Add plugin validity checks to isPlugin

Signed-off-by: Zethan <zetHannes@outlook.com>

pkg/plugin/installer/installer.go

@@ -17,6 +17,7 @@ package installer
 
 import (
 	"fmt"
+	"io/ioutil"
 	"log"
 	"net/http"
 	"os"
@@ -26,6 +27,7 @@ import (
 	"github.com/pkg/errors"
 
 	"helm.sh/helm/v3/pkg/plugin"
+	"sigs.k8s.io/yaml"
 )
 
 // ErrMissingMetadata indicates that plugin.yaml is missing.
@@ -120,10 +122,18 @@ func isRemoteHTTPArchive(source string) bool {
 	return false
 }
 
-// isPlugin checks if the directory contains a plugin.yaml file.
+// isPlugin checks if the directory contains a valid plugin.yaml file
 func isPlugin(dirname string) bool {
-	_, err := os.Stat(filepath.Join(dirname, plugin.PluginFileName))
-	return err == nil
+	fpath := filepath.Join(dirname, plugin.PluginFileName)
+	if _, err := os.Stat(fpath); err != nil {
+		return false
+	}
+	plug := &plugin.Plugin{Dir: dirname}
+	data, _ := ioutil.ReadFile(fpath)
+	if err := yaml.UnmarshalStrict(data, &plug.Metadata); err != nil || plug.Metadata == nil {
+		return false
+	}
+	return true
 }
 
 var logger = log.New(os.Stderr, "[debug] ", log.Lshortfile)

pkg/plugin/installer/installer_test.go

@@ -38,3 +38,15 @@ func TestIsRemoteHTTPArchive(t *testing.T) {
 		t.Error("Expected media type match to fail")
 	}
 }
+
+func TestIsPlugin(t *testing.T) {
+	if isPlugin("../testdata/plugdir/bad/empty-config") {
+		t.Errorf("Expected empty plugin file not to be considered a plugin")
+	}
+	if !isPlugin("../testdata/plugdir/good/echo") {
+		t.Errorf("Expected valid plugin file to be considered a plugin")
+	}
+	if isPlugin("../testdata/plugdir/bad/invalid") {
+		t.Errorf("Expected invalid plugin not to be considered a plugin")
+	}
+}

pkg/plugin/testdata/plugdir/bad/empty-config/plugin.yaml

@@ -0,0 +1 @@
+ 

pkg/plugin/testdata/plugdir/bad/invalid/plugin.yaml

@@ -0,0 +1,3 @@
+name: "invalid-test"
+version: "1.2.3"
+usa