app/lib/negotiate.mjs

Functions

Imports

It imports no other module of this repo. Imported by app/lib/markdown-twin.ts, app/routes/admin.media._index.tsx, app/routes/search.tsx, workers/app.ts.

Source

1// Plain .mjs so `node --test` can import it; the types are JSDoc under checkJs.
2
3/**
4 * @param {Request} request
5 * @returns {Map<string, number>}
6 */
7export function acceptQValues(request) {
8  /** @type {Map<string, number>} */
9  const values = new Map();
10  const accept = request.headers.get("accept");
11  if (!accept) return values;
12
13  for (const part of accept.split(",")) {
14    const [range, ...params] = part.trim().split(";");
15    const type = (range ?? "").trim().toLowerCase();
16    if (!type) continue;
17
18    let q = 1;
19    for (const param of params) {
20      const [key, value] = param.trim().split("=");
21      if (key?.trim().toLowerCase() === "q") {
22        const parsed = Number.parseFloat(value ?? "");
23        if (!Number.isNaN(parsed)) q = parsed;
24      }
25    }
26
27    values.set(type, Math.max(values.get(type) ?? -1, q));
28  }
29
30  return values;
31}
32
33/** Wildcards count as votes for HTML, the default representation. */
34const HTML_RANGES = ["text/html", "text/*", "*/*"];
35
36/**
37 * @param {Map<string, number>} values
38 * @returns {number}
39 */
40function htmlWeight(values) {
41  let html = -1;
42  for (const range of HTML_RANGES) {
43    html = Math.max(html, values.get(range) ?? -1);
44  }
45  return html;
46}
47
48/**
49 * A tie goes to HTML, the safer default for a client that guessed.
50 *
51 * @param {Request} request @param {string} wanted
52 * @returns {boolean}
53 */
54export function prefersType(request, wanted) {
55  const values = acceptQValues(request);
56  const target = values.get(wanted.toLowerCase()) ?? -1;
57  return target > 0 && target > htmlWeight(values);
58}
59
60/**
61 * `caches.default` ignores `Vary: Accept`, so a non-HTML request must bypass the
62 * Worker's cache or it is served the stored HTML. Deliberately wider than the
63 * routes that negotiate: being wide costs a miss, being narrow serves wrong bytes.
64 *
65 * @param {Request} request
66 * @returns {boolean}
67 */
68export function negotiatesAwayFromHtml(request) {
69  const values = acceptQValues(request);
70  if (values.size === 0) return false;
71
72  const html = htmlWeight(values);
73  for (const [type, q] of values) {
74    if (HTML_RANGES.includes(type)) continue;
75    if (q > 0 && q > html) return true;
76  }
77  return false;
78}