react-relay-network-modern/es/middlewares/upload.js

Network Layer for React Relay and Express (Batch Queries, AuthToken, Logging, Retry)

import { extractFiles } from 'extract-files';
import RelayRequestBatch from '../RelayRequestBatch';
export default function uploadMiddleware() {
  return next => async req => {
    if (req instanceof RelayRequestBatch) {
      throw new Error('RelayRequestBatch is not supported');
    }
    const operations = {
      query: req.operation.text,
      variables: req.variables
    };
    const {
      clone: extractedOperations,
      files
    } = extractFiles(operations);
    if (files.size) {
      const formData = new FormData();
      formData.append('operations', JSON.stringify(extractedOperations));
      const pathMap = {};
      let i = 0;
      files.forEach(paths => {
        pathMap[++i] = paths;
      });
      formData.append('map', JSON.stringify(pathMap));
      i = 0;
      files.forEach((paths, file) => {
        formData.append(++i, file, file.name);
      });
      req.fetchOpts.method = 'POST';
      req.fetchOpts.body = formData;
      delete req.fetchOpts.headers['Content-Type'];
    }
    const res = await next(req);
    return res;
  };
}