How to receive shared files
The modern way #
Using the Web Share Target API #
First, declare a share_target
in your web app manifest that lists an action
(your URL that handles shared files), a method
("POST"
for files) and an enctype
("multipart/form-data"
for files) and a params
object that contains a files
property with an array of objects with a name
and accept
property that list the sharable file types and the name to obtain them.
{
"share_target": {
"action": "/receive-files/",
"method": "POST",
"enctype": "multipart/form-data",
"params": {
"files": [
{
"name": "image",
"accept": ["image/jpeg", "image/png", "image/webp", "image/gif"]
}
]
}
}
}
You then need to handle incoming POST
requests in the service worker. The file is temporarily stored in a media cache, so it can be consumed in the client. This can be done by redirecting the app to a URL with a special marker query parameter like share-target
.
self.addEventListener('fetch', (fetchEvent) => {
if (fetchEvent.request.url.endsWith('/receive-files/') && fetchEvent.request.method === 'POST') {
return fetchEvent.respondWith(
(async () => {
const formData = await fetchEvent.request.formData();
const image = formData.get('image');
const keys = await caches.keys();
const mediaCache = await caches.open(keys.filter((key) => key.startsWith('media'))[0]);
await mediaCache.put('shared-image', new Response(image));
return Response.redirect('./?share-target', 303);
})(),
);
}
});
Finally, you need to consume the file in the client.
window.addEventListener('load', async () => {
if (location.search.includes('share-target')) {
const keys = await caches.keys();
const mediaCache = await caches.open(
keys.filter((key) => key.startsWith('media'))[0],
);
const image = await mediaCache.match('shared-image');
if (image) {
const blob = await image.blob();
await mediaCache.delete('shared-image');
// Handle the shared file somehow.
}
}
});
Browser support
- Chrome 89, Supported 89
- Firefox, Not supported
- Edge 89, Supported 89
- Safari, Not supported
Further reading #
Demo #
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<link rel="manifest" href="manifest.json" />
<title>How to receive shared files</title>
<link rel="stylesheet" href="style.css" />
<script>
if ('serviceWorker' in navigator) {
window.addEventListener('load', async () => {
const registration = await navigator.serviceWorker.register(
'sw.js',
);
console.log(
'Service worker registered for scope',
registration.scope,
);
});
}
</script>
<script src="script.js" type="module"></script>
</head>
<body>
<h1>How to receive shared files</h1>
<p>Install the app. After the installation, try sharing an image to it from another app.
</body>
</html>
{
"name": "How to receive shared files",
"short_name": "Shared files",
"start_url": "../demo.html",
"id": "../demo.html",
"icons": [
{
"src": "../assets/favicon.png",
"type": "image/png",
"sizes": "512x512"
},
{
"src": "../assets/favicon.svg",
"type": "image/svg+xml",
"sizes": "any"
}
],
"display": "standalone",
"share_target": {
"action": "../receive-files/",
"method": "POST",
"enctype": "multipart/form-data",
"params": {
"files": [
{
"name": "image",
"accept": ["image/jpeg", "image/png", "image/webp", "image/gif"]
}
]
}
}
}
window.addEventListener('load', async () => {
if (location.search.includes('share-target')) {
const keys = await caches.keys();
const mediaCache = await caches.open(
keys.filter((key) => key.startsWith('media'))[0],
);
const image = await mediaCache.match('shared-image');
if (image) {
const blob = await image.blob();
await mediaCache.delete('shared-image');
// Handle the shared file somehow.
}
}
});
html {
box-sizing: border-box;
font-family: system-ui, sans-serif;
color-scheme: dark light;
}
*, *:before, *:after {
box-sizing: inherit;
}
body {
margin: 1rem;
}
img {
height: auto;
max-width: 100%;
display: block;
}