Migrate eventlet→gevent: fix WebSocket upgrade failure and EBADF errors

- eventlet worker deprecated in gunicorn 25+; WebSocket hijack broken,
  causing all socket.io connections to stay on long-polling forever and
  produce 'Bad file descriptor' errors on every poll cycle.
- Replace eventlet monkey_patch / spawn / sleep with gevent equivalents
- async_mode='gevent' in both SocketIO instances
- worker_class='gevent' in gunicorn.conf.py
- Add gevent-websocket to requirements (needed for WS upgrade in gunicorn)

gunicorn.conf.py

@@ -21,7 +21,7 @@ def _load_cfg():
 _cfg = _load_cfg()
 
 # ── Gunicorn settings ─────────────────────────────────────────────────────────
-worker_class = 'eventlet'
+worker_class = 'gevent'
 workers      = 1          # Must be 1 — eventlet handles concurrency via greenlets
                           # and both apps share in-process state.
 bind         = f"{_cfg.get('host', '0.0.0.0')}:{_cfg.get('dj_port', 5000)}"

requirements.txt

@@ -1,7 +1,8 @@
 # TechDJ Requirements - Web Server
 flask
 flask-socketio
-eventlet
+gevent
+gevent-websocket
 gunicorn
 python-dotenv
 

server.py

@@ -1,6 +1,7 @@
 # Monkey patch MUST be first - before any other imports!
-import eventlet
-eventlet.monkey_patch()
+from gevent import monkey
+monkey.patch_all()
+import gevent
 
 import os
 import json
@@ -191,8 +192,8 @@ def _start_transcoder_if_needed(is_mp3_input=False):
         except: break
 
     # Define greenlets INSIDE so they close over THIS specific 'proc'.
-    # Blocking subprocess pipe I/O is delegated to eventlet.tpool so it runs
-    # in a real OS thread, preventing it from stalling the eventlet hub.
+    # Blocking subprocess pipe I/O runs in a real OS thread via gevent's
+    # threadpool, preventing it from stalling the gevent hub.
 
     def _stderr_drain(proc):
         """Drain ffmpeg's stderr pipe so it never fills the OS buffer (64 KB on
@@ -205,8 +206,7 @@ def _start_transcoder_if_needed(is_mp3_input=False):
         except Exception:
             pass
 
-    eventlet.spawn(_stderr_drain, _ffmpeg_proc)
-
+    gevent.spawn(_stderr_drain, _ffmpeg_proc)
     def _writer(proc):
         global _transcoder_last_error
         print(f"[THREAD] Transcoder writer started (PID: {proc.pid})")
@@ -265,8 +265,8 @@ def _start_transcoder_if_needed(is_mp3_input=False):
         print(f"[THREAD] Transcoder reader finished (PID: {proc.pid})")
 
     # Spawn as greenlets — tpool handles the blocking subprocess I/O internally
-    eventlet.spawn(_writer, _ffmpeg_proc)
-    eventlet.spawn(_reader, _ffmpeg_proc)
+    gevent.spawn(_writer, _ffmpeg_proc)
+    gevent.spawn(_reader, _ffmpeg_proc)
 
 
 def _stop_transcoder():
@@ -381,7 +381,7 @@ def _start_srt_transcoder():
             except: pass
         print(f'[THREAD] SRT reader finished (PID: {proc.pid})')
 
-    eventlet.spawn(_srt_reader, _srt_ffmpeg_proc)
+    gevent.spawn(_srt_reader, _srt_ffmpeg_proc)
 
 
 def _stop_srt_transcoder():
@@ -651,7 +651,7 @@ def setup_shared_routes(app, index_file='index.html'):
 
             waited = 0.0
             while not _active_transcoder() and waited < 5.0:
-                eventlet.sleep(0.5)
+                gevent.sleep(0.5)
                 waited += 0.5
 
             if not _active_transcoder():
@@ -833,7 +833,7 @@ def client_config():
 dj_socketio = SocketIO(
     dj_app, 
     cors_allowed_origins=CONFIG_CORS, 
-    async_mode='eventlet',
+    async_mode='gevent',
     max_http_buffer_size=CONFIG_MAX_UPLOAD_MB * 1024 * 1024,
     ping_timeout=60, 
     ping_interval=25,
@@ -853,7 +853,7 @@ def _dj_disconnect_grace():
     """Auto-stop broadcast if no DJ reconnects within the grace period."""
     global _dj_grace_greenlet, _mp3_broadcast_announced
     print(f"INFO: Grace period started — {DJ_GRACE_PERIOD_SECS}s for DJ to reconnect")
-    eventlet.sleep(DJ_GRACE_PERIOD_SECS)
+    gevent.sleep(DJ_GRACE_PERIOD_SECS)
     if broadcast_state.get('active') and not dj_sids:
         print("WARNING: Grace period expired, no DJ reconnected — auto-stopping broadcast")
         broadcast_state['active'] = False
@@ -874,7 +874,7 @@ def dj_disconnect():
     # If broadcast is active and no other DJs remain, start the grace period
     if broadcast_state.get('active') and not dj_sids:
         if _dj_grace_greenlet is None:
-            _dj_grace_greenlet = eventlet.spawn(_dj_disconnect_grace)
+            _dj_grace_greenlet = gevent.spawn(_dj_disconnect_grace)
     elif not broadcast_state.get('active'):
         # Nothing to do — no active broadcast
         pass
@@ -1049,7 +1049,7 @@ def _restrict_listener_routes():
 listener_socketio = SocketIO(
     listener_app, 
     cors_allowed_origins=CONFIG_CORS, 
-    async_mode='eventlet',
+    async_mode='gevent',
     max_http_buffer_size=CONFIG_MAX_UPLOAD_MB * 1024 * 1024,
     # Lower timeouts: stale connections detected in ~25s instead of ~85s
     # ping_interval: how often to probe (seconds)
@@ -1247,14 +1247,14 @@ def _transcoder_watchdog():
                 if _ffmpeg_proc is None or _ffmpeg_proc.poll() is not None:
                     print('WARNING: Watchdog: Transcoder dead during active broadcast, reviving...')
                     _start_transcoder_if_needed(is_mp3_input=False)
-        eventlet.sleep(5)
+        gevent.sleep(5)
 
 
 def _listener_count_sync_loop():
     """Periodic reconciliation — catches any edge cases where connect/disconnect
-    events were missed (e.g. server under load, eventlet greenlet delays)."""
+    events were missed (e.g. server under load, gevent greenlet delays)."""
     while True:
-        eventlet.sleep(5)
+        gevent.sleep(5)
         _broadcast_listener_count()
 
 
@@ -1274,9 +1274,9 @@ def _start_background_tasks():
             return
         _background_tasks_started = True
 
-    eventlet.spawn(_listener_count_sync_loop)
-    eventlet.spawn(_transcoder_watchdog)
-    eventlet.spawn(
+    gevent.spawn(_listener_count_sync_loop)
+    gevent.spawn(_transcoder_watchdog)
+    gevent.spawn(
         listener_socketio.run,
         listener_app,
         host=CONFIG_HOST,