+		gotest.Args = append(gotest.Args, "-v")
+	}
 
 	gotest.Args = append(gotest.Args, packages...)
 	build.MustRun(gotest)
 }
 
-// runs gometalinter on requested packages
+// doLint runs golangci-lint on requested packages.
 func doLint(cmdline []string) {
+	var (
+		cachedir = flag.String("cachedir", "./build/cache", "directory for caching golangci-lint binary.")
+	)
 	flag.CommandLine.Parse(cmdline)
-
 	packages := []string{"./..."}
 	if len(flag.CommandLine.Args()) > 0 {
 		packages = flag.CommandLine.Args()
 	}
-	// Get metalinter and install all supported linters
-	build.MustRun(goTool("get", "gopkg.in/alecthomas/gometalinter.v2"))
-	build.MustRunCommand(filepath.Join(GOBIN, "gometalinter.v2"), "--install")
 
-	// Run fast linters batched together
-	configs := []string{
-		"--vendor",
-		"--tests",
-		"--deadline=2m",
-		"--disable-all",
-		"--enable=goimports",
-		"--enable=varcheck",
-		"--enable=vet",
-		"--enable=gofmt",
-		"--enable=misspell",
-		"--enable=goconst",
-		"--min-occurrences=6", // for goconst
-	}
-	build.MustRunCommand(filepath.Join(GOBIN, "gometalinter.v2"), append(configs, packages...)...)
+	linter := downloadLinter(*cachedir)
+	lflags := []string{"run", "--config", ".golangci.yml"}
+	build.MustRunCommand(linter, append(lflags, packages...)...)
+	fmt.Println("You have achieved perfection.")
+}
 
-	// Run slow linters one by one
-	for _, linter := range []string{"unconvert", "gosimple"} {
-		configs = []string{"--vendor", "--tests", "--deadline=10m", "--disable-all", "--enable=" + linter}
-		build.MustRunCommand(filepath.Join(GOBIN, "gometalinter.v2"), append(configs, packages...)...)
+// downloadLinter downloads and unpacks golangci-lint.
+func downloadLinter(cachedir string) string {
+	const version = "1.22.2"
+
+	csdb := build.MustLoadChecksums("build/checksums.txt")
+	base := fmt.Sprintf("golangci-lint-%s-%s-%s", version, runtime.GOOS, runtime.GOARCH)
+	url := fmt.Sprintf("https://github.com/golangci/golangci-lint/releases/download/v%s/%s.tar.gz", version, base)
+	archivePath := filepath.Join(cachedir, base+".tar.gz")
+	if err := csdb.DownloadFile(url, archivePath); err != nil {
+		log.Fatal(err)
 	}
+	if err := build.ExtractTarballArchive(archivePath, cachedir); err != nil {
+		log.Fatal(err)
+	}
+	return filepath.Join(cachedir, base, "golangci-lint")
 }
 
 // Release Packaging
@@ -460,11 +471,13 @@ func maybeSkipArchive(env build.Environment) {
 // Debian Packaging
 func doDebianSource(cmdline []string) {
 	var (
-		signer  = flag.String("signer", "", `Signing key name, also used as package author`)
-		upload  = flag.String("upload", "", `Where to upload the source package (usually "ethereum/ethereum")`)
-		sshUser = flag.String("sftp-user", "", `Username for SFTP upload (usually "geth-ci")`)
-		workdir = flag.String("workdir", "", `Output directory for packages (uses temp dir if unset)`)
-		now     = time.Now()
+		goversion = flag.String("goversion", "", `Go version to build with (will be included in the source package)`)
+		cachedir  = flag.String("cachedir", "./build/cache", `Filesystem path to cache the downloaded Go bundles at`)
+		signer    = flag.String("signer", "", `Signing key name, also used as package author`)
+		upload    = flag.String("upload", "", `Where to upload the source package (usually "ethereum/ethereum")`)
+		sshUser   = flag.String("sftp-user", "", `Username for SFTP upload (usually "geth-ci")`)
+		workdir   = flag.String("workdir", "", `Output directory for packages (uses temp dir if unset)`)
+		now       = time.Now()
 	)
 	flag.CommandLine.Parse(cmdline)
 	*workdir = makeWorkdir(*workdir)
@@ -478,12 +491,39 @@ func doDebianSource(cmdline []string) {
 		build.MustRun(gpg)
 	}
 
