middleware.js

import path from 'path';

import mime from 'mime-types';

import getFilenameFromUrl from './utils/getFilenameFromUrl';
import handleRangeHeaders from './utils/handleRangeHeaders';
import ready from './utils/ready';

export default function wrapper(context) {
  return async function middleware(req, res, next) {
    const acceptedMethods = context.options.methods || ['GET', 'HEAD'];

    // fixes #282. credit @cexoso. in certain edge situations res.locals is undefined.
    // eslint-disable-next-line no-param-reassign
    res.locals = res.locals || {};

    if (!acceptedMethods.includes(req.method)) {
      await goNext();
      return;
    }

    ready(context, processRequest, req);

    async function goNext() {
      if (!context.options.serverSideRender) {
        return next();
      }

      return new Promise((resolve) => {
        ready(
          context,
          () => {
            // eslint-disable-next-line no-param-reassign
            res.locals.webpack = { devMiddleware: context };

            resolve(next());
          },
          req
        );
      });
    }

    async function processRequest() {
      const filename = getFilenameFromUrl(context, req.url);
      const { headers } = context.options;
      let content;

      if (!filename) {
        await goNext();
        return;
      }

      try {
        content = context.outputFileSystem.readFileSync(filename);
      } catch (_ignoreError) {
        await goNext();
        return;
      }

      const contentTypeHeader = res.get
        ? res.get('Content-Type')
        : res.getHeader('Content-Type');

      if (!contentTypeHeader) {
        // content-type name(like application/javascript; charset=utf-8) or false
        const contentType = mime.contentType(path.extname(filename));

        // Only set content-type header if media type is known
        // https://tools.ietf.org/html/rfc7231#section-3.1.1.5
        if (contentType) {
          // Express API
          if (res.set) {
            res.set('Content-Type', contentType);
          }
          // Node.js API
          else {
            res.setHeader('Content-Type', contentType);
          }
        }
      }

      if (headers) {
        const names = Object.keys(headers);

        for (const name of names) {
          // Express API
          if (res.set) {
            res.set(name, headers[name]);
          }
          // Node.js API
          else {
            res.setHeader(name, headers[name]);
          }
        }
      }

      // Buffer
      content = handleRangeHeaders(context, content, req, res);

      // Express API
      if (res.send) {
        res.send(content);
      }
      // Node.js API
      else {
        res.setHeader('Content-Length', content.length);

        if (req.method === 'HEAD') {
          res.end();
        } else {
          res.end(content);
        }
      }
    }
  };
}