Edge Functions

Handling WebSockets

Handle WebSocket connections in Edge Functions.

Edge Functions supports hosting WebSocket servers that can facilitate bi-directional communications with browser clients.

This allows you to:

  • Build real-time applications like chat or live updates
  • Create WebSocket relay servers for external APIs
  • Establish both incoming and outgoing WebSocket connections

Creating WebSocket servers

Here are some basic examples of setting up WebSocket servers using Deno and Node.js APIs.

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Deno.serve((req) => {
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  const upgrade = req.headers.get('upgrade') || ''
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  if (upgrade.toLowerCase() != 'websocket') {
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    return new Response("request isn't trying to upgrade to WebSocket.", { status: 400 })
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  }
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  const { socket, response } = Deno.upgradeWebSocket(req)
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  socket.onopen = () => console.log('socket opened')
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  socket.onmessage = (e) => {
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    console.log('socket message:', e.data)
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    socket.send(new Date().toString())
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  }
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  socket.onerror = (e) => console.log('socket errored:', e.message)
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  socket.onclose = () => console.log('socket closed')
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  return response
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})

Outbound WebSockets

You can also establish an outbound WebSocket connection to another server from an Edge Function.

Combining it with incoming WebSocket servers, it's possible to use Edge Functions as a WebSocket proxy, for example as a relay server for the OpenAI Realtime API.

Authentication

WebSocket browser clients don't have the option to send custom headers. Because of this, Edge Functions won't be able to perform the usual authorization header check to verify the JWT.

You can skip the default authorization header checks by explicitly providing --no-verify-jwt when serving and deploying functions.

To authenticate the user making WebSocket requests, you can pass the JWT in URL query params or via a custom protocol.

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import { createClient } from 'npm:@supabase/supabase-js@2'
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const supabase = createClient(
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  Deno.env.get('SUPABASE_URL'),
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  Deno.env.get('SUPABASE_SERVICE_ROLE_KEY')
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)
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Deno.serve((req) => {
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  const upgrade = req.headers.get('upgrade') || ''
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  if (upgrade.toLowerCase() != 'WebSocket') {
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    return new Response("request isn't trying to upgrade to WebSocket.", { status: 400 })
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  }
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  // Please be aware query params may be logged in some logging systems.
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  const url = new URL(req.url)
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  const jwt = url.searchParams.get('jwt')
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  if (!jwt) {
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    console.error('Auth token not provided')
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    return new Response('Auth token not provided', { status: 403 })
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  }
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  const { error, data } = await supabase.auth.getClaims()
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  if (error) {
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    console.error(error)
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    return new Response('Invalid token provided', { status: 403 })
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  }
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  if (!data.user) {
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    console.error('user is not authenticated')
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    return new Response('User is not authenticated', { status: 403 })
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  }
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  const { socket, response } = Deno.upgradeWebSocket(req)
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  socket.onopen = () => console.log('socket opened')
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  socket.onmessage = (e) => {
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    console.log('socket message:', e.data)
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    socket.send(new Date().toString())
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  }
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  socket.onerror = (e) => console.log('socket errored:', e.message)
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  socket.onclose = () => console.log('socket closed')
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  return response
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})

Testing WebSockets locally

When testing Edge Functions locally with Supabase CLI, the instances are terminated automatically after a request is completed. This will prevent keeping WebSocket connections open.

To prevent that, you can update the supabase/config.toml with the following settings:

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[edge_runtime]
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policy = "per_worker"