sync.v

1//! Sync: offer and steal.2//!3//! All the cleverness sits here, above the five-operation remote interface, so4//! the backends stay thin and this logic is written once and tested offline.5//!6//! The remote is a line of saves, the same shape as the local one. `offer`7//! pushes local saves the remote lacks; `steal` pulls remote saves and, when8//! both sides moved, replays the local work on top of the remote's. Divergence9//! is resolved per file, never per line.1011module sync1213import os14import src.events15import src.history16import src.remote17import src.snapshot18import src.storage1920// Where the repo's name on the remote is remembered.21const repo_state_key = 'remote_repo'2223// The remote head as of this machine's last successful offer, as the document24// asks; nothing reads it back yet.25const remote_head_key = 'remote_head'2627pub const no_saves = 'this repo has no saves yet — nothing to offer'2829pub struct OfferReport {30pub mut:31	repo    string32	saves   int33	objects int34	events  int35	head    string36}3738// remember_repo binds a repo to its name on the remote. A clone does it at39// once: its folder may be renamed before it ever offers.40pub fn remember_repo(store &storage.Store, name string) ! {41	store.set_state(repo_state_key, name)!42}4344// repo_name is the folder's name at first offer, remembered in the repo so45// renaming the folder later changes nothing.46pub fn repo_name(store &storage.Store, mut backend remote.Backend) !string {47	if remembered := store.state(repo_state_key) {48		return remembered49	}50	name := os.base(store.root)51	existing := backend.get(head_key(name))!52	if existing.found {53		theirs := existing.body.bytestr().trim_space()54		if history.by_id(store, theirs) == none {55			return error('the remote already has "${name}" with a history this repo does not share — rename the folder, or use another remote')56		}57	}58	store.set_state(repo_state_key, name)!59	return name60}6162// offer sends what the remote lacks and then swaps `head`. Nothing is ever63// queued: the next offer simply sends everything the remote does not have.64pub fn offer(store &storage.Store, mut backend remote.Backend) !OfferReport {65	name := repo_name(store, mut backend)!66	local := history.head(store) or { return error(no_saves) }67	mut report := OfferReport{68		repo: name69		head: local.id70	}71	remote_head := backend.get(head_key(name))!72	// Records offered by a machine that has not applied a strip would put the73	// stripped path back on the remote, where nothing would rewrite it again.74	// ponytail: an offer racing a strip on another machine inside the same few75	// seconds can still slip through; closing that needs a remote lock.76	if unapplied_strip(store, mut backend, name)! {77		return error('the remote has a strip this repo has not applied — run koh steal')78	}79	if remote_head.found {80		theirs := remote_head.body.bytestr().trim_space()81		newer := saves_after(store, local.id, theirs) or {82			return error('remote has new saves — run koh steal')83		}84		for save in newer {85			upload_save(store, mut backend, name, save, mut report)!86		}87	} else {88		oldest_first := history.line(store)!89		for index := oldest_first.len - 1; index >= 0; index-- {90			upload_save(store, mut backend, name, oldest_first[index], mut report)!91		}92	}93	upload_events(store, mut backend, name, mut report)!94	if !backend.put_if_match(head_key(name), local.id.bytes(), remote_head.tag)! {95		return error('remote has new saves — run koh steal')96	}97	store.set_state(remote_head_key, local.id)!98	return report99}100101// saves_after lists the local saves newer than `theirs`, oldest first. It fails102// when `theirs` is not on this line, which is the honest answer: we cannot103// offer on top of a save we do not have.104fn saves_after(store &storage.Store, ours string, theirs string) ![]history.Save {105	mut newer := []history.Save{}106	mut cursor := ours107	for cursor != '' && cursor != theirs {108		save := history.by_id(store, cursor) or { return error('save ${cursor} is missing') }109		newer << save110		cursor = save.parent111	}112	if cursor != theirs {113		return error('${theirs} is not on this line')114	}115	newer.reverse_in_place()116	return newer117}118119fn upload_save(store &storage.Store, mut backend remote.Backend, repo string, save history.Save, mut report OfferReport) ! {120	files := history.files_of(store, save.id)!121	for file in files {122		if backend.put_if_absent(object_key(repo, file.hash), store.object_blob(file.hash)!)