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.storage1819// Where the repo's name on the remote and the last offered head are remembered.20const repo_state_key = 'remote_repo'21const offered_head_key = 'remote_head'2223pub const no_saves = 'this repo has no saves yet — nothing to offer'2425pub struct OfferReport {26pub mut:27	repo    string28	saves   int29	objects int30	events  int31	head    string32}3334// remember_repo binds a repo to its name on the remote. A clone does it at35// once: its folder may be renamed before it ever offers.36pub fn remember_repo(store &storage.Store, name string) ! {37	store.set_state(repo_state_key, name)!38}3940// repo_name is the folder's name at first offer, remembered in the repo so41// renaming the folder later changes nothing.42pub fn repo_name(store &storage.Store, mut backend remote.Backend) !string {43	if remembered := store.state(repo_state_key) {44		return remembered45	}46	name := os.base(store.root)47	existing := backend.get(head_key(name))!48	if existing.found {49		theirs := existing.body.bytestr().trim_space()50		if history.by_id(store, theirs) == none {51			return error('the remote already has "${name}" with a history this repo does not share — rename the folder, or use another remote')52		}53	}54	store.set_state(repo_state_key, name)!55	return name56}5758// offer sends what the remote lacks and then swaps `head`. Nothing is ever59// queued: the next offer simply sends everything the remote does not have.60pub fn offer(store &storage.Store, mut backend remote.Backend) !OfferReport {61	name := repo_name(store, mut backend)!62	local := history.head(store) or { return error(no_saves) }63	mut report := OfferReport{64		repo: name65		head: local.id66	}67	remote_head := backend.get(head_key(name))!68	// Records offered by a machine that has not applied a strip would put the69	// stripped path back on the remote, where nothing would rewrite it again.70	// ponytail: an offer racing a strip on another machine inside the same few71	// seconds can still slip through; closing that needs a remote lock.72	if unapplied_strip(store, mut backend, name)! {73		return error('the remote has a strip this repo has not applied — run koh steal')74	}75	if remote_head.found {76		theirs := remote_head.body.bytestr().trim_space()77		newer := saves_after(store, local.id, theirs) or {78			return error('remote has new saves — run koh steal')79		}80		for save in newer {81			upload_save(store, mut backend, name, save, mut report)!82		}83	} else {84		oldest_first := history.line(store)!85		for index := oldest_first.len - 1; index >= 0; index-- {86			upload_save(store, mut backend, name, oldest_first[index], mut report)!87		}88	}89	upload_events(store, mut backend, name, mut report)!90	if !backend.put_if_match(head_key(name), local.id.bytes(), remote_head.tag)! {91		return error('remote has new saves — run koh steal')92	}93	store.set_state(offered_head_key, local.id)!94	return report95}9697// saves_after lists the local saves newer than `theirs`, oldest first. It fails98// when `theirs` is not on this line, which is the honest answer: we cannot99// offer on top of a save we do not have.100fn saves_after(store &storage.Store, ours string, theirs string) ![]history.Save {101	mut newer := []history.Save{}102	mut cursor := ours103	for cursor != '' && cursor != theirs {104		save := history.by_id(store, cursor) or { return error('save ${cursor} is missing') }105		newer << save106		cursor = save.parent107	}108	if cursor != theirs {109		return error('${theirs} is not on this line')110	}111	newer.reverse_in_place()112	return newer113}114115fn upload_save(store &storage.Store, mut backend remote.Backend, repo string, save history.Save, mut report OfferReport) ! {116	files := history.files_of(store, save.id)!117	for file in files {118		if backend.put_if_absent(object_key(repo, file.hash), store.object_blob(file.hash)!)