mirror of
https://github.com/storytold/figcraft.git
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bflatastic
6720ea4a21
The Share popover is one flow: Online (the file is published to the server in
Preferences and the server names its links with short codes) or Local network
(the app hosts; the code carries its address and the session's secret), one
Start sharing button, the code large with Copy code and Copy link, who is here,
can edit / can view, and Stop sharing. Join with a code is one field in the
popover, on the home screen and in the Join dialog, for a code of either kind
or an invite link.
Protocol (within version 2, new variants last): Resolve / Resolved and Admin
code. The server keeps a stretched hash and the wrapped token, never the code,
and limits wrong codes per address (with a lockout) and for everyone. Older
servers leave the links in place of a code; older apps join by link.
collab.share, collab.join {code}, code and share in collab.peers; the server
preference defaults to the built-in server and can be reset or turned off.
600 lines
26 KiB
Rust
600 lines
26 KiB
Rust
//! The session server for one file: the single authority that orders, validates and rebroadcasts
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//! batches. A pure state machine: the transport feeds it messages and delivers what it returns.
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use std::collections::{BTreeMap, BTreeSet, VecDeque};
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use figcraft_doc::{Document, NodeId};
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use serde::{Deserialize, Serialize};
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use crate::change::{Change, Entry, Prop, Target};
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use crate::message::{Accepted, Access, CatchUp, ClientMsg, Hello, PROTOCOL, Peer, Presence, Processed, ServerMsg, Signal, reads_signals};
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use crate::replica::{Mode, Replica, create_change};
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use crate::{Error, Limits, docprops, same_secret};
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/// A message for the transport to deliver.
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#[derive(Clone, Debug, PartialEq)]
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pub enum Outgoing {
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/// To one client.
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To(u32, ServerMsg),
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/// To every client.
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All(ServerMsg),
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/// To every client but one.
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Others(u32, ServerMsg),
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}
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/// Why a viewer's batch is refused.
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pub const VIEW_ONLY: &str = "you can only view this file (your link is view-only)";
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/// What changed a server's lasting state, in order: what a store appends to its log between
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/// snapshots ([`Server::journaling`]) and replays over the last snapshot after a restart
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/// ([`Server::replay`]). Presence and who is connected aren't in it.
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#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
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#[serde(rename_all = "camelCase")]
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pub enum Journal {
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/// A client id was handed out.
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Issued { client: u32 },
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/// A batch was accepted.
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Accepted(Accepted),
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/// A client's batch was refused.
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Refused { client: u32, batch_id: u64 },
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}
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/// A session server for one file.
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#[derive(Clone, Debug)]
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pub struct Server {
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/// This session's identity (random): clients resume only into the session they were in.
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session: u64,
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state: Replica,
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seq: u64,
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token: String,
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limits: Limits,
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next_client: u32,
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peers: BTreeMap<u32, Peer>,
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presence: BTreeMap<u32, Presence>,
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acked: BTreeMap<u32, u64>,
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/// Deleted node ids: only these may be created again (by undo); new ids must come from the
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/// creating client's id space.
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deleted: BTreeSet<NodeId>,
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/// Removed document-level entries (styles, variables, collections, comments): these may be
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/// put back by anyone (undo); a new one must not have an id from another client's space.
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removed: BTreeSet<Entry>,
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/// Every client id handed out (a reconnecting client keeps its id) and what was done with
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/// its batches.
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issued: BTreeMap<u32, Processed>,
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/// The latest accepted batches, oldest first (a reconnecting client gets what it missed).
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log: VecDeque<Accepted>,
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/// Changes in `log`, and about how many bytes it holds ([`weight`]).
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log_changes: usize,
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log_bytes: usize,
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/// The connected clients that may only view.
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viewers: BTreeSet<u32>,
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/// What changed the lasting state since it was last taken (`None`: not kept).
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journal: Option<Vec<Journal>>,
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/// The connected clients that read signals (cursor chat, spotlight).
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signals: BTreeSet<u32>,
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/// Who spotlights now (a newcomer is told).
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spotlight: Option<u32>,
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}
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/// The most client ids a session remembers for reconnecting (the oldest disconnected ones go
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/// first; a forgotten client joins as new).
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const MAX_REMEMBERED: usize = 65_536;
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/// What a session server needs to carry on after a restart: the document, the sequence number,
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/// the client-id counter (so ids are never handed out twice), the clients that can reconnect,
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/// the deleted ids and removed entries that may be created again and the log of recent batches.
