Local-ESI

Make your Express app work like it had Akamai Edge Side Includes parsing or just stream your ESI decorated markup to the parser.

API

• ESI: transform class that returns an ESI transform stream
• HTMLWriter: transform class that returns markup from object stream
• parse: async function that returns ESI evaluated markup

new ESI([options])

Create an ESI transform stream. Emits events.

Arguments:

• options: optional options object with headers and cookies
  • headers: request headers, accessible through ESI globals HTTP_<HEADER_NAME>, x-forwarded-for will be accessible as REMOTE_ADDR
  • cookies: object with request cookies, accessible through ESI global HTTP_COOKIE
  • path: string request path, mapped to ESI global REQUEST_PATH
  • query: object request query parameters, accessible through ESI global QUERY_STRING
  • localhost: host to use when a relative src is used by eval or include, defaults to headers.host

Returns:

• esi evaluated object stream

Example express route:

"use strict";

const HTMLParser = require("@bonniernews/atlas-html-stream");
const {ESI, HTMLWriter} = require("@bonniernews/local-esi");
const {pipeline} = require("stream");

module.exports = function streamRender(req, res, next) {
  const { headers, cookies, path, query } = req;

  const options = {
    headers,
    cookies,
    path,
    query,
    localhost: `localhost:${req.socket.server.address().port}`,
  };

  const esi = new ESI(options)
    .once("set_redirect", function onSetRedirect(statusCode, location) {
      res.status(statusCode).redirect(location);
      this.destroy();
    })
    .on("set_response_code", function onSetResponseCode(statusCode, body) {
      res.status(statusCode);
      if (!body) return;
      res.send(body);
      this.destroy();
    })
    .on("add_header", (name, value) => {
      res.set(name, value);
    });

  const body = "";

  pipeline([
    res.render("index"),
    new HTMLParser({preserveWS: true}),
    esi,
    new HTMLWriter(),
  ], (err) => {
    if (err?.code === "ERR_STREAM_PREMATURE_CLOSE"]) {
      return;
    } else if (err) {
      return next(err);
    }

    return res.send(body);
  }).on("data", (chunk) => {
    body += chunk;
  });
};

parse(html, options)

Arguments:

• html: markup to parse
• options: same as for for ESI

Returns promise:

• body: string with ESI evaluated markup or body from $set_response_code
• statusCode: occasional status code from $set_response_code or $set_redirect
• headers: object with added headers (in lowercase) from $add_header or $set_redirect(location), NB! set-cookie will be in a list

Example express route:

"use strict";

const {parse} = require("@bonniernews/local-esi");

module.exports = function render(req, res, next) {
  const { headers, cookies, path, query } = req;

  const options = {
    headers,
    cookies,
    path,
    query,
    localhost: `localhost:${req.socket.server.address().port}`,
  };

  const html = res.render("index");

  const {statusCode, headers, body} = await parse(html, options);
  if (statusCode < 309 && statusCode > 300) {
    return res.redirect(response.statusCode, headers.location);
  }

  res.status(statusCode || 200);
  return res.send(body);
};

new HTMLWriter()

Returns transform object stream to markup buffer stream.

ESI Parsing Events

ESI instructions are emitted as events.

set_response_code

Parser encountered a $set_response_code instruction with status code and optional body.

Signature:

• statusCode: number HTTP status code
• body: optional string body

add_header

Parser encountered a $add_header instruction with HTTP header name and value.

Signature:

• name: HTTP header name
• value: HTTP header value

set_redirect

Parser encountered a $set_redirect instruction with optional status code and location.

Signature:

• statusCode: redirect HTTP status code
• location: redirect location

Markup object stream

Object streams requires the schema {name, data, text} representing tag name, tag attributes, and text. This project uses @bonniernews/atlas-html-stream for html parsing.