feat: [backend] vision support (#1510)

Co-authored-by: Garfield Dai <dai.hai@foxmail.com>

api/controllers/files/image_preview.py

@@ -0,0 +1,40 @@
+from flask import request, Response
+from flask_restful import Resource
+
+import services
+from controllers.files import api
+from libs.exception import BaseHTTPException
+from services.file_service import FileService
+
+
+class ImagePreviewApi(Resource):
+    def get(self, file_id):
+        file_id = str(file_id)
+
+        timestamp = request.args.get('timestamp')
+        nonce = request.args.get('nonce')
+        sign = request.args.get('sign')
+
+        if not timestamp or not nonce or not sign:
+            return {'content': 'Invalid request.'}, 400
+
+        try:
+            generator, mimetype = FileService.get_image_preview(
+                file_id,
+                timestamp,
+                nonce,
+                sign
+            )
+        except services.errors.file.UnsupportedFileTypeError:
+            raise UnsupportedFileTypeError()
+
+        return Response(generator, mimetype=mimetype)
+
+
+api.add_resource(ImagePreviewApi, '/files/<uuid:file_id>/image-preview')
+
+
+class UnsupportedFileTypeError(BaseHTTPException):
+    error_code = 'unsupported_file_type'
+    description = "File type not allowed."
+    code = 415