-	// Create Debian packages and upload them
+	// Download and verify the Go source package.
+	gobundle := downloadGoSources(*goversion, *cachedir)
+
+	// Download all the dependencies needed to build the sources and run the ci script
+	srcdepfetch := goTool("install", "-n", "./...")
+	srcdepfetch.Env = append(os.Environ(), "GOPATH="+filepath.Join(*workdir, "modgopath"))
+	build.MustRun(srcdepfetch)
+
+	cidepfetch := goTool("run", "./build/ci.go")
+	cidepfetch.Env = append(os.Environ(), "GOPATH="+filepath.Join(*workdir, "modgopath"))
+	cidepfetch.Run() // Command fails, don't care, we only need the deps to start it
+
+	// Create Debian packages and upload them.
 	for _, pkg := range debPackages {
-		for _, distro := range debDistros {
-			meta := newDebMetadata(distro, *signer, env, now, pkg.Name, pkg.Version, pkg.Executables)
+		for distro, goboot := range debDistroGoBoots {
+			// Prepare the debian package with the go-ethereum sources.
+			meta := newDebMetadata(distro, goboot, *signer, env, now, pkg.Name, pkg.Version, pkg.Executables)
 			pkgdir := stageDebianSource(*workdir, meta)
-			debuild := exec.Command("debuild", "-S", "-sa", "-us", "-uc", "-d", "-Zxz")
+
+			// Add Go source code
+			if err := build.ExtractTarballArchive(gobundle, pkgdir); err != nil {
+				log.Fatalf("Failed to extract Go sources: %v", err)
+			}
+			if err := os.Rename(filepath.Join(pkgdir, "go"), filepath.Join(pkgdir, ".go")); err != nil {
+				log.Fatalf("Failed to rename Go source folder: %v", err)
+			}
+			// Add all dependency modules in compressed form
+			os.MkdirAll(filepath.Join(pkgdir, ".mod", "cache"), 0755)
+			if err := cp.CopyAll(filepath.Join(pkgdir, ".mod", "cache", "download"), filepath.Join(*workdir, "modgopath", "pkg", "mod", "cache", "download")); err != nil {
+				log.Fatalf("Failed to copy Go module dependencies: %v", err)
+			}
+			// Run the packaging and upload to the PPA
+			debuild := exec.Command("debuild", "-S", "-sa", "-us", "-uc", "-d", "-Zxz", "-nc")
 			debuild.Dir = pkgdir
 			build.MustRun(debuild)
 
@@ -503,6 +543,17 @@ func doDebianSource(cmdline []string) {
 	}
 }
 
+func downloadGoSources(version string, cachedir string) string {
+	csdb := build.MustLoadChecksums("build/checksums.txt")
+	file := fmt.Sprintf("go%s.src.tar.gz", version)
+	url := "https://dl.google.com/go/" + file
+	dst := filepath.Join(cachedir, file)
+	if err := csdb.DownloadFile(url, dst); err != nil {
+		log.Fatal(err)
+	}
+	return dst
+}
+
 func ppaUpload(workdir, ppa, sshUser string, files []string) {
 	p := strings.Split(ppa, "/")
 	if len(p) != 2 {
@@ -562,7 +613,9 @@ type debPackage struct {
 }
 
 type debMetadata struct {
-	Env build.Environment
+	Env           build.Environment
+	GoBootPackage string
+	GoBootPath    string
 
 	PackageName string
 
@@ -591,19 +644,21 @@ func (d debExecutable) Package() string {
 	return d.BinaryName
 }
 
