rspc JS/TS impl for testing new stuff

modern.ts

function concatArrayBuffers(chunks: Uint8Array[]): Uint8Array {
    const result = new Uint8Array(chunks.reduce((a, c) => a + c.length, 0));
    let offset = 0;
    for (const chunk of chunks) {
        result.set(chunk, offset);
        offset += chunk.length;
    }
    return result;
}

class LineSplitter extends TransformStream<Uint8Array, Uint8Array> {
    protected _buffer: Uint8Array[] = [];

    constructor() {
        super({
            transform: (chunk, controller) => {
                let index;
                let rest = chunk;
                while ((index = rest.indexOf(0x0a)) !== -1) {
                    controller.enqueue(concatArrayBuffers([...this._buffer, rest.slice(0, index + 1)]));
                    rest = rest.slice(index + 1);
                    this._buffer = [];
                }

                if (rest.length > 0) {
                    this._buffer.push(rest);
                }
            },
            flush: (controller) => {
                if (this._buffer.length > 0) {
                    controller.enqueue(concatArrayBuffers(this._buffer));
                }
            }
        });
    }
}

async function makeRequest(url: string) {
    const resp = await fetch(url, {
        headers: {
            "x-rspc": "0.3.0",
            "content-type": "application/json"
        }
    });
    
    if (resp.headers.get("content-type") === "application/jsonl") {
        const linesStream = resp.body
            .pipeThrough(new LineSplitter());
    
        const tx = new TextDecoder();
    
        const r: any[] = [];
        for await (const line of linesStream) {
            r.push(JSON.parse(tx.decode(line)));
        }

        return "S " + JSON.stringify(r);
    } else if (resp.headers.get("content-type") === "application/json") {
        if (resp.status === 200) {
            return "T " + await resp.text();  // `T`
        } else if (resp.status > 300 && resp.status < 600) {
            // TODO: We need to detect `#rspc#error` and convert it into a class.
            return "TError " + await resp.text();  // `TError | RspcError`
        } else {
            // Error: rspc won't produce any other status code.
            throw new Error("Unknown status code");
        }  
    } else {
        // Error: We have hit a Vercel checkpoint or something else.
        throw new Error("Unknown content type");
    }    
}

console.log(await makeRequest("http://localhost:3000/rspc/version"));
console.log(await makeRequest("http://localhost:3000/rspc/error2"));
console.log(await makeRequest("http://localhost:3000/rspc/streamingNone"));
console.log(await makeRequest("http://localhost:3000/rspc/streamingError"));
console.log(await makeRequest("http://localhost:3000/rspc/streamingErrorFlip"));
console.log(await makeRequest("http://localhost:3000/rspc/streaming"));