Meta: more correct handling of HTML-unescaping

It turns out that straight byte-based replacements of unicode escape
characters back to their ascii representations is invalid if the unicode
escape character itself is escaped (e.g. "\u003c" => "\\u003c" => "\<").

To solve this, we will instead unmarshal Meta objects to
map[string]interface{}, extract the expected Meta fields from the map,
and then use a JSON encoder with SetEscapeHTML(false) to re-encode the
map back to JSON to be stored in Meta.Blob.

Signed-off-by: Joe Lanford <[email protected]>

Author: joelanford

alpha/declcfg/declcfg.go

@@ -7,8 +7,6 @@ import (
 	"fmt"
 	"strings"
 
-	"go4.org/bytereplacer"
-
 	"github.com/operator-framework/operator-registry/alpha/property"
 )
 
@@ -100,25 +98,27 @@ func (m Meta) MarshalJSON() ([]byte, error) {
 }
 
 func (m *Meta) UnmarshalJSON(blob []byte) error {
-	blob = bytereplacer.New(`\u003c`, "<", `\u003e`, ">", `\u0026`, "&").Replace(blob)
-
-	type tmp struct {
-		Schema     string              `json:"schema"`
-		Package    string              `json:"package,omitempty"`
-		Name       string              `json:"name,omitempty"`
-		Properties []property.Property `json:"properties,omitempty"`
+	blobMap := map[string]interface{}{}
+	if err := json.Unmarshal(blob, &blobMap); err != nil {
+		return err
+	}
+	for key, ptr := range map[string]*string{"schema": &m.Schema, "package": &m.Package, "name": &m.Name} {
+		if _, ok := blobMap[key]; !ok {
+			continue
+		}
+		v, ok := blobMap[key].(string)
+		if !ok {
+			return fmt.Errorf("expected value for key %q to be a string, got %t: %v", key, blobMap[key], blobMap[key])
+		}
+		*ptr = v
 	}
-	var t tmp
-	if err := json.Unmarshal(blob, &t); err != nil {
-		// TODO: return an error that includes the the full JSON message,
-		//    the offset of the error, and the error message. Let callers
-		//    decide how to format it.
-		return errors.New(resolveUnmarshalErr(blob, err))
+	buf := bytes.Buffer{}
+	enc := json.NewEncoder(&buf)
+	enc.SetEscapeHTML(false)
+	if err := enc.Encode(blobMap); err != nil {
+		return err
 	}
-	m.Schema = t.Schema
-	m.Package = t.Package
-	m.Name = t.Name
-	m.Blob = blob
+	m.Blob = buf.Bytes()
 	return nil
 }