Add function to render HTML directly into ByteBuffer

[Cyberbeni]

I am creating a HTMX SSE based website where I want to send the same event to all the clients, so I want to just render that event into a ByteBuffer once and then pass a copy of that buffer to all the ResponseBodyWriter instances. Currently I'm rendering into a string and then writing that into the buffer which works fine, just copies the data more than necessary.

[Cyberbeni]

This is what I ended on:

import Elementary
import NIO

extension ByteBuffer {
	mutating func writeHTML(_ html: consuming any HTML, chunkSize: Int = 1024) async throws {
		try await html.render(into: &self, chunkSize: chunkSize)
	}
}

private extension HTML {
	consuming func render(into buffer: UnsafeMutablePointer<ByteBuffer>, chunkSize: Int) async throws {
		try await render(into: ByteBufferWriter(buffer: buffer), chunkSize: chunkSize)
	}
}

private class ByteBufferWriter: HTMLStreamWriter {
	private let buffer: UnsafeMutablePointer<ByteBuffer>

	init(buffer: UnsafeMutablePointer<ByteBuffer>) {
		self.buffer = buffer
	}

	func write(_ bytes: ArraySlice<UInt8>) async throws {
		buffer.pointee.writeBytes(bytes)
	}
}

[sliemeobn]

Hi, thanks for getting in touch!

At the moment Elementary is dependency-free, and to me adding a dependency (even NIO) has a very high bar.
I understand where you are coming from though, there should a be a lean way to get this done.

At the very least, I am pretty sure it will be possible to do something like your snippet above, but without unsafe pointers. (We could add an implementation of this to the hummingbird/vapor integration packages maybe?)

The real "fix" should come with the introduction of RawSpans to Swift - then we should be able to add a zero-allocation, zero-generics render implementation.

[Cyberbeni]

Ah, my previous code relied on undefined behaviour (https://github.com/swiftlang/swift/blob/974767eb830620a32abaa98aa3402d0caab0d7ad/stdlib/public/core/UnsafePointer.swift#L649-L657), fixed it in case someone wants to copy paste it.