Here is the list of changes for the next major version of Socket.IO. This list is obviously up for discussions, so please do not hesitate to comment here.

• remove the reference to the handshake request (socket.request)

Rationale: keeping a reference to thehttp.IncomingMessage increases the memory footprint. Note: we should provide an alternative to be used withexpress-session and such.

Related:#3792

• when callingio.close() do not close the HTTP server if it was not created by the library

Related:#4002 (reply in thread)

• use private properties ("#") in order to improve the minification of the client bundle

Note: we might need to drop support for some older versions of Node.js.

Update: using private class fields does not significantly reduce the bundle size after minification + gzip (and is a breaking change since it is only supported starting with Node.js 14.6.0) so this change makes little sense for now.

• remove the "error" event emitted by thesocket object

Related:#2047

Update: fixed in15af22f

• implement various quality of services:quality of service features #3649

Rationale: currently we have "at-most-once" semantics, possibly "at-least-once" with acknowledgements and manual retry, but we could provide additional guarantees. Might be linked to#4510

Update: implemented insocketio/socket.io-client@655dce9

• prevent users from shooting themselves in the foot withsocket.leave(socket.id);

Related:#4524

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