build: add -dlgo flag in ci.go (#21824)

This new flag downloads a known version of Go and builds with it. This is meant for environments where we can't easily upgrade the installed Go version. * .travis.yml: remove install step for PR test builders We added this step originally to avoid re-building everything for every test. go test has become much smarter in recent go releases, so we no longer need to install anything here.
2020-11-11 14:34:43 +01:00 · 2020-11-11 14:34:43 +01:00 · 27d93c1848
commit 27d93c1848
parent 70868b1e4a
6 changed files with 246 additions and 101 deletions
--- a/.travis.yml
+++ b/.travis.yml
@ -31,7 +31,6 @@ jobs:
      env:
        - GO111MODULE=on
      script:
-        - go run build/ci.go install
        - go run build/ci.go test -coverage $TEST_PACKAGES

    # These are the latest Go versions.
@ -43,7 +42,6 @@ jobs:
      env:
        - GO111MODULE=on
      script:
-        - go run build/ci.go install
        - go run build/ci.go test -coverage $TEST_PACKAGES

    - stage: build
@ -55,7 +53,6 @@ jobs:
      env:
        - GO111MODULE=on
      script:
-        - go run build/ci.go install
        - go run build/ci.go test -coverage $TEST_PACKAGES

    - stage: build
@ -74,7 +71,6 @@ jobs:
        - ulimit -S -n $NOFILE
        - ulimit -n
        - unset -f cd # workaround for https://github.com/travis-ci/travis-ci/issues/8703
-        - go run build/ci.go install
        - go run build/ci.go test -coverage $TEST_PACKAGES

    # This builder does the Ubuntu PPA upload
@ -99,7 +95,7 @@ jobs:
            - python-paramiko
      script:
        - echo '|1|7SiYPr9xl3uctzovOTj4gMwAC1M=|t6ReES75Bo/PxlOPJ6/GsGbTrM0= ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA0aKz5UTUndYgIGG7dQBV+HaeuEZJ2xPHo2DS2iSKvUL4xNMSAY4UguNW+pX56nAQmZKIZZ8MaEvSj6zMEDiq6HFfn5JcTlM80UwlnyKe8B8p7Nk06PPQLrnmQt5fh0HmEcZx+JU9TZsfCHPnX7MNz4ELfZE6cFsclClrKim3BHUIGq//t93DllB+h4O9LHjEUsQ1Sr63irDLSutkLJD6RXchjROXkNirlcNVHH/jwLWR5RcYilNX7S5bIkK8NlWPjsn/8Ua5O7I9/YoE97PpO6i73DTGLh5H9JN/SITwCKBkgSDWUt61uPK3Y11Gty7o2lWsBjhBUm2Y38CBsoGmBw==' >> ~/.ssh/known_hosts
-        - go run build/ci.go debsrc -goversion 1.15 -upload ethereum/ethereum -sftp-user geth-ci -signer "Go Ethereum Linux Builder <geth-ci@ethereum.org>"
+        - go run build/ci.go debsrc -upload ethereum/ethereum -sftp-user geth-ci -signer "Go Ethereum Linux Builder <geth-ci@ethereum.org>"

    # This builder does the Linux Azure uploads
    - stage: build
@ -119,22 +115,22 @@ jobs:
            - gcc-multilib
      script:
        # Build for the primary platforms that Trusty can manage
-        - go run build/ci.go install
+        - go run build/ci.go install -dlgo
        - go run build/ci.go archive -type tar -signer LINUX_SIGNING_KEY -upload gethstore/builds
-        - go run build/ci.go install -arch 386
+        - go run build/ci.go install -dlgo -arch 386
        - go run build/ci.go archive -arch 386 -type tar -signer LINUX_SIGNING_KEY -upload gethstore/builds

        # Switch over GCC to cross compilation (breaks 386, hence why do it here only)
        - sudo -E apt-get -yq --no-install-suggests --no-install-recommends --force-yes install gcc-arm-linux-gnueabi libc6-dev-armel-cross gcc-arm-linux-gnueabihf libc6-dev-armhf-cross gcc-aarch64-linux-gnu libc6-dev-arm64-cross
        - sudo ln -s /usr/include/asm-generic /usr/include/asm