-func newDebMetadata(distro, author string, env build.Environment, t time.Time, name string, version string, exes []debExecutable) debMetadata {
+func newDebMetadata(distro, goboot, author string, env build.Environment, t time.Time, name string, version string, exes []debExecutable) debMetadata {
 	if author == "" {
 		// No signing key, use default author.
 		author = "Ethereum Builds <fjl@ethereum.org>"
 	}
 	return debMetadata{
-		PackageName: name,
-		Env:         env,
-		Author:      author,
-		Distro:      distro,
-		Version:     version,
-		Time:        t.Format(time.RFC1123Z),
-		Executables: exes,
+		GoBootPackage: goboot,
+		GoBootPath:    debGoBootPaths[goboot],
+		PackageName:   name,
+		Env:           env,
+		Author:        author,
+		Distro:        distro,
+		Version:       version,
+		Time:          t.Format(time.RFC1123Z),
+		Executables:   exes,
 	}
 }
 
@@ -668,7 +723,6 @@ func stageDebianSource(tmpdir string, meta debMetadata) (pkgdir string) {
 	if err := os.Mkdir(pkgdir, 0755); err != nil {
 		log.Fatal(err)
 	}
-
 	// Copy the source code.
 	build.MustRunCommand("git", "checkout-index", "-a", "--prefix", pkgdir+string(filepath.Separator))
 
@@ -686,7 +740,6 @@ func stageDebianSource(tmpdir string, meta debMetadata) (pkgdir string) {
 		build.Render("build/deb/"+meta.PackageName+"/deb.install", install, 0644, exe)
 		build.Render("build/deb/"+meta.PackageName+"/deb.docs", docs, 0644, exe)
 	}
-
 	return pkgdir
 }
 
@@ -715,7 +768,7 @@ func doWindowsInstaller(cmdline []string) {
 			continue
 		}
 		allTools = append(allTools, filepath.Base(file))
-		if filepath.Base(file) == "geth.exe" {
+		if filepath.Base(file) == "bor.exe" {
 			gethTool = file
 		} else {
 			devTools = append(devTools, file)
@@ -729,14 +782,17 @@ func doWindowsInstaller(cmdline []string) {
 		"Geth":     gethTool,
 		"DevTools": devTools,
 	}
-	build.Render("build/nsis.geth.nsi", filepath.Join(*workdir, "geth.nsi"), 0644, nil)
+	build.Render("build/nsis.bor.nsi", filepath.Join(*workdir, "bor.nsi"), 0644, nil)
 	build.Render("build/nsis.install.nsh", filepath.Join(*workdir, "install.nsh"), 0644, templateData)
 	build.Render("build/nsis.uninstall.nsh", filepath.Join(*workdir, "uninstall.nsh"), 0644, allTools)
 	build.Render("build/nsis.pathupdate.nsh", filepath.Join(*workdir, "PathUpdate.nsh"), 0644, nil)
 	build.Render("build/nsis.envvarupdate.nsh", filepath.Join(*workdir, "EnvVarUpdate.nsh"), 0644, nil)
-	build.CopyFile(filepath.Join(*workdir, "SimpleFC.dll"), "build/nsis.simplefc.dll", 0755)
-	build.CopyFile(filepath.Join(*workdir, "COPYING"), "COPYING", 0755)
-
+	if err := cp.CopyFile(filepath.Join(*workdir, "SimpleFC.dll"), "build/nsis.simplefc.dll"); err != nil {
+		log.Fatal("Failed to copy SimpleFC.dll: %v", err)
+	}
+	if err := cp.CopyFile(filepath.Join(*workdir, "COPYING"), "COPYING"); err != nil {
+		log.Fatal("Failed to copy copyright note: %v", err)
+	}
 	// Build the installer. This assumes that all the needed files have been previously
 	// built (don't mix building and packaging to keep cross compilation complexity to a
 	// minimum).
@@ -744,16 +800,15 @@ func doWindowsInstaller(cmdline []string) {
 	if env.Commit != "" {
 		version[2] += "-" + env.Commit[:8]
 	}
-	installer, _ := filepath.Abs("geth-" + archiveBasename(*arch, params.ArchiveVersion(env.Commit)) + ".exe")
+	installer, _ := filepath.Abs("bor-" + archiveBasename(*arch, params.ArchiveVersion(env.Commit)) + ".exe")
 	build.MustRunCommand("makensis.exe",
 		"/DOUTPUTFILE="+installer,
 		"/DMAJORVERSION="+version[0],
 		"/DMINORVERSION="+version[1],
 		"/DBUILDVERSION="+version[2],
 		"/DARCH="+*arch,
-		filepath.Join(*workdir, "geth.nsi"),
+		filepath.Join(*workdir, "bor.nsi"),
 	)
-
 	// Sign and publish installer.
 	if err := archiveUpload(installer, *upload, *signer); err != nil {
 		log.Fatal(err)
@@ -826,7 +881,6 @@ func gomobileTool(subcmd string, args ...string) *exec.Cmd {
 	cmd := exec.Command(filepath.Join(GOBIN, "gomobile"), subcmd)
 	cmd.Args = append(cmd.Args, args...)
 	cmd.Env = []string{
-		"GOPATH=" + build.GOPATH(),
 		"PATH=" + GOBIN + string(os.PathListSeparator) + os.Getenv("PATH"),
 	}
 	for _, e := range os.Environ() {
@@ -899,7 +953,7 @@ func doXCodeFramework(cmdline []string) {
 	// Build the iOS XCode framework
 	build.MustRun(goTool("get", "golang.org/x/mobile/cmd/gomobile", "golang.org/x/mobile/cmd/gobind"))
 	build.MustRun(gomobileTool("init"))
-	bind := gomobileTool("bind", "-ldflags", "-s -w", "--target", "ios", "--tags", "ios", "-v", "github.com/maticnetwork/bor/mobile")
+	bind := gomobileTool("bind", "-ldflags", "-s -w", "--target", "ios", "-v", "github.com/maticnetwork/bor/mobile")
 
