Streaming quotes, live rates and price alerts

Three sources, three cadences

Consuming the stream

const res = await fetch(sseURL, {
  headers: { "X-API-Key": key, Accept: "text/event-stream" },
});
const reader = res.body.pipeThrough(new TextDecoderStream()).getReader();

let buf = "";
for (;;) {
  const { value, done } = await reader.read();
  if (done) break;
  buf += value;

  let i;
  while ((i = buf.indexOf("\n\n")) !== -1) {          // one SSE frame
    const frame = buf.slice(0, i); buf = buf.slice(i + 2);
    const event = /^event:\s*(.+)$/m.exec(frame)?.[1];
    const data = JSON.parse(/^data:\s*(.+)$/m.exec(frame)?.[1] ?? "null");

    if (event === "offer") render(data);             // draw it the moment it lands
    if (event === "provider_error") log(data);       // log, never show
    if (event === "done") rerank(data.deviations);   // final ranking of what you drew
  }
}

Building price alerts

1. Poll the feed, not the quote endpoint

   /v1/export/rates.xml is keyless, cached and covers every direction at once — one request serves every alert you hold. Quoting each user's pair separately is what gets a partner throttled by providers.

2. Compare against the direction, with its limits

   An alert on BTC → USDTTRC20 is only meaningful within minamount and maxamount. Store both with the threshold so you never notify someone about a rate they cannot take.

3. Debounce before you notify

   Rates wobble. Require the threshold to hold for two consecutive reads, and re-arm an alert only after the rate has moved back by a margin — otherwise a flat market sends a hundred notifications.

4. Turn the alert into an offer

   The moment the user acts, quote the pair properly with /quotes or /quotes-sse: the feed says what was available a few seconds ago, and only an offer is executable — for five minutes.

Status alerts work the same way in reverse: one poll loop per open order, your own fan-out to whatever your users listen on — a websocket, a webhook of your own, a Telegram message.

What is not real-time

Who runs on this

• Monitors and aggregators reading rates.xml in the format they already parse.
• Alert bots — Telegram, Discord, email — firing on an executable rate rather than an exchange ticker.
• B2B partners with dashboards, streaming their own customers' order statuses out of one poll loop.
• Wallets and calculators where the number on screen has to move while the user thinks.

Questions