Server sent events

[gogins]

Use server-sent events to implement:

• [x] Setting the Csound message callback in the Web page.
• [ ] Sending a generated score to the Web page for display.
• [x] Document.

[gogins]

• https://www.w3schools.com/html/html5_serversentevents.asp
• https://github.com/yhirose/cpp-httplib/blob/master/example/ssesvr.cc

[gogins]

I'm not sure how general-purpose this will be, there is a primitive wire format like this:

event:message
data:{0}

I'm not sure whether or how to deal with two newlines in the body of the data.

Solution: Use one data: line, which contains any JSON-encoded data.

[gogins]

I think this is done. It works for the Csound message callback, so should work for other event sources.