Modify our error handler

core/app_server.py

@@ -11,7 +11,7 @@
 import flask
 from flask import Response, make_response, url_for
 from flask_pydantic_spec import FlaskPydanticSpec
-from psycopg2 import DatabaseError
+from psycopg2 import DatabaseError, OperationalError
 from werkzeug.exceptions import HTTPException
 
 import core
@@ -21,9 +21,10 @@
 from core.model import Identifier
 from core.problem_details import *
 from core.service.logging.configuration import LogLevel
+from core.util.http import RemoteIntegrationException
 from core.util.log import LoggerMixin
 from core.util.opds_writer import OPDSMessage
-from core.util.problem_detail import ProblemDetail
+from core.util.problem_detail import ProblemDetail, ProblemError
 
 if TYPE_CHECKING:
     from api.util.flask import PalaceFlask
@@ -214,12 +215,13 @@ def handle(self, exception: Exception) -> Response | HTTPException:
         # By default, the error will be logged at log level ERROR.
         log_method = self.log.error
 
-        # Okay, it's not a database error. Turn it into a useful HTTP error
-        # response.
-        if hasattr(exception, "as_problem_detail_document"):
-            # This exception can be turned directly into a problem
-            # detail document.
-            document = exception.as_problem_detail_document(self.debug)
+        # Try to turn the exception into a useful HTTP error response.
+        if isinstance(exception, (RemoteIntegrationException, ProblemError)):
+            if isinstance(exception, RemoteIntegrationException):
+                document = exception.as_problem_detail_document(self.debug)
+            else:
+                document = exception.problem_detail
+
             if not self.debug:
                 document.debug_message = None
             else:
@@ -234,6 +236,17 @@ def handle(self, exception: Exception) -> Response | HTTPException:
                 # WARN.
                 log_method = self.log.warning
             response = make_response(document.response)
+        elif isinstance(exception, OperationalError):
+            # This is an error, but it is probably unavoidable. Likely it was caused by
+            # the database dropping our connection which can happen then the database is
+            # restarted for maintenance. We'll log it at log level WARN.
+            log_method = self.log.warning
+            body = (
+                tb
+                if self.debug
+                else "Service temporarily unavailable. Please try again later."
+            )
+            response = make_response(body, 503, {"Content-Type": "text/plain"})
         else:
             # There's no way to turn this exception into a problem
             # document. This is probably indicative of a bug in our