HTTP Content Negotiation in Golang reverse proxy

	remote:= some_remote_host
	proxy := httputil.NewSingleHostReverseProxy(remote)
	proxy.Director = func(req *http.Request) {
		req.Header = ctx.Request.Header
		req.Host = remote.Host
		req.URL.Scheme = remote.Scheme
		req.URL.Host = remote.Host
		req.URL.Path = ctx.Request.URL.Path
	}

	proxy.ServeHTTP(ctx.Writer, ctx.Request)

httputil: ReverseProxy read error during body copy: unexpected EOF

2021/12/04 16:47:40 [Recovery] 2021/12/04 - 16:47:40 panic recovered:
net/http: abort Handler
/usr/local/Cellar/go/1.17.2/libexec/src/net/http/httputil/reverseproxy.go:349 (0x12ba9a4)
(*ReverseProxy).ServeHTTP: panic(http.ErrAbortHandler)

// copyBuffer returns any write errors or non-EOF read errors, and the amount
// of bytes written.
func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
	if len(buf) == 0 {
		buf = make([]byte, 32*1024)
	}
	var written int64
	for {
		nr, rerr := src.Read(buf)
		if rerr != nil && rerr != io.EOF && rerr != context.Canceled {
			p.logf("httputil: ReverseProxy read error during body copy: %v", rerr)
		}
		if nr > 0 {
			nw, werr := dst.Write(buf[:nr])
			if nw > 0 {
				written += int64(nw)
			}
			if werr != nil {
				return written, werr
			}
			if nr != nw {
				return written, io.ErrShortWrite
			}
		}
		if rerr != nil {
			if rerr == io.EOF {
				rerr = nil
			}
			return written, rerr
		}
	}
}

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8

Accept-Language: pt-PT,pt;q=0.8,en;q=0.5,en-US;q=0.3

Accept-Encoding: gzip, deflate

// Read implements io.Reader, reading uncompressed bytes from its underlying Reader.
func (z *Reader) Read(p []byte) (n int, err error) {
	if z.err != nil {
		return 0, z.err
	}

	n, z.err = z.decompressor.Read(p)
	z.digest = crc32.Update(z.digest, crc32.IEEETable, p[:n])
	z.size += uint32(n)
	if z.err != io.EOF {
		// In the normal case we return here.
		return n, z.err
	}

	// Finished file; check checksum and size.
	if _, err := io.ReadFull(z.r, z.buf[:8]); err != nil {
		z.err = noEOF(err)

		return n, z.err
	}

	digest := le.Uint32(z.buf[:4])
	size := le.Uint32(z.buf[4:8])
	if digest != z.digest || size != z.size {
		z.err = ErrChecksum
		return n, z.err
	}
	z.digest, z.size = 0, 0

	// File is ok; check if there is another.
	if !z.multistream {
		return n, io.EOF
	}
	z.err = nil // Remove io.EOF

	if _, z.err = z.readHeader(); z.err != nil {
		return n, z.err
	}

	// Read from next file, if necessary.
	if n > 0 {
		return n, nil
	}
	return z.Read(p)
}

// readHeader reads the GZIP header according to section 2.3.1.
// This method does not set z.err.
func (z *Reader) readHeader() (hdr Header, err error) {
	n, err := io.ReadFull(z.r, z.buf[:10])
	if err != nil {
		// RFC 1952, section 2.2, says the following:
		//	A gzip file consists of a series of "members" (compressed data sets).
		//
		// Other than this, the specification does not clarify whether a
		// "series" is defined as "one or more" or "zero or more". To err on the
		// side of caution, Go interprets this to mean "zero or more".
		// Thus, it is okay to return io.EOF here.
		fmt.Println("READ FULL ERROR ", err, z.buf[0] != gzipID1, z.buf[1] != gzipID2, z.buf[2] != gzipDeflate)

		return hdr, err
	}

	// Ask for a compressed version if the caller didn't set their
	// own value for Accept-Encoding. We only attempt to
	// uncompress the gzip stream if we were the layer that
	// requested it.
	requestedGzip := false
	if !pc.t.DisableCompression &&
		req.Header.Get("Accept-Encoding") == "" &&
		req.Header.Get("Range") == "" &&
		req.Method != "HEAD" {
		// Request gzip only, not deflate. Deflate is ambiguous and
		// not as universally supported anyway.
		// See: https://zlib.net/zlib_faq.html#faq39
		//
		// Note that we don't request this for HEAD requests,
		// due to a bug in nginx:
		//   https://trac.nginx.org/nginx/ticket/358
		//   https://golang.org/issue/5522
		//
		// We don't request gzip if the request is for a range, since
		// auto-decoding a portion of a gzipped document will just fail
		// anyway. See https://golang.org/issue/8923
		requestedGzip = true
		req.extraHeaders().Set("Accept-Encoding", "gzip")
	}