| 1 | package calendar |
| 2 | |
| 3 | import ( |
| 4 | "net" |
| 5 | "net/http" |
| 6 | "strconv" |
| 7 | "strings" |
| 8 | "sync" |
| 9 | "time" |
| 10 | |
| 11 | "amadan.net/oficina/calendar/internal/calendar/seal" |
| 12 | ) |
| 13 | |
| 14 | // What every public booking route shares (booking spec §2.7, §4.2, §5, |
| 15 | // §7.2): the client's IP, the cheap gate in front of the expensive |
| 16 | // work, the two headers, the zone the page offers, and the semaphore on |
| 17 | // slot computation. |
| 18 | |
| 19 | // clientIP is the LAST element of X-Forwarded-For — the platform edge |
| 20 | // REPLACES that header with the dialling client, and the app's socket |
| 21 | // is reachable only from the edge — or the host of RemoteAddr when the |
| 22 | // header is absent (tests, rastrillo dev). Canonicalised; unparseable |
| 23 | // is the literal "unknown", one bucket for all of it. Never logged. |
| 24 | func clientIP(r *http.Request) string { |
| 25 | raw := "" |
| 26 | if xff := r.Header.Get("X-Forwarded-For"); xff != "" { |
| 27 | parts := strings.Split(xff, ",") |
| 28 | raw = strings.TrimSpace(parts[len(parts)-1]) |
| 29 | } else if host, _, err := net.SplitHostPort(r.RemoteAddr); err == nil { |
| 30 | raw = host |
| 31 | } else { |
| 32 | raw = r.RemoteAddr |
| 33 | } |
| 34 | if ip := net.ParseIP(raw); ip != nil { |
| 35 | return ip.String() |
| 36 | } |
| 37 | return "unknown" |
| 38 | } |
| 39 | |
| 40 | // ipFingerprint is the keyed fingerprint the abuse caps are counted by. |
| 41 | func (h *handlers) ipFingerprint(r *http.Request) string { |
| 42 | fp, err := h.store.seal.Fingerprint(seal.PurposeBookingIP, clientIP(r)) |
| 43 | if err != nil { |
| 44 | return "unknown" |
| 45 | } |
| 46 | return fp |
| 47 | } |
| 48 | |
| 49 | // publicHeaders: the token is in the path. |
| 50 | func publicHeaders(w http.ResponseWriter) { |
| 51 | w.Header().Set("Cache-Control", "no-store") |
| 52 | w.Header().Set("Referrer-Policy", "no-referrer") |
| 53 | } |
| 54 | |
| 55 | // notFoundLikeTheRouter is the SAME 404 an unknown route gets, so a |
| 56 | // wrong token and a wrong path are indistinguishable (B10). chi's |
| 57 | // default NotFound is http.NotFound. |
| 58 | func notFoundLikeTheRouter(w http.ResponseWriter, r *http.Request) { |
| 59 | http.NotFound(w, r) |
| 60 | } |
| 61 | |
| 62 | // zoneChoices is CommonZones plus the host's own zone when it is not |
| 63 | // among them — the two sources a booker's zone may come from (§5.1). |
| 64 | func zoneChoices(host Person) []string { |
| 65 | out := append([]string(nil), CommonZones...) |
| 66 | if host.Zone != "" && !IsCommonZone(host.Zone) { |
| 67 | out = append(out, host.Zone) |
| 68 | } |
| 69 | return out |
| 70 | } |
| 71 | |
| 72 | // pickZone reads ?zone= / the form's zone, bounded to zoneChoices; |
| 73 | // anything else is the host's zone. chosen says whether the request |
| 74 | // carried one, so the page can tell booking.js not to guess. |
| 75 | func pickZone(r *http.Request, host Person) (zone string, chosen bool) { |
| 76 | _ = r.ParseForm() |
| 77 | want := strings.TrimSpace(r.FormValue("zone")) |
| 78 | for _, z := range zoneChoices(host) { |
| 79 | if z == want { |
| 80 | return z, true |
| 81 | } |
| 82 | } |
| 83 | if host.Zone == "" { |
| 84 | return defaultZone, false |
| 85 | } |
| 86 | return host.Zone, false |
| 87 | } |
| 88 | |
| 89 | // The gate: an in-process token bucket per IP fingerprint on every |
| 90 | // public route (§7.2). 60 a minute, refilled one a second. Bounded to |
| 91 | // gateMaxKeys; a key idle for gateIdle is evicted on the next insert; |
| 92 | // full with no idle key, a NEW key is refused. Memory only. |
| 93 | const ( |
| 94 | gateBurst = 60 |
| 95 | gateRefill = time.Second |
| 96 | gateMaxKeys = 10000 |
| 97 | gateIdle = 5 * time.Minute |
| 98 | ) |
| 99 | |
| 100 | type gateEntry struct { |
| 101 | tokens float64 |
| 102 | last time.Time |
| 103 | } |
| 104 | |
| 105 | type gate struct { |
| 106 | mu sync.Mutex |
| 107 | keys map[string]*gateEntry |
| 108 | now func() time.Time |
| 109 | } |
| 110 | |
| 111 | func newGate() *gate { return &gate{keys: map[string]*gateEntry{}, now: time.Now} } |
| 112 | |
| 113 | // allow spends one token for key, or says why not: false with full=true |
| 114 | // when the bucket had no room for a new key at all. |
| 115 | func (g *gate) allow(key string) (ok bool) { |
| 116 | g.mu.Lock() |
| 117 | defer g.mu.Unlock() |
| 118 | now := g.now() |
| 119 | e := g.keys[key] |
| 120 | if e == nil { |
| 121 | if len(g.keys) >= gateMaxKeys { |
| 122 | g.evictIdle(now) |
| 123 | if len(g.keys) >= gateMaxKeys { |
| 124 | return false |
| 125 | } |
| 126 | } |
| 127 | e = &gateEntry{tokens: gateBurst, last: now} |
| 128 | g.keys[key] = e |
| 129 | } |
| 130 | e.tokens += now.Sub(e.last).Seconds() / gateRefill.Seconds() |
| 131 | if e.tokens > gateBurst { |
| 132 | e.tokens = gateBurst |
| 133 | } |
| 134 | e.last = now |
| 135 | if e.tokens < 1 { |
| 136 | return false |
| 137 | } |
| 138 | e.tokens-- |
| 139 | return true |
| 140 | } |
| 141 | |
| 142 | func (g *gate) evictIdle(now time.Time) { |
| 143 | for k, e := range g.keys { |
| 144 | if now.Sub(e.last) > gateIdle { |
| 145 | delete(g.keys, k) |
| 146 | } |
| 147 | } |
| 148 | } |
| 149 | |
| 150 | // size is for the test that proves the bound. |
| 151 | func (g *gate) size() int { |
| 152 | g.mu.Lock() |
| 153 | defer g.mu.Unlock() |
| 154 | return len(g.keys) |
| 155 | } |
| 156 | |
| 157 | // publicGate wraps every public route: the bucket, then the headers. |
| 158 | func (h *handlers) publicGate(next http.HandlerFunc) http.HandlerFunc { |
| 159 | return func(w http.ResponseWriter, r *http.Request) { |
| 160 | publicHeaders(w) |
| 161 | if !h.gate.allow(h.ipFingerprint(r)) { |
| 162 | w.Header().Set("Retry-After", "60") |
| 163 | http.Error(w, "Too many requests. Try again in a minute.", http.StatusTooManyRequests) |
| 164 | return |
| 165 | } |
| 166 | next(w, r) |
| 167 | } |
| 168 | } |
| 169 | |
| 170 | // slotSem bounds concurrent public slot computation (§4.2). Full → 503, |
| 171 | // never a page computed from less than the whole busy list. |
| 172 | var slotSem = make(chan struct{}, 4) |
| 173 | |
| 174 | func acquireSlots() (release func(), ok bool) { |
| 175 | select { |
| 176 | case slotSem <- struct{}{}: |
| 177 | return func() { <-slotSem }, true |
| 178 | default: |
| 179 | return nil, false |
| 180 | } |
| 181 | } |
| 182 | |
| 183 | func busyNow(w http.ResponseWriter) { |
| 184 | w.Header().Set("Retry-After", "5") |
| 185 | http.Error(w, "Busy just now. Try again in a moment.", http.StatusServiceUnavailable) |
| 186 | } |
| 187 | |
| 188 | // parseUnix reads a form's instant. |
| 189 | func parseUnix(s string) (int64, bool) { |
| 190 | n, err := strconv.ParseInt(strings.TrimSpace(s), 10, 64) |
| 191 | return n, err == nil && n > 0 |
| 192 | } |
| 193 | |
| 194 | func hostNameOf(host Person) string { |
| 195 | if host.Handle != nil { |
| 196 | return *host.Handle |
| 197 | } |
| 198 | return "" |
| 199 | } |
| 200 | |
| 201 | // hasControl reports a control character (a line break, a NUL) in a |
| 202 | // single-line field. |
| 203 | func hasControl(s string) bool { |
| 204 | for _, r := range s { |
| 205 | if r < 0x20 || r == 0x7f { |
| 206 | return true |
| 207 | } |
| 208 | } |
| 209 | return false |
| 210 | } |
| 211 | |
amadan