! {123			report.objects++124		}125	}126	record := save_record(store, save)!127	if backend.put_if_absent(save_key(repo, save.id), encode_save(record).bytes())! {128		report.saves++129	}130}131132// upload_events sends every event the remote does not have. Events are tiny, so133// listing them costs less than tracking which ones were sent.134fn upload_events(store &storage.Store, mut backend remote.Backend, repo string, mut report OfferReport) ! {135	already := backend.list(events_prefix(repo))!136	mut already_sent := map[string]bool{}137	for key in already {138		already_sent[os.base(key)] = true139	}140	for event in events.all(store)! {141		if event.id in already_sent {142			continue143		}144		if backend.put_if_absent(event_key(repo, event.id), encode_event(event).bytes())! {145			report.events++146		}147	}148}149150// fetched holds everything a steal read from the remote, before any of it is151// written locally. Network work happens first; the database gets one152// transaction, so a failure leaves nothing half-applied.153pub struct Fetched {154pub mut:155	repo_objects map[string][]u8156	saves        []SaveRecord // oldest first157	events_out   []events.Event158	head         string159	base         string // the newest save both sides already shared, '' when none160}161162pub fn fetch_back_to_known(store &storage.Store, mut backend remote.Backend, repo string) !Fetched {163	remote_head := backend.get(head_key(repo))!164	if !remote_head.found {165		return error('the remote has no "${repo}" yet — run koh offer here first')166	}167	mut fetched := Fetched{168		head: remote_head.body.bytestr().trim_space()169	}170	mut cursor := fetched.head171	for cursor != '' && history.by_id(store, cursor) == none {172		record_object := backend.get(save_key(repo, cursor))!173		if !record_object.found {174			return error('the remote is missing save ${cursor} — run koh offer there')175		}176		record := decode_save(record_object.body)!177		for file in record.files {178			if !store.has_object(file.hash)! && file.hash !in fetched.repo_objects {179				blob := backend.get(object_key(repo, file.hash))!180				if !blob.found {181					return error('the remote is missing object ${file.hash} that save ${record.id} needs')182				}183				fetched.repo_objects[file.hash] = blob.body184			}185		}186		fetched.saves << record187		cursor = record.parent188	}189	fetched.saves.reverse_in_place()190	fetched.base = cursor191	fetched.events_out = fetch_events(store, mut backend, repo)!192	return fetched193}194195fn fetch_events(store &storage.Store, mut backend remote.Backend, repo string) ![]events.Event {196	have := events.all(store)!197	mut known := map[string]bool{}198	for event in have {199		known[event.id] = true200	}201	mut incoming := []events.Event{}202	for key in backend.list(events_prefix(repo))! {203		id := os.base(key)204		if id in known {205			continue206		}207		body := backend.get(event_key(repo, id))!208		if !body.found {209			continue210		}211		incoming << decode_event(body.body)!212	}213	return incoming214}215216// write_fetched lands a fetch in one transaction: objects first (verified),217// then the events, then the saves they belong to. A new strip reaches every218// save already here, but an arriving save only when `reaches` says so: one219// made after the strip is new work, not what the strip removed.220pub fn write_fetched(store &storage.Store, fetched Fetched) ! {221	for hash, blob in fetched.repo_objects {222		store.put_object_blob(hash, blob)!223	}224	mut strips := []events.Event{}225	for event in fetched.events_out {226		if !events.receive(store, event)! {227			continue228		}229		if event.kind == events.kind_strip {230			// Somebody stripped a path: remove it here too, so the two231			// histories agree from now on. Objects go once the saves are in.232			remove_path(store, event.path, event.save_id)!233			strips << event234		}235	}236	for record in fetched.saves {237		files := to_files(record).filter(fn [strips, record] (file snapshot.FileEntry) bool {238			return !strips.any(reaches(it, record.id, record.created_at)239				&& covers(it.path, file.path))240		})241		history.import_save(store, to_save(record), files)!242	}243	if strips.len > 0 {244		store.drop_unreferenced_objects()!245	}246}247248// reaches reports whether a strip event applies to a save arriving from the249// remote. A strip of every save covers the saves made up to its own time.250fn reaches(strip events.Event, save_id string, created_at i64) bool {251	if strip.save_id != '' {252		return strip.save_id == save_id253	}254	return created_at <= strip.created_at255}