request-time

Timings for HTTP requests

Understanding and measuring HTTP timings helps us to discover performance. bottlenecks in client to server or server to server communication.

Timings explained

• DNS Lookup: Time spent performing the DNS lookup. DNS lookup resolves domain names to IP addresses. Every new domain requires a full round trip to do the DNS lookup.

  • There is no DNS lookup when the destination is already an IP address.

• TCP Connection: Time it took to establish TCP connection between a source host and destination host. Connections must be properly established in a multi-step handshake process. TCP connection is managed by an operating system, if the underlying TCP connection cannot be established, the OS-wide TCP connection timeout will overrule the timeout config of our application.

• TLS handshake: Time spent completing a TLS handshake. During the handshake process endpoints exchange authentication and keys to establish or resume secure sessions.

  • There is no TLS handshake with a not HTTPS request.

• Time to First Byte (TTFB): Time spent waiting for the initial response. This time captures the latency of a round trip to the server in addition to the time spent waiting for the server to process the request and deliver the response.

• Content Transfer: Time spent receiving the response data. The size of the response data and the available network bandwidth determinates its duration.

Installation

NPM:

npm install @abellsmythe/request-time

Usage

'use strict';

const https = require('https');
const timer = require('@abellsmythe/request-time').default;

const request = https.get('https://google.com');
const timings = timer(request);

request.on('response', response => {
    response.on('data', () => {
        // Do something
    });
    response.on('end', () => {
        console.log(timings);
    });
});

{
    start: 20019170.414002,
    socket: 20019171.943738,
    dnsLookup: 20019182.811348,
    connect: 20019194.637675,
    tlsHandshake: 20019245.32874,
    upload: 20019246.615841,
    response: 20019284.613933,
    end: 20019288.80115,
    error: undefined,
    phases:
    {
        wait: 1.5297359973192215,
        dns: 10.86761000007391,
        tcp: 11.826326999813318,
        request: 51.9781660027802,
        firstByte: 37.998091999441385,
        download: 4.187217000871897,
        total: 118.38714800029993
    }
}

API

timer(request)

Returns: Object

• start - Time when the request started.
• socket - Time when a socket was assigned to the request.
• dnsLookup - Time when the DNS lookup finished.
• tlsHandshake - Time when the secure connection is done.
• connect - Time when the socket successfully connected.
• upload - Time when the request finished uploading.
• response - Time when the request fired the response event.
• end - Time when the response fired the end event.
• error - Time when the request fired the error event.
• phases
  • wait - timings.socket - timings.start
  • dns - timings.dnsLookup - timings.socket
  • tcp - timings.connect - timings.dnsLookup
  • request - timings.upload - timings.connect
  • firstByte - timings.response - timings.upload
  • download - timings.end - timings.response
  • total - timings.end - timings.start or timings.error - timings.start

If something is not measured yet, it will be undefined.

Note: The time is a number representing the milliseconds without elapsing since the UNIX epoch.

Note: request-time uses process.hrtime() from node as it's not a subject of clock drift