recipe_modules/yaml/api.py

# Copyright 2020 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

from recipe_engine import recipe_api


class YamlApi(recipe_api.RecipeApi):
    """Provides functions to parse YAML files."""

    def parse_yaml(self, file_path):
        """parse a yaml file and return its content as a JSON object.

        E.g. api.yaml.parse_yaml(file_path)

            will read yaml file from file_path and converted into a JSON
            object.

        Args:
          * file_path (Path) - The path to the dockerfile.
        """
        return self.m.python(
            "load yaml %s" % file_path,
            self.resource("parse_yaml.py"),
            args=[file_path],
            stdout=self.m.json.output(),
        ).stdout

    def _traverse_json(self, json_data, field):
        if isinstance(json_data, dict):
            if field in json_data:
                return json_data[field]
            for key in json_data:
                return_val = self._traverse_json(json_data[key], field)
                if return_val != None:
                    return return_val
        if isinstance(json_data, list):
            for item in json_data:
                return_val = self._traverse_json(item, field)
                if return_val != None:
                    return return_val
        return None

    def retrieve_field(self, file_path, field_name):
        """retrieve a field from a YAML file and return the first found value if it
        exists. Otherwise return None.

        E.g. api.yaml.retrieve_field(file_path, 'region')

        Args:
          * file_path (Path) - The path to the YAML file.
          * field_name (str) - The name of the field.
        """
        return self._traverse_json(self.parse_yaml(file_path), field_name)