Real-Time Swap Transactions Streaming

event: pool
request_id: 1
data: {"chain":"solana","pool_id":"Czfq3xZZDmsdGdUyrNLtRhGc47cXcZtLG4crryfu44zE","block_number":"440660176","block_timestamp":"2026-08-21T09:49:04Z","tx_hash":"xdEpqxQp4Pp1NNceoaiqkSrc7EYn5zQGNNsobBdsu1au9EiE88TX3GQ1iY1hxsJjkpMq9ufqLd5irVthJSddmPQ","sender":"9TiD2JbKz7tphbs1LzjFR7HbXhVfeRW2vhWVisKqwme","recipient":"AdphhurSRH4euoAasqypvoJLbD8XpuztVSzg2nqmPxcx","token_0":"So11111111111111111111111111111111111111112","token_1":"EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v","amount_0":4841787021,"amount_1":-445711274,"amount_0_usd":445.8084604429579,"amount_1_usd":445.4707026504548,"price_0_usd":92.07519011253054,"price_1_usd":0.9994602529404603,"volume_usd":225.2765305105}

STREAM  token_0 = 0xa0b8…eb48 (USDC)   price_0_usd = 1.00
REST    token_0 = 0xc02a…6cc2 (WETH)   price_0_usd = 2398.24

JSON.parse('{"amount_1":32267156849925919299}').amount_1
// 32267156849925920000   <- 701 wei gone, silently

amount_0_usd = 445.81   amount_1_usd = 445.47   volume_usd = 225.28

// swap-tail.mjs: Node 18+, no dependencies. Needs DEXPAPRIKA_API_KEY.
const KEY = process.env.DEXPAPRIKA_API_KEY;
const SUBS = [
  { chain: "solana", address: "Czfq3xZZDmsdGdUyrNLtRhGc47cXcZtLG4crryfu44zE", method: "pool", request_id: 1 },
];

// Tokens are resolved by ADDRESS, never by index: _0 is not the same token
// across REST and streaming for some EVM pools.
const WATCH = {
  So11111111111111111111111111111111111111112: "SOL",
  EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v: "USDC",
};

const seen = new Set();
let lastBeat = Date.now();

async function tail() {
  const res = await fetch("https://streaming.dexpaprika.com/sse/transactions", {
    method: "POST",
    // The key is the whole Authorization value. No "Bearer".
    headers: {
      authorization: KEY,
      accept: "text/event-stream",
      "content-type": "application/json",
    },
    body: JSON.stringify(SUBS),
  });

  if (!res.ok) {
    // 403 = no key, 401 = key rejected, 400 = the subscription is wrong.
    // Only the last one is worth retrying after a change.
    throw new Error(`${res.status} ${await res.text()}`);
  }

  const decoder = new TextDecoder();
  let buffer = "";

  for await (const chunk of res.body) {
    buffer += decoder.decode(chunk, { stream: true });
    const frames = buffer.split("\n\n");
    buffer = frames.pop() ?? "";

    for (const frame of frames) {
      const name = frame.match(/^event: (.+)$/m)?.[1];
      const data = frame.match(/^data: (.+)$/m)?.[1];
      if (!name || !data) continue;

      if (name === "ping") { lastBeat = Date.now(); continue; }
      if (name === "warning") { console.warn("[warning]", data); continue; }
      if (name === "error") { throw new Error(`stream error: ${data}`); }
      if (name !== "pool" && name !== "token") continue;

      const s = JSON.parse(data);

      // A reconnect can redeliver, and one swap can match two subscriptions.
      const id = `${s.tx_hash}:${s.pool_id}`;
      if (seen.has(id)) continue;
      seen.add(id);

      // amount_0/amount_1 are raw JSON numbers and lose precision above
      // 2^53 on 18-decimal tokens. The _usd fields are ordinary floats.
      const sold = s.amount_0 > 0 ? WATCH[s.token_0] : WATCH[s.token_1];
      const bought = s.amount_0 > 0 ? WATCH[s.token_1] : WATCH[s.token_0];
      const size = Math.abs(s.amount_0 > 0 ? s.amount_0_usd : s.amount_1_usd);

      console.log(
        `${s.block_timestamp}  ${sold} -> ${bought}  $${size.toFixed(2)}  ${s.tx_hash.slice(0, 12)}`,
      );
    }
  }
}

// Watchdog: pings every 15s, so 45s of silence means the socket is gone,
// not that the pool is quiet.
setInterval(() => {
  if (Date.now() - lastBeat > 45_000) {
    console.error("no heartbeat, exiting for the supervisor to restart");
    process.exit(1);
  }
}, 5_000);

let delay = 1_000;
for (;;) {
  try {
    await tail();
    delay = 1_000;
  } catch (err) {
    console.error(String(err));
    if (/^4(0[013])/.test(String(err))) process.exit(1); // fix the request, do not retry
    await new Promise((r) => setTimeout(r, delay + Math.random() * 500));
    delay = Math.min(delay * 2, 60_000);
  }
}