Function fetchWasm

web/app.js:95–119

()

// plain main.wasm fetch below gets the negotiated encoding, which the
// browser decompresses itself.
async function fetchWasm() {
  const gz = await fetch("main.wasm.gz");
  if (gz.ok) {
    // The counted stream sees compressed bytes, so progress runs
    // against the compressed size on the wire.
    const size = Number(gz.headers.get("Content-Length")) || 0;
    const wasm = countProgress(gz.body, size, size)
      .pipeThrough(new DecompressionStream("gzip"));
    return new Response(wasm, { headers: { "Content-Type": "application/wasm" } });
  }

  const resp = await fetch("main.wasm");
  if (!resp.ok) {
    throw new Error(`fetching main.wasm: ${resp.status}`);
  }
  // The body stream yields decompressed bytes, so progress is
  // tracked against the uncompressed size, but the size shown to the
  // user is what actually crosses the wire.
  const total = Number(resp.headers.get("X-Uncompressed-Size")) ||
    Number(resp.headers.get("Content-Length")) || 0;
  const wireBytes = Number(resp.headers.get("X-Compressed-Size")) ||
    Number(resp.headers.get("Content-Length")) || 0;
  const counted = countProgress(resp.body, total, wireBytes);
  return new Response(counted, { headers: { "Content-Type": "application/wasm" } });
}

// Boot the wasm module.
const ready = new Promise((resolve) => { globalThis.onTailcatReady = resolve; });