Server-Sent Events queries

3
votes

We have a requirement wherein the server needs to push the data to various clients. So we went ahead with SSE (Server-Sent events). I went through the documentation but am still not clear with the concept. I have following queries :

Scenario 1. Suppose there are 10 clients. So all the 10 clients will send the initial request to server. 10 connections are established. When the data enters the server, a message is pushed from server to client.

  • Query 1 : Will the server maintain the IP address of all the client? If yes is there an API to check it?
  • Query 2: What will happen if all the 10 client windows are closed? Will the server abort all connections after a period of time?
  • Query 3: What will happen if the Server is unable to send messages to client due to unavailability of client like machine shutdown. Will the server abort all connections after a period of time for those client for whom they are unable to send the message?

Please clarify?

1
server-sent-events
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1 Answers

0
votes

This depends on how you implement the server.

If using PHP, as an Apache module, then each SSE connection creates a new PHP instance running in memory. Each "server" is only serving one client at a time. Q1: yes, but not your problem: you just echo messages to stdout. Q2/Q3: If the client closes the connection, for any reason, the PHP process will shutdown when it detects this.

If you are using a multi-threaded server, e.g. using http in node.js. Q1: the client IP is part of the socket abstraction, and you just send messages to the response object. Q2/Q3: as each client connection closes the socket, the request process that was handling it will end. Once all 10 have closed your server will still be running, but not sending data to any clients.

One key idea to realize with SSE is that each client is a dedicated socket. It is not a broadcast protocol, where you push out one message and all clients get exactly the same message. Instead, you have to send the data to each client, individually. But that also means you are free to send customized data to each client.