v0.8.0

Better SSE Version 0.8.0

npm install better-sse@latest

This release adds significant performance improvements as well as adding an intermediary data buffer to each session, support for HTTP/2 and the ability to overwrite the default response headers.

Changes

⚠ BREAKING: Sessions will now buffer data before sending it to the client

The Session class has been updated to buffer all data until it is explicitly flushed to the client.

This significantly improves performance due to less calls to the underlying res.write method, as well as reducing overall bandwidth usage by sending all data at once (and thus less TCP ACKs being sent back and forth).

If you only use the helper methods push, iterate and stream this change should be transparent to you. More advanced users using the individual field-writing methods event, data, id, retry or comment should keep in mind that the client will now no longer receive that data until it is sent explicitly with the flush method.

The dispatch method will now also only write a newline to the buffer, instead of writing a newline and flushing the data to the client.

// Before
session.event().data().id().retry().comment().dispatch();

// After
session.event().data().id().retry().comment().dispatch().flush(); // All data is sent once over the network

// Or to match the exact previous behaviour, flush after each field write
session.event().flush().data().flush().id().flush().retry().flush().comment().flush().dispatch().flush();

⚠ BREAKING: Event ID format guarantee removed

Event IDs are no longer guaranteed to be 8-character alphanumeric strings, but are still guaranteed to be cryptographically pseudo random.

This is due to a performance bottleneck being caused by Node's random byte generation, which has been replaced with a faster mechanism.

⚠ BREAKING: Session id method no longer accepts null

The Session#id method no longer accepts null as an argument. Simply pass no arguments instead to wipe the ID.

⚠ BREAKING: Channel registration methods short-circuit on already-registered sessions

The Channel#register and Channel#deregister now short-circuit and thus do not emit events when the session is already registered or not registered, respectively.

Performance improvements

This release brings significant performance improvements when using both individual sessions or multiple sessions with channels.

v0.7.1:

Benchmarking "Push events with channels".
better-sse x 11,421 ops/sec ±6.10% (75 runs sampled)

v0.8.0

Benchmarking "Push events with channels".
better-sse x 44,702 ops/sec ±6.08% (81 runs sampled)

That's almost a 4x performance improvement!

Feel free to try the benchmarks yourself in the examples directory.

Session default headers can now be overridden

Headers you pass in the header option will now overwrite the values of the default headers they are the same as, instead of being ignored.

// Before
const session = await createSession({ headers: { Connection: "something-else" } });

// "Connection: keep-alive" is sent

// After
const session = await createSession({ headers: { Connection: "something-else" } });

// "Connection: something-else" is sent

HTTP/2 Support

HTTP/2 support is now available via the Node HTTP/2 compatibility API.

Note that this is only adding support for the compatibility version of the Node HTTP/2 implementation, not the direct core API, as that would be a more challenging task most likely requiring breaking changes to the package API. Support for the core API is not currently planned.

const server = http2.createServer().listen();

server.on("request", (req, res) => {
    const session = new Session(req, res);
});

Full Changelog

Added

• Added an internal data buffer to Session that buffers written data internally until it is flushed to the client using the new Session#flush method.
• Added the Pragma, X-Accel-Buffering headers and add additional values to the Cache-Control default header to further disable all forms of caching.
• Added support for supplying the Node HTTP/2 compatibility API Http2ServerRequest and Http2ServerResponse objects to the Session constructor req and res parameters, respectively.

Changed

• Update the Session#event, Session#data, Session#id, Session#retry and Session#comment methods to write to the internal data buffer instead of sending the field data over the wire immediately.
• Update the Session#dispatch method to only write a newline (and to the internal data buffer) and not flush the written data to the client.
• Update the Channel#broadcast method to generate its own custom event ID and thus add it as an additional argument to its broadcast event callback function.
• Update the Channel#register and Channel#deregister to not do anything if the channel is already registered or deregistered, respectively.
• Update the Session constructor options header field to overwrite conflicting default headers instead of being ignored.
• Update auto-generated event IDs to be guaranteed to be a cryptographically unique string instead of a pseudorandomly generated string of eight characters.

Fixed

• Fixed the Channel session-disconnected being fired after instead of before the session is deregistered.

Removed

• Removed the ability to pass null to Session#id. Give no arguments at all instead.