 	if *local {
 		// If we're building locally, use the build folder and stop afterwards
@@ -907,7 +961,7 @@ func doXCodeFramework(cmdline []string) {
 		build.MustRun(bind)
 		return
 	}
-	archive := "geth-" + archiveBasename("ios", params.ArchiveVersion(env.Commit))
+	archive := "bor-" + archiveBasename("ios", params.ArchiveVersion(env.Commit))
 	if err := os.Mkdir(archive, os.ModePerm); err != nil {
 		log.Fatal(err)
 	}
@@ -1014,16 +1068,10 @@ func doXgo(cmdline []string) {
 
 func xgoTool(args []string) *exec.Cmd {
 	cmd := exec.Command(filepath.Join(GOBIN, "xgo"), args...)
-	cmd.Env = []string{
-		"GOPATH=" + build.GOPATH(),
+	cmd.Env = os.Environ()
+	cmd.Env = append(cmd.Env, []string{
 		"GOBIN=" + GOBIN,
-	}
-	for _, e := range os.Environ() {
-		if strings.HasPrefix(e, "GOPATH=") || strings.HasPrefix(e, "GOBIN=") {
-			continue
-		}
-		cmd.Env = append(cmd.Env, e)
-	}
+	}...)
 	return cmd
 }
 

internal/build/archive.go

@@ -183,3 +183,48 @@ func (a *TarballArchive) Close() error {
 	}
 	return a.file.Close()
 }
+
+func ExtractTarballArchive(archive string, dest string) error {
+	// We're only interested in gzipped archives, wrap the reader now
+	ar, err := os.Open(archive)
+	if err != nil {
+		return err
+	}
+	defer ar.Close()
+
+	gzr, err := gzip.NewReader(ar)
+	if err != nil {
+		return err
+	}
+	defer gzr.Close()
+
+	// Iterate over all the files in the tarball
+	tr := tar.NewReader(gzr)
+	for {
+		// Fetch the next tarball header and abort if needed
+		header, err := tr.Next()
+		if err != nil {
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		}
+		// Figure out the target and create it
+		target := filepath.Join(dest, header.Name)
+
+		switch header.Typeflag {
+		case tar.TypeReg:
+			if err := os.MkdirAll(filepath.Dir(target), 0755); err != nil {
+				return err
+			}
+			file, err := os.OpenFile(target, os.O_CREATE|os.O_RDWR, os.FileMode(header.Mode))
+			if err != nil {
+				return err
+			}
+			if _, err := io.Copy(file, tr); err != nil {
+				return err
+			}
+			file.Close()
+		}
+	}
+}

