fix: enable preview for legacy .doc documents in Go server (#17767)

internal/service/document/document_artifact.go

@@ -9,6 +9,7 @@ import (
 	"ragflow/internal/common"
 	"ragflow/internal/dao"
 	"ragflow/internal/entity"
+	"ragflow/internal/parser/parser"
 	"ragflow/internal/storage"
 	"ragflow/internal/utility"
 )
@@ -225,9 +226,28 @@ func (s *DocumentService) GetDocumentPreview(ctx context.Context, docID string)
 	ext := utility.GetFileExtension(fileName)
 	contentType := utility.GetContentType(ext, doc.Type)
 
+	// Legacy .doc (OLE2) documents cannot be rendered by the
+	// .docx-only web previewer; serve extracted plain text instead.
+	if ext == "doc" {
+		if text, cerr := extractDOCPreviewText(ctx, fileName, data); cerr == nil {
+			data = []byte(text)
+			contentType = "text/plain; charset=utf-8"
+		}
+	}
+
 	return &DocumentPreview{
 		Data:        data,
 		ContentType: contentType,
 		FileName:    fileName,
 	}, nil
 }
+
+// extractDOCPreviewText extracts plain text from a legacy .doc
+// document via the office_oxide-backed DOCParser.
+func extractDOCPreviewText(ctx context.Context, filename string, data []byte) (string, error) {
+	res := parser.NewDOCParser().ParseWithResult(ctx, filename, data)
+	if res.Err != nil {
+		return "", res.Err
+	}
+	return res.Text, nil
+}