1// SPDX-License-Identifier: AGPL-3.0-or-later
2
3package app
4
5import (
6 "context"
7 "errors"
8 "fmt"
9 "strconv"
10 "strings"
11 "sync"
12 "time"
13
14 "github.com/bnema/zerowrap"
15
16 "bnema.dev/ermite/internal/domain"
17 "bnema.dev/ermite/internal/ports"
18)
19
20// DefaultEventBuffer is the number of events the Events use case remembers.
21const DefaultEventBuffer = 1024
22
23// Limits of the watchers.
24const (
25 // MaxWatchTopics is the most topics one watch may follow.
26 MaxWatchTopics = 64
27 // MaxWatchers is the most watches in progress at once.
28 MaxWatchers = 256
29 // MaxWatchersPerClient is the most watches in progress for one client
30 // address (see WatchParams.Client).
31 MaxWatchersPerClient = 16
32 // DefaultRevalidateEvery is how long a watcher with a stored token goes
33 // without asking the token store whether the token still exists.
34 DefaultRevalidateEvery = 5 * time.Second
35)
36
37// Topics a watcher may follow.
38const (
39 // TopicHome follows every repository the caller may see.
40 TopicHome = "home"
41 // topicRepoPrefix starts the topic of one repository: "repo:<name>".
42 topicRepoPrefix = "repo:"
43)
44
45// bufferedEvent is an event with its sequence number in the buffer, and what
46// was true of its repository when it was buffered. Access to an event is
47// decided from that, and from the repository as it is when the event is
48// delivered: a repository made public later does not reveal what happened
49// while it was private, and a repository deleted and created again under the
50// same name does not inherit the events of the old one.
51type bufferedEvent struct {
52 seq uint64
53 ev domain.Event
54
55 // known is false when the repository did not exist any more when the
56 // event was buffered: nobody is told about it.
57 known bool
58 // vis is the visibility of the repository at that time.
59 vis domain.Visibility
60 // created is the creation time of that repository.
61 created time.Time
62}
63
64// Events keeps the last events of the bus in a ring buffer, numbers them, and
65// lets callers watch them: live, or replayed from the id of the last event
66// they saw. Events of a private repository only reach callers that may read
67// it, checked again for every event.
68//
69// Event ids are opaque to clients: "<boot>-<seq>", where boot identifies this
70// run of the server, so that an id from before a restart is unknown rather
71// than taken for a newer event.
72//
73// The goroutine that feeds the buffer uses the logger of the context given to
74// NewEvents and lives until Close.
75type Events struct {
76 repos *Repos
77 auth Revalidator
78 clock ports.Clock
79 boot string
80 size int
81 every time.Duration // see EventsConfig.RevalidateEvery
82
83 stop context.CancelFunc
84 done chan struct{}
85
86 mu sync.Mutex
87 ring []bufferedEvent // capacity size, oldest first
88 nextSeq uint64 // sequence number of the next event, from 1
89 changed chan struct{} // closed and replaced on every append and on close
90 closed bool
91 watches int
92 clients map[string]int // watches in progress by client
93}
94
95// EventsConfig configures Events.
96type EventsConfig struct {
97 // Size is the number of events remembered; DefaultEventBuffer when not
98 // positive.
99 Size int
100 // Auth confirms that the token of a watcher still exists. Required.
101 Auth Revalidator
102 // RevalidateEvery is how long the answer of Auth is kept for a watcher;
103 // DefaultRevalidateEvery when zero, and negative to ask for every event.
104 RevalidateEvery time.Duration
105}
106
107// NewEvents subscribes to the bus and starts remembering its events. ctx
108// carries the logger; its cancellation is not followed, call Close.
109func NewEvents(ctx context.Context, repos *Repos, bus ports.EventBus, clock ports.Clock, cfg EventsConfig) *Events {
110 size := cfg.Size
111 if size <= 0 {
112 size = DefaultEventBuffer
113 }
114 every := cfg.RevalidateEvery
115 if every == 0 {
116 every = DefaultRevalidateEvery
117 }
118 run, stop := context.WithCancel(context.WithoutCancel(ctx))
119 e := &Events{
120 repos: repos,
121 auth: cfg.Auth,
122 clock: clock,
123 every: every,
124 clients: make(map[string]int),
125 boot: strconv.FormatInt(clock.Now().UnixMilli(), 36),
126 size: size,
127 stop: stop,
128 done: make(chan struct{}),
129 nextSeq: 1,
130 changed: make(chan struct{}),
131 }
132 sub := bus.Subscribe(run) // before returning: nothing published after is missed
133 go e.feed(run, sub)
134 return e
135}
136
137// feed appends the events of the bus until it stops.