! {119			report.objects++120		}121	}122	record := save_record(store, save)!123	if backend.put_if_absent(save_key(repo, save.id), encode_save(record).bytes())! {124		report.saves++125	}126}127128// upload_events sends every event the remote does not have. Events are tiny, so129// listing them costs less than tracking which ones were sent.130fn upload_events(store &storage.Store, mut backend remote.Backend, repo string, mut report OfferReport) ! {131	already := backend.list(events_prefix(repo))!132	mut already_sent := map[string]bool{}133	for key in already {134		already_sent[os.base(key)] = true135	}136	for event in events.all(store)! {137		if event.id in already_sent {138			continue139		}140		if backend.put_if_absent(event_key(repo, event.id), encode_event(event).bytes())! {141			report.events++142		}143	}144}145146// fetched holds everything a steal read from the remote, before any of it is147// written locally. Network work happens first; the database gets one148// transaction, so a failure leaves nothing half-applied.149pub struct Fetched {150pub mut:151	repo_objects    map[string][]u8152	saves           []SaveRecord // oldest first153	events_out      []events.Event154	head            string155	base            string // the newest save both sides already shared, '' when none156	remote_save_ids map[string]bool157}158159pub fn fetch_back_to_known(store &storage.Store, mut backend remote.Backend, repo string) !Fetched {160	remote_head := backend.get(head_key(repo))!161	if !remote_head.found {162		return error('the remote has no "${repo}" yet — run koh offer here first')163	}164	mut fetched := Fetched{165		head:            remote_head.body.bytestr().trim_space()166		remote_save_ids: map[string]bool{}167	}168	mut cursor := fetched.head169	for cursor != '' && history.by_id(store, cursor) == none {170		record_object := backend.get(save_key(repo, cursor))!171		if !record_object.found {172			return error('the remote is missing save ${cursor} — run koh offer there')173		}174		record := decode_save(record_object.body)!175		for file in record.files {176			if !store.has_object(file.hash)! && file.hash !in fetched.repo_objects {177				blob := backend.get(object_key(repo, file.hash))!178				if !blob.found {179					return error('the remote is missing object ${file.hash} that save ${record.id} needs')180				}181				fetched.repo_objects[file.hash] = blob.body182			}183		}184		fetched.remote_save_ids[record.id] = true185		fetched.saves << record186		cursor = record.parent187	}188	fetched.saves.reverse_in_place()189	fetched.base = cursor190	fetched.events_out = fetch_events(store, mut backend, repo)!191	return fetched192}193194fn fetch_events(store &storage.Store, mut backend remote.Backend, repo string) ![]events.Event {195	have := events.all(store)!196	mut known := map[string]bool{}197	for event in have {198		known[event.id] = true199	}200	mut incoming := []events.Event{}201	for key in backend.list(events_prefix(repo))! {202		id := os.base(key)203		if id in known {204			continue205		}206		body := backend.get(event_key(repo, id))!207		if !body.found {208			continue209		}210		incoming << decode_event(body.body)!211	}212	return incoming213}214215// write_fetched lands a fetch in one transaction: objects first (verified), then216// the saves they belong to, then the events.217pub fn write_fetched(store &storage.Store, fetched Fetched) ! {218	for hash, blob in fetched.repo_objects {219		store.put_object_blob(hash, blob)!220	}221	for record in fetched.saves {222		history.import_save(store, to_save(record), to_files(record))!223	}224	for event in fetched.events_out {225		if !events.receive(store, event)! {226			continue227		}228		if event.kind == events.kind_strip {229			// Somebody stripped a path: remove it here too, so the two230			// histories agree from now on.231			apply_strip(store, event)!232		}233	}234}235236// can_fast_forward reports whether our line sits behind the remote's, which is237// the case when every local save is an ancestor of the remote head.238pub fn can_fast_forward(store &storage.Store, remote_head string, remote_ids map[string]bool) bool {239	mut cursor := remote_head240	for cursor != '' {241		if history.by_id(store, cursor) == none {242			return false243		}244		save := history.by_id(store, cursor) or { return false }245		if save.parent == '' {246			// Reached the first save without leaving the line we have.247			return true248		}249		cursor = save.parent250	}251	return false252}