Luci+Ucode Streaming only possible with 1kb chunks

Zerogiven · May 17, 2026, 11:24am

Hi everyone,

I have a question regarding a live text stream I am implementing using ucode inside LuCI.

To avoid polling every X seconds, I am keeping a request open until just before the timeout, and then restarting it (long-polling/streaming). While this works perfectly in principle, I am facing an annoying buffering issue and I'm wondering if this behavior can be configured.

The Problem: I only receive data in the LuCI request once my stream chunks from ucode reach a size of around 1,152 bytes. It seems like something along the pipeline is buffering the output, but I can't figure out where.

Interestingly, I am pretty sure this wasn't happening in version 24.10, so it feels like something changed recently. I've spent a lot of time digging through recent commits on GitHub but couldn't find the culprit.

My Current Workaround: I am using this setup to stream data from the Podman API. Most of the time, the chunks returned by Podman are well under 1 KB. My current "fix" is to pad the chunked data with dummy bytes until it hits the ~1 KB threshold, which forces the stream to flush immediately.

Naturally, this feels like a very hacky solution. Is there a way to disable or configure this buffering behavior (e.g., forcing a flush in ucode or uhttpd)? Or am I missing something in my implementation?

You can see my actual code here:

github.com/Zerogiven-OpenWRT-Packages/luci-app-podman

ucode/controller/podman.uc

main


      
          		}
          	};
          }
          
          /**
           * @param {string} api_path
           * @param {function} on_data
           * @param {boolean} early_headers
           * @param {int} timer
           */
          function stream_podman(api_path, on_data, early_headers, timer) {
          	let sock = socket.connect(PODMAN_SOCKET);
          	if (!sock) {
          		error_response(502, 'Cannot connect to Podman socket');
          		return;
          	}
          
          	sock.send(sprintf('GET %s HTTP/1.0\r\nHost: localhost\r\n\r\n', api_path));
          
          	let t = _uci_timeouts;
          	let ka_ms = (t.network - 5) * 1000;

github.com/Zerogiven-OpenWRT-Packages/luci-app-podman

ucode/controller/podman.uc

main


      
          	uloop.run();
          
          	handle.delete();
          	sock.close();
          
          	if (!response_started)
          		error_response(504, 'Podman did not respond');
          }
          
          return {
          	container_logs: (id) => {
          		if (!validate_id(id)) { error_response(400, 'Invalid container ID'); return; }
          
          		let timer = session_timer(ctx?.authsession); // ucode-lsp disable
          		if (!timer) { error_response(403, 'Session expired'); return; }
          
          		let tail   = http.formvalue('tail')   || '100';
          		let since  = http.formvalue('since')  || '';
          		let until  = http.formvalue('until')  || '';
          		let follow = http.formvalue('follow') !== 'false';

github.com/Zerogiven-OpenWRT-Packages/luci-app-podman

ucode/controller/podman.uc

main


      
          const BLOCKSIZE = 4096;
          
          const FLUSH_SIZE = 1500;
          const PAD_STR = (() => {
          	let s = ''; let i = 0;
          	while (i < FLUSH_SIZE) { s += ' '; i++; }
          	return s;
          })();
          
          /** @param {string} data */
          function http_write_padded(data) {
          	let n = length(data);
          	if (n >= FLUSH_SIZE)
          		return http.write(data); // ucode-lsp disable
          	return http.write(data + substr(PAD_STR, 0, FLUSH_SIZE - n)); // ucode-lsp disable
          }
          
          const _uci_timeouts = (() => {
          	let c = cursor();
          	let s = c.get('uhttpd', 'main', 'script_timeout');
          	let n = c.get('uhttpd', 'main', 'network_timeout');