static-cms/packages/netlify-cms-lib-util/src/backendUtil.js

import { get } from "lodash";
import { fromJS } from "immutable";
import { fileExtension } from "./path";

export const filterByPropExtension = (extension, propName) => arr =>
  arr.filter(el => fileExtension(get(el, propName)) === extension);

const catchFormatErrors = (format, formatter) => res => {
  try {
    return formatter(res);
  } catch (err) {
    throw new Error(`Response cannot be parsed into the expected format (${ format }): ${ err.message }`);
  }
};

const responseFormatters = fromJS({
  json: async res => {
    const contentType = res.headers.get("Content-Type");
    if (!contentType.startsWith("application/json") && !contentType.startsWith("text/json")) {
      throw new Error(`${ contentType } is not a valid JSON Content-Type`);
    }
    return res.json();
  },
  text: async res => res.text(),
  blob: async res => res.blob(),
}).mapEntries(
  ([format, formatter]) => [format, catchFormatErrors(format, formatter)]
);

export const parseResponse = async (res, { expectingOk = true, format = "text" } = {}) => {
  if (expectingOk && !res.ok) {
    throw new Error(`Expected an ok response, but received an error status: ${ res.status }.`);
  }
  const formatter = responseFormatters.get(format, false);
  if (!formatter) {
    throw new Error(`${ format } is not a supported response format.`);
  }
  const body = await formatter(res);
  return body;
};

export const responseParser = options => res => parseResponse(res, options);