-        - GOARM=5 go run build/ci.go install -arch arm -cc arm-linux-gnueabi-gcc
+        - GOARM=5 go run build/ci.go install -dlgo -arch arm -cc arm-linux-gnueabi-gcc
        - GOARM=5 go run build/ci.go archive -arch arm -type tar -signer LINUX_SIGNING_KEY -upload gethstore/builds
-        - GOARM=6 go run build/ci.go install -arch arm -cc arm-linux-gnueabi-gcc
+        - GOARM=6 go run build/ci.go install -dlgo -arch arm -cc arm-linux-gnueabi-gcc
        - GOARM=6 go run build/ci.go archive -arch arm -type tar -signer LINUX_SIGNING_KEY -upload gethstore/builds
-        - GOARM=7 go run build/ci.go install -arch arm -cc arm-linux-gnueabihf-gcc
+        - GOARM=7 go run build/ci.go install -dlgo -arch arm -cc arm-linux-gnueabihf-gcc
        - GOARM=7 go run build/ci.go archive -arch arm -type tar -signer LINUX_SIGNING_KEY -upload gethstore/builds
-        - go run build/ci.go install -arch arm64 -cc aarch64-linux-gnu-gcc
+        - go run build/ci.go install -dlgo -arch arm64 -cc aarch64-linux-gnu-gcc
        - go run build/ci.go archive -arch arm64 -type tar -signer LINUX_SIGNING_KEY -upload gethstore/builds

    # This builder does the Linux Azure MIPS xgo uploads
@ -219,7 +215,7 @@ jobs:
      git:
        submodules: false # avoid cloning ethereum/tests
      script:
-        - go run build/ci.go install
+        - go run build/ci.go install -dlgo
        - go run build/ci.go archive -type tar -signer OSX_SIGNING_KEY -upload gethstore/builds

        # Build the iOS framework and upload it to CocoaPods and Azure
--- a/appveyor.yml
+++ b/appveyor.yml
@ -30,7 +30,7 @@ install:
  - gcc --version

 build_script:
-  - go run build\ci.go install
+  - go run build\ci.go install -dlgo

 after_build:
  - go run build\ci.go archive -type zip -signer WINDOWS_SIGNING_KEY -upload gethstore/builds
--- a/build/checksums.txt
+++ b/build/checksums.txt
@ -1,6 +1,13 @@
 # This file contains sha256 checksums of optional build dependencies.

-69438f7ed4f532154ffaf878f3dfd83747e7a00b70b3556eddabf7aaee28ac3a  go1.15.src.tar.gz
+063da6a9a4186b8118a0e584532c8c94e65582e2cd951ed078bfd595d27d2367  go1.15.4.src.tar.gz
+aaf8c5323e0557211680960a8f51bedf98ab9a368775a687d6cf1f0079232b1d  go1.15.4.darwin-amd64.tar.gz
+6b2f6d8afddfb198bf0e36044084dc4db4cb0be1107375240b34d215aa5ff6ad  go1.15.4.linux-386.tar.gz
+eb61005f0b932c93b424a3a4eaa67d72196c79129d9a3ea8578047683e2c80d5  go1.15.4.linux-amd64.tar.gz
+6f083b453484fc5f95afb345547a58ccc957cde91348b7a7c68f5b060e488c85  go1.15.4.linux-arm64.tar.gz
+fe449ad3e121472e5db2f70becc0fef9d1a7188616c0605ada63f1e3bbad280e  go1.15.4.linux-armv6l.tar.gz
+3be3cfc08ccc7e7056fdee17b6f5d18e9d7f3d1351dcfec8de34b1c95cb05b50  go1.15.4.windows-386.zip
+3593204e3851be577e4209900ece031b36f1e9ce1671f3f3221c9af7a090a941  go1.15.4.windows-amd64.zip

