Serve a transparent GIF from NodeJS

transparent-gif.js

// Two ways to serve transparent GIF

var buf = new Buffer([
    0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x01, 0x00, 0x01, 0x00, 
    0x80, 0x00, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x2c, 
    0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x02, 
    0x02, 0x44, 0x01, 0x00, 0x3b]);

res.send(buf, { 'Content-Type': 'image/gif' }, 200);

// --- OR ----

var buf = new Buffer(35);
buf.write("R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=", "base64");
res.send(buf, { 'Content-Type': 'image/gif' }, 200);

and these 35 bytes actually represent 1x1 white pixel GIF, not transparent.

To have the browser render an inline image, rather than forcing a download of the file, try the following to serve the image:

res.writeHead(200, {'Content-Type': 'image/gif' });
res.end(img, 'binary');

Thanks. @primaryobjects update worked well for displaying inline.

@primaryobjects thank you!

and these 35 bytes actually represent 1x1 white pixel GIF, not transparent.

This is true, the 35 bytes are not a transparent pixel:

Buffer constructor is now deprecated (Node 10), suggested to use Buffer.alloc.

let buffer = Buffer.alloc(35)
buffer.write('R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=', 'base64')
res.writeHead(200, {'Content-Type': 'image/gif'})
res.end(buffer, 'binary')

Edit - thanks Chris for pointing out the transparency issue with the base64 image from this gist - use theirs or the following snippet instead:

const b64blob = 'R0lGODlhAQABAPAAAAAAAAAAACH5BAUKAAAALAAAAAABAAEAQAICRAEAOw=', buffer = Buffer.alloc(b64blob.length)
buffer.write(b64blob, 'base64')
res.writeHead(200, {'Content-Type': 'image/gif'})
res.end(buffer, 'binary')

const TRANSPARENT_GIF_BUFFER = Buffer.from('R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=', 'base64');

function someHandler(req, res) {
  res.writeHead(200, { 'Content-Type': 'image/gif' });
  res.end(TRANSPARENT_GIF_BUFFER, 'binary');
}

@elhardoum and @eliseumds:

I tried both of your versions, but on a 100% black background both of them do not show up as transparent but white (in Google Chrome). See the white dot on the screenshot:

I ended up using the suggestions from the top with a buffer size of 43 (which can also be set with a const buffer instead of a let since the assignment actually does not change):

import { Buffer } from 'node:buffer'
const buffer = Buffer.alloc(43)
buffer.write('R0lGODlhAQABAIAAAAAAAAAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw=', 'base64')
response.writeHead(200, { 'Content-Type': 'image/gif' })
response.end(buffer, 'binary')

@chrisspiegl chrome, since not so long ago, started adding grey backgrounds to their image viewer. If you inspect the img tag, you'll see it adds these inline styles, one of them is a grey background:

-webkit-user-select: none;
margin: auto;
background-color: hsl(0, 0%, 90%);
transition: background-color 300ms;

@elhardoum Not sure where you got these from. I don't see those stylings in the most recent version of Chrome 98.0.4758.80.

When I inspect the img element they don't show up (even when ticking the Show all checkbox).

But the 35 byte one shows up as a white pixel and the 43 byte one is transparent and invisible on a black background.

@chrisspiegl my bad, didn't pay close attention - the image is shown on a website not the standard chrome image viewer page. I'll improve my answer, ty

@chrisspiegl solution worked like a charm. Displays perfectly transparent. Thanks