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#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
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pub struct SessionState {
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pub session: u64,
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pub snapshot: Vec<Change>,
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pub seq: u64,
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pub next_client: u32,
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pub issued: BTreeMap<u32, Processed>,
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pub deleted: BTreeSet<NodeId>,
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/// Absent in states saved before entries were tracked.
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#[serde(default)]
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pub removed: BTreeSet<Entry>,
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pub log: Vec<Accepted>,
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}
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impl Server {
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/// A session for `doc`. Joining requires `token` (empty: no token). Client ids start above every
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/// client id space already used in the document (by layers, styles, variables, collections,
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/// modes or comments), so ids from earlier sessions are never handed out again.
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pub fn new(doc: Document, token: impl Into<String>, limits: Limits) -> Server {
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let next_client = doc.highest_id_space().saturating_add(1);
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Server {
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session: new_session_id(),
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state: Replica::new(doc),
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seq: 0,
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token: token.into(),
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limits,
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next_client,
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peers: BTreeMap::new(),
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presence: BTreeMap::new(),
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acked: BTreeMap::new(),
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deleted: BTreeSet::new(),
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removed: BTreeSet::new(),
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issued: BTreeMap::new(),
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log: VecDeque::new(),
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log_changes: 0,
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log_bytes: 0,
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viewers: BTreeSet::new(),
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journal: None,
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signals: BTreeSet::new(),
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spotlight: None,
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}
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}
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/// The session's state, to save (see [`restore`](Self::restore)).
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pub fn state(&self) -> Result<SessionState, Error> {
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Ok(SessionState {
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session: self.session,
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snapshot: self.state.snapshot()?,
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seq: self.seq,
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next_client: self.next_client,
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issued: self.issued.clone(),
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deleted: self.deleted.clone(),
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removed: self.removed.clone(),
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log: self.log.iter().cloned().collect(),
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})
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}
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/// A session carrying on from a saved [`state`](Self::state) (nobody is connected yet; clients
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/// reconnect with their ids). A log that doesn't lead up to the sequence number is dropped
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/// (clients then catch up with a snapshot).
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pub fn restore(state: SessionState, token: impl Into<String>, limits: Limits) -> Result<Server, Error> {
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let replica = Replica::from_snapshot(&state.snapshot)?;
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let mut server = Server::new(replica.document().clone(), token, limits);
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server.state = replica;
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server.session = state.session;
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server.seq = state.seq;
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server.next_client = server.next_client.max(state.next_client);
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server.issued = state.issued.into_iter().filter(|(id, _)| *id < server.next_client).collect();
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server.deleted = state.deleted;
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server.removed = state.removed;
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let contiguous = state.log.windows(2).all(|w| matches!(w, [a, b] if a.seq + 1 == b.seq));
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if contiguous && state.log.last().is_none_or(|a| a.seq == state.seq) {
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for a in state.log {
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server.remember(a);
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}
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}
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Ok(server)
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}
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/// Keep a [`Journal`] of what changes the lasting state (`on`), or stop (dropping what wasn't
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/// taken).
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pub fn journaling(&mut self, on: bool) {
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self.journal = on.then(|| self.journal.take().unwrap_or_default());
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}
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/// What changed the lasting state since the last call, oldest first.
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pub fn take_journal(&mut self) -> Vec<Journal> {
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self.journal.as_mut().map(std::mem::take).unwrap_or_default()
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}
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fn note(&mut self, j: Journal) {
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if let Some(v) = self.journal.as_mut() {
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v.push(j);
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}
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}
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/// Apply a journal entry over a restored state (after a restart). What the state already has
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/// (a batch at or below its sequence number, a client id it knows, a refusal it noted)
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/// changes nothing; a batch that doesn't follow the sequence number, or doesn't apply, is an
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/// error (the rest of that log can't be trusted). Replayed entries aren't journaled again.
