add missing util file

cmd/util/pluginDownload.go

@@ -0,0 +1,151 @@
+/*
+Copyright © 2020-2021 The k3d Author(s)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+package util
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"reflect"
+	"runtime"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// ReleaseAsset maps a single asset in a GitHub Release
+type ReleaseAsset struct {
+	Name        string `json:"name"`
+	DownloadUrl string `json:"browser_download_url"`
+}
+
+// ReleaseResponse maps GitHub Release APIs response
+type ReleaseResponse struct {
+	Tag    string         `json:"tag_name"`
+	Assets []ReleaseAsset `json:"assets"`
+}
+
+// findCompatiblePackageUrl looks for assets compatible with the current system
+// Return the first compatible asset if found, else nil
+func (r *ReleaseResponse) findCompatibleAsset() *ReleaseAsset {
+	expectedSuffix := fmt.Sprintf("%s-%s", runtime.GOOS, runtime.GOARCH)
+
+	for _, asset := range r.Assets {
+		if strings.HasSuffix(asset.DownloadUrl, expectedSuffix) {
+			return &asset
+		}
+	}
+
+	return nil
+}
+
+// download downloads the asset in the given filepath
+func (ra *ReleaseAsset) download(destinationPath string) error {
+	response, err := http.Get(ra.DownloadUrl)
+	if err != nil {
+		return err
+	}
+	defer response.Body.Close()
+
+	if response.StatusCode != 200 {
+		return errors.New("download received non 200 status code")
+	}
+
+	// Create empty file
+	file, err := os.Create(destinationPath)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	// Write response to file
+	_, err = io.Copy(file, response.Body)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func pluginUrl(repo, tag string) string {
+	url := "https://api.github.com/repos/%s/releases/tags/%s"
+
+	if tag == "latest" {
+		url = "https://api.github.com/repos/%s/releases/%s"
+	}
+	return fmt.Sprintf(url, repo, tag)
+}
+
+// fetchRelease fetches the latest release of a GitHub Release.
+// githubRepository has to be formatted as username/repository.
+func fetchRelease(githubRepository, tag string) (*ReleaseResponse, error) {
+	var apiUrl = pluginUrl(githubRepository, tag)
+
+	response, err := http.Get(apiUrl)
+	if err != nil {
+		return nil, err
+	}
+	defer response.Body.Close()
+
+	release := &ReleaseResponse{}
+	err = json.NewDecoder(response.Body).Decode(release)
+	if err != nil {
+		return nil, err
+	}
+
+	return release, nil
+}
+
+// DownloadPlugin downloads the tag release of
+// githubRepository's repo and save it in filepath
+func DownloadPlugin(githubRepository, tag, pluginPath string) error {
+	// Fetch info about the specified release
+	release, err := fetchRelease(githubRepository, tag)
+	if err != nil {
+		log.Error(err)
+		return errors.New("error while fetching releases")
+	}
+
+	// Make sure response is not empty
+	// An empty response means that the given release does not exist
+	// Reflect is used since release is a pointer to a struct
+	if reflect.DeepEqual(release, &ReleaseResponse{}) {
+		return errors.New("unable to fetch specified release tag. Make sure it exists")
+	}
+
+	// Get the URL to download the plugin
+	asset := release.findCompatibleAsset()
+	if asset == nil {
+		return errors.New("plugin not found. Make sure it exists")
+	}
+
+	// Download the plugin
+	err = asset.download(pluginPath)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}