first implementation of binary update with uncompressing

cmd/selfupdate-example/main.go

@@ -14,7 +14,7 @@ func selfUpdate() error {
 	selfupdate.EnableLog()
 
 	previous := semver.Make(version)
-	latest, err := selfupdate.TryUpdate(previous, "go-github-selfupdate", nil)
+	latest, err := selfupdate.UpdateSelf(previous, "rhysd/go-github-selfupdate")
 	if err != nil {
 		return err
 	}

selfupdate/update.go

@@ -0,0 +1,115 @@
+package selfupdate
+
+import (
+	"archive/tar"
+	"archive/zip"
+	"bytes"
+	"compress/gzip"
+	"fmt"
+	"github.com/blang/semver"
+	"github.com/inconshreveable/go-update"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func uncompress(src io.ReadCloser, url, cmd string) (io.Reader, error) {
+	if strings.HasSuffix(url, ".zip") {
+		// Zip format requires its file size for uncompressing.
+		// So we need to read the HTTP response into a buffer at first.
+		buf, err := ioutil.ReadAll(src)
+		if err != nil {
+			return nil, err
+		}
+
+		r := bytes.NewReader(buf)
+		z, err := zip.NewReader(r, r.Size())
+		if err != nil {
+			return nil, err
+		}
+
+		for _, file := range z.File {
+			if file.Name == cmd {
+				return file.Open()
+			}
+		}
+
+		return nil, fmt.Errorf("File '%s' for the command is not found in %s", cmd, url)
+	} else if strings.HasSuffix(url, ".gzip") {
+		return gzip.NewReader(src)
+	} else if strings.HasSuffix(url, ".tar.gz") {
+		gz, err := gzip.NewReader(src)
+		if err != nil {
+			return nil, err
+		}
+
+		t := tar.NewReader(gz)
+		for {
+			h, err := t.Next()
+			if err == io.EOF {
+				break
+			}
+			if err != nil {
+				return nil, err
+			}
+			if h.Name == cmd {
+				return t, nil
+			}
+		}
+
+		return nil, fmt.Errorf("File '%s' for the command is not found in %s", cmd, url)
+	}
+
+	return src, nil
+}
+
+// UpdateTo download an executable from assetURL and replace the current binary with the downloaded one. cmdPath is a file path to command executable.
+func UpdateTo(assetURL, cmdPath string) error {
+	res, err := http.Get(assetURL)
+	if err != nil {
+		return err
+	}
+
+	if res.StatusCode != 200 {
+		return fmt.Errorf("Failed to download a release file from %s ", assetURL)
+	}
+
+	defer res.Body.Close()
+	_, cmd := filepath.Split(cmdPath)
+	asset, err := uncompress(res.Body, assetURL, cmd)
+	if err != nil {
+		return err
+	}
+
+	return update.Apply(asset, update.Options{
+		TargetPath: cmdPath,
+	})
+}
+
+// UpdateCommand updates a given command binary to the latest version.
+// 'slug' represents 'owner/name' repository on GitHub and 'current' means the current version.
+func UpdateCommand(cmdPath string, current semver.Version, slug string) (*Release, error) {
+	rel, ok, err := DetectLatest(slug)
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
+		return &Release{Version: current}, nil
+	}
+	if current.Equals(rel.Version) {
+		return rel, nil
+	}
+	if err := UpdateTo(rel.AssetURL, cmdPath); err != nil {
+		return nil, err
+	}
+	return rel, nil
+}
+
+// UpdateSelf updates the running executable itself to the latest version.
+// 'slug' represents 'owner/name' repository on GitHub and 'current' means the current version.
+func UpdateSelf(current semver.Version, slug string) (*Release, error) {
+	return UpdateCommand(os.Args[0], current, slug, os.Args[0])
+}