138func (e *Events) feed(ctx context.Context, sub <-chan domain.Event) {
139 defer close(e.done)
140 defer e.shutdown()
141 for {
142 select {
143 case ev, ok := <-sub:
144 if !ok {
145 return
146 }
147 e.append(ctx, ev)
148 case <-ctx.Done():
149 return
150 }
151 }
152}
153
154// snapshot records the visibility and the generation of the repository an
155// event is about. Every event of the repository carries them.
156func (e *Events) snapshot(ctx context.Context, ev domain.Event) bufferedEvent {
157 switch ev := ev.(type) {
158 case domain.RepoCreated:
159 return bufferedEvent{known: true, vis: ev.Visibility, created: ev.At}
160 case domain.RepoUpdated:
161 return bufferedEvent{known: true, vis: ev.Visibility, created: ev.CreatedAt}
162 case domain.RepoDeleted:
163 return bufferedEvent{known: true, vis: ev.Visibility, created: ev.CreatedAt}
164 case domain.PushEvent:
165 if ev.CreatedAt.IsZero() {
166 return bufferedEvent{} // repository unknown at publish time: nobody is told
167 }
168 return bufferedEvent{known: true, vis: ev.Visibility, created: ev.CreatedAt}
169 }
170 return bufferedEvent{known: true}
171}
172
173func (e *Events) append(ctx context.Context, ev domain.Event) {
174 be := e.snapshot(ctx, ev) // outside the lock: it reads the store
175 e.mu.Lock()
176 defer e.mu.Unlock()
177 if len(e.ring) == e.size {
178 copy(e.ring, e.ring[1:])
179 e.ring = e.ring[:e.size-1]
180 }
181 be.seq, be.ev = e.nextSeq, ev
182 e.ring = append(e.ring, be)
183 e.nextSeq++
184 e.wake()
185}
186
187// wake releases the watchers waiting for news. The caller holds mu.
188func (e *Events) wake() {
189 close(e.changed)
190 e.changed = make(chan struct{})
191}
192
193func (e *Events) shutdown() {
194 e.mu.Lock()
195 defer e.mu.Unlock()
196 if !e.closed {
197 e.closed = true
198 e.wake()
199 }
200}
201
202// Close ends every watch cleanly, stops feeding and waits for the feeder,
203// until ctx ends. It is safe to call more than once.
204func (e *Events) Close(ctx context.Context) {
205 e.stop()
206 select {
207 case <-e.done:
208 case <-ctx.Done():
209 }
210}
211
212// Watchers returns the number of watches in progress.
213func (e *Events) Watchers() int {
214 e.mu.Lock()
215 defer e.mu.Unlock()
216 return e.watches
217}
218
219func (e *Events) id(seq uint64) string { return e.boot + "-" + strconv.FormatUint(seq, 10) }
220
221// parseID returns the sequence number of an id of this run.
222func (e *Events) parseID(id string) (uint64, bool) {
223 boot, seq, ok := strings.Cut(id, "-")
224 if !ok || boot != e.boot {
225 return 0, false
226 }
227 n, err := strconv.ParseUint(seq, 10, 64)
228 return n, err == nil && n > 0
229}
230
231// WatchParams select the events of a watch.
232type WatchParams struct {
233 // Topics are TopicHome or "repo:<name>"; empty means TopicHome.
234 Topics []string
235 // ResumeAfter is the id of the last event the caller saw; empty to
236 // receive only new events.
237 ResumeAfter string
238 // Client identifies where the watch comes from, for the limit per client
239 // (MaxWatchersPerClient): an opaque key such as a normalized address; the
240 // web passes its visitor's. Empty only for callers with no client, which
241 // count against MaxWatchers alone.
242 Client string
243 // Ready, when not nil, is called once the topics are valid and the watch
244 // is registered: events published from then on are not missed. Nothing is
245 // sent before it returns.
246 Ready func()
247}
248
249// WatchEvent is one item of a watch.
250type WatchEvent struct {
251 // ID identifies the event, for resuming. Empty on a gap.
252 ID string
253 // Gap tells that events were lost: the caller must reload what it shows.
254 // Event is nil then.
255 Gap bool
256 // Event is a domain.RepoCreated, RepoUpdated, RepoDeleted or PushEvent.
257 Event domain.Event
258 // Repo is the state of the repository at delivery, for RepoCreated and
259 // RepoUpdated.
260 Repo *RepoView
261}
262
263// watch is the state of one Watch call.
264type watch struct {
265 p domain.Principal
266 home bool
267 repos map[domain.RepoName]bool
268
269 checked time.Time // when the token store last confirmed the principal
270}
271
272func (w *watch) wants(name domain.RepoName) bool { return w.home || w.repos[name] }
273
274// parseTopics validates the topics of a watch. A repository topic needs a
275// repository the principal may read (else domain.ErrNotFound); an unknown
276// topic, or more than MaxWatchTopics, is domain.ErrInvalid.
