MPP

import { createSessionFetch, createPaymentChannelSessionOpener } from "@solana/mpp/client";
import { createKeyPairSignerFromBytes, getBase58Encoder } from "@solana/kit";

const payer = await createKeyPairSignerFromBytes(
  new Uint8Array(getBase58Encoder().encode(process.env.PAYER_SECRET_KEY!)),
);

const session = createSessionFetch({
  opener: createPaymentChannelSessionOpener({
    signer: payer,
    deposit: 1_000_000n, // 1 USDC escrowed up front; the unused part refunds at close
    rpcUrl: "https://api.mainnet-beta.solana.com",
  }),
  // The gateway answers anonymous requests with 401 — signal the Payment scheme
  // so the first attempt receives the 402 session challenge instead.
  prepareRequest: ({ input, init }) => {
    const headers = new Headers(init?.headers);
    if (!headers.has("authorization")) headers.set("authorization", "Payment e30");
    return { input, init: { ...init, headers } };
  },
});

const res = await session.fetchWithSession("https://gateway.venna.net/v1/chat/completions", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({ model: "venna-fast", messages: [{ role: "user", content: "ping" }] }),
});

const directive = JSON.parse(
  Buffer.from(res.headers.get("Payment-Metering")!, "base64url").toString("utf8"),
);
session.recordCumulative(BigInt(directive.requiredCumulative));
await session.flush();

import OpenAI from "openai";
import { createSessionFetch, createPaymentChannelSessionOpener } from "@solana/mpp/client";
import { createKeyPairSignerFromBytes, getBase58Encoder } from "@solana/kit";

const payer = await createKeyPairSignerFromBytes(
  new Uint8Array(getBase58Encoder().encode(process.env.PAYER_SECRET_KEY!)),
);

const session = createSessionFetch({
  opener: createPaymentChannelSessionOpener({
    signer: payer,
    deposit: 1_000_000n,
    rpcUrl: "https://api.mainnet-beta.solana.com",
  }),
});

// Drop the SDK's Bearer key, hint the Payment scheme so the first attempt gets
// the 402 session challenge, then fund the next call from the metering header.
const meteredFetch: typeof fetch = async (input, init) => {
  const headers = new Headers(init?.headers);
  headers.set("authorization", "Payment e30"); // session overwrites this on the paid retry
  const res = await session.fetchWithSession(input, { ...init, headers });
  const directive = res.headers.get("Payment-Metering");
  if (directive) {
    const { requiredCumulative } = JSON.parse(Buffer.from(directive, "base64url").toString("utf8"));
    session.recordCumulative(BigInt(requiredCumulative));
    await session.flush();
  }
  return res;
};

const client = new OpenAI({
  baseURL: "https://gateway.venna.net/v1",
  apiKey: "mpp", // placeholder; the signed voucher is the auth, not a key
  fetch: meteredFetch,
});

const completion = await client.chat.completions.create({
  model: "venna-fast",
  messages: [{ role: "user", content: "Paid straight from a Solana wallet." }],
});