 d998a84eea42f2271aca792a7b027ca5c1edfcba229e8e5a844c9ac3f336df35  golangci-lint-1.27.0-linux-armv7.tar.gz
 bf781f05b0d393b4bf0a327d9e62926949a4f14d7774d950c4e009fc766ed1d4  golangci-lint.exe-1.27.0-windows-amd64.zip
--- a/build/ci.go
+++ b/build/ci.go
@ -46,12 +46,11 @@ import (
 	"encoding/base64"
 	"flag"
 	"fmt"
-	"go/parser"
-	"go/token"
 	"io/ioutil"
 	"log"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
 	"regexp"
 	"runtime"
@ -148,6 +147,11 @@ var (
 		"golang-1.11": "/usr/lib/go-1.11",
 		"golang-go":   "/usr/lib/go",
 	}
+
+	// This is the version of go that will be downloaded by
+	//
+	//     go run ci.go install -dlgo
+	dlgoVersion = "1.15.4"
 )

 var GOBIN, _ = filepath.Abs(filepath.Join("build", "bin"))
@ -198,19 +202,19 @@ func main() {

 func doInstall(cmdline []string) {
 	var (
+		dlgo = flag.Bool("dlgo", false, "Download Go and build with it")
 		arch = flag.String("arch", "", "Architecture to cross build for")
 		cc   = flag.String("cc", "", "C compiler to cross build with")
 	)
 	flag.CommandLine.Parse(cmdline)
 	env := build.Env()

-	// Check Go version. People regularly open issues about compilation
+	// Check local Go version. People regularly open issues about compilation
 	// failure with outdated Go. This should save them the trouble.
 	if !strings.Contains(runtime.Version(), "devel") {
 		// Figure out the minor version number since we can't textually compare (1.10 < 1.9)
 		var minor int
 		fmt.Sscanf(strings.TrimPrefix(runtime.Version(), "go1."), "%d", &minor)
-
 		if minor < 13 {
 			log.Println("You have Go version", runtime.Version())
 			log.Println("go-ethereum requires at least Go version 1.13 and cannot")
@ -218,90 +222,108 @@ func doInstall(cmdline []string) {
 			os.Exit(1)
 		}
 	}
-	// Compile packages given as arguments, or everything if there are no arguments.
-	packages := []string{"./..."}
-	if flag.NArg() > 0 {
-		packages = flag.Args()
+
+	// Choose which go command we're going to use.
+	var gobuild *exec.Cmd
+	if !*dlgo {
+		// Default behavior: use the go version which runs ci.go right now.
+		gobuild = goTool("build")
+	} else {
+		// Download of Go requested. This is for build environments where the
+		// installed version is too old and cannot be upgraded easily.
+		cachedir := filepath.Join("build", "cache")
+		goroot := downloadGo(runtime.GOARCH, runtime.GOOS, cachedir)
+		gobuild = localGoTool(goroot, "build")
 	}

-	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, "-trimpath")
-		goinstall.Args = append(goinstall.Args, "-v")
-		goinstall.Args = append(goinstall.Args, packages...)
-		build.MustRun(goinstall)
-		return
+	// Configure environment for cross build.
+	if *arch != "" || *arch != runtime.GOARCH {
+		gobuild.Env = append(gobuild.Env, "CGO_ENABLED=1")
+		gobuild.Env = append(gobuild.Env, "GOARCH="+*arch)
 	}

-	// Seems we are cross compiling, work around forbidden GOBIN
-	goinstall := goToolArch(*arch, *cc, "install", buildFlags(env)...)
-	goinstall.Args = append(goinstall.Args, "-trimpath")
-	goinstall.Args = append(goinstall.Args, "-v")
-	goinstall.Args = append(goinstall.Args, []string{"-buildmode", "archive"}...)
-	goinstall.Args = append(goinstall.Args, packages...)
-	build.MustRun(goinstall)
+	// Configure C compiler.
+	if *cc == "" {
+		gobuild.Env = append(gobuild.Env, "CC="+*cc)
+	} else if os.Getenv("CC") != "" {
+		gobuild.Env = append(gobuild.Env, "CC="+os.Getenv("CC"))
+	}