277func (e *Events) parseTopics(ctx context.Context, p domain.Principal, topics []string) (*watch, error) {
278 if len(topics) > MaxWatchTopics {
279 return nil, fmt.Errorf("%w: %d topics, at most %d", domain.ErrInvalid, len(topics), MaxWatchTopics)
280 }
281 w := &watch{p: p, repos: make(map[domain.RepoName]bool), checked: time.Now()}
282 if len(topics) == 0 {
283 w.home = true
284 }
285 for _, t := range topics {
286 if t == TopicHome {
287 w.home = true
288 continue
289 }
290 raw, ok := strings.CutPrefix(t, topicRepoPrefix)
291 if !ok {
292 return nil, fmt.Errorf("%w: unknown topic %q (want %q or \"repo:<name>\")", domain.ErrInvalid, t, TopicHome)
293 }
294 name, err := domain.ParseRepoName(raw)
295 if err != nil {
296 return nil, err
297 }
298 if _, err := e.repos.Get(ctx, p, name); err != nil {
299 return nil, err
300 }
301 w.repos[name] = true
302 }
303 return w, nil
304}
305
306// Watch calls send for the events the principal may see until ctx ends, the
307// buffer closes (both return nil) or send fails (its error is returned).
308//
309// A principal with a stored token is checked again for every event, and every
310// few seconds when idle: when the token expired or was revoked the watch ends
311// with domain.ErrUnauthenticated and nothing more is sent. More watches than
312// MaxWatchers, or than MaxWatchersPerClient for one Client, give
313// domain.ErrResourceExhausted.
314//
315// Without ResumeAfter only new events are sent. With it, the buffered events
316// after that id are sent first, then new ones. When the id is no longer
317// buffered, or was not issued by this run, a gap comes first and the oldest
318// buffered event follows. A watcher that falls more than the buffer behind
319// gets a gap too, and carries on with the oldest buffered event.
320func (e *Events) Watch(ctx context.Context, p domain.Principal, params WatchParams, send func(WatchEvent) error) error {
321 w, err := e.parseTopics(ctx, p, params.Topics)
322 if err != nil {
323 return err
324 }
325
326 e.mu.Lock()
327 next := e.nextSeq // only new events
328 gap := false
329 if params.ResumeAfter != "" {
330 seq, ok := e.parseID(params.ResumeAfter)
331 oldest := e.nextSeq - uint64(len(e.ring)) // first buffered sequence, nextSeq when empty
332 switch {
333 case ok && seq >= oldest-1 && seq < e.nextSeq:
334 next = seq + 1
335 default:
336 next, gap = oldest, true
337 }
338 }
339 if e.watches >= MaxWatchers || (params.Client != "" && e.clients[params.Client] >= MaxWatchersPerClient) {
340 e.mu.Unlock()
341 return fmt.Errorf("%w: too many watchers", domain.ErrResourceExhausted)
342 }
343 e.watches++
344 if params.Client != "" {
345 e.clients[params.Client]++
346 }
347 e.mu.Unlock()
348 defer func() {
349 e.mu.Lock()
350 e.watches--
351 if params.Client != "" {
352 if e.clients[params.Client]--; e.clients[params.Client] == 0 {
353 delete(e.clients, params.Client)
354 }
355 }
356 e.mu.Unlock()
357 }()
358
359 if params.Ready != nil {
360 params.Ready()
361 }
362 log := zerowrap.FromCtx(ctx)
363 log.Debug().Strs("topics", params.Topics).Bool("resume", params.ResumeAfter != "").Bool("gap", gap).Msg("watch started")
364 if gap {
365 if err := send(WatchEvent{Gap: true}); err != nil {
366 return err
367 }
368 }
369 for {
370 if err := e.stillAllowed(ctx, w); err != nil {
371 return err
372 }
373 batch, changed, oldest, lost, closed := e.since(next)
374 if lost {
375 if err := send(WatchEvent{Gap: true}); err != nil {
376 return err
377 }
378 next = oldest
379 continue
380 }
381 for _, be := range batch {
382 if err := e.deliver(ctx, w, be, send); err != nil {
383 return err
384 }
385 next = be.seq + 1
386 }
387 if len(batch) > 0 {
388 continue
389 }
390 if closed {
391 return nil
392 }
393 e.wait(ctx, w, changed)
394 if ctx.Err() != nil {
395 return nil
396 }
397 }
398}
399
400// wait blocks until more events arrive or ctx ends. A watcher with a stored
401// token also wakes up every few seconds, so that a revocation ends the watch
402// of a quiet forge too (the caller checks the token on the next turn).