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pub fn replay(&mut self, j: Journal) -> Result<(), Error> {
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match j {
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Journal::Issued { client } => {
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if let std::collections::btree_map::Entry::Vacant(v) = self.issued.entry(client) {
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v.insert(Processed::default());
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self.next_client = self.next_client.max(client.saturating_add(1));
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self.forget_oldest();
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}
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Ok(())
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}
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Journal::Accepted(acc) if acc.seq <= self.seq => Ok(()),
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Journal::Accepted(acc) => {
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if acc.seq != self.seq + 1 {
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return Err(Error::Protocol(format!("batch {} after {}", acc.seq, self.seq)));
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}
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self.accept(acc.author, self.seq, &acc.changes)?;
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self.issued.entry(acc.author).or_default().note(acc.batch_id, false);
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self.next_client = self.next_client.max(acc.author.saturating_add(1));
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self.remember(acc);
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Ok(())
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}
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Journal::Refused { client, batch_id } => {
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if let Some(p) = self.issued.get_mut(&client).filter(|p| batch_id > p.last_batch) {
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p.note(batch_id, true);
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}
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Ok(())
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}
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}
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}
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/// Beyond [`MAX_REMEMBERED`] client ids, forget the oldest one that isn't connected.
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fn forget_oldest(&mut self) {
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if self.issued.len() > MAX_REMEMBERED
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&& let Some(old) = self.issued.keys().copied().find(|k| !self.peers.contains_key(k))
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{
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self.issued.remove(&old);
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}
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}
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/// The authoritative document.
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pub fn document(&self) -> &Document {
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self.state.document()
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}
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/// The authoritative state (document and positions).
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pub fn replica(&self) -> &Replica {
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&self.state
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}
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/// The sequence number of the last accepted batch (0: none yet).
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pub fn seq(&self) -> u64 {
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self.seq
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}
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/// Who is in the session.
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pub fn peers(&self) -> impl Iterator<Item = &Peer> {
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self.peers.values()
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}
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/// The highest sequence number client `id` reported applying.
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pub fn acked(&self, id: u32) -> Option<u64> {
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self.acked.get(&id).copied()
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}
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/// A new connection says hello: on success its client id and the messages to send (its
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/// `Welcome`, everyone else's `PeerJoined`); otherwise the `Refused` to send back. A client
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/// coming back ([`Hello::resume`]) keeps its id (taking over from its old connection if that
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/// is still open: the transport closes the old one) and gets the batches it missed, or a
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/// snapshot when they are no longer in the log; an id this session never gave out joins as
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/// new.
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pub fn join(&mut self, hello: Hello) -> Result<(u32, Vec<Outgoing>), ServerMsg> {
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self.join_as(hello, Access::Edit)
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}
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/// [`join`](Self::join) with what the client may do: every batch of a viewer is refused.
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pub fn join_as(&mut self, hello: Hello, access: Access) -> Result<(u32, Vec<Outgoing>), ServerMsg> {
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let refuse = |reason: &str| ServerMsg::Refused { reason: reason.to_string() };
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if hello.protocol != PROTOCOL {
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return Err(refuse(&format!("protocol {} isn't supported (this server speaks {PROTOCOL})", hello.protocol)));
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}
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if !same_secret(&hello.token, &self.token) {
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return Err(refuse("wrong session token"));
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}
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let resume = hello.resume.filter(|r| r.session == self.session && self.issued.contains_key(&r.client_id));
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if self.peers.len() >= self.limits.max_peers && resume.is_none_or(|r| !self.peers.contains_key(&r.client_id)) {
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return Err(refuse("the session is full"));
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}
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if hello.name.chars().count() > self.limits.max_name || hello.color.chars().count() > self.limits.max_name {
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return Err(refuse("name or colour too long"));
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}
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if resume.is_none() && self.next_client == u32::MAX {
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return Err(refuse("no client ids left in this session"));
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}
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// The log holds every batch after `floor`.
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let floor = self.log.front().map_or(self.seq, |a| a.seq.saturating_sub(1));
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let catch_up = match resume {
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Some(r) if r.seq <= self.seq && r.seq >= floor => CatchUp::Delta(self.log.iter().filter(|a| a.seq > r.seq).cloned().collect()),
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_ => CatchUp::Snapshot(self.state.snapshot().map_err(|e| refuse(&e.to_string()))?),
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};
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let id = match resume {
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Some(r) => r.client_id,
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None => {
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let id = self.next_client;
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self.next_client += 1;
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self.issued.insert(id, Processed::default());
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self.forget_oldest();
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self.note(Journal::Issued { client: id });
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id
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}
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};
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let processed = self.issued.get(&id).cloned().unwrap_or_default();
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self.presence.remove(&id);
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let signals = reads_signals(&hello.client_version);
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let peer = Peer { client_id: id, name: hello.name, color: hello.color };
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let others = self.peers.values().filter(|p| p.client_id != id).cloned().collect();
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let welcome = ServerMsg::Welcome { session: self.session, client_id: id, seq: self.seq, catch_up, processed, peers: others, access };
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self.peers.insert(id, peer.clone());
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if access == Access::View {
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self.viewers.insert(id);
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} else {
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self.viewers.remove(&id);
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}
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let mut outs = vec![Outgoing::To(id, welcome), Outgoing::Others(id, ServerMsg::PeerJoined(peer))];
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if signals {
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self.signals.insert(id);
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outs.push(Outgoing::To(id, ServerMsg::Signal { client_id: id, signal: Signal::ready() }));
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if let Some(p) = self.spotlight.filter(|p| *p != id) {
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outs.push(Outgoing::To(id, ServerMsg::Signal { client_id: p, signal: Signal::spotlight(true) }));
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}
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} else {
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self.signals.remove(&id);
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}
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Ok((id, outs))
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}
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/// Client `id`'s connection closed.
