Adds functionality to krew to download a binary and reference a link …

…to a LICENSE file

internal/download/downloader.go

@@ -34,7 +34,7 @@ import (
 func download(url string, verifier Verifier, fetcher Fetcher) (io.ReaderAt, int64, error) {
 	body, err := fetcher.Get(url)
 	if err != nil {
-		return nil, 0, errors.Wrapf(err, "failed to obtain plugin archive")
+		return nil, 0, errors.Wrapf(err, "failed to obtain plugin")
 	}
 	defer body.Close()
 
@@ -161,6 +161,25 @@ func extractTARGZ(targetDir string, at io.ReaderAt, size int64) error {
 	return nil
 }
 
+// Dowloads the given binary to the target directory
+func downloadBinary(targetDir string, read io.ReaderAt, size int64) error {
+	klog.V(4).Infof("Downloading binary to %q", targetDir) 
+
+	in := io.NewSectionReader(read, 0, size)
+	buf := make([]byte, size)
+
+	if _, err := in.Read(buf); err != nil {
+		return errors.Wrap(err, "failed to read binary")
+	}
+
+	if err := os.WriteFile(filepath.Join(targetDir, "binary"), buf, 0o755); err != nil {
+		return errors.Wrap(err, "failed to write binary")
+	}
+
+	klog.V(4).Infof("download of binary complete to %s complete", targetDir)
+	return nil
+}
+
 func suspiciousPath(path string) error {
 	if strings.Contains(path, "..") {
 		return errors.Errorf("refusing to unpack archive with suspicious entry %q", path)
@@ -193,6 +212,7 @@ type extractor func(targetDir string, read io.ReaderAt, size int64) error
 var defaultExtractors = map[string]extractor{
 	"application/zip":    extractZIP,
 	"application/x-gzip": extractTARGZ,
+	"application/octet-stream": downloadBinary,
 }
 
 func extractArchive(dst string, at io.ReaderAt, size int64) error {
@@ -203,7 +223,7 @@ func extractArchive(dst string, at io.ReaderAt, size int64) error {
 	klog.V(4).Infof("detected %q file type", t)
 	exf, ok := defaultExtractors[t]
 	if !ok {
-		return errors.Errorf("mime type %q for archive file is not a supported archive format", t)
+		return errors.Errorf("mime type %q for file is not a supported format", t)
 	}
 	return errors.Wrap(exf(dst, at, size), "failed to extract file")
 }

internal/installation/install.go

@@ -15,6 +15,7 @@
 package installation
 
 import (
+	"io"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -108,6 +109,16 @@ func install(op installOperation, opts InstallOpts) error {
 		return errors.Wrap(err, "failed to unpack into staging dir")
 	}
 
+	// Download Liscense file from given URI and rename downloaded binary to plugin name
+	if op.platform.License != "" {
+		if err:= downloadLicenseFile(downloadStagingDir, op.platform.License); err != nil {
+			return errors.Wrap(err, "failed downloading license file to installation directory")
+		}
+		if err := renameBinary(downloadStagingDir, op.platform.Bin); err != nil {
+			return errors.Wrap(err, "failed renaming binary in installation directory")
+		}
+	}
+
 	applyDefaults(&op.platform)
 	if err := moveToInstallDir(downloadStagingDir, op.installDir, op.platform.Files); err != nil {
 		return errors.Wrap(err, "failed while moving files to the installation directory")
@@ -137,7 +148,7 @@ func applyDefaults(platform *index.Platform) {
 }
 
 // downloadAndExtract downloads the specified archive uri (or uses the provided overrideFile, if a non-empty value)
-// while validating its checksum with the provided sha256sum, and extracts its contents to extractDir that must be.
+// while validating its checksum with the provided sha256sum, and extracts its contents to extractDir that must be
 // created.
 func downloadAndExtract(extractDir, uri, sha256sum, overrideFile string) error {
 	var fetcher download.Fetcher = download.HTTPFetcher{}
@@ -150,6 +161,33 @@ func downloadAndExtract(extractDir, uri, sha256sum, overrideFile string) error {
 	return errors.Wrap(err, "failed to unpack the plugin archive")
 }
 
+// downloadLicenseFile will download the license file from the given URI and save it to the installation directory
+// of the plugin.
+func downloadLicenseFile(extractDir, uri string) error {
+	var fetcher download.Fetcher = download.HTTPFetcher{}
+
+	body, err := fetcher.Get(uri)
+	if err != nil {
+		return errors.Wrap(err, "failed to download the license file")
+	}
+	defer body.Close()
+
+	out, err := os.Create(filepath.Join(extractDir, "LICENSE"))
+	if err != nil {
+		return errors.Wrap(err, "failed to create LICENSE file")
+	}
+	defer out.Close()
+
+	_, err = io.Copy(out, body)
+
+	return err
+}
+
+// renames the binary in the installation directory to the plugin name if the binary is given temporary "binary" name
+func renameBinary(extractDir, plugin string) error {
+	return os.Rename(filepath.Join(extractDir, "binary"), filepath.Join(extractDir, plugin))
+}
+
 // Uninstall will uninstall a plugin.
 func Uninstall(p environment.Paths, name string) error {
 	if name == constants.KrewPluginName {

pkg/index/types.go

@@ -46,6 +46,8 @@ type Platform struct {
 	Selector *metav1.LabelSelector `json:"selector,omitempty"`
 	Files    []FileOperation       `json:"files"`
 
+	License string `json:"license,omitempty"`
+
 	// Bin specifies the path to the plugin executable.
 	// The path is relative to the root of the installation folder.
 	// The binary will be linked after all FileOperations are executed.