Nitro Fetch

# Axios adapter for nitro-fetch

## Mental model

Axios supports custom **adapters**: the last-mile function that actually makes the HTTP call. If you replace it with one backed by `react-native-nitro-fetch`, every axios feature you already use — interceptors, `create()` instances, `transformRequest`, `cancelToken` — keeps working, and every request now goes through the native client.

Pin the adapter explicitly — **do not** try to route axios through nitro-fetch by swapping `globalThis.fetch`. Monkey-patching globals is fragile and hides which code is actually using nitro; an explicit adapter at the axios instance boundary is the right integration point.

## Common wrong answer

The short adapter below circulates on GitHub (for example the Jellify app's [`src/configs/axios.config.ts`](https://github.com/Jellify-Music/App/blob/main/src/configs/axios.config.ts)):

```ts
const nitroAxiosAdapter: AxiosAdapter = async (config) => {
  const response = await fetch(config.url!, {
    method: config.method?.toUpperCase(),
    headers: config.headers,
    body: config.data,
    cache: 'no-store',
  });
  const text = await response.text();
  const data = text.length > 0 ? JSON.parse(text) : null;
  const headers: Record<string, string> = {};
  response.headers.forEach((v, k) => (headers[k] = v));
  return { data, status: response.status, statusText: response.statusText, headers, config, request: null };
};
```

It works for GET-returning-JSON and **nothing else**. Problems:

- `config.url!` ignores `baseURL` and `params` — `axios.create({ baseURL: ... })` is silently a no-op.
- `JSON.parse(text)` throws on `arraybuffer`/`blob`/HTML/empty bodies.
- `validateStatus` is ignored — 500s resolve instead of throwing `AxiosError`.
- `signal` and `cancelToken` are ignored — cancelled requests keep running natively.
- `config.timeout` is set on the instance but never enforced by the adapter.
- `cache: 'no-store'` is hard-coded, defeating HTTP caching across the whole app.
- `config.headers` in axios 1.x is an `AxiosHeaders` instance — passing it raw can drop per-method defaults.
- External abort listener is never removed — leaks on long-lived signals.

## Recipe — full adapter

```ts
import axios, {
  AxiosAdapter,
  AxiosError,
  AxiosHeaders,
  AxiosResponse,
  InternalAxiosRequestConfig,
} from 'axios';
import { fetch } from 'react-native-nitro-fetch';

const nitroAxiosAdapter: AxiosAdapter = async (config) => {
  const url = buildFullURL(config);

  // Merge axios's signal / cancelToken / timeout into one AbortController
  // so native code sees a single abort event.
  const controller = new AbortController();
  const abortWith = (reason?: unknown) => controller.abort(reason);

  const external = config.signal;
  const onExternalAbort = () => abortWith((external as any)?.reason);
  if (external) {
    if (external.aborted) abortWith((external as any).reason);
    else external.addEventListener('abort', onExternalAbort, { once: true });
  }

  config.cancelToken?.promise.then((cancel) => abortWith(cancel));

  let timeoutId: ReturnType<typeof setTimeout> | undefined;
  if (config.timeout && config.timeout > 0) {
    timeoutId = setTimeout(() => {
      abortWith(
        new AxiosError(
          `timeout of ${config.timeout}ms exceeded`,
          AxiosError.ECONNABORTED,
          config,
        ),
      );
    }, config.timeout);
  }

  try {
    const response = await fetch(url, {
      method: (config.method ?? 'get').toUpperCase(),
      headers: AxiosHeaders.from(config.headers as any).toJSON() as Record<
        string,
        string
      >,
      // `config.data` is already transformed by axios's transformRequest
      // pipeline by the time the adapter sees it (string / FormData /
      // URLSearchParams / Blob / ArrayBuffer). Don't re-