Why is Swift NIO example uses HTTP/2 to HTTP/1 protocol conversion?

Question

What's the purpose the HTTP2ToHTTP1ServerCodec. Why is it required to convert the HTTP/2 to HTTP/1 protocol?

channel.configureHTTP2Pipeline(mode: .server) { (streamChannel, streamID) -> EventLoopFuture<Void> in
    // For every HTTP/2 stream that the client opens, we put in the `HTTP2ToHTTP1ServerCodec` which
    // transforms the HTTP/2 frames to the HTTP/1 messages from the `NIOHTTP1` module.
    streamChannel.pipeline.addHandler(HTTP2ToHTTP1ServerCodec(streamID: streamID)).flatMap { () -> EventLoopFuture<Void> in
        // And lastly, we put in our very basic HTTP server :).
        streamChannel.pipeline.addHandler(HTTPServer())

This is a modified code snippet from the Swift NIO example repo.

Answer 1

HTTP/2 is HTTP(/1) semantics over multiple streams in a single TCP connection (and a new wire protocol). As an option, SwiftNIO therefore can allow you to use the HTTP(/1) data types to handle HTTP/2. That allows you to fully re-use your server/client implementations that you wrote using SwiftNIO and HTTP/1 for HTTP/2 too which for most people is a benefit.

That translation however is absolutely not required. If you prefer to operate on HTTP2 frames directly, you don't need to add the HTTP2ToHTTP1ServerCodec to your pipeline.

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Later edit: I should also point out that the HTTP2toHTTP1ServerCodec is actually quite a simple piece of code that literally just translates the inbound and outbound messages between HTTP/2 frames and HTTP/1 message parts. Code is here.