feat(multiplayer): add idempotent client mutation retries

Game/scripts/control_plane_client.gd

@@ -27,6 +27,8 @@ var assignment: AssignmentState
 var _request: HTTPRequest
 var _operation := ""
 var _last_queue_create: Dictionary = {}
+var _last_mutation: Dictionary = {}
+var _last_mutation_retryable := false
 var _websocket: WebSocketPeer
 var _websocket_status := "DISCONNECTED"
 var _websocket_retry_seconds := 0.0
@@ -159,6 +161,17 @@ func can_retry_queue_create() -> bool:
 	return not _last_queue_create.is_empty() and state.phase == MatchmakingState.FAILED and String(_last_queue_create.get("ticket_id", "")) == state.ticket_id
 
 
+func retry_last_mutation() -> Error:
+	if not can_retry_last_mutation():
+		return ERR_INVALID_DATA
+	var request := _last_mutation.duplicate(true)
+	return _start_request(String(request["operation"]), int(request["method"]), String(request["path"]), request["payload"], String(request["key"]), int(request["expected_revision"]))
+
+
+func can_retry_last_mutation() -> bool:
+	return _last_mutation_retryable and not _last_mutation.is_empty() and _operation.is_empty() and not auth_expired and is_valid_access_token(access_token)
+
+
 func recover_queue(ticket_id: String) -> Error:
 	if ticket_id.is_empty():
 		return ERR_INVALID_PARAMETER
@@ -256,6 +269,10 @@ static func is_valid_access_token(token: String) -> bool:
 	return separator > 0 and separator < token.length() - 1 and token.length() <= 4096 and not token.contains("\r") and not token.contains("\n")
 
 
+static func is_retryable_mutation_response(response_code: int) -> bool:
+	return response_code == 0 or response_code == HTTPClient.RESPONSE_REQUEST_TIMEOUT or response_code == HTTPClient.RESPONSE_TOO_MANY_REQUESTS or response_code >= 500
+
+
 static func normalize_ticket(payload: Dictionary) -> Dictionary:
 	var result := payload.duplicate(true)
 	if result.has("expires_at") and result["expires_at"] is String:
@@ -281,6 +298,9 @@ func _start_request(operation: String, method: HTTPClient.Method, path: String,
 	if err != OK:
 		_operation = ""
 		return err
+	if not idempotency_key.is_empty():
+		_last_mutation = {"operation": operation, "method": method, "path": path, "payload": payload.duplicate(true), "key": idempotency_key, "expected_revision": expected_revision}
+		_last_mutation_retryable = false
 	return OK
 
 
@@ -288,6 +308,7 @@ func _on_request_completed(result: HTTPRequest.Result, response_code: int, _head
 	var operation := _operation
 	_operation = ""
 	if result != HTTPRequest.RESULT_SUCCESS:
+		_last_mutation_retryable = _last_mutation.get("operation", "") == operation
 		if operation == "ranked_profile":
 			ranked_profile.set_error("Ranked profile request failed")
 		elif operation == "queue_create" or operation == "queue_recover" or operation == "proposal_recover":
@@ -298,6 +319,7 @@ func _on_request_completed(result: HTTPRequest.Result, response_code: int, _head
 		return
 	var parsed = JSON.parse_string(body.get_string_from_utf8())
 	if not parsed is Dictionary:
+		_last_mutation_retryable = _last_mutation.get("operation", "") == operation
 		if operation == "ranked_profile":
 			ranked_profile.set_error("Ranked profile returned invalid JSON")
 		elif operation == "queue_create" or operation == "queue_recover" or operation == "proposal_recover":
@@ -307,6 +329,7 @@ func _on_request_completed(result: HTTPRequest.Result, response_code: int, _head
 		request_failed.emit(operation, response_code, "invalid JSON")
 		return
 	if response_code < 200 or response_code >= 300:
+		_last_mutation_retryable = _last_mutation.get("operation", "") == operation and is_retryable_mutation_response(response_code)
 		var detail := String(parsed.get("error", "request rejected"))
 		var recover_proposal_after_conflict := response_code == HTTPClient.RESPONSE_CONFLICT and (operation == "proposal_accept" or operation == "proposal_decline") and not state.proposal_id.is_empty()
 		if response_code == HTTPClient.RESPONSE_UNAUTHORIZED:
@@ -334,6 +357,7 @@ func _on_request_completed(result: HTTPRequest.Result, response_code: int, _head
 			call_deferred("_run_pending_resync")
 		return
 	var payload: Dictionary = parsed
+	_last_mutation_retryable = false
 	if operation == "steam_session":
 		var returned_token := String(payload.get("access_token", ""))
 		var returned_player_id := String(payload.get("player_id", ""))