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pub fn leave(&mut self, id: u32) -> Vec<Outgoing> {
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self.presence.remove(&id);
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self.acked.remove(&id);
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self.viewers.remove(&id);
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self.signals.remove(&id);
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if self.spotlight == Some(id) {
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self.spotlight = None;
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}
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match self.peers.remove(&id) {
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Some(_) => vec![Outgoing::Others(id, ServerMsg::PeerLeft { client_id: id })],
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None => Vec::new(),
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}
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}
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/// A message from client `from` (which has joined).
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pub fn receive(&mut self, from: u32, msg: ClientMsg) -> Vec<Outgoing> {
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if !self.peers.contains_key(&from) {
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return vec![Outgoing::To(from, ServerMsg::Refused { reason: "say hello first".into() })];
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}
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match msg {
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ClientMsg::Hello(_) => vec![Outgoing::To(from, ServerMsg::Refused { reason: "already joined".into() })],
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// A batch already processed (a copy sent again around a reconnect) is ignored: the
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// client learned what happened to it from the catch-up.
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ClientMsg::Changes { batch_id, .. } if self.issued.get(&from).is_some_and(|p| batch_id <= p.last_batch) => Vec::new(),
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ClientMsg::Changes { base_seq, batch_id, changes } => {
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let result = if self.viewers.contains(&from) { Err(Error::Invalid(VIEW_ONLY.into())) } else { self.accept(from, base_seq, &changes) };
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if let Some(p) = self.issued.get_mut(&from) {
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p.note(batch_id, result.is_err());
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}
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match result {
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Ok(()) => {
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let acc = Accepted { seq: self.seq, author: from, batch_id, changes };
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self.remember(acc.clone());
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self.note(Journal::Accepted(acc.clone()));
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vec![Outgoing::All(ServerMsg::Changes(acc))]
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}
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Err(e) => {
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self.note(Journal::Refused { client: from, batch_id });
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let fixes = self.fixes(&changes).unwrap_or_default();
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vec![Outgoing::To(from, ServerMsg::Reject { batch_id, reason: reason(&e), fixes })]
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}
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}
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}
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ClientMsg::Presence(p) => {
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self.presence.insert(from, p.clone());
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vec![Outgoing::Others(from, ServerMsg::Presence { client_id: from, presence: p })]
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}
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// Checked and cleaned, then passed on to those who read signals; never stored but the
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// current spotlight.
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ClientMsg::Signal(sig) => {
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let Some(sig) = sig.clean().filter(|s| s.kind != Signal::READY) else { return Vec::new() };
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if sig.kind == Signal::SPOTLIGHT {
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if sig.on() {
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self.spotlight = Some(from);
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} else if self.spotlight == Some(from) {
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self.spotlight = None;
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}
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}
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let to = self.signals.iter().filter(|id| **id != from);
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to.map(|id| Outgoing::To(*id, ServerMsg::Signal { client_id: from, signal: sig.clone() })).collect()
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}
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ClientMsg::Ack { seq } => {
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self.acked.insert(from, seq.min(self.seq));
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Vec::new()
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}
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ClientMsg::Ping => vec![Outgoing::To(from, ServerMsg::Pong)],
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ClientMsg::Manage(_)
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| ClientMsg::Admin(_)
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| ClientMsg::OpenLibrary(_)
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| ClientMsg::Library(_)
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| ClientMsg::OpenPlugins(_)
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| ClientMsg::Plugins(_)
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| ClientMsg::OpenHosting(_)
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| ClientMsg::Resolve(_)
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| ClientMsg::Report { .. } => {
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vec![Outgoing::To(from, ServerMsg::Refused { reason: "managing files and libraries needs a connection of its own".into() })]
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}
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}
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}
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/// Keep an accepted batch in the log (dropping the oldest beyond the limits).