-	if cmds, err := ioutil.ReadDir("cmd"); err == nil {
-		for _, cmd := range cmds {
-			pkgs, err := parser.ParseDir(token.NewFileSet(), filepath.Join(".", "cmd", cmd.Name()), nil, parser.PackageClauseOnly)
-			if err != nil {
-				log.Fatal(err)
-			}
-			for name := range pkgs {
-				if name == "main" {
-					gobuild := goToolArch(*arch, *cc, "build", buildFlags(env)...)
-					gobuild.Args = append(gobuild.Args, "-v")
-					gobuild.Args = append(gobuild.Args, []string{"-o", executablePath(cmd.Name())}...)
-					gobuild.Args = append(gobuild.Args, "."+string(filepath.Separator)+filepath.Join("cmd", cmd.Name()))
-					build.MustRun(gobuild)
-					break
-				}
-			}
-		}
+	// arm64 CI builders are memory-constrained and can't handle concurrent builds,
+	// better disable it. This check isn't the best, it should probably
+	// check for something in env instead.
+	if runtime.GOARCH == "arm64" {
+		gobuild.Args = append(gobuild.Args, "-p", "1")
+	}
+
+	// Put the default settings in.
+	gobuild.Args = append(gobuild.Args, buildFlags(env)...)
+
+	// Show packages during build.
+	gobuild.Args = append(gobuild.Args, "-v")
+
+	// Now we choose what we're even building.
+	// Default: collect all 'main' packages in cmd/ and build those.
+	packages := flag.Args()
+	if len(packages) == 0 {
+		packages = build.FindMainPackages("./cmd")
+	}
+
+	// Do the build!
+	for _, pkg := range packages {
+		args := make([]string, len(gobuild.Args))
+		copy(args, gobuild.Args)
+		args = append(args, "-o", executablePath(path.Base(pkg)))
+		args = append(args, pkg)
+		build.MustRun(&exec.Cmd{Path: gobuild.Path, Args: args, Env: gobuild.Env})
 	}
 }

+// buildFlags returns the go tool flags for building.
 func buildFlags(env build.Environment) (flags []string) {
 	var ld []string
 	if env.Commit != "" {
 		ld = append(ld, "-X", "main.gitCommit="+env.Commit)
 		ld = append(ld, "-X", "main.gitDate="+env.Date)
 	}
+	// Strip DWARF on darwin. This used to be required for certain things,
+	// and there is no downside to this, so we just keep doing it.
 	if runtime.GOOS == "darwin" {
 		ld = append(ld, "-s")
 	}
-
 	if len(ld) > 0 {
 		flags = append(flags, "-ldflags", strings.Join(ld, " "))
 	}
+	// We use -trimpath to avoid leaking local paths into the built executables.
+	flags = append(flags, "-trimpath")
 	return flags
 }

+// goTool returns the go tool. This uses the Go version which runs ci.go.
 func goTool(subcmd string, args ...string) *exec.Cmd {
-	return goToolArch(runtime.GOARCH, os.Getenv("CC"), subcmd, args...)
+	cmd := build.GoTool(subcmd, args...)
+	goToolSetEnv(cmd)
+	return cmd
 }

-func goToolArch(arch string, cc string, subcmd string, args ...string) *exec.Cmd {
-	cmd := build.GoTool(subcmd, args...)
-	if arch == "" || arch == runtime.GOARCH {
-		cmd.Env = append(cmd.Env, "GOBIN="+GOBIN)
-	} else {
-		cmd.Env = append(cmd.Env, "CGO_ENABLED=1")
-		cmd.Env = append(cmd.Env, "GOARCH="+arch)
-	}
-	if cc != "" {
-		cmd.Env = append(cmd.Env, "CC="+cc)
-	}
+// localGoTool returns the go tool from the given GOROOT.
+func localGoTool(goroot string, subcmd string, args ...string) *exec.Cmd {
+	gotool := filepath.Join(goroot, "bin", "go")
+	cmd := exec.Command(gotool, subcmd)
+	goToolSetEnv(cmd)
+	cmd.Env = append(cmd.Env, "GOROOT="+goroot)
+	cmd.Args = append(cmd.Args, args...)
+	return cmd
+}
+
+// goToolSetEnv forwards the build environment to the go tool.
+func goToolSetEnv(cmd *exec.Cmd) {
 	for _, e := range os.Environ() {
-		if strings.HasPrefix(e, "GOBIN=") {
+		if strings.HasPrefix(e, "GOBIN=") || strings.HasPrefix(e, "CC=") {
 			continue
 		}
 		cmd.Env = append(cmd.Env, e)
 	}
-	return cmd
 }

