app/lib/search/sse.mjs

Functions

Imports

It imports no other module of this repo. Imported by app/enhance/ask.ts, app/lib/search/ask-prompt.mjs, app/lib/search/ask.server.ts.

Source

1// Server-sent-event frame reading for the Ask stream, shared by the reader's enhancement, the answer
2// cache and the draft guard, so all three read one frame the same way. No imports: the enhancement
3// bundle carries it.
4
5/**
6 * One frame's event name and its data lines joined, each line with its `data:` prefix removed.
7 *
8 * @param {string} frame one frame, without its blank-line terminator
9 * @returns {{ event: string, data: string }}
10 */
11export function frameFields(frame) {
12  let event = "";
13  /** @type {string[]} */
14  const dataLines = [];
15  for (const line of frame.split("\n")) {
16    if (line.startsWith("event:")) event = line.slice(6).trim();
17    else if (line.startsWith("data:")) dataLines.push(line.slice(5).trim());
18  }
19  return { event, data: dataLines.join("\n") };
20}
21
22/**
23 * Takes the complete frames off the front of a buffer, leaving the unfinished tail as `rest`. A
24 * frame with no data, the `[DONE]` sentinel, or data that is not JSON carries nothing to show and
25 * is left out.
26 *
27 * @param {string} buffer everything decoded and not yet consumed
28 * @returns {{ frames: Array<{ event: string, data: unknown }>, rest: string }}
29 */
30export function takeSseFrames(buffer) {
31  const parts = buffer.split("\n\n");
32  const rest = parts.pop() ?? "";
33  /** @type {Array<{ event: string, data: unknown }>} */
34  const frames = [];
35  for (const part of parts) {
36    const { event, data } = frameFields(part);
37    if (!data || data === "[DONE]") continue;
38    let parsed;
39    try {
40      parsed = JSON.parse(data);
41    } catch {
42      continue;
43    }
44    frames.push({ event, data: parsed });
45  }
46  return { frames, rest };
47}
48
49/**
50 * The text a completion frame adds to the answer, or undefined for a frame that adds none.
51 *
52 * @param {unknown} data a parsed frame's data
53 * @returns {string | undefined}
54 */
55export function answerDelta(data) {
56  const delta = /** @type {{ choices?: Array<{ delta?: { content?: unknown } }> } | null} */ (data)
57    ?.choices?.[0]?.delta?.content;
58  return typeof delta === "string" ? delta : undefined;
59}