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fn remember(&mut self, acc: Accepted) {
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self.log_changes += acc.changes.len();
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self.log_bytes = self.log_bytes.saturating_add(weight(&acc.changes));
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self.log.push_back(acc);
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while !self.log.is_empty()
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&& (self.log.len() > self.limits.max_log_batches
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|| self.log_changes > self.limits.max_log_changes
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|| self.log_bytes > self.limits.max_log_bytes)
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{
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if let Some(old) = self.log.pop_front() {
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self.log_changes = self.log_changes.saturating_sub(old.changes.len());
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self.log_bytes = self.log_bytes.saturating_sub(weight(&old.changes));
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}
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}
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|
}
|
|
|
|
/// About how many bytes the batches kept for reconnecting clients hold.
|
|
pub fn log_bytes(&self) -> usize {
|
|
self.log_bytes
|
|
}
|
|
|
|
/// Validate and apply a batch; on success it has the next sequence number.
|
|
fn accept(&mut self, from: u32, base_seq: u64, changes: &[Change]) -> Result<(), Error> {
|
|
if changes.len() > self.limits.max_changes {
|
|
return Err(Error::Invalid(format!("{} changes in one batch (at most {})", changes.len(), self.limits.max_changes)));
|
|
}
|
|
if base_seq > self.seq {
|
|
return Err(Error::Protocol(format!("based on sequence {base_seq}, but the server is at {}", self.seq)));
|
|
}
|
|
for c in changes {
|
|
if let Change::Create { id, .. } = c
|
|
&& !self.state.document().contains(*id)
|
|
&& !self.deleted.contains(id)
|
|
&& id.0 >> 32 != u64::from(from)
|
|
{
|
|
return Err(Error::Invalid(format!("new node {id} isn't in client {from}'s id space")));
|
|
}
|
|
}
|
|
let mut next = self.state.clone();
|
|
let applied = next.apply(changes, Mode::Strict)?;
|
|
if next.document().node_count() > self.limits.max_nodes {
|
|
return Err(Error::Invalid(format!("more than {} layers", self.limits.max_nodes)));
|
|
}
|
|
let entries = self.check_entries(from, changes, next.document())?;
|
|
for c in changes {
|
|
if let Change::Create { id, .. } = c {
|
|
self.deleted.remove(id);
|
|
}
|
|
}
|
|
self.deleted.extend(applied.deleted);
|
|
for (entry, now) in entries {
|
|
if now {
|
|
self.removed.remove(&entry);
|
|
} else {
|
|
self.removed.insert(entry);
|
|
}
|
|
}
|
|
self.state = next;
|
|
self.seq += 1;
|
|
Ok(())
|
|
}
|
|
|
|
/// The document-level entries (styles, variables, collections, comments) a batch adds or
|
|
/// removes, each with whether it is there afterwards. A new one is refused when its id lies in
|
|
/// the space of another client this session gave an id to (unless it was removed before: undo
|
|
/// puts entries back); ids from before the session (space 0, earlier sessions, other files)
|
|
/// are fine.
|
|
fn check_entries(&self, from: u32, changes: &[Change], after: &Document) -> Result<Vec<(Entry, bool)>, Error> {
|
|
let before = self.state.document();
|
|
let mut touched: BTreeSet<Entry> = BTreeSet::new();
|
|
for c in changes {
|
|
match c {
|
|
Change::Put { entry, .. } | Change::Remove { entry } if entry.id_space().is_some() => {
|
|
touched.insert(entry.clone());
|
|
}
|
|
// A whole list replaced (the fallback for lists whose ids aren't unique).
|
|
Change::SetDoc { prop, .. } => {
|
|
if let Some(Ok(family)) = prop.list() {
|
|
touched.extend(docprops::entries(before, family));
|
|
touched.extend(docprops::entries(after, family));
|
|
}
|
|
}
|
|
_ => {}
|
|
}
|
|
}
|
|
let mut out = Vec::new();
|
|
for entry in touched {
|
|
let (was, now) = (docprops::has(before, &entry), docprops::has(after, &entry));
|
|
if was == now {
|
|
continue;
|
|
}
|
|
if now
|
|
&& !self.removed.contains(&entry)
|
|
&& let Some(space) = entry.id_space().filter(|s| *s != from && self.issued.contains_key(s))
|
|
{
|
|
return Err(Error::Invalid(format!("new {} isn't in client {from}'s id space (it is client {space}'s)", entry.describe())));
|
|
}
|
|
out.push((entry, now));
|
|
}
|
|
Ok(out)
|
|
}
|
|
|
|
/// The current values of what a refused batch touched, so a client can roll its optimistic
|
|
/// copy back: nodes that don't exist are deleted, deleted subtrees come back whole, edited
|
|
/// properties get their current values, document-level data likewise.