403func (e *Events) wait(ctx context.Context, w *watch, changed <-chan struct{}) {
404 var idle <-chan time.Time
405 if w.p.TokenID() != "" {
406 t := time.NewTimer(e.idleCheck())
407 defer t.Stop()
408 idle = t.C
409 }
410 select {
411 case <-changed:
412 case <-idle:
413 case <-ctx.Done():
414 }
415}
416
417// idleCheck is how long a watcher with a stored token waits for news before
418// checking its token anyway.
419func (e *Events) idleCheck() time.Duration {
420 if e.every <= 0 {
421 return DefaultRevalidateEvery
422 }
423 return min(e.every, DefaultRevalidateEvery)
424}
425
426// stillAllowed checks that the holder of a stored token may still watch: the
427// token has not expired and, at most every few seconds, still exists. Root and
428// anonymous callers have nothing to lose.
429func (e *Events) stillAllowed(ctx context.Context, w *watch) error {
430 if w.p.TokenID() == "" {
431 return nil
432 }
433 if exp := w.p.ExpiresAt(); !exp.IsZero() && !e.clock.Now().Before(exp) {
434 return domain.ErrUnauthenticated
435 }
436 if e.every > 0 && time.Since(w.checked) < e.every {
437 return nil
438 }
439 if err := e.auth.Revalidate(ctx, w.p); err != nil {
440 if ctx.Err() != nil {
441 return nil
442 }
443 return err
444 }
445 w.checked = time.Now()
446 return nil
447}
448
449// since returns the buffered events from sequence next on, and the channel
450// that closes when more arrive. lost is true when next fell out of the buffer;
451// the caller then restarts from oldest, the first buffered sequence. The
452// returned slice is a copy.
453func (e *Events) since(next uint64) (batch []bufferedEvent, changed <-chan struct{}, oldest uint64, lost, closed bool) {
454 e.mu.Lock()
455 defer e.mu.Unlock()
456 oldest = e.nextSeq - uint64(len(e.ring))
457 if next < oldest {
458 return nil, e.changed, oldest, true, e.closed
459 }
460 batch = append(batch, e.ring[next-oldest:]...)
461 return batch, e.changed, oldest, false, e.closed
462}
463
464// deliver sends the event if the watcher follows its topic and may see it.
465func (e *Events) deliver(ctx context.Context, w *watch, be bufferedEvent, send func(WatchEvent) error) error {
466 if err := e.stillAllowed(ctx, w); err != nil {
467 return err
468 }
469 out := WatchEvent{ID: e.id(be.seq), Event: be.ev}
470 switch ev := be.ev.(type) {
471 case domain.EventGap:
472 // The feeder lost events: tell every watcher.
473 return send(WatchEvent{Gap: true})
474 case domain.RepoDeleted:
475 // The repository is gone: use the visibility it had.
476 if !w.wants(ev.Repo) || !canReadAs(w.p, ev.Repo, ev.Visibility) {
477 return nil
478 }
479 return send(out)
480 case domain.RepoCreated:
481 return e.deliverRepo(ctx, w, ev.Repo, true, be, out, send)
482 case domain.RepoUpdated:
483 return e.deliverRepo(ctx, w, ev.Repo, true, be, out, send)
484 case domain.PushEvent:
485 return e.deliverRepo(ctx, w, ev.Repo, false, be, out, send)
486 }
487 return nil // an event this version does not stream
488}
489
490// deliverRepo sends an event about a repository if the watcher could read the
491// repository when the event happened and can read it now, and the repository
492// is still the one the event is about. A repository that no longer exists is
493// skipped: its RepoDeleted follows or came before.
494//
495// The exception is a repository that became private: the watchers who could
496// read it before are told once, with its name and its new visibility only,
497// so that what they show can be removed.
498func (e *Events) deliverRepo(ctx context.Context, w *watch, name domain.RepoName, withRepo bool, be bufferedEvent, out WatchEvent, send func(WatchEvent) error) error {
499 if !w.wants(name) || !be.known {
500 return nil
501 }
502 repo, err := lookupRepo(ctx, e.repos.meta, name)
503 switch {
504 case errors.Is(err, domain.ErrNotFound):
505 return nil
506 case ctx.Err() != nil:
507 return nil
508 case err != nil:
509 return fmt.Errorf("check access to %q: %w", name, err)
510 }
511 if repo.CreatedAt.After(be.created) {
512 return nil // the event is about a repository of this name that was deleted
513 }
514 if !canReadAs(w.p, name, be.vis) {
515 if up, ok := be.ev.(domain.RepoUpdated); ok && canReadAs(w.p, name, up.Previous) {
516 out.Repo = &RepoView{Repo: domain.Repo{Name: name, Visibility: up.Visibility}}
517 return send(out)
518 }
519 return nil
520 }
521 if !canRead(w.p, repo) {
522 return nil
523 }
524 if withRepo {
525 view, err := e.repos.View(ctx, repo)
526 if err != nil {
527 return err
528 }
529 out.Repo = &view
530 }
531 return send(out)
532}