The fix does not sound right, and the test is odd. See my comment in #24.

I don't understand why the test is odd.
In my app, when I call s.Shutdown while at least one client is waiting for events, I get a panic.

I would not get it if my app exited quickly enough to actually not shut down, like in other tests.

Calling defer s.Shutdown() in main(), while s.Shutdown() doesn't wait for completion, is almost a no-op indeed.
A Go app doesn't wait for any goroutine to complete before exiting, so s.Shutdown() hardly has any chance to do anything.

See http.Server.Shutdown() which blocks until either its completion or a context cancellation. I think this is how it should work in go-sse.

Here is a little more material, hopping it helps:

• In the examples, the call to s.Shutdown() will never happen, because one has to "kill" the program to exit.
  • Here is a simple example of an HTTP server with graceful shutdown.
• Channels are not meant to be closed unless you have a range loop. Here is a quote from Ian Lance Taylor, and a comment from the Go Tour.

Finally, if you modify the examples a little, you can reproduce the bug using curl as a client:

• In net_http.go, for example, remove defer s.Shutdown() and replace the last line (call to http.ListenAndServe) with the code bellow
• run the test
• In another terminal run curl http://localhost:3000/events/channel-1
• Wait a little and it should panic

go http.ListenAndServe(":3000", nil)
time.Sleep(5 * time.Second) // Use this time to run "curl http://localhost:3000/events/channel-1"
s.Shutdown()
time.Sleep(10 * time.Millisecond) // Should panic, now that s.Shutdown() has time to complete

In my test, I was trying to:

• Let the shut down actually happen
• Have the client part happen without running curl

Is it why it looked odd?

I hope it's all clearer now :) Thanks again.

You have found a very unusual bug, it only fails if the remote client closes the connection while the shutdown is in progress.

To explain a bit:

• Shutdown forces all see channels to close
• SSE Channel close forces all clients to be disconnected
• Shutdown closes all go channels
• Client disconnect is received by ServeHTTP because it's released
• ServeHTTP attempt to remove a client that does not exist anymore by sending a message to a closed channel because it was shutdown
• bang, panic

I managed to reproduce it and I managed to fix (I think) the proper way. The wrong part is in ServeHTTP function. I also have found that the Shutdown never really waited on anything to be shut down, also fixing that.

I'll be closing this PR because there's a better way to fix it, but this helped me understand the problem.

Thanks.

I've actually found and fixed several other issues, but found it a little difficult to move forward through PR, so decided to keep my fork and use it instead. You can have a look at it if you want to spot other minor mistakes or lacks.
Thanks again.

I took a look, lots of changes.

My changes will be a major refactoring, rewriting the server, I'll probably fix some issues and create new ones. I also have a plan to create on connect/disconnect functions.