internal/build/download.go

@@ -0,0 +1,151 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package build
+
+import (
+	"bufio"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// ChecksumDB keeps file checksums.
+type ChecksumDB struct {
+	allChecksums []string
+}
+
+// MustLoadChecksums loads a file containing checksums.
+func MustLoadChecksums(file string) *ChecksumDB {
+	content, err := ioutil.ReadFile(file)
+	if err != nil {
+		log.Fatal("can't load checksum file: " + err.Error())
+	}
+	return &ChecksumDB{strings.Split(string(content), "\n")}
+}
+
+// Verify checks whether the given file is valid according to the checksum database.
+func (db *ChecksumDB) Verify(path string) error {
+	fd, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer fd.Close()
+
+	h := sha256.New()
+	if _, err := io.Copy(h, bufio.NewReader(fd)); err != nil {
+		return err
+	}
+	fileHash := hex.EncodeToString(h.Sum(nil))
+	if !db.findHash(filepath.Base(path), fileHash) {
+		return fmt.Errorf("invalid file hash %s", fileHash)
+	}
+	return nil
+}
+
+func (db *ChecksumDB) findHash(basename, hash string) bool {
+	want := hash + "  " + basename
+	for _, line := range db.allChecksums {
+		if strings.TrimSpace(line) == want {
+			return true
+		}
+	}
+	return false
+}
+
+// DownloadFile downloads a file and verifies its checksum.
+func (db *ChecksumDB) DownloadFile(url, dstPath string) error {
+	if err := db.Verify(dstPath); err == nil {
+		fmt.Printf("%s is up-to-date\n", dstPath)
+		return nil
+	}
+	fmt.Printf("%s is stale\n", dstPath)
+	fmt.Printf("downloading from %s\n", url)
+
+	resp, err := http.Get(url)
+	if err != nil {
+		return fmt.Errorf("download error: %v", err)
+	} else if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("download error: status %d", resp.StatusCode)
+	}
+	defer resp.Body.Close()
+	if err := os.MkdirAll(filepath.Dir(dstPath), 0755); err != nil {
+		return err
+	}
+	fd, err := os.OpenFile(dstPath, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0644)
+	if err != nil {
+		return err
+	}
+	dst := newDownloadWriter(fd, resp.ContentLength)
+	_, err = io.Copy(dst, resp.Body)
+	dst.Close()
+	if err != nil {
+		return err
+	}
+
+	return db.Verify(dstPath)
+}
+
+type downloadWriter struct {
+	file    *os.File
+	dstBuf  *bufio.Writer
+	size    int64
+	written int64
+	lastpct int64
+}
+
+func newDownloadWriter(dst *os.File, size int64) *downloadWriter {
+	return &downloadWriter{
+		file:   dst,
+		dstBuf: bufio.NewWriter(dst),
+		size:   size,
+	}
+}
+
+func (w *downloadWriter) Write(buf []byte) (int, error) {
+	n, err := w.dstBuf.Write(buf)
+
+	// Report progress.
+	w.written += int64(n)
+	pct := w.written * 10 / w.size * 10
+	if pct != w.lastpct {
+		if w.lastpct != 0 {
+			fmt.Print("...")
+		}
+		fmt.Print(pct, "%")
+		w.lastpct = pct
+	}
+	return n, err
+}
+
+func (w *downloadWriter) Close() error {
+	if w.lastpct > 0 {
+		fmt.Println() // Finish the progress line.
+	}
+	flushErr := w.dstBuf.Flush()
+	closeErr := w.file.Close()
+	if flushErr != nil {
+		return flushErr
+	}
+	return closeErr
+}