fix(postrenderer): correctly serialize manifests for WASM plugins

WASM post-renderer plugins were receiving empty manifests because
bytes.Buffer does not serialize its contents when encoded to JSON.

This change updates the schema to use string and converts between
string and bytes.Buffer at runtime boundaries so manifests are passed
correctly to and from plugins.

Signed-off-by: samuraikillers <fatechanger77@gmail.com>

internal/plugin/runtime_subprocess.go

@@ -255,7 +255,7 @@ func (r *SubprocessPluginRuntime) runPostrenderer(input *Input) (*Output, error)
 
 	go func() {
 		defer stdin.Close()
-		io.Copy(stdin, msg.Manifests)
+		io.Copy(stdin, bytes.NewBufferString(msg.Manifests))
 	}()
 
 	postRendered := &bytes.Buffer{}
@@ -272,7 +272,7 @@ func (r *SubprocessPluginRuntime) runPostrenderer(input *Input) (*Output, error)
 
 	return &Output{
 		Message: schema.OutputMessagePostRendererV1{
-			Manifests: postRendered,
+			Manifests: postRendered.String(),
 		},
 	}, nil
 }

internal/plugin/schema/postrenderer.go

@@ -16,19 +16,15 @@ limitations under the License.
 
 package schema
 
-import (
-	"bytes"
-)
-
 // InputMessagePostRendererV1 implements Input.Message
 type InputMessagePostRendererV1 struct {
-	Manifests *bytes.Buffer `json:"manifests"`
+	Manifests string   `json:"manifests"`
 	// from CLI --post-renderer-args
 	ExtraArgs []string `json:"extraArgs"`
 }
 
 type OutputMessagePostRendererV1 struct {
-	Manifests *bytes.Buffer `json:"manifests"`
+	Manifests string   `json:"manifests"`
 }
 
 type ConfigPostRendererV1 struct{}

pkg/postrenderer/postrenderer.go

@@ -64,7 +64,7 @@ func (r *postRendererPlugin) Run(renderedManifests *bytes.Buffer) (*bytes.Buffer
 	input := &plugin.Input{
 		Message: schema.InputMessagePostRendererV1{
 			ExtraArgs: r.args,
-			Manifests: renderedManifests,
+			Manifests: renderedManifests.String(),
 		},
 	}
 	output, err := r.plugin.Invoke(context.Background(), input)
@@ -76,9 +76,9 @@ func (r *postRendererPlugin) Run(renderedManifests *bytes.Buffer) (*bytes.Buffer
 
 	// If the binary returned almost nothing, it's likely that it didn't
 	// successfully render anything
-	if len(bytes.TrimSpace(outputMessage.Manifests.Bytes())) == 0 {
+	if len(bytes.TrimSpace([]byte(outputMessage.Manifests))) == 0 {
 		return nil, fmt.Errorf("post-renderer %q produced empty output", r.plugin.Metadata().Name)
 	}
 
-	return outputMessage.Manifests, nil
+	return bytes.NewBufferString(outputMessage.Manifests), nil
 }