const COMPRESSIBLE = /^(text\/(?!event-stream)|application\/(javascript|json|xml|manifest\+json|ld\+json|rss\+xml|atom\+xml)|image\/svg\+xml)/i;
/** Smaller bodies aren't worth the gzip overhead. */
const MIN_SIZE = 1024;
/**
 * Gzips `res` when the client accepts gzip and the body is compressible
 * text. Streams (no buffering), so it is safe for large and streamed
 * responses. Responses that are already encoded, ranged, bodiless or
 * event streams pass through untouched.
 */
export default function compressResponse(req, res) {
    if (!res.body || req.method === "HEAD")
        return res;
    if (res.status < 200 || res.status === 204 || res.status === 206) {
        return res;
    }
    if (res.headers.has("Content-Encoding"))
        return res;
    if (!/\bgzip\b/i.test(req.headers.get("Accept-Encoding") || "")) {
        return res;
    }
    if (!COMPRESSIBLE.test(res.headers.get("Content-Type") || ""))
        return res;
    if (/\bno-transform\b/i.test(res.headers.get("Cache-Control") || "")) {
        return res;
    }
    const length = Number(res.headers.get("Content-Length"));
    if (length && length < MIN_SIZE)
        return res;
    // Copy: headers of fetch()/Response.redirect responses are immutable
    const headers = new Headers(res.headers);
    headers.set("Content-Encoding", "gzip");
    headers.delete("Content-Length");
    const vary = headers.get("Vary");
    if (!vary) {
        headers.set("Vary", "Accept-Encoding");
    }
    else if (!/\b(accept-encoding|\*)\b/i.test(vary)) {
        headers.set("Vary", `${vary}, Accept-Encoding`);
    }
    return new Response(res.body.pipeThrough(new CompressionStream("gzip")), {
        status: res.status,
        statusText: res.statusText,
        headers,
    });
}