|
|
fn fixes(&self, changes: &[Change]) -> Result<Vec<Change>, Error> {
|
|
let doc = self.state.document();
|
|
let mut props: BTreeMap<NodeId, BTreeSet<Prop>> = BTreeMap::new();
|
|
let mut gone: BTreeSet<NodeId> = BTreeSet::new();
|
|
let mut out = Vec::new();
|
|
for c in changes {
|
|
match c {
|
|
Change::Create { id, .. } => {
|
|
props.entry(*id).or_default().extend(Prop::FIELDS.iter().copied().chain([Prop::Parent, Prop::Position]));
|
|
}
|
|
Change::Set { id, prop, .. } => {
|
|
props.entry(*id).or_default().insert(*prop);
|
|
}
|
|
Change::Delete { id } => {
|
|
gone.insert(*id);
|
|
}
|
|
other => {
|
|
if let Some(fix) = docprops::current(doc, other)?
|
|
&& !out.contains(&fix)
|
|
{
|
|
out.push(fix);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
let mut nodes = Vec::new();
|
|
for (id, ps) in props {
|
|
if !doc.contains(id) {
|
|
nodes.push(Change::Delete { id });
|
|
continue;
|
|
}
|
|
for p in ps {
|
|
let t = Target::Node(id, p);
|
|
nodes.extend(t.write(self.state.value(&t)?.as_ref()));
|
|
}
|
|
}
|
|
for id in gone {
|
|
match doc.node(id) {
|
|
Some(_) => {
|
|
for d in doc.subtree(id) {
|
|
if let Some(n) = doc.node(d) {
|
|
nodes.push(create_change(n, self.state.key(d))?);
|
|
}
|
|
}
|
|
}
|
|
None => nodes.push(Change::Delete { id }),
|
|
}
|
|
}
|
|
nodes.extend(out);
|
|
Ok(nodes)
|
|
}
|
|
}
|
|
|
|
/// A fresh session identity: random per server (std's hasher keys are seeded from the OS).
|
|
fn new_session_id() -> u64 {
|
|
use std::hash::{BuildHasher, Hasher};
|
|
let mut h = std::collections::hash_map::RandomState::new().build_hasher();
|
|
h.write_u8(0);
|
|
h.finish()
|
|
}
|
|
|
|
/// Why a batch was refused, for the person who made it.
|
|
fn reason(e: &Error) -> String {
|
|
match e {
|
|
Error::Unknown(_) => "a layer it changes was deleted by someone else".into(),
|
|
e => e.to_string(),
|
|
}
|
|
}
|
|
|
|
/// About how many bytes `changes` take in memory: their values' text and a little per change.
|
|
pub fn weight(changes: &[Change]) -> usize {
|
|
fn json(v: &serde_json::Value) -> usize {
|
|
match v {
|
|
serde_json::Value::String(s) => s.len() + 2,
|
|
serde_json::Value::Array(a) => a.iter().map(json).fold(2, usize::saturating_add),
|
|
serde_json::Value::Object(o) => o.iter().map(|(k, v)| k.len() + 3 + json(v)).fold(2, usize::saturating_add),
|
|
_ => 8,
|
|
}
|
|
}
|
|
changes
|
|
.iter()
|
|
.map(|c| match c {
|
|
Change::Create { kind, position, props, .. } => {
|
|
props.iter().map(|(_, v)| 16 + json(&v.0)).fold(64 + json(&kind.0) + position.len(), usize::saturating_add)
|
|
}
|
|
Change::Set { value, .. } | Change::SetDoc { value, .. } => 32 + json(&value.0),
|
|
Change::Put { value, .. } => 64 + json(&value.0),
|
|
Change::Delete { .. } => 16,
|
|
Change::Remove { .. } => 64,
|
|
})
|
|
.fold(0, usize::saturating_add)
|
|
}
|