Allow using the --from to get template from a github release

Currently, `clusterctl generate cluster`'s `--from` flag only support
yaml files from github code. Trying to get template from a rlease tag is
failing.

This PR adds the option to use the `--form` also for release assets.

Signed-off-by: Nahshon Unna-Tsameret <nunnatsa@redhat.com>

cmd/clusterctl/client/cluster/template.go

@@ -19,6 +19,7 @@ package cluster
 import (
 	"context"
 	"encoding/base64"
+	"fmt"
 	"io"
 	"net/http"
 	"net/url"
@@ -181,35 +182,77 @@ func (t *templateClient) getGitHubFileContent(rURL *url.URL) ([]byte, error) {
 
 	// Extract all the info from url split.
 	owner := urlSplit[0]
-	repository := urlSplit[1]
+	repo := urlSplit[1]
+	linkType := urlSplit[2]
 	branch := urlSplit[3]
 	path := strings.Join(urlSplit[4:], "/")
 
 	// gets the GitHub client
-	client, err := t.gitHubClientFactory(t.configClient.Variables())
+	ghClient, err := t.gitHubClientFactory(t.configClient.Variables())
 	if err != nil {
 		return nil, err
 	}
 
 	// gets the file from GiHub
-	fileContent, _, _, err := client.Repositories.GetContents(context.TODO(), owner, repository, path, &github.RepositoryContentGetOptions{Ref: branch})
+	switch linkType {
+	case "blob": // get file from a code in a github repo
+		return getGithubFileContentFromCode(ghClient, rURL.Path, owner, repo, path, branch)
+
+	case "releases": // get a github release asset
+		tag := urlSplit[4]
+		assetName := urlSplit[5]
+
+		return getGithubAssetFromRelease(rURL.Path, ghClient, owner, repo, tag, assetName)
+
+	default:
+		return nil, fmt.Errorf("unknown github URL: %v", rURL)
+	}
+}
+
+func getGithubFileContentFromCode(ghClient *github.Client, fullPath string, owner string, repo string, path string, branch string) ([]byte, error) {
+	fileContent, _, _, err := ghClient.Repositories.GetContents(ctx, owner, repo, path, &github.RepositoryContentGetOptions{Ref: branch})
 	if err != nil {
-		return nil, handleGithubErr(err, "failed to get %q", rURL.Path)
+		return nil, handleGithubErr(err, "failed to get %q", fullPath)
 	}
 	if fileContent == nil {
-		return nil, errors.Errorf("%q does not return a valid file content", rURL.Path)
+		return nil, errors.Errorf("%q does not return a valid file content", fullPath)
 	}
 	if fileContent.Encoding == nil || *fileContent.Encoding != "base64" {
-		return nil, errors.Errorf("invalid encoding detected for %q. Only base64 encoding supported", rURL.Path)
+		return nil, errors.Errorf("invalid encoding detected for %q. Only base64 encoding supported", fullPath)
 	}
-
 	content, err := base64.StdEncoding.DecodeString(*fileContent.Content)
 	if err != nil {
-		return nil, errors.Wrapf(err, "failed to decode file %q", rURL.Path)
+		return nil, errors.Wrapf(err, "failed to decode file %q", fullPath)
 	}
 	return content, nil
 }
 
+func getGithubAssetFromRelease(path string, ghClient *github.Client, owner string, repo string, tag string, assetName string) ([]byte, error) {
+	release, _, err := ghClient.Repositories.GetReleaseByTag(ctx, owner, repo, tag)
+	if err != nil {
+		return nil, handleGithubErr(err, "failed to get release '%s' from %s%s repository", tag, owner, repo)
+	}
+
+	var rc io.ReadCloser
+	for _, asset := range release.Assets {
+		if asset.Name != nil && *asset.Name == assetName {
+			rc, _, err = ghClient.Repositories.DownloadReleaseAsset(ctx, owner, repo, asset.GetID(), ghClient.Client())
+			if err != nil {
+				return nil, errors.Wrapf(err, "failed to download file %q", path)
+			}
+			break
+		}
+	}
+
+	if rc == nil {
+		return nil, fmt.Errorf("failed to download the file %q", path)
+	}
+
+	defer func() { _ = rc.Close() }()
+
+	return io.ReadAll(rc)
+}
+
 func getGitHubClient(configVariablesClient config.VariablesClient) (*github.Client, error) {
 	var authenticatingHTTPClient *http.Client
 	if token, err := configVariablesClient.Get(config.GitHubTokenVariable); err == nil {

cmd/clusterctl/client/cluster/template_test.go

@@ -304,6 +304,25 @@ func Test_templateClient_GetFromURL(t *testing.T) {
 		}`)
 	})
 
+	mux.HandleFunc("/repos/some-owner/some-repo/releases/tags/v1.0.0", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{
+		  "tag_name": "v1.0.0",
+		  "name": "v1.0.0",
+		  "id": 12345678,
+		  "url": "https://api.github.com/repos/some-owner/some-repo/releases/12345678",
+		  "assets": [
+			{
+			  "id": 87654321,
+			  "name": "cluster-template.yaml"
+			}
+		  ]
+		}`)
+	})
+
+	mux.HandleFunc("/repos/some-owner/some-repo/releases/assets/87654321", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, template)
+	})
+
 	path := filepath.Join(tmpDir, "cluster-template.yaml")
 	g.Expect(os.WriteFile(path, []byte(template), 0600)).To(Succeed())
 
@@ -344,6 +363,16 @@ func Test_templateClient_GetFromURL(t *testing.T) {
 			want:    template,
 			wantErr: false,
 		},
+		{
+			name: "Get asset from GitHub release",
+			args: args{
+				templateURL:         "https://github.com/some-owner/some-repo/releases/download/v1.0.0/cluster-template.yaml",
+				targetNamespace:     "",
+				skipTemplateProcess: false,
+			},
+			want:    template,
+			wantErr: false,
+		},
 		{
 			name: "Get from stdin",
 			args: args{