KY

The KY library is a tiny wrapper over fetch providing a simpler API and some useful shortcuts. KY provides functionality allowing all requests & responses to be intercepted, exposing metadata which can be passed onto the Performance Monitoring library.

Before Request Hook

Before HTTP requests are sent out of the React Native environment, a number of functions can be called to modify or do things based on the current request. We can use this beforeRequest hook to create our HTTP metric.

import perf from '@react-native-firebase/perf';
import ky from 'ky';

const getContentLength = headers => {
  const length = getHeader('Content-Length', headers);
  return length ? Number(length) : null;
};

const getHeader = (header, headers) => headers.get(header) || headers.get(header.toLowerCase());

const api = ky.create({
  hooks: {
    beforeRequest: [
      async (request, options) => {
        const { url, method } = request;
        options.metric = await perf().newHttpMetric(url, method);

        // add any extra metric attributes, if required
        // options.metric.putAttribute('userId', '12345678');
        // options.metric.setRequestPayloadSize(1234)

        await options.metric.start();
      },
    ],
  },
});

export default api;

This callback attaches the HTTP metric returned onto the request metadata, which can later be used on an incoming response.

After Request Hook

Similar to the before request hook, we can also hook into all responses from HTTP calls.

import ky from 'ky';

const getContentLength = headers => {
  const length = getHeader('Content-Length', headers);
  return length ? Number(length) : null;
};

const getHeader = (header, headers) => headers.get(header) || headers.get(header.toLowerCase());

const api = ky.create({
  hooks: {
    afterResponse: [
      async (request, options, response) => {
        const { status, headers } = response;
        const { metric } = options;
        metric.setHttpResponseCode(status);
        metric.setResponseContentType(getHeader('Content-Type', headers));
        metric.setResponsePayloadSize(getContentLength(headers));
        await metric.stop();
      },
    ],
  },
});

export default api;

All outbound requests sent from KY will appear in your Firebase console, detailing information such as how long the request took, response codes & more. Such data can give you greater insight into the performance of your application via any external APIs you may be using.

Full Example

A working example is provided below. Please adjust and extend according to your use case.

import perf from '@react-native-firebase/perf';
import ky from 'ky';

const getContentLength = headers => {
  const length = getHeader('Content-Length', headers);
  return length ? Number(length) : null;
};

const getHeader = (header, headers) => headers.get(header) || headers.get(header.toLowerCase());

const api = ky.create({
  // prevent circular dependency warning
  fetch: fetch,
  hooks: {
    beforeRequest: [
      async (request, options) => {
        const { url, method } = request;
        options.metric = await perf().newHttpMetric(url, method);

        // add any extra metric attributes, if required
        // options.metric.putAttribute('userId', '12345678');
        // options.metric.setRequestPayloadSize(1234)

        await options.metric.start();
      },
    ],

    afterResponse: [
      async (request, options, response) => {
        const { status, headers } = response;
        const { metric } = options;
        metric.setHttpResponseCode(status);
        metric.setResponseContentType(getHeader('Content-Type', headers));
        metric.setResponsePayloadSize(getContentLength(headers));
        await metric.stop();
      },
    ],
  },
});

export default api;