Initial QSfera import

Server/services/search/pkg/content/extractor.go

@@ -0,0 +1,31 @@
+package content
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	provider "github.com/cs3org/go-cs3apis/cs3/storage/provider/v1beta1"
+)
+
+// Extractor is responsible to extract content and meta information from documents.
+type Extractor interface {
+	Extract(ctx context.Context, ri *provider.ResourceInfo) (Document, error)
+}
+
+func getFirstValue(m map[string][]string, key string) (string, error) {
+	if m == nil {
+		return "", errors.New("undefined map")
+	}
+
+	v, ok := m[key]
+	if !ok {
+		return "", fmt.Errorf("unknown key: %v", key)
+	}
+
+	if len(m) == 0 {
+		return "", fmt.Errorf("no values for: %v", key)
+	}
+
+	return v[0], nil
+}