Make question loading resilient to network failures

scripts/autoload/question_bank_service.gd

@@ -7,6 +7,7 @@ const DEFAULT_QUESTION_API_BASE_URL := "https://s3q.ranaze.com/api/questions"
 const DEFAULT_RATINGS_API_URL := "https://s3q.ranaze.com/api/ratings/me"
 const DEFAULT_QUESTION_REPORTS_API_URL := "https://s3q.ranaze.com/api/question-reports"
 const RETRY_DELAYS := [2, 5, 10, 20, 30]
+const REQUEST_TIMEOUT_SECONDS := 30.0
 const IMAGE_QUESTION_SEARCH_LIMIT := 200
 const ATTEMPT_QUEUE_PATH := "user://pending_question_attempts.json"
 
@@ -65,18 +66,22 @@ func _ready() -> void:
 		str(ProjectSettings.get_setting("step3/question_reports_api_url", DEFAULT_QUESTION_REPORTS_API_URL)),
 		"/api/question-reports")
 	request = HTTPRequest.new()
+	request.timeout = REQUEST_TIMEOUT_SECONDS
 	request.request_completed.connect(_on_api_questions_loaded)
 	add_child(request)
 
 	attempt_request = HTTPRequest.new()
+	attempt_request.timeout = REQUEST_TIMEOUT_SECONDS
 	attempt_request.request_completed.connect(_on_first_attempt_recorded)
 	add_child(attempt_request)
 
 	rating_request = HTTPRequest.new()
+	rating_request.timeout = REQUEST_TIMEOUT_SECONDS
 	rating_request.request_completed.connect(_on_ratings_loaded)
 	add_child(rating_request)
 
 	report_request = HTTPRequest.new()
+	report_request.timeout = REQUEST_TIMEOUT_SECONDS
 	report_request.request_completed.connect(_on_question_report_submitted)
 	add_child(report_request)
 
@@ -108,6 +113,15 @@ func load_questions_from_api(reset_retry: bool = true, excluded_question_ids: Ar
 		retry_attempt = 0
 		next_retry_seconds = 0
 		retry_timer.stop()
+		if is_loading or request.get_http_client_status() != HTTPClient.STATUS_DISCONNECTED:
+			request.cancel_request()
+			is_loading = false
+			call_deferred("load_questions_from_api", false, pending_excluded_question_ids, pending_require_media)
+			return
+	elif is_loading or request.get_http_client_status() != HTTPClient.STATUS_DISCONNECTED:
+		# A late timer or repeated click must not turn an active request into an
+		# immediate ERR_BUSY failure.
+		return
 
 	var should_load_ratings := load_state == "idle"
 	is_loading = true
@@ -130,18 +144,21 @@ func load_questions_from_api(reset_retry: bool = true, excluded_question_ids: Ar
 	}
 	var err := request.request(questions_api_url, headers, HTTPClient.METHOD_POST, JSON.stringify(payload))
 	if err != OK:
-		_set_load_error("Failed to request questions API.")
+		_set_load_error("Unable to connect to the question service.")
 
 
 func _on_api_questions_loaded(result: int, response_code: int, _headers: PackedStringArray, body: PackedByteArray) -> void:
 	is_loading = false
 	if result != HTTPRequest.RESULT_SUCCESS or response_code < 200 or response_code >= 300:
-		_set_load_error("Questions API request failed with status %d." % response_code)
+		var message := "The connection to the question service was interrupted."
+		if response_code > 0:
+			message = "Questions API request failed with status %d." % response_code
+		_set_load_error(message, _is_transient_question_failure(result, response_code))
 		return
 
 	var parsed: Variant = JSON.parse_string(body.get_string_from_utf8())
 	if typeof(parsed) != TYPE_ARRAY:
-		_set_load_error("Questions API response was not an array.")
+		_set_load_error("Questions API response was not an array.", false)
 		return
 
 	var api_questions: Array = []
@@ -151,7 +168,7 @@ func _on_api_questions_loaded(result: int, response_code: int, _headers: PackedS
 			api_questions.append(normalized)
 
 	if api_questions.is_empty():
-		_set_load_error("Questions API returned no usable questions.")
+		_set_load_error("Questions API returned no usable questions.", false)
 		return
 	if pending_require_media and not _contains_question_with_media(api_questions):
 		for question in api_questions:
@@ -178,7 +195,10 @@ func retry_now() -> void:
 	retry_attempt = 0
 	next_retry_seconds = 0
 	retry_timer.stop()
-	load_questions_from_api(false, pending_excluded_question_ids)
+	if is_loading or request.get_http_client_status() != HTTPClient.STATUS_DISCONNECTED:
+		request.cancel_request()
+		is_loading = false
+	call_deferred("load_questions_from_api", false, pending_excluded_question_ids, pending_require_media)
 
 
 func load_next_random_question(excluded_question_ids: Array) -> void:
@@ -323,15 +343,22 @@ func _set_load_error(message: String, schedule_retry: bool = true) -> void:
 	is_loading = false
 	last_error = message
 	push_warning(message)
-	questions_load_failed.emit(message)
 	if schedule_retry and not AuthState.access_token.is_empty():
 		_schedule_retry()
 	else:
 		load_state = "failed"
 		next_retry_seconds = 0
+	questions_load_failed.emit(message)
 	questions_changed.emit()
 
 
+func _is_transient_question_failure(result: int, response_code: int) -> bool:
+	if result != HTTPRequest.RESULT_SUCCESS:
+		return true
+	return response_code == 0 or response_code == 408 or response_code == 425 \
+		or response_code == 429 or response_code >= 500
+
+
 func _schedule_retry() -> void:
 	var delay_index := retry_attempt
 	if delay_index >= RETRY_DELAYS.size():
@@ -344,6 +371,9 @@ func _schedule_retry() -> void:
 
 func _on_retry_timer_timeout() -> void:
 	next_retry_seconds = 0
+	if is_loading or request.get_http_client_status() != HTTPClient.STATUS_DISCONNECTED:
+		retry_timer.start(1.0)
+		return
 	load_questions_from_api(false)