 // Running The Tests
@ -363,7 +385,7 @@ func downloadLinter(cachedir string) string {
 	if err := csdb.DownloadFile(url, archivePath); err != nil {
 		log.Fatal(err)
 	}
-	if err := build.ExtractTarballArchive(archivePath, cachedir); err != nil {
+	if err := build.ExtractArchive(archivePath, cachedir); err != nil {
 		log.Fatal(err)
 	}
 	return filepath.Join(cachedir, base, "golangci-lint")
@ -469,13 +491,12 @@ func maybeSkipArchive(env build.Environment) {
 // Debian Packaging
 func doDebianSource(cmdline []string) {
 	var (
-		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()
+		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)
@ -490,7 +511,7 @@ func doDebianSource(cmdline []string) {
 	}

 	// Download and verify the Go source package.
-	gobundle := downloadGoSources(*goversion, *cachedir)
+	gobundle := downloadGoSources(*cachedir)

 	// Download all the dependencies needed to build the sources and run the ci script
 	srcdepfetch := goTool("install", "-n", "./...")
@ -509,7 +530,7 @@ func doDebianSource(cmdline []string) {
 			pkgdir := stageDebianSource(*workdir, meta)

 			// Add Go source code
-			if err := build.ExtractTarballArchive(gobundle, pkgdir); err != nil {
+			if err := build.ExtractArchive(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 {
@ -541,9 +562,10 @@ func doDebianSource(cmdline []string) {
 	}
 }

-func downloadGoSources(version string, cachedir string) string {
+// downloadGoSources downloads the Go source tarball.
+func downloadGoSources(cachedir string) string {
 	csdb := build.MustLoadChecksums("build/checksums.txt")
-	file := fmt.Sprintf("go%s.src.tar.gz", version)
+	file := fmt.Sprintf("go%s.src.tar.gz", dlgoVersion)
 	url := "https://dl.google.com/go/" + file
 	dst := filepath.Join(cachedir, file)
 	if err := csdb.DownloadFile(url, dst); err != nil {
@ -552,6 +574,41 @@ func downloadGoSources(version string, cachedir string) string {
 	return dst
 }

+// downloadGo downloads the Go binary distribution and unpacks it into a temporary
+// directory. It returns the GOROOT of the unpacked toolchain.
+func downloadGo(goarch, goos, cachedir string) string {
+	if goarch == "arm" {
+		goarch = "armv6l"
+	}
+
+	csdb := build.MustLoadChecksums("build/checksums.txt")
+	file := fmt.Sprintf("go%s.%s-%s", dlgoVersion, goos, goarch)
+	if goos == "windows" {
+		file += ".zip"
+	} else {
+		file += ".tar.gz"
+	}
+	url := "https://golang.org/dl/" + file
+	dst := filepath.Join(cachedir, file)
+	if err := csdb.DownloadFile(url, dst); err != nil {
+		log.Fatal(err)
+	}
+
+	ucache, err := os.UserCacheDir()
+	if err != nil {
+		log.Fatal(err)
+	}
+	godir := filepath.Join(ucache, fmt.Sprintf("geth-go-%s-%s-%s", dlgoVersion, goos, goarch))
+	if err := build.ExtractArchive(dst, godir); err != nil {
+		log.Fatal(err)
+	}
+	goroot, err := filepath.Abs(filepath.Join(godir, "go"))
+	if err != nil {
+		log.Fatal(err)
+	}
+	return goroot
+}
+
 func ppaUpload(workdir, ppa, sshUser string, files []string) {
 	p := strings.Split(ppa, "/")
 	if len(p) != 2 {
--- a/internal/build/archive.go
+++ b/internal/build/archive.go
@ -184,24 +184,35 @@ 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
+// ExtractArchive unpacks a .zip or .tar.gz archive to the destination directory.
+func ExtractArchive(archive string, dest string) error {
 	ar, err := os.Open(archive)
 	if err != nil {
 		return err
 	}
 	defer ar.Close()

