Cache the Dell token to disk so it survives restarts

The in-process token cache was lost on every app restart, forcing a new token
request each time and tripping Dell's token-endpoint rate limit. Add an L2 file
cache in the instance dir (keyed by a hash of the client id, so the id never
lands on disk), mirroring warranty_sync.py. Once one token is obtained it is
reused for ~1h across restarts and workers, avoiding the cooldown in normal use.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/warranty/services/providers.py

@@ -8,17 +8,49 @@ Per-vendor config lives in settings (warranty_<name>_*), masked where secret,
 so nothing is hardcoded and the integration is toggled per site.
 """
 
+import hashlib
+import json
+import os
 import time
 
 import requests
+from flask import current_app
 
 from shopdb.api import db
 from shopdb.core.models import Setting
 
-# Process-wide Dell token cache. Dell rate-limits the token endpoint, so a fresh
-# request per refresh trips a 401 cooldown. Tokens live ~1h; cache + reuse.
+# Two-level Dell token cache. Dell rate-limits the token endpoint, so a fresh
+# request per refresh (or per app restart) trips a 401 cooldown. Tokens live ~1h.
+# L1 = process memory (fast); L2 = a file in the instance dir so the token
+# survives restarts and is shared across workers - mirrors warranty_sync.py.
 _dell_token_cache = {}
 
+
+def _token_file(clientid):
+    # Per-client file, name keyed by a hash so the id never lands on disk.
+    tag = hashlib.sha256((clientid or '').encode()).hexdigest()[:16]
+    return os.path.join(current_app.instance_path, f'.dell_token_{tag}.json')
+
+
+def _read_file_token(clientid):
+    try:
+        with open(_token_file(clientid)) as handle:
+            cached = json.load(handle)
+        if cached.get('expires_at', 0) > time.time() + 60:
+            return cached['token']
+    except (OSError, ValueError, KeyError):
+        pass
+    return None
+
+
+def _write_file_token(clientid, token, expires_at):
+    try:
+        os.makedirs(current_app.instance_path, exist_ok=True)
+        with open(_token_file(clientid), 'w') as handle:
+            json.dump({'token': token, 'expires_at': expires_at}, handle)
+    except OSError:
+        pass
+
 # Dell TechDirect defaults, overridable via settings if Dell changes endpoints.
 # The asset-entitlements service lives under sbil/eapi (device.warranty path 404s
 # with "Service Not Found" for this account). Verified against the live API.
@@ -82,10 +114,15 @@ class DellProvider(WarrantyProvider):
         }
 
     def _get_token(self, config):
-        # Reuse a cached token while valid - Dell rate-limits the token endpoint.
-        cached = _dell_token_cache.get(config['clientid'])
+        clientid = config['clientid']
+        # L1: process memory.
+        cached = _dell_token_cache.get(clientid)
         if cached and cached['expires_at'] > time.time() + 60:
             return cached['token']
+        # L2: file cache (survives restarts / shared across workers).
+        file_token = _read_file_token(clientid)
+        if file_token:
+            return file_token
 
         # Dell expects the client id/secret as HTTP Basic auth, grant type in the
         # body. (Passing them in the body trips the token endpoint's rate limiter.)
@@ -111,9 +148,9 @@ class DellProvider(WarrantyProvider):
             raise WarrantyLookupError(f'Dell auth failed: {exc}')
         if not token:
             raise WarrantyLookupError('Dell auth returned no access_token')
-        _dell_token_cache[config['clientid']] = {
-            'token': token, 'expires_at': time.time() + expires_in - 60,
-        }
+        expires_at = time.time() + expires_in - 60
+        _dell_token_cache[clientid] = {'token': token, 'expires_at': expires_at}
+        _write_file_token(clientid, token, expires_at)
         return token
 
     def _fetch(self, config, token, servicetag):