1// SPDX-License-Identifier: AGPL-3.0-or-later
2
3package web
4
5import (
6 "context"
7 "errors"
8 "fmt"
9 "io"
10 "net/http"
11 "net/url"
12 "strconv"
13 "strings"
14 "sync"
15 "time"
16
17 "github.com/bnema/zerowrap"
18
19 "bnema.dev/ermite/internal/clientlimit"
20 "bnema.dev/ermite/internal/domain"
21 "bnema.dev/ermite/internal/ports"
22)
23
24// Live updates. A page that can change under the eyes of its reader opens
25// GET /-/events (the Live component of the hint badge). The handler follows
26// EventService.Watch as the principal of the request and turns each event into
27// the HTML fragments the page shows, sent as Server-Sent Events:
28//
29// GET /-/events?topic=home
30// GET /-/events?topic=repo:<name>&view=summary|refs
31// GET /-/events?topic=repo:<name>&view=commits&ref=<branch>&head=<sha>
32// GET /-/events?topic=repo:<name>&view=mrs
33// GET /-/events?topic=repo:<name>&view=mr&n=<number>&ref=<source branch>
34// GET /-/events?topic=repo:<name>&view=actions
35// GET /-/events?topic=repo:<name>&view=run&n=<run id>
36// GET /-/events?topic=repo:<name>&view=job&job=<job id>
37//
38// topic is the Watch topic. view says which fragments of a repository the
39// page shows, so that the server renders only those (summary when absent).
40// On the commits page, ref is the branch it lists and head the commit it
41// lists first: the banner counts the commits between that head and the new
42// tip, so it stays right however many pushes came in and however often the
43// stream reconnected. A Last-Event-ID header resumes the stream
44// (resume_after).
45//
46// Events, each with the id of the Watch event it comes from:
47//
48// home-list data: <tr id="repo-<name>">…</tr>, or <tr id="repo-<name>" data-gone></tr>
49// for a repository that is deleted or no longer visible
50// repo-last-push data: <dd id="last-push-<name>">…</dd>
51// refs-list data: <tbody id="ref-rows">…</tbody>, and again with
52// <dl id="refs-kv">…</dl>, the facts of the rail
53// commits-head data: <div id="commits-head">N new commits — reload</div>
54// mr-notice data: <div id="mr-notice">…</div>, on the merge request pages:
55// something changed, with the link that reloads the page
56// ci-run data: <tr id="run-<id>">…</tr> (the list of runs) or
57// <div id="run-body">…</div> (one run)
58// ci-job data: <h2 id="job-head">…</h2> and <ol id="job-steps">…</ol>; the log
59// itself is never sent in this stream: the page follows it on its own
60// feed, /<repo>/actions/runs/<id>/job/<job>/stream?from=<line>
61// gap data: gap; events were lost, or what the page shows is gone or
62// changed: the page fetches itself again (ermiteLive in ermite.js)
63//
64// The data of an event is one fragment, a top-level element with an id, one
65// "data:" line per line of HTML; the page swaps the element that has that id
66// (ermiteLive.swap). The slots of the banners (commits-head, mr-notice) are
67// status regions that stay in the page: only their children are replaced, so
68// that a screen reader announces the banner.
69// An event that changes nothing on the page is still sent as an id alone, so
70// that a reconnection resumes after it.
71
72// DefaultHeartbeat is how often an idle stream gets a comment line, so that
73// proxies keep it open and a dead peer is noticed.
74const DefaultHeartbeat = 25 * time.Second
75
76const (
77 // writeWindow bounds one write to the visitor, whatever the write timeout
78 // of the server is.
79 writeWindow = 30 * time.Second
80 // retryAfter is the delay asked from a visitor refused for lack of room.
81 retryAfter = 10
82)
83
84// parseTopic reads "home" or "repo:<name>"; repo is "" for home.
85func parseTopic(topic string) (repo string, ok bool) {
86 if topic == "home" {
87 return "", true
88 }
89 if name, found := strings.CutPrefix(topic, "repo:"); found && name != "" {
90 return name, true
91 }
92 return "", false
93}
94
95// events is GET /-/events.
96func (s *Server) events(w http.ResponseWriter, r *http.Request) {
97 if s.cfg.Events == nil {
98 http.NotFound(w, r)
99 return
100 }
101 q := r.URL.Query()
102 topic := q.Get("topic")
103 repo, ok := parseTopic(topic)
104 if !ok {
105 denyStream(w, http.StatusBadRequest, "topic must be home or repo:<name>")
106 return
107 }
108 ctx, cancel := context.WithCancel(r.Context())
109 defer cancel()
110 log := zerowrap.FromCtx(ctx)
111
112 if repo != "" {
113 // A repository the visitor cannot see is a missing one (AC2).
114 cctx, ccancel := context.WithTimeout(ctx, requestTimeout)
115 err := s.canSee(cctx, repo)
116 ccancel()
117 if err != nil {
118 s.denyEvents(ctx, w, err)
119 return
120 }
121 }
122
123 // The watch runs in a goroutine and hands each event to this one through
124 // an unbuffered channel: a visitor that reads slowly holds the watch in
125 // its send, falls behind the buffer of the use case, and gets a gap.
126 msgs := make(chan recvd)
127 started := make(chan struct{})
128 var startOnce sync.Once
129 start := func() { startOnce.Do(func() { close(started) }) }
130 finished := make(chan struct{})
131 params := ports.WatchParams{
132 Topics: []string{topic}, ResumeAfter: r.Header.Get("Last-Event-ID"),
133 // The visitor is the client of the watch, for the limit per client.
134 Client: clientlimit.Key(clientlimit.ClientAddr(r, s.cfg.TrustedProxies)),
135 Ready: start,
136 }
137 go func() {
138 defer close(finished)
139 defer close(msgs)
140 // net/http only recovers the handler goroutine: a panic in the watch
141 // would end the process. It ends this stream as an error instead.
142 defer func() {
143 if v := recover(); v != nil {
144 log.Error().Interface("panic", v).Msg("event watch panicked")
145 select {
146 case msgs <- recvd{err: fmt.Errorf("watch panicked: %v", v)}:
147 case <-ctx.Done():
148 }
149 }
150 }()
151 err := s.cfg.Events.Watch(ctx, principal(ctx), params, func(we ports.WatchEvent) error {
152 start()
153 select {
154 case msgs <- recvd{ev: we}:
155 return nil
156 case <-ctx.Done():
157 return ctx.Err()
158 }
159 })
160 if err != nil && ctx.Err() == nil {
161 select {
162 case msgs <- recvd{err: err}:
163 case <-ctx.Done():
164 }
165 }
166 }()
167 defer func() {
168 cancel()
169 <-finished
170 }()
171
172 // The watch is registered (or refused, which ends it before): only then
173 // does the answer commit to 200.
174 var first *recvd
175 select {
176 case <-started:
177 case m, open := <-msgs:
178 if !open {
179 return // the server is stopping
180 }
181 if m.err != nil {
182 s.denyEvents(ctx, w, m.err)
183 return
184 }
185 first = &m
186 case <-ctx.Done():
187 return
188 }
189
190 rc := http.NewResponseController(w)
191 hdr := w.Header()
192 hdr.Set("Content-Type", "text/event-stream")
193 cacheHeaders(ctx, hdr, "no-cache, no-transform", sessionCache+", no-transform")
194 if hdr.Get("Cache-Control") == noStore { // an invalid cookie was cleared
195 hdr.Set("Cache-Control", noStore+", no-transform")
196 }
197 hdr.Set("X-Accel-Buffering", "no")
198 _ = rc.SetWriteDeadline(time.Now().Add(writeWindow))
199 w.WriteHeader(http.StatusOK)
200 out := &sseWriter{w: w, rc: rc}
201 if err := out.raw(": connected\n\n"); err != nil {
202 return
203 }
204
205 st := &liveStream{s: s, repo: repo, view: q.Get("view"), ref: q.Get("ref"), head: q.Get("head"), n: q.Get("n"), job: q.Get("job")}
206 handle := func(m recvd) bool {
207 if m.err != nil {
208 if ctx.Err() == nil && !errors.Is(m.err, context.Canceled) {
209 log.Debug().Err(m.err).Str("topic", topic).Msg("event stream ended")
210 }
211 return false
212 }
213 if !liveEvent(m.ev) {
214 return true // nothing to show, not even an id to resume after
215 }
216 // An owner's stream ends when the session does, before it sends
217 // anything more: an event can carry what only the owner may see, and
218 // waiting for the next heartbeat would leave a window.
219 if SignedIn(ctx) && !s.sessionStillValid(ctx, r) {
220 return false
221 }
222 rctx, rcancel := context.WithTimeout(ctx, requestTimeout)
223 frags, err := st.render(rctx, m.ev)
224 rcancel()
225 if err != nil {
226 if ctx.Err() != nil {
227 return false
228 }
229 // What the page shows can no longer be told from the events:
230 // have it fetch itself again.
231 log.Warn().Err(err).Str("topic", topic).Msg("render live fragment")
232 frags = gap
233 }
234 return out.send(m.ev.ID, frags) == nil
235 }
236 if first != nil && !handle(*first) {
237 return
238 }
239
240 beat := s.cfg.Heartbeat
241 if beat <= 0 {
242 beat = DefaultHeartbeat
243 }
244 tick := time.NewTicker(beat)
245 defer tick.Stop()
246 for {
247 select {
248 case m, open := <-msgs:
249 if !open || !handle(m) {
250 return
251 }
252 case <-tick.C:
253 // A stream opened by the owner ends when the session does
254 // (sign out everywhere, expiry): the page reconnects as it can.
255 if SignedIn(ctx) && !s.sessionStillValid(ctx, r) {
256 return
257 }
258 if out.raw(": heartbeat\n\n") != nil {
259 return
260 }
261 case <-ctx.Done():
262 return
263 }
264 }
265}
266
267// recvd is a message of the Watch stream, or how it failed.
268type recvd struct {
269 ev ports.WatchEvent
270 err error
271}
272
273// canSee checks that the caller of the request may see the repository named in
274// a topic: one it may not is as missing as one that does not exist.
275func (s *Server) canSee(ctx context.Context, rawName string) error {
276 name, err := domain.ParseRepoName(rawName)
277 if err != nil {
278 return err
279 }
280 _, err = s.cfg.Repos.Get(ctx, principal(ctx), name)
281 return err
282}
283
284// denyStream answers a request that gets no stream.
285func denyStream(w http.ResponseWriter, status int, msg string) {
286 w.Header().Set("Cache-Control", "no-store")
287 http.Error(w, msg, status)
288}
289
290// denyEvents maps an error of a use case, before the stream started, to a
291// status. Not found and invalid are 404 whatever the reason: a private
292// repository is a missing one.
293func (s *Server) denyEvents(ctx context.Context, w http.ResponseWriter, err error) {
294 switch {
295 case errors.Is(err, context.Canceled):
296 // The visitor is gone.
297 case errors.Is(err, domain.ErrNotFound), domain.IsInvalid(err):
298 denyStream(w, http.StatusNotFound, "not found")
299 case errors.Is(err, domain.ErrResourceExhausted):
300 w.Header().Set("Retry-After", strconv.Itoa(retryAfter))
301 denyStream(w, http.StatusServiceUnavailable, "too many event streams, retry later")
302 case errors.Is(err, domain.ErrUnauthenticated):
303 denyStream(w, http.StatusUnauthorized, "unauthorized")
304 default:
305 log := zerowrap.FromCtx(ctx)
306 log.Error().Err(err).Msg("open event stream")
307 denyStream(w, http.StatusInternalServerError, "internal error")
308 }
309}
310
311// fragment is one SSE event to send: the name and the HTML of the fragment.
312type fragment struct{ event, html string }
313
314// sseWriter writes events to a visitor, flushing each, under a deadline of
315// its own so that the write timeout of the server cannot end the stream.
316type sseWriter struct {
317 w http.ResponseWriter
318 rc *http.ResponseController
319}
320
321func (o *sseWriter) raw(s string) error {
322 _ = o.rc.SetWriteDeadline(time.Now().Add(writeWindow))
323 if _, err := io.WriteString(o.w, s); err != nil {
324 return err
325 }
326 return o.rc.Flush()
327}
328
329// send writes the fragments of one Watch event under its id. An event that
330// has no fragment still carries its id, so that a reconnection resumes after
331// it.
332func (o *sseWriter) send(id string, frags []fragment) error {
333 if len(frags) == 0 {
334 if id == "" {
335 return nil
336 }
337 return o.raw(formatEvent(id, "", "", false))
338 }
339 for _, f := range frags {
340 if err := o.raw(formatEvent(id, f.event, f.html, true)); err != nil {
341 return err
342 }
343 }
344 return nil
345}
346
347// formatEvent is one SSE event. Each line of data is a "data:" field, and a
348// browser joins them back with newlines.
349func formatEvent(id, event, data string, hasData bool) string {
350 var b strings.Builder
351 if event != "" {
352 b.WriteString("event: " + event + "\n")
353 }
354 if id != "" {
355 b.WriteString("id: " + id + "\n")
356 }
357 if hasData {
358 data = strings.ReplaceAll(strings.ReplaceAll(data, "\r\n", "\n"), "\r", "\n")
359 for line := range strings.SplitSeq(data, "\n") {
360 b.WriteString("data: " + line + "\n")
361 }
362 }
363 b.WriteString("\n")
364 return b.String()
365}
366
367// liveURL is the stream a page follows: the topic and, for a repository
368// page, what it shows (see the comment on events).
369func liveURL(topic, query string) string {
370 u := "/-/events?topic=" + url.QueryEscape(topic)
371 if query != "" {
372 u += "&" + query
373 }
374 return u
375}