Zooming caused "I/Q capture process exited immediately" because the client
closed the WebSocket and opened a new one, racing with the old rtl_sdr
process releasing the USB device. Now zoom/retune sends a start command on
the existing WebSocket, and the server adds a USB release delay plus retry
loop when restarting capture within the same connection.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
After a WebSocket handler exits, flask-sock returns a Response to
Werkzeug which writes "HTTP/1.1 200 OK..." on the still-open socket.
Browsers see these HTTP bytes as a malformed WebSocket frame, causing
"Invalid frame header".
Now the handler explicitly closes the raw TCP socket after the
WebSocket close handshake, so Werkzeug's write harmlessly fails.
Applied to both waterfall and audio WebSocket handlers.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
simple-websocket 1.1.0's receive(timeout=N) returns None on timeout
instead of raising TimeoutError. The handler treated None as
"connection closed" and broke out of the loop, causing Werkzeug to
write its HTTP 200 response on the still-open WebSocket socket.
The browser saw those HTTP bytes as an invalid WebSocket frame.
Now checks ws.connected to distinguish timeout (None + connected)
from actual close (None + not connected).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The fft_reader thread was calling ws.send() concurrently with
ws.receive() in the main loop. simple-websocket is not thread-safe
for simultaneous read/write, corrupting frame headers. Now the reader
thread enqueues frames and only the main loop touches the WebSocket.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Replace the batch rtl_power SSE pipeline with continuous I/Q streaming
via WebSocket for smooth ~25fps waterfall display. The server captures
raw I/Q samples (rtl_sdr/rx_sdr), computes Hann-windowed FFT, and
sends compact binary frames (1035 bytes vs ~15KB JSON, 93% reduction).
Client falls back to existing SSE path if WebSocket is unavailable.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