+	switch {
+	case strings.HasSuffix(archive, ".tar.gz"):
+		return extractTarball(ar, dest)
+	case strings.HasSuffix(archive, ".zip"):
+		return extractZip(ar, dest)
+	default:
+		return fmt.Errorf("unhandled archive type %s", archive)
+	}
+}
+
+// extractTarball unpacks a .tar.gz file.
+func extractTarball(ar io.Reader, dest string) error {
 	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
+		// Move to the next file header.
 		header, err := tr.Next()
 		if err != nil {
 			if err == io.EOF {
@ -209,22 +220,69 @@ func ExtractTarballArchive(archive string, dest string) error {
 			}
 			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))
+		// We only care about regular files, directory modes
+		// and special file types are not supported.
+		if header.Typeflag == tar.TypeReg {
+			armode := header.FileInfo().Mode()
+			err := extractFile(header.Name, armode, tr, dest)
 			if err != nil {
-				return err
+				return fmt.Errorf("extract %s: %v", header.Name, err)
 			}
-			if _, err := io.Copy(file, tr); err != nil {
-				return err
-			}
-			file.Close()
 		}
 	}
 }
+
+// extractZip unpacks the given .zip file.
+func extractZip(ar *os.File, dest string) error {
+	info, err := ar.Stat()
+	if err != nil {
+		return err
+	}
+	zr, err := zip.NewReader(ar, info.Size())
+	if err != nil {
+		return err
+	}
+
+	for _, zf := range zr.File {
+		if !zf.Mode().IsRegular() {
+			continue
+		}
+
+		data, err := zf.Open()
+		if err != nil {
+			return err
+		}
+		err = extractFile(zf.Name, zf.Mode(), data, dest)
+		data.Close()
+		if err != nil {
+			return fmt.Errorf("extract %s: %v", zf.Name, err)
+		}
+	}
+	return nil
+}
+
+// extractFile extracts a single file from an archive.
+func extractFile(arpath string, armode os.FileMode, data io.Reader, dest string) error {
+	// Check that path is inside destination directory.
+	target := filepath.Join(dest, filepath.FromSlash(arpath))
+	if !strings.HasPrefix(target, filepath.Clean(dest)+string(os.PathSeparator)) {
+		return fmt.Errorf("path %q escapes archive destination", target)
+	}
+
+	// Ensure the destination directory exists.
+	if err := os.MkdirAll(filepath.Dir(target), 0755); err != nil {
+		return err
+	}
+
+	// Copy file data.
+	file, err := os.OpenFile(target, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, armode)
+	if err != nil {
+		return err
+	}
+	if _, err := io.Copy(file, data); err != nil {
+		file.Close()
+		os.Remove(target)
+		return err
+	}
+	return file.Close()
+}
--- a/internal/build/util.go
+++ b/internal/build/util.go
@ -20,6 +20,8 @@ import (
 	"bytes"
 	"flag"
 	"fmt"
+	"go/parser"
+	"go/token"
 	"io"
 	"io/ioutil"
 	"log"
@ -152,3 +154,28 @@ func UploadSFTP(identityFile, host, dir string, files []string) error {
 	stdin.Close()
 	return sftp.Wait()
 }
+
+// FindMainPackages finds all 'main' packages in the given directory and returns their
+// package paths.
+func FindMainPackages(dir string) []string {
+	var commands []string
+	cmds, err := ioutil.ReadDir(dir)
+	if err != nil {
+		log.Fatal(err)
+	}
+	for _, cmd := range cmds {
+		pkgdir := filepath.Join(dir, cmd.Name())
+		pkgs, err := parser.ParseDir(token.NewFileSet(), pkgdir, nil, parser.PackageClauseOnly)
+		if err != nil {
+			log.Fatal(err)
+		}
+		for name := range pkgs {
+			if name == "main" {
+				path := "./" + filepath.ToSlash(pkgdir)
+				commands = append(commands, path)
+				break
+			}
+		}
+	}
+	return commands
+}