How to program a UDP webserver since HTTP normally uses TCP?

Question

Here is my understanding of how a client-server HTTP server works.

The client creates a TCP socket connection to connect to the server and sends data.
The server creates a TCP socket connection to listen for incoming requests.

So it looks like both the client and the server need to agree on the use of the Transport protocol to use (in this case TCP). But if we want a website to work over UDP/QUIC protocol then we need both the client and the server to create a UDP socket connection. But some websites use TCP and others use UDP...

So does it mean it would need to look like this? To know beforehand which protocol a website uses?

if (URI == 'https://www.google.com') {
  // Website that works over UDP
  client.create.UDP.socket
  client.sendData

  server.create.UDP.socket
  server.receive.data
} else {
  // Website that works over TCP
  client.create.TCP.socket
  client.sendData

  server.create.TCP.socket
  server.receive.data
}

So the client needs to keep a record of which website uses TCP and which websites use UDP/QUIC and create that kind of socket to communicate with it?

rveerd rveerd · Accepted Answer · 2020-01-08T13:18:20

If a protocol supports both TCP and UDP, the server listens both on the TCP port and the UDP port. The port number is generally the same, e.g. DNS uses TCP port 53 and UDP port 53.

Usually the client has a preference. Let's say it prefers TCP. The client will first try to connect with TCP. If the server does not respond, the client will retry with UDP. Alternatively, the server can respond over TCP but ask the client to switch to UDP. The client can then decide to continue with TCP or switch to UDP.

For QUIC ^{1 2}, the browser will first connect using HTTP over TCP. The server will respond with a message stating that it also supports QUIC. If the browser also supports this protocol, the browser will reconnect to the server using QUIC.

How to program a UDP webserver since HTTP normally